NATIONALSYNCHROTRONSLIGHTSOURCE

Forthe period October 1,

.

1997 through September 30, 1998

May 1999

Managing Editor

E.Z. Ro&nan

Science Editor

JB. H2stings

Production Assists.mi

L. Feierabend

L. Rogers

N. Wright

nsl’S

The NationalSynchrotronsLightSource Deparrrnent

is supportedbythe

Oi%ce of Basic Energy Sciences

United States Department of Energy

Washington, D.C.

Brookhaven National Laboratory, Brookhaven Science Associates, Inc., Upton, New York 11973

Under Contract No. DE-ACO2-98CH1O886
,—. .———. —.. .—: —— ——.. .

INTRODUflfOfv

INTRODUCTIONBYTHECHAIRMAN......................................................................................... 1-2

Michael Hart

USERS’ EXECUTIVECOMMImEE.............................................................................................. 1-4

John B.Parke

STRLKWRE SOLUTION FROM POWDER DIFFRAaION.............................................................. 2-4

APPLIED SCIENCES................................................................................................................2-12

BIOLOGICAL SCIENCES..........................................................................................................2-18

CHEMICAL SCIENCES............................................................................................................ 2-34

GEOLOGICALSCIENCES........................................................................................................ 2-47

MATERIAKSCIENCES........................................................................................................... 2-60

NUCLEAR SCIENCE............................................................................................................... 2-78

TECHNIQUESANDINSTRUMENTATION.................................................................................. 2-82

MEETiNGS~ WORKSHOPS

THE 1998 NSLSANNUAL USERS’

John B.Parke

...................................................................... 3-2

USINC POWDERDATATO SOLVECRYSTALSTRUCTURES......................................................... 3-5

David Cox,Peter W.Stephens

IN SITU SURFACEMANIPULATION........................................................................................... 3-6

Ian Robinson

CRYSTALLOGRAPHY UNDER HIGHPRESSURE: TECHNIQUESFOREVERYONE............................ 3-7

Jiuhua Chen

BIOLOGICAL ANDENVIRONMENTALAPPLICATIONS.................................................................. 3-8

Barbara Ilknan

XANESANDNEXAFS

Boyan Boyanov

INFRARED SYNCHROTRONS

LawrenceCarr

THEORY ANDAPPLICATIONS................................ 3-9

APPLICATIONS .. ... .. ... .... ... ... ... ... .. ... ... .... ... ... ... ... .. 3-1o

ii
DISCLAIMER

This repott was prepared as an account of work sponsored

by an agency of the United States Government. Neither

the United States Government nor any agency thereof, nor

any of their employees, make any warranty, express or

implied, or assumes any legal liability or responsibility for

the accuracy, completeness, or usefulness of any

information, apparatus, product, or process disclosed, or

represents that its use would not infringe privately owned

rights. Reference herein to any specific commercial

product, process, or service by trade name, trademark,

manufacturer, or otherwise does not necessarily constitute

or imply its endorsement, recommendation, or favoring by

the United States Government or any agency thereof. The

views and opinions of authors expressed herein do not

necessarily state or reflect those of the United States

Government or any agency thereof.

,> -..., ...,,
DISCLAIMER

Portions of this document may be illegible

in electronic image products. Images are

produced from the best available original

document.

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OPERATIONS

VUVMACHINE . .. ... .... ... .. ... ... ... ... ... ... ... ... ... ... ... .. ... ... ... .... ... .. ... ... ... ... ... ... ... ... ... ... .. ... ... .... ... ... . 4-2

Stephen Kramer

VUVSTORACE RINGPARAMETERS .. ... ... ... ... ... .. ... ... ... ... ... ... ... ... ... ... ... .. .... ... .. ... ... ... ... ... ... ... ... 4-5

Stephen Kramer

X-RAYRING.......................................................................................................................... 4-6

Roger Klafi

X-RAYSTORAGE RINGPARAMETERS .. .... .. ... ... ... ... ... ... ... ... ... ... ... .. ... ... .... .. ... ... ... ... ... ... ... ... ... ... . 4-9

RogerKla~

BEAMLINE TECHNICAL IMPROVEMENTS . .. ... ... ... ... ... .. ... .... .. .... .. ... .... ... .. ... ... ... ... ... ... ... .. .... .. .... . 4-1o

Roger Klaj%y

PROJECTS

THE DEEP ULTRA-VIOLET FREE ELECTRON LASER(DUV-FEL) ..............................................5-2

ErikD.Johnson

THE ACCELERATOR TEST FACILITY (ATF) ... ... .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... .. ... ... ... ... ... .. .... ... ... 5-6

NSLS

IlanBen-Zvi

FACILIN IMPROVEMENTS .. ... ... ... ... ... .. ... ... ... ... ... ... ... ... ... ... .. ... .... .. ... .... .. ... ... ... ... ... ... ... ... 5-8

Frank Terrano

,

ORGANIZATION

NSLSADVISORYCOMMITTEES.............................................................................................. 6-2

NSLSSTAFF.......................................................................................................................... 6-4

VUVBEAMLINE GUIDE .. ... ... ... ... ... ... .. ... ... ... ... ... ... ... .. .... ... .. ... ... ... ... ... ... ... ... ... .. .... .. ... ... ... ... .... 6-6

X-RAY BEAMLINE GUIDE .. ... ... ... ... .. .... .. ... ... .. .... .. ... ... ... ... ... ... ... .... .. ... ... ... .. .... ... .. ... ... ... ... ... ... . 6-10

PUBLICATIONS 8 EXperimentREPORTS

NSLSUSER PUBLICATIONS....................................................................................................A-1

NSLSSTAFF PUBLICATIONS . .... ... ... ... ... .. ... ... ... .. ... .... .. ... .... ... .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... B-1

BNLFORMAL ANDINFORMALREPORTS................................................................................ B-7

VUVBEAMLINEAND X-RAY BEAMLINEEXPERIMENTREPORTS................................CD-ROM

...

111


Michael Hart

NSLSChairman

In FY 1998, following the 50* Anniversary Year of During the 1998 NSLS Annual Users’ Meeting

Brookhaven National Laboratory, Brookhaven Science (described in Part 3 of this Activity Report), the DOE

Associate-s became the new Managers of BNL. The new Laboratory Operations Board, Chaired by the Under

start is an appropriate time to take stock of past Secretary for Energy, Ernest Moniz met at BNL. By

achievements and to renew or confirm fhture goals. chance all the NSLS Chairmen except Martin Blume

The NSLS Annual Users’

Meeting and the Laboratory

Operations Board meeting held

at BNL the same week made

possible this unusual gathering

of current and former

administrators of BN13

National Synchrotrons Light

Source (NS@. (from left)

Michael Khotek, NSLS Chair

1985-1989, and now program

advisor for Science &

Technology in the Office of the

Under Secretary of Energy;

current NSLS Chair Michael

Hart, who has held the post

since 1995; current Deputy

NSLS Chair Samuel Krinsky,

who served as Acting Chair

from 1989-1990; Denis

McWhan, NSLS Chair 1990-

1995, and now BNL’s Associate

Director for Basic Energy

Sciences; Arie Van

Steenbergen, who headed the

NSLS Construction Project 1977-

1982, and who is now actively

retired from BN~ and John

McTague, NSLS Chair 1982-

1984, and now Vice President,

Technical Affairs, Ford Motor

Company. Not shown is Martin

Blume, who was Acting NSIS

Chair 1984-1985 and is now

Editor-in-Chief of the American

Physical Society.

1-2

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(acting NSLS Chair 84 – 85) were present

as recorded in the picture. Under their

leadership the NSLS has improved

dramatically

● The VUV Ring current has

increased from 100 mA in October 1982

to nearly 1 A today. For the following few

years 10 Ahrs of current were delivered most

weeks - NSLS now exceeds that everyday.

● When the first experiments were

performed on the X-rayring during FY1985

the electron energy was 2 GeV and the

current up to 100 mA – the X-Ray Ring

now runs routinely at 2.5 GeV and at 2.8

GeV with up to 350 mAof current, with a

very much longer beam half-life and

improved reliability.

i

1997 1

II Beam Current IIisto?wof X-ray and VUV R%ngs HI

-—— .—— -—— ——..

II X-nq C9rl’enq

I ‘y”’i;$g$q‘“’f8&:&$, 1 I

ev. ..f.... . .. .:..........-. ..:.. --.. ....7 . .. . . . . .. . . .

* ........ . '...ll...........-. ................{................... .................. ..................................

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..... 1... ... . ....... . ....

,,,, ...

~ ,*3 ,.,,, ,IT..,,.,,, ,*X,“,,, !*Z. ,“.., L*A m.., w.., m+, ! !*.) !“!,!

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. Starting in FY 1984 the proposal for the Phase

H upgrade, mainly for a building extension and a suite of

insertion devices and their associated beamlines, was

pursued - the promises were delivered in fill so that for

some years now the NSLS has been running with two

undulatory in the VUV Ring and three wigglers and an

undulator in the X-Ray Ring. In addition two novel

insertion devices have been commissioned in the X13

straight.

● At the stint of FY 1998 the NSLS welcomed its

7000’h user – attracted by the opportunity for pursuing

research with high quality beams, guaranteed not to be

interrupted by “delivery failures”, and welcomed by an

efilcient and caring user office and first class teams of

PRT and NSLS staff

R & D have lead to the possibility of running the

X-Ray Ring at the higher energy of 2.8 GeV. Figure 1

shows the first user beam, which was provided thereafter

for half of the running time in FY 1998. In combination

with the development of narrow gap undulatory this mode

opens the possibility of new undulatory which could

produce hard X-rays in the fimdamental, perhaps up to.

10 keV.

On 27 September 1998, a Iowhorizontal emittance

lattice became operational at 2.584 GeV. This results in

approximately a 5OO/odecrease in the horizontal beamsize on dipole bending magnet bearnlines, and somewhat

less of a decrease on the insertion device lines. The beam

lifetime is not degraded by the low emittance lattice. This

represents an important achievement, enhancing for all

users the x-ray ring brightness. The reduced horizontal

emittance electron beam will produce brighter x-ray

beams for all the bean-dines, both bending magnets and

insertion devices, adding to other recent increases in the

X-Ray ring brightness. During FY 1999 users will gain

Figure 1: The first week of user beam time at 2.800 GeV.

Horizontal Profile

300~

I

— present optics

250 (e =101 nm*rad,

uXx=389~m) A

:$

●

200 ----- low emittance ) \

(~..=QGnm*rad, ; !

v

– 1000 –500 o 500

x(~m)

Figure 2. The source profile with “normal” and

reduced emittance magnet lattice.

experience of the new running mode and plans are in

place to do the same at 2.8GeV during fhrther studies

sessions. Independent evidence of the reduced emittance

is shown in Figure 2. This is a pinhole camera scan

showing the X-ray beam profile, obtained on the

diagnostic beandine X28.

Finally work has begun to update and refine the

proposal of the Phase III upgrade endorsed by the

Birgeneau panel and BESAC last year. With the whole

NSLS facility in teenage years and with many

demonstrated enhancements available, the time has come

to herald in the next stage of life at the Light Source.H

1-3
,.,

John B.Parise - –

SUNY@Stony Brook

UECChair

The UEC represents the interests of the users to

NSLS and BNL Administrations as well as to the

community outside BNL. Those interests include

continued access to reliable X-ray and UV beams and to

a working environment supportive of their research.

Almost 2400 users carried out experiments at the NSLS

during 1998. “Users” are defined as researchers who

actually showed up at the User Administration OffIce and

were given access to the experimental floor to perform

experiments on a beamline. With over 970\oreliability

on both X-ray and W storage rings, most users are

satisfied that the NSLS can provide what they need to

fulfil their research obligations. More and more of these

users however, are regarding the NSLS as an extension of

their home laboratory and this raises issues of access to

resources and infrastructure. In order to transmit those

interests as “cleanly” as possible, the UEC has studiously

cultivated its independence from the NSLS

Administration, while closely coordinating efforts with

it to improve services for the user. The UEC provides

independent advice with minimal influence from the

Laboratory or Light Source.

There are several avenues for users to express

opinions and suggestions, on subjects as varied as the

availability of consumables for experiments to the impact

of changing the characteristics of the storage rings.

Examples include prompting the NSLS to send out

regular news announcements to keep the user communi~

informed about the general goings on. A problem of

security for privately ordered specialty gas bottles was

brought to the attention of the UEC and a commitment

to provide a locked and controlled space under

management of the operations coordinator was made by

the NSLS. Several Special Interest Groups (SpIGs) serve

specific experiments or techniques and information on

these can be found at the following web address - http://

www.nsls.bnl.gov/UserGrp/spiginfo.html. The SpIGrepresentatives, as members of the UEC, can transmit a

user’s concerns. These representatives were elected in an

electronic ballot for the first time in 1999 thanks to the

efforts of Malcolm Capel (BNL - Biology) and Carl Zimba

(NIST). Quarterly town meetings are held in the NSLS

1-4

—.

seminar room and this provides another opportunity for

users to voice users’ concerns. While most of the attendees

at these meetings are frequent users, local beamline

contacts and NSLS st~, I urge everyone who can make

these meetings to do so or to email concerns to any UEC .

member or SpIG representative. Again, details are posted

on the NSLS web site. With the NSLS and BNL stailin

attendance, there are opportunities for immediate

discussion and feedback. The UEC then meets with

NSLS and BNL stfland management to discuss relevant

issues afier the Town Meeting.

The main topics at recent UEC meetings have been

the fate of the weekend food service and participation in

a Community Advisory Committee (CAC) formed to

advise the laboratory on its operations and their potential

impact on the broader Long Island community. The users

attending the town meetings were able to assure BNL

Management of their strong desire to have access to food

on the BNL campus during weekends, and as a result of

this input Management established expanded food service

hours on both Saturdays and Sundays at the Center. As

for maintaining a reasoned voice in the CAC, the UEC is

grateful to Jean Jordan-Sweet (IBM) for advancing our

interests from the early planning stages of the advisory

group. Peter Stephens (SUNY @ Stony Brook, past UECchair) has recently joined her as an alternate UECrepresentative. The relationship between BNL and the

community is a delicate one. It is one with the potential

to help or harm the interests of NSLS users. We all hope

the independent voice of the UEC will be heeded in this

forum.

Many users operate research programs at more than

one light source, and the four DOE-fimded synchrotrons

(NSLS, APS, SSRL and ALS) have similar interests in

terms of maintaining viable and expanding research

programs. In recognition of their common interests in

synchrotrons radiation research, the chairs of the User

groups at NSLS, APS and SSRL co-signed a letter urging

the implementation ofa BESAC-report recommendation

for increased fimding for synchrotrons research. The letter

reaa, m part:

demand for

1. “Our c;mm&ities are growing rapidly and

beam time continues to increase at each
I

I

I

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1.

facility.. we’d like to offer the assistance of our community

by providing full support of DOE efforts to acquire the

necessary additional funds to fully implement the

Birgeneau-Shen recommendations and continue support

for other important areas in the ERprogram.” In addition

to such joint letters, fimther user group coordination on

issues such as fimding and joint meetings of the light

source chairs are in the best interests of the whole

synchrotrons communi~.

The Annual Users’ Meeting, flmded largely out of

registration and vendor fees, is the most visible fimction

organized by the UEC. Along with celebrating scientific

accomplishments, the meeting serves to bring changes

and proposed changes, which have the potential to alter

the physical and intellectual environment in which the

users operate, to their attention. This meeting is an

opportunity for the UEC to devise workshops, invite

overview talks from leaders in the arenas of science and

science administration, and to set a tone for the year to

come by electing representatives to join the UEC. The

1998 meeting was a great success thanks mainly to the

efforts of workshop organizers, and particularlyJohn Hill

who attracted one of the best slate of speakers on record

for the one-day Users’ meeting. Excellent presentations

emphasized science, the future of the NSLS, and DOE

funding initiatives, The need to improve infrastructure

and -user support were common themes of the talks by

John Marburger, Director of the BNL, Michael Hart,

Chairman of ‘&e NSLS, Robert Marianelli, Director of

the Division of Chemical Sciences for the OffIce of Basic I

Energy Sciences (BES) and Dr. Ernest J. Moniz, Under

Secretary of Energy at the US Department of Energy. A

complete report appears in Section 3 of this Activity

Report. Apart for the annual meeting, the UEC from

time to time uses its funds to further the science agenda

and advertise the capabilities of the Light Source. To this

end the UEC was among the sponsors of the Montauk

conference on Inelastic X-ray Scattering in November

1998 and helped with other activities which raised the

profile of the NSLS at other conferences.

I am gratefid to all the members of the UEC (see

photograph with this article), to the User Administration ,

OffIce and to the staff of the NSLS for all their efforts

over the past year. Some, such as the restoration of power

during the unscheduled shutdown in December 1997,

were Herculean efforts. More typically they involve the !,

steady production of high quality beams. They also

include patient implementation of DOE directives, and

molli&i;g users who run afoul of these, the planning of

1

meetings, the compilation of this Activity Report, and

many other efforts impacting every user. Whether they

are aware of them or not, the user community depends

on these efforts to produce the science presented in this -

annual report. I am grateful to you all. ■

Users’ Executive Committee and

Special Interest Group Representatives

Seated: Malcolm Capel (BNL-Biology), Lisa Kelly (U. of Maryland); Michael Dudley (SUNY@ Stony Brook);

John Parise (SUNY @ Stony Brook); Jean Jordan-Sweet (IBM); Luz Martinez-Miranda (U. of Maryland);

Carol Hirschmugl (U. of Wisconsin); Mark Chance (Albert Einstein College of Medicine).

Standing Eva Rothman (NSK); George Cody (Carnegie Inst. of Wash.); Joel Brock (Cornell U.); Steve Whisnant

(U. of S. Carolina); Paul Stevens (Exxon); Gwyn Williams (NSLS); Larry Carr (NSLS); Barbara Illman (U. of

Wisconsin/USDA Forest Products Lab).

1-5


SCIENCEHIG~LiGFITS

SPECIALFEATURE: STRUCTURESOLUTIONFROMPOWDERDIFFRACTION.................................... 2-4

PW.Stephens, D.COX

APPLIEDSCIENCES

RAPIDAT-WAVELENGTHINSPEaiONOFEUV MASKBLANKSBYPHOTORESISTTRANSFER....................... 2-12

ATOM-SPECIFICCHEMInRYINHALOGENREACTIONSWITH 111-VSEMICONDUCTORS ................................ 2-14

BIOLOGICAL SCiENCES

SOLVINGTHESTRUCTUREOFA HISTONEACETYLTRANSFERASE: PUSHINGTHELIMITS OF MAD ................2-18

CHEMICALDIFFERENCESINSUBCHONDRALOSteOarthritiS BONEOBSERVEDWITH

SYNCHROTRONS IFRAREDMICROSPE~ROSCOPY................................................................................... 2-21

CRY~ALSTRUCRJREOFA HEPATITISDELTAVIRUSRIBOZYMEREVEALSA BURIEDACTWE

SITECLEFi_REMINISCENTPROTEINENZYMES........................................................................................2-24

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AT 2.8 A RESOLUTION......................................................................................................................... 2-26

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CD4 ANDA NEUTRALIZINGHUMANANTIBODY..................................................................................2-28

STRUCi_URALBASISFORTHEINTERACHONOFRASWITHRALGDS ............................................................ 2-30

STRUCTUREOF THE LARGERIBOSOMALSUBUNITFROMH. MARISMORTUIAT5.5 A RESOLUTION.............2-32

CHEMICALSCIENCES

CHEMI~RYOFSOZ ANDORGANOSULFURMOLECULESONMETALANDOXiDESURFACES: UnraVeling

THEMYSTERiESBEHINDCATALYSTPOISONINGANDDESULFURIZATION ................................................. 2-34

USINGX-RAY“VISION”TOUNDERSTANDSELF-ASSEMBLY......................................................................... 2-37

IONICSTATESOFSMALLMOLECULESINVESTIGATEDBYVIBRATIONALLY RESOLVEDCORE-LEVEL

PHOTOELECTRONSPEmROSCOPY........................................................................................................... 2-41

X-RAYSCAHER[NGFROMA SOLUBLEMONOLAYERATTHEWATER-HEXANEINTERFACE............................. 2-44

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COMPARATIVERHEOLOGYOFMANTLEPHASES........................................................................................... 2-50

IRONINMARTIANMETEORITES: MICROANALYSES OFFE3+/XFEBY SYNCHROTRONS

MICROXANES (SMX)ASINDICATORSOFVARIABLEOXYGENFUGACiTY............................................ 2-53

FIRS- XAFSMEASUREMENTS ONFERROUSCHLORIDEHYDROTHERMAL SOLUTIONSUSINGA

NOVELDIAMONDANVILCELL..........................................................................................0.................. 2-57

MATERIALSSCiENCES

QUANTIFYINGMAGNETICDOMAINCORRELATIONS iN MULTH-AYERFILMS.................................................. 2-60

ORIENTATIONAL CORRELATIONS INLIQUIDCRYqALLINEPHASES

REVEALEDBYPOLARIZATION-ANALWED RESONANTX-RAYSCATTERING............................................. 2-64

SURFACEANDBULKELEaRONICSTRUCIUREINWIDEBANDGAPNITRIDESEMICONDUaORS................2-67

X-RAYDIFFRACTIONSTUDIESONLEVITATEDLIQUIDS................................................................................. 2-72

DiRECTOBSERVATIONOFCHARGEANDORBITALORDERINGINMANGANITES........................................... 2-76

NUCLEARSCJENCE

THELEGSCOLLABORATION ATBEAMLINEX5 ..........................................................................................2-78

TECJYNIQUES fl INSTRUMEWATION

Son X-RAYSPECKLEANDSURFACEMORPHOLOGY................................................................................... 2-82

A NEWMETHODFOREXAMININGTHEDYNAMICSOFMACROMOLCULES:TIME-RESOLVED

SYNCHROTRONS X-RAY“FOOTPRINTING” ................................................................................................ 2-85

HIGH-RESOLUTIONX-RAYFLUORESCENCE SPE~ROSCOPYATX25: WHEREARETHE

ELEmRONS?WHO ARETHELIGANDS?.................................................................................................2-88

NEWLYCOMMISSIONED3-30EV UNDULATORBEAMLINEUI3UB...........................................................2-90

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TWO-DIMENSIONALPERiODICITY................................................................................................................2-96

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StructureSolutionfrom PowderDiffractionat the NSLS

Peter W.Stephens (SUNYStony Brook, Physics~ Astronomy Department)

DavidE.Cox (BNLPhysicsDepartment)

INTRODUCTION

Over the last few years, there has been a rapid growth

in the development and application of methods for the

ab inifi”o solution of unknown crystal structures from

powder diffraction data. Although conventional

laboratory techniques have been successful in solving

many heavy-atom inorganic structures, the most exciting

recent advances have centered around the use of

synchrotrons x-ray powder data for the solution of

molecular and organic structures, and framework

structures such as zeolites. For structure solution

problems, synchrotrons radiation offers two outstanding

advantages: the very high instrumental resolution that

can be achieved with the use of a crystal analyzer mounted

in the diffracted beam (about an order-of-magnitude

better than that of a conventional diffractometer), and

the feasibility of using samples loaded in thin-walled

capillaries (which can be up to 2 mm in diameter

depending on the sample transparency) without any loss

in resolution. Other significant advantages are accurate

peak positions, improved peak-to-background

discrimination, wavelength tunability, well-characterized

peak shapes, and the ease with which data can be collected

at low temperatures in order to minimize thermal dkorder.

Most ab initio powder studies at the National

Synchrotrons Light Source (NSLS) are carried out at the

bending-magnet beam lines X3B1 and X7A, which have

a long and productive history in this field. In a typical

experiment, a double-crystal Si or Ge (1 11)

monochromator is used in conjunction with a flat Si or

Ge analyzer crystal, usually in the wavelength range 0.7-

1.3 ~. The capillary sample is rotated or rocked during

data collection (which in favorable circumstances might

extend to a d-spacing of 0.8&, and the raw data converted

to a diffraction histogram. The standard procedure at

this point is to: (1) index the unit cell using one of several

powerfid auto-indexing programs, (2) extract the structure

factors, (3) solve at least part of the structure using

tradkional methods, and (4) locate the rest of the atoms

by a combination of Rietveld refinement and difference

Fourier synthesis.

At stage (3) the problem is basically reduced to a

single crystal structure determination with a limited and

noisy data set, and can be tackled by the application of

traditional Patterson and direct methods. The powder

technique has been successfidly exploited for a number

of structures containing 30 to 50 atoms in the asymmetric

unit, and in the future may perhaps be extended to 70-

100 atom problems. Some examples are described below.

a

Figure 1: Structure of Uranyl Methylphosphonate,

from Reference 1, determined by powder

diffraction data.

2-4
Although the powerfid multiple anomalous diffraction

techniques increasingly being used for protein

crystallography cannot be exploited in the same way for

powder data, anomalous scattering can nevertheless be

applied in principle to the solution of unknown structures

through the generation of partial Patterson maps of the

anomalous scatterer, and a test case is described below.

The most recent developments in the application

of powder techniques have focused on more novel

approaches to the solution of organic compounds,

molecular crystals and other light-atom structures such

as zeolites. These approaches include Monte Carlo

maximization and maximum likelihood, Fourier recycling

with a specialized topology search specific to zeolites, and

the use ofperiodic nodal surfice.s. Several of these methods

operate in direct rather than reciprocal or Patterson space,

and rely on random displacements ofstructural fragments

to generate an acceptable fit to the diffraction pattern,

thereby avoiding the necessity of extracting structure

factors in step (2) above.

A one-day workshop, “Using Powder Data to Solve

Crystal Structures,” reviewing thk area of crystallography

was held at the NSLS 1998 Annual Users’ Meeting. There

were eigh~ participants, testifying to the exceptionally

procedures, simulated annealing techniques, global high level of interest in this topic. -

optimization based on a genetic algorithm, entropy

MEMcalculation y=o Y=I12

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Figure 2: MEMvs. Fourier maps of the Sr partial Patterson function

in SrSOQ,determined by anomalous scattering.

2-5
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TRADITIONAL METHODS

Some of the traditional methods used to phase

single-crystal diffraction patterns have been adapted to

powder data sers, andarein productive use. Structure

solutions from powder data are never as routine as singlecrystal experiments, because the collapse of the diffraction

pattern into one dimension generally requires close human

supervision and evaluation of the quality of the raw data,

determination of the unit cell, extraction of integrated

intensities, etc. Patterson methods are very powerfid for

cases in which there are a few heavy atoms. One recent

example is the structure of uranyl methylphosphonate,

. ---

UO,(OZPCHq), illustrated in Figure l.[’] This layered -. .

compound is of interest because metal phosphonate

systems can be synthesized with a variety of fictional

groups, and are able to self-assemble into lattices with

interesting potential materials properties, in this case,

luminescence. The approximate structure was solved from

laboratory x-ray data using Patterson methods, and

completed by successive Fourier difference calculations,

but synchrotrons data were necessary to obtain a stable

refinement.

Direct methods constitute the current workhorse

technique for phasing single crystal diffraction patterns,

based on statistical relationships of the phases and the

Figure 3: Crystal structure of RbC60and Na2RbC60

polymeric ground states. From Reference 3.

2-6

intensities of combinations of three or more

diffraction peaks. Powder data would seem

to be ill-equipped to meet the condition of

the number of independent observations

much greater than the number of atom

coordinates for any but the simplest problems,

but the combination of high resolution

experiments with advances in sofbvare has

increased the power of this technique. Several

recent examples of newly-solved structures,

drawn from this year’s experimental abstracts,

include Rb~Pb Clj, the charge-transfer

complex ~l(dmit)2]2- DPD-Me2+, and the

alkali salicylates CTHjO~Rb and C7Hj0,K.

In contrast to macromolecular

crystallography, anomalous scattering

techniques have not yet been used for ab ir.zitio

structure solution from powder data. The

key to the use of anomalous dispersion in

phasing single crystal diffraction patterns lies

in the fact that it produces a different intensity

for the ——— two members of Bijvoet pairs

lzkl and hkl. The technique iS not directlY

transferable to powder diffraction, because all

such pairs of reflections are superimposed, but

it is nevertheless possible in principle to

determine the difference Patterson density of

the anomalously scattering atom from two

measurements, close to and far from the

absorption edge. The application of this

technique to the test case of SrSOi is

illustrated in Figure 2, which shows the partial

Patterson density of Sr.[21A notable feature of

this work is the obvious superiority of

maximum entropy methods over

conventional Fourier synthesis in the

reconstruction of the density maps.
SIMULATED ANNEALING TECHNIQUES

FOR MOLECULAR SOLIDS

In the cases of organic solids, one can usually make

a fairly good guess of the molecular structure from

chemical principles (bond lengths and angles) and so there

are only a few degrees of freedom in determining how

the molecules might pack into a lattice. Organic

molecules typically occupy the general position of a lattice,

and so a structure is specified by six real numbers to locate

the position and orientation of the molecule’s center, plus

however many internal degrees of freedom are described

by torsion angles. In these techniques, the agreement

between a calculated diffraction pattern and the observed

data is regarded as an energy to be minimized, and

exhaustive searches or simulated annealing algorithms are

applied to determine the best fit between model and data.

There are several interesting new results from recent

experiments at the NSL.S.

The developing story of polymerization of CGOhas

been fi.dl of surprises. In 1994, experiments at the NSLS

showed that RbCGO and KCGO had different lowtemperature states depending on their thermal history.

If cooled slowly they polymerized spontaneously into the

ground state structure illustrated in Figure 3a, with two

single bonds (a [2+2] cycloaddition) linking adjacent

fi.dlerenes into chains. If quenched, the fi.dlerenes paired

off into dimers; surprisingly, it was found that the dimers

were linked by a single carbon-carbon bond, different

than the polymer. More recently it was found that if the

fidlerene charge state is increased to 3-, in N~RbCGO or

Na,KCGO, it has a polymeric ground state (Figure 3b)

connected by the same single bond as the singly charged

fi.dlerenes in quenched Rbz(Cb~2 and ~(CG~2.131 These

results imply that the charge state has a crucial effect on

determining the available routes of interfidlerene bonding.

In this work, the fullerenes were previously known to be

centered at special positions of the crystal lattice, but the

. ....

Figure 4: l+-, Na2-,and

1$-terephthalate structures

from powder diffraction data.

2-7
,.,

.. ~ ,, .!. ... .’ . .,, ., —.

. ., ;-.: ,. .,”.,<. . -. ..;

orientation had to be determined in order to find the

plausible bonding geometry. The high angle part of the

diffraction pattern suffered from such severe peak overlap

that no progress could be made with extracted intensities,

but the- pr~blem could be attacked by comparing the

entire cal&lated &fFraction profile. Thls would only-work

for a molecule that largely retains its rigid identity in

different crystal structures, but the successfid refinements

prove that this premise is correct.

A very different example comes from the chemical

industry. Amoco technology produces over four million

tons annually of purified terephthalic acid (1,4-

benzenedicarboxylic- acid). Unde&ndlng the natures

of terephthalate complexes of catalyst and co~rosion metals

will lead to process insights and improvements. Nothing,

however, is known about the solid state structures of such

complexes, because they are intractable solids, available

only as powders. Despite the importance of this problem,

there has been little progress from applying conventional

crystallographic techniques to the powder patterns of

transition metal terephthalates. There area great number

of possible metal-carbo~late binding modes, and so it is

worthwhile to develop skills and techniques for solving

the structures of such coordination compounds, and to

gain insight into how terephthalate anions pack in the

solid state. Toward that end, J.A. Kaduk at Amoco has

studied a number of terephthalate salts of non-transition

metal cations. Combinations of Monte Carlo simulated

annealing, molecular mechanics, and crystallographic

techniques have proven successful in obtaining the

structures of such salts. The structures of dilithium,

disodium, and diammonium terephthalates have been

solved ab initio using synchrotrons powder data and

simulated annealing sofnvare from Molecular Simulations

Inc., and can be compared to the structure of dipotassium

terephthalate, determined using conventional singlecrystal techniques. The structures of the three alkali salts

are shown in Figure 4, which illustrates large differences

between the structures of these closely related compounds.

For example, the terephthalates in the Li, K, and

ammonium salts are nearly planar, but the carbonates

are rotated approximately 20° out of the ring plane in

disodium terephthalate. These four structures provide

enough of a “database” to begin to understand the

‘oocs $

TH20H

cH30J&@ocH3

r-f (’-)

I

HS_’_’__ ~

.. “00 ‘-”3”’Kc~ I

I

kH3

Figure 5: An assortment of

molecules whose crystal

structures have been determined

by ab inifio powder diffraction

techniques. Circular arrows

indicate molecular torsion angles

that must be determined

experimentally.

I

\R

2-8
!

energetic of these structures. Such understanding is

proving useful in determining the structures of more

process-related salts.

Simulated annealing techniques, both as developed

by users and in commercial sofiware, and with varying

degrees of input from calculations of the confirmational

and packing energetic, have been applied to first

determine the solutions of a large number of different

molecular solids. The range of complexity is illustrated

in the molecular diagrams in Figure 5. More details on

all of these structures are available in the experimental

abstracts from beamlines X3B 1 and X7A.

It is worth pointing out that synchrotrons data is

often crucial for solving organic structures, not only

because it yields better structure factors, but because it

permits determination of the correct unit cells and space

groups, The systematic errors inherent in a laboratory

Bragg-Brentano experiment, particularly peak shifis due

to the penetration of x-rays into weakly absorbing samples,

make it difflcuk to index the laboratory patterns. One

often thinks of the determination of the unit cell as

mechanical, but it is crucial to obtaining the correct

structure. Furthermore, the high angular resolution and

high signal to background ratio of data sets usually

collected with synchrotrons radiation are of great

importance in the determination of systematic absences

and therefore of the correct space group.

FRAMEWORK COMPOUNDS

Framework compounds such as zeolites are very

widely used as catalysts, absorbents and ion-exchangers

in industrial processes. The catalytic activity and

selectivity of zeolites depend upon active sites which are

accessed by reactant organic molecules through pores of

about the same size as the molecules. Understanding

zeolite structures is thus of utmost importance in

optimizing the properties of these materials for industrial

use. Since most zeolites are synthesized via the use of

organo-cation templates under hydrothermal conditions

which typically yield crystals less than 5 microns in size,

powder techniques are vital in structural studies, and many

such structures have been successfully solved by industrial

and academic groups in the past decade. The techniques

to solve zeolite structures from powder data are somewhat

different than molecular structures. Instead of a distinct

molecule which can be moved around in the unit cell (by

computer), one has a Klghly connected framework, with

a large number of tetrahedrally coordinated (Si~) atoms.

It is therefore necessary to generate and test a number of

different framework topologies against the experimental

data, and several recently developed algorithms have

extended the utility of these techniques.

A striking recent example is the structure of a new

small-pore zeolite, ERS-7, with the approximate

Figure 6: The 17-sided ‘picnicbasket” cage element in the

structure of the new zeolite

ERS-7,determined by powder

diffraction.

2-9
. .,

. .

... . ..

composition NaXRY(Sil-zM)Oz, where R is the

template ion, N, N-dimethylpiperidhium and

x- O.03, y+O.09, and z-O. 1. The correct structure

was identified as one of 373 unique framework

topologies generated by a simulated annealing

tecluique using MSI software, and was verified

by Rletveld refinement and lattice energy

minimization calculations. (41The orthorhombic

framework has twenty atoms in the asymmetric

unit, and consists of 17-sided cages with a “picnicbasker” shape connected by an eight-membered

ring system such that the ring channels run

through the “handles” of the picnic basket,

depicted in Figure 6.

Many groups are actively seeking new

zeolites with even larger pores, consisting of rings

of twelve or more tetrahedral atoms, for catalysis

or absorption on large organic molecules.

Materials with a high-silica content are

particularly desirable because of their high acidity

and thermal stability. The structure of a novel

compound with a 14-membered ring, CIT-5, was

recently determined at the NSL.S by an iterative

process of model building, distance-least-squares

refinement of the model parameters, and

comparison of the simulated and experimental

patterns until the closest match was found151.

Rietveld refinement was carried out on this

structure, which is orthorhombic with 5 Si and 8

0 atoms in the asymmetric unit, and is composed

of one-dimensional extra-large pores of nearly

circular cross-section (Figure 7).

Another interesting example is the A initio

solution of the structure of two closely-related

Figure 7: Structure of CIT-5viewed down the [010] axis,

showing the large pores circumscribed by 14-membered

rings of tetrahedral Si atoms.

large-pore high-silica molecular sieve materials, SS2-44

and SS2-35. The first was solved by application of the

Fourier recycling and topology search (FOCUS)

method,{q followed by Rietveld refinement. The structure

is monoclinic with 8 Si and 170 atoms in the asymmetric

unit, and consists of unusual one-dimensional straight

channels containing pore openings that oscillate between

rings often and eighteen tetrahedral atoms in layer-like

unirsv]. An interesting feature of thk structure is that the

powder diffraction experiments revealed that SS2-44 and

SS2-35 are very similar, with ABAB and ABCABC

stacking, respectively, of layers along the pore direction.

It was previously known that SS2-44 and SS2-35 had

similar catalytic properties, and this new structural

information shows that they are the pure end-member

polymorphs of a newfauk series, which allow investigation

of the relationship between the organic structure-directing

agent and the stacking fault structure of the zeolite

framework.

2-1o

MARGINAL MATERIALS

Du Pent Corporate Research and Development is

working on new families of catalysts for Freon@

replacements, and this has prompted work in various

aluminum fluoride preparations. Compounds which are

industrially usefid catalysts ofien give very poor diffraction

patterns which make them difficult to attack. One wellpublicized example was the DuPont powder challenge.

Data sets collected at two NSLS beamlines of a material

alleged to be HalF4 proved to be intractable, and so

Richard Harlow issued a $1000 cash challenge to the

crystallographic community for the first acceptable

solution from the data plotted in Figure 8.18] Relative to

other work described here, this data is of extremely poor

quality, having broad, overlapped peaks, with a limited

range of d-spacings. Several entries (including the

proposer) correctly found part of the structure, layers of
10000+

1000:

100T

10 z

So-called HAIF4

,.,

l“’’I’’’’ 1’’’’ 1’’’’ 1’’” 1“”1

0.00 0.10 0.20 0.30 0.40 0.50 0,60

sinell

edge- andcorner-sharing AIFG octahedra, but the credit theme that runs through much of the work reviewed here:,.

for a complete solution goes-to Leonid Solovyov and chemical information beyond the diffraction data is ofien

Sergei Kirik from the Institute ofChemistryand Chemical crucial to solve a structural problem, but that information

Engineering, Russian Academy of Sciences in had better be correct! It also shows that if one is

Krasnoyarsk, Russia. By chemical tests on samples sufficiently motivated, one can solve significant problems

provided by DuPont, they suspected the presence of from rather poor samples, and that we can expect to see

organic material, and so converged to the correct solution, considerable fimher progress in the utility of ZZ6z%itz”o

with pyridinium counterions. This brings us back to a powder techniques to interesting problems. ■

[1]

[2]

[3]

[4]

[51

[6]

[71

[8]

i

D. Grohol, F. Gingl, and A. Clearfield, submitted to Inorganic Chemistry

K. Burger, D.E. Cox, R. Papoular, and W. Prandl, J. Appl Ciystallog., in press.

G.M. Bendele et a~, Phys. Rev. Letters, 80,736, (1998).

B.J. Campbell eta~ Cbem. Commzm., 1998, 1725, (1998).

1?Wagner, M. Yoshikawa, M. Lovallo, K. Tsuji, M. T~patsis, and M.E. Davis,

Chem. Commun., 1997,2179, (1997).

R.W. Grosse-Kunstleve, L.B. McCusker, and Ch. Baerlocher, J Appl. Cgut., 30,985, (1997).

1?Wagner, S.1. Zones, M.E. Davis, and R.C. Medrud, Azzgew. Cbern. Int. Es!, in press.

DuPont Powder Challenge posted on the world wide web: vvww.pitt.edu/.geib/powder.html.

2-11

:.

t

1
. .

. ..

,

RapidAt-WavelengthInspectionofEUVMaskBlanksby

PhotoresistTransfer

S.J. Spector, D.L.White, and O.R.Wood, [1

(BellLaboratories, Lucent Technologies)

Extreme-ultraviolet (EUV) lithography is an

advanced form of optical projection lithography being

developed by a consortium of integrated circuit

manufacturers to print features .0.1 ~m[ll. EUV

lithography will likely employ a reflective mask consisting

of a patterned absorber on a mukilayer coated substrate

(mask blank) that reflects a narrow band of EUV

wavelengths near 13.4 nm. Such masks have the advantage

of being thick and dimensionally stable, however, the use

of such masks presents some challenges. Because it is

currently impossible to repair certain types of defects in a

mask blank, it will likely be necessary to begin with a

defect free mask blanks. An effort is being made to

produce defect free blarddzl. Blanks with as few as three

defects, as determined by optical means, have been

produced.

Unlike other existing and likely future technologies,

optical inspection may not be sufficient to find all defects

in an EW mask. While optical inspection tools can be

used to find certain defects (such as particles and scratches)

on such a mask, subtle anomalies in the reflective

multilayer coating can produce dramatic changes in the

real and imaginary components of the reflectivity at the

EW wavelength but have no apparent effect on visible

light. Indeed, such defects have already been observed in

EUV imaging experiments 131. Because of this, atwavelength techniques, i. e. techniques using light of the

wavelength at which the mask blanks are to be used, must

be used to locate and mark defect sites. However, because

optical inspection tools are so fast and efficient, it would

be very economical to read out these marked defects

optically. Therefore, we have developed a new EW mask

inspection technique in which defects are marked by a

brief flood exposure to EUV radiation (from a

synchrotrons or laser-plasma point source) and then

examined optically141.

In the simplest experimental arrangement for the

new inspection technique, illustrated in Figure A-1, an

EUV sensitive resist is deposited directly on the

multilayer-coated mask blank. During a flood exposure,

incoming EW radiation passes through the thin layer of

resist, reflects off the multilayer coating and then passes

,Resist (withbump)

— Muttilayer

b — Substrate w

Figure A-1. Diagram illustrating the photoresist transfer process. a) A photoresist is applied directly to an EUV

reflective multilayer coated substrate that is subsequently flood exposed with EUV radiation. A reflectivity

defect results in less exposure to the resist above the defect. b) After patilal development of a positive tone

resist a bump remains above the defect.

2-12
back through the resist once again. A local decrease in

reflectivi~ will reduce the resist exposure above defect

sites, Under these conditions, partial development of the

resist will show reflectance defecE as mounds (pits) in a

positive (negative) tone resist. Once the EW flood

exposure has created features in the resist immediately

above defect sites, these mounds or pits can be detected

by an optical scanning instrument, allowing rapid flagging

of EW defects.

The experiment was performed on an EW mask

blank, a2° diameter Mo/Si mukilayer-coated silicon wafer

with a peak reflectance of (52Y0 at a wavelength of 13.4

nm. To demonstrate the detection of known defects,

reflectivity defects (of approximately 12c!loless reflectivi~

than normal) were created in the mask blank using a

focused ion beam of Ga+. Before exposure, the mukiiayercoated EW mask blank was spin-coated with an 800

Angstrom thickness of ZEP resist and baked at 190”C

for 1 hour. The exposure was performed with 13.4 nm

radiation from the 3rdharmonic of the U13 undulator.

Following EWexposure, the sample was spin-developed

in xylenes and rinsed in isopropyl alcohol.

AFM images of an area of an EW mask blank

containing a programmed defect both before and after

EW exposure and development are shown in Figures

A-2a and A-2b. In Figure A-2a, an AFM image of an

area containing a bare programmed defect, there is a

rectangular shaped depression in the surface of the

multilayer coating in the implanted region approximately

10 ~ deep, In Figure A-2b, an AFM image of the same

area afier EW exposure and development, there is no

longer a small depression; instead, there is a mound in

the photoresist at the site of the defect approximately 40-

Current research efforts include the use of a higher

contrast resist to create taller resist features. The taller

features should be easier to detect, hence improving the

sensitivity of our technique. Also currently being

researched is an alternative technique which greatly

reduces the risk of contaminating the mask blank. In

this method, the resist is applied to a EW-transmitting

membrane which is placed in near contact with the mask

blank during flood exposure. ■

WegtatejdlyacknowhdgethetechnicalassistanceofDon Tmnant,

Leo OcoLz,DavidBarr (withtheliicrz”onFIB),RayCirelli,Llqd

HarrioG andStevenHulbert (with U13 BeamlineOperation).

Wea.kotbankJimUnderwoodatThe Centerfor X-ray Optics@r

makingre~ectz”vitymeasurements,the assistanceof the .$mjican

ApplicationsGroupat ILL4-TmcofiandtheiVSLSforaliowingus

to usethe U13 undulatorbeamline.

REFERENCES

[1] C. W. Gwyn, R. Stulen, D. Sweeny, and D. Athvoo4

“Extreme ultraviolet lithography: 1 Pizc.Sci. Tech. B

16, pp.3142-3149 (1998).

[2] S. P. Vernon, D. R. Kania, P. A. Kearney, and R. A.

Levesque, “Reticle blanks for extreme ultraviolet

lithography: ion beam sputter deposition of low defect

density MolSi multilayers;’ OSA Trends in Optics and

Photonics 4, pp. 44-48,1996

[3] D. M. Tennant, L. A. Fetter, L. R. Harriott, A. A.

MacDowell, P.P. Mulgrew, J. Z. Pastalan, W. K.

Waskiewicz, D.L. Windt, and O. R. Wood 11, “Mask

technologies for soft-x-ray projection lithography at 13

nm~’Applied Optics 32, pp. 7007-7011, 1993.

[4] S. J. Spector, D. L. White, D. M. Tennant, F?Luo, and

O.R. Wood II, “Rapid at-wavelength inspection of EW

mask blanks by photoresist transfer,” Proceeding of

50 ~ high. ~ 3546, Pp. 548-555 (1998).

Figure A-2. Atomic force microscope images of a 40 ~m x 50 pm area of the surface of-an EUV mask blank

containing a programmed defect. a) Bare defect. Only a small depres~ion of about 10A can be seen in the

defect region. b) Defect after EUV exposure and development. A 50 A high bump in the ZEP photoresist is

now visible in the defect region.

2-13
Atom-SpecificChemistryinHalogenReactions

Semiconductors

W.K.Wang, W.C.Simpson and J.A.Yarmoff

Department of Physics, University of California, Riverside

and Materials Sciences Division,Lawrence Berkeley National Laboratory

with III-V

Gaseous processes, such as plasma or reactive ion

beam etching, are routinely used to fabricate structures

for microelectronic devices. As device dimensions shrink

and three-dimensional topography becomes more

complex, however, these methods need to be better

characterized and controlled. This requires that the gassurface interactions be understood at the most

fimdamental level. Silicon etching is, by fir, the system

that has been the most widely studied, yet significant

questions still remain. The situation for compound

semiconductor materials is much worse [Il. Despite their

importance for photonic and electro-optic devices, factors

affecting their processability by gaseous methods are

poorly understood.

We have been using a number of surface-sensitive

techniques, most notably synchrotron-based sofi x-ray

photoelectron spectroscopy (SXPS), to investigate the

interaction of halogens with III-V semiconductor surfaces.

Our group and others have found that not only are the-se

reactions technically relevant, but there is also a rich

chemistry involved. For example, ordered halogen

overlayers form under certain conditions, while etching

occurs under other conditions121.Also, afier large exposures

at room temperature, surfaces are ofien covered with a

thick halogenated reaction layer131.

Another useful by-product of our work has been

the identification of methods whereby particular surface

structures can be prepared in a simple manner via dry

chemical methods, i.e., without the need for a complex

and expensive procedure such as molecular beam epitaxy

(MBE). For example, we showed how to prepare highquaiity GaAs(l 10) surfaces by reaction with Clz at elevated

temperaturet41, and how to prepare a group V-terminated

(001) surface by saturating a group III-terminated surface

with 12and then annealing 12,5*Q.These methods ofsurface

preparation can now be developed for use in other

applications.

Most of our work has been with the (001) surface.

This surface can be prepared to be either group III- or

group V-terminated, so that the relationship between the

surface termination and the reaction pathway can be

directly determined. Note that this is also the surface

employed for the fabrication of devices. We have used

low energy electron diffraction (LEED) to measure the

ordering and SXPS to determine the bonding

configuration on the surface. “

One of the remarkable observations is that, at room

temperature, halogen adsorption on certain III-V

semiconductor surfaces forms ordered overlayers, while

other surfaces become disordered. The disorder is

presumably the precursor to etching. Sometimes these

complementary reaction pathways are obtained from

initial surface conditions that are not too different from

each other. Figure A-3 summarizes whether particular

(001) surfaces become ordered or disordered following a

moderate exposure to Iz or C12, as determined by LEED.

—. .

I

12 I

C12 I

Material Grotm 111- GrOUDV- GrOUD111- GrOUDVTerminated Terminated Terminated Terminated

InAs Order - Disorder Disorder Disorder

InSb Disorder Disorder Disorder Disorder

GaAs I

Order I

Order I

Disorder/ Order I

Disorder I

Figure A-3. The experimentally determined reaction pathways of various Ill-V (001) surfaces

when exposed to 12and C12.

2-14
As can be seen, chlorine will almost

always induce disorder (@en sufi-lcient

exposure), while iodine sometimes

orders and sometimes disorders.

There are a few factors that appear

to control most of the observed

behavior. For one, the various surfaces

have different relative amounts of

group III vs. group V atoms directly

exposed to the incoming reactants.

Note that, although a surface maybe

terminated with one element, there are

most often vacancies in the first layer

which expose some of the second layer

atoms. Next, there is always a

preference for reaction with group III,

rather than group V, elements. On the

reconstructed surface, group HI

elements have empty orbitals that

protrude into the vacuum, while group

V elements have filled lone pairs. The

closed-shell halogen molecular orbitals

are attracted to the empty surface

orbitals, while they are repelled by the

filled surface orbitals. Thus, the

bonding of halogens is more likely to

occur at group 111surface sites than at

group Vsites. The degree ofpreference

varies from system to system, however.

Finally an inability to form higher

halides can passivate surfaces with

respect to further reaction following the

formation of a single monolayer of

adsorbates.

For 1, reacted with InAs(OOl),

there is a big difference in the reaction

pathway for the two terminations[zl.

On the In-terminated surface, a wellordered (1 X 1) structure forms in which

all of the iodine is attached to In, mosdy

in the form of the monoiodide, i.e,, InI.

The As-terminated surface becomes

disordered, however, and iodine

attaches to both In and As. SXPS

spectra collected from Iz-reacted

InAs(OOl) are shown in Figure A-4.

These observations can be

explained by assuming that iodine

initially bonds to the group 111 In

atoms, whether they are in the first or

second layer121. On the In-terminated

surface, iodine attaches to the

In& reacted with C&

En‘k% As 3d I 1 6

*

-4 -2 ,0

“*

2-4 -2 0 2

Binding Energy (eV, relative to bulk)

Figure A-4. High-resolution SXPS In 4d and As 3d

spectra collected from In- and As-terminated InAs(OOl)

after exposure to 12

InSb(OOl) reacted with ~

li14d Sb 4d

A k

Bdk

T-T Bulk i

m

W2

w

\

1 I I I 1 I i I I

-4 -2 4

Bin&g e;ergy (eV,~elati;e to &k)2

Figure A-5. Schematic illustration of the reaction

mechanism for 12with In- and As-terminated lnAs(OOl).

c

‘,

/

I

1

2-15
— . . . . >

In-terminated surface As-terminated surface

???

/+@* &~..*

I attaches to 1st layer In ato~ I attaches to 2nd layer IW

In-In dimera break charge transfers to 1 depleting

As orbitals

~a &<&

As orbitals remti ~, As atoms 1 can now attach to the As atom,

still unreactive In-As bondabreak

@%?%b.

1 is bonded rimarily to @

f

I ia bondedto both In andk,

formation o InI ia inhibited; surface is disordered

some lateral M?%sion occw, an

ordered 1x1 structure ia obtained

Figure A-7. High-resolution In 4d and As 3d core-level spectra collected atler

exposure of the indicated InAs(OOl) surface to C12.

outermost In atoms forming an ordered overlayer of

monoiodides. This surface pa.ssivates, as the formation

of diiodides is limited. On the As-terminated surface,

on the orher hand, iodine initially bonds to a second layer

In atom. Upon bonding, charge is transferred away from

the fdled orbitals associated with surface As. Thk makes

rhe first layer As atoms reactive to additional incoming

Iz. When iodine has bonded to both In and As, the InAs bonds break and the surface eventually becomes

disordered. This mechanism is illustrated in FigureA-5.

On some surfaces, however, the preference for

bonding to the group III element overwhelms all other

factors. An example of this is given by the reaction of 1,

with InSb(OO 1). As seen in Figure A-(i, InIz is the major

surface product, and the two terminations produce nearly

identical spectra following reaction.

Clz reactions appear to not be limited by either the

preference for bonding to a group III atom, or by the

stabili~ of monoha.lides. Instead, it appears that chlorine

can easily bond to either the group III or group V atom,

and can easily form higher ha.lidesL71.This is seen in Figure

A-7, which shows spectra collected from three InAs(OOl)

surfaces following C4reaction. InCl is the primary species

formed on all three surfaces, although some InCl,, InCl,,

AsCI and AsCIZ also form (AsCl~ is volatile). On the

initially As-terminated surface, relatively more of the

higher In chlorides and As chlorides are produced. On

the sputtered surface, however, relatively more In chlorides

form, possibly because As was preferentially removed by

the sputtering. Thus, although the relative amounts of

the chlorides produced depend on the initial surface

stoichiometry, the basic reaction pathway is essentially

2-16
I

i

/

IIAs(OO1) reacted with ~

In 4d As 3d

A II

-4 -2 0 2 -4 -2 0 2

Binding energy (eV, relative to bulk)

Figure A-6. High-resolution SXPSIn 4d and Sb 4d spectra collected from

In- and Sb-terminated InSb(OOl) after exposure to 12

independent of termination. The same type of behavior

is seen for Clz reaction with GaAs(OO1) ’81.

In summary, we have used synchrotrons radiation

and other surface-sensitive probes to enable a fi.mdamental

understanding of halogen reactions with III-V

semiconductor surfaces. We found that the surface

stoichiometry and the relative ease of formation of the

higher halides determine the reaction pathway. These

experiments (1) provide good basic physical and chemical

insight into surface reactions, (2) will enable the

development of a more rational approach to dry

processing procedures, and (3) provide the understanding

necessary for chemically producing suri%cestructures with

atomic precision. This last point will become even more

crucial as the size scales on which we work get smaller. ■

REFERENCES

[1]

[2]

[3]

[4]

[51

[71

[8]

W.C. Simpson and J.A. Ytimoff, Ann. Rev. Phys. Cbenz. 47,527 (199 G).

W.K. Wang, W.C. Simpson, and J.A. Yarmoff, Pbys. Rev. Lett. 81, 1465 (1998).

WC. Simpson, D.K. Shuh, and J.A. YarmofE j Mc. Sci. Ecbnol B 14,2909 (1996).

W.C. Simpson, W.M. Tong, C.B. Weare, D.K. Shuh, and J.A. Yarmo& J Cbein. Pbys. 104,320 (1995).

I?R. Varekamp, M.C. H&nsson, J. Kanski, M. Bjorkqvist, M. Gothelid, B.J. Kowalski, Z.Q. He, D.K. Shuh,

J.A. YarmoK and U.O. Karlsson, U.O. Karlsson, andJ.A. Yamofi Pkys. Rev. B 54,2101 (1996).

W.K. Wang, W.C. Simpson, and J.A. Yarmoff, to republished

W.C. Simpson, D.K. Shuh, W.H. Hung, M.C. H5kansson, J. Kanski, U.O. Kadsson, and J.A. Yarmofi J V~c.

Sci. Zcbnol A 14, 1815 (199G).

2-17
.-

/)

if “.

,.—.--:. -

.—,-

,,, !

.,

,,

Solvingthe Structureof a HistoneAcetyltransferase:

Pushingthe LimitsofMAD

R.N.Dutnall,S.T.Tafrov,R.Sternglanz, and V.Ramakrishnan

(U. of Utah School of Medi&e) -

Chromatin is a complex between the genetic

material DNA and some highly charged proteins called

histones. It is built up from a repeating units called

nucleosomes, which under the electron microscope appear

like beads on a string of DNA. Wkhin each nucleosome

the DNA is wrapped nearly twice around a core structure

composed of two copies each of the core histones H2A,

H2B, H3 and H4. Beyond this fundamental level,

nucleosomes form complex interactions with each other

and with other chromatin components to form

chromosomes.

Organizing DNA this way has two major

advantages. Firstly it means that the large amount of

information contained within the genomes of higher

organisms can be packaged into a nucleus. For example,

the DNA in the chromosomes of a human genome, if

laid out end to end, would measure roughly two metres

long but has to be contained wit&n a nucleus that is only

about I o-20 ~m in dkuneter. Secondly it is a powerful

way of regulating how the information within a genome

is expressed.

The first step in gene expression involves the

formation of mRNA by a complex machinery of proteins

that interact with DNA during the process of

transcription. Eventually the mRNA serves as a template

for the production of specific proteins. By changing the

structure of chromatin so that it is more or less accessible

to components of the transcription machinery, cells can

regulate which genes are expressed and which are not.

Changes in the pattern of genes that are expressed drive

the differentiation of different cell types during the

development of an organism. After development is

complete, maintaining these patterns helps to define the

behaviour of the various cell types found within a complex

organism. Failures in thk complex control can result in

developmental disorders, cancer, or other diseases

One way that cells regulate the structure of

chromatin is by modlfjing specific lysine residues of the

histones by attaching an acetyl group. Each core histone

is made up of a globular region that is involved in

interaction with the other histones and with DNA, and

more flexible, highly charged tails at each end of the

globular region. The N-terminal tails in particular contain

many positively charged arginine and lysine residues.

Many of the Iysine residues have been found to be

acetylated under dKferent condkions, and it has been

known for a long time that the level of ace~lation of

histones in different regions of chromatin correlates well

with the activity of the chromatin in terms of gene

expression. For example, genes that are active often are

associated with chromatin in which the histories are highly

acetylated, while inactive genes are associated with

chromatin made up from less acetylated histones. Despite

this correlation it still is not known for certain how histone

acetylation alters the structure of chromatin. One

possibility is that acetylation reduces the positive charge

of the histone tails, making them less able to bind DNA

where they could interfere with binding of various

transcription factors. A second is that it alters the way in

which the nucleosomes interact with each other so that

chromatin becomes generally more open to the large

protein complexes involved in transcription. Finally it

may act as a signal or flag, similar to phosphorylation of

proteins during signal transduction, so that it alters the

interaction of other proteins with nucleosomes.

Histone acetylation is controlled by specific histone

aceryltransferase (HAT) enzymes and histone deacetylase

enzymes. Many of the genes that encode these enzymes

have been identified within the past few years, which has

enabled a more detailed examination of the way in which

they fimction. One difference between HAT enzymes that

has emerged from biochemical studies relates to their

specificity toward histones. Some have very broad

specificity, being able to acerylate lysine residues in any

of the four core histones, while others discriminate more

highly showing a marked preference for modifjing one

2-18
.. . . ..

or two lysine residues within one or sometimes two of

the histones. Some HATs also can aceqdate non-histone

substrates such as proteins involved in the transcription

machinery itsel~

There are examples of chromosome translocations

that fuse a HAT gene with another gene. These

translocations often are associated with leukemia,

indicating that uncontrolled acetylation could be a major

factor in promoting cancer formation. Therefore it is

important to understand how these enzymes work, in

particular how they achieve specificity for a particular

target protein. From comparisons of protein sequences it

also has been shown that many of the known HATs belong

to a large superfamily of enzymes that acetylate a variety

of different types of substrate, including antibiotic

compounds and factors involved in regulating circadian

rhythm. There is therefore more widespread interest in

this class of enzymes because of their roles in gene

regulation, bacterial antibiotic resistance, and control of

day/night cycles.

In collaboration with Rolf Sternglanz from SUNY

Stonybrook we set out to determine the structure of the

enzyme Hatl, a HAT gene from baker’s yeast. Hatl was

the first HAT gene to be identified, both by Sternglanz

and separately by Dan Gottschling’s group at the

University of Chicago. We initially tried to crystallize the

fi.dl length 374 residue protein, and eventually ended up

with some large crystals, but they took several months to

grow and diffracted X-rays only to medium resolution.

To fm the problem we used an approach that is quite

often adopted by structural biologists. We used proteases

to probe the Hatl protein for flexible regions that might

be interfering with the formation of crystals. However

we wanted to be carefid not to destroy the catalytic activity

of the protein, so we combined these proteolytic assays

with HAT activity assays to be sure that we retained an

active fragment. From this analysis we were able to

determine that 54 residues at the C-terminal end of the

protein were probably more flexible, and that we could

remove them without reducing the activity of the protein.

When we made this new protein (residues 1-320) we

quickly obtained crystals that diffracted to high resolution

(.2A at Beamline X12C of the NSLS) giving us the

opportunity to solve the structure.

However there was still one potential obstacle in

our way which was how to solve the phase problem. Two

methods are available for determining phases for a new

structure. The first is multiple isomorphous replacement

(MIR) which involves soaking crystals in compounds of

various heavy metals and comparing the diffraction

Structureof the Hatl-Acetyl CoenzymeAcomplex ModeIof a histonepeptidehoundto Hatl

199

.

N-terminal

domain

Figure B-1. (left) A cartoon style representation of the modifies a particular lysine side chain in histone H4.

Hatl -Acetyl COA complex structure. The acetyl The panel shows a close up of a surface

coenzymeA (acetyl COA) is shown in a stick representation of Hatl in the vicinity of the actNe

representation and marks the active site of the site, highlighting the features of a possible peptide

enzyme. The two topological folding domains of the binding channel that complement the structural and

protein are marked. chemical features of the histone peptide (shown in

(right) A model for how Hatl might bind a substrate a stick representation). This stereochemicai

histone molecule. The modei was developed on the complementarily helps to explain why Hatl prefers

basis of our structure in conjunction with biochemical to modify Iysine residue 12 of histone H4 and not

data and helps to explain why Hatl specifically other iysine side chains.

2-19
patterns from these “derivative” crystals to those of

“native” untreated crystals to yield phase information.

One drawback of this approach is that attaching the heavy

metal to the protein must not severely disrupt the crystal

lattice, otherwise it is impossible to compare the

“derivative” and “native” diffraction patterns. This often

means that a large number of heavy metal compounds

have to be screened to find a reasonable number ofsuitable

derivatives. An alternative approach is to incorporate an

atom into the protein that scatters X-rays anomalously.

X-Ray diffraction patterns then are collected using Xrays at different wavelengths, typically two wavelengths

around the X-ray absorption edge of the atom and another

at a remote wavelength. The information from these data

sets collected at different wavelengths can be treated in a

fashion analogous to the “native” and “derivative” data

sets of MIR to calculate phases. This multiple wavelength

anomalous diffraction (MAD) method is becoming an

increasingly popular way to solve protein structures. One

reason for this is that it requires only a single crystal of

the protein and so the problem ofnon-isomorphism that

often makes MIR difflcuk does not exist. However, it

does require that data can be collected at a tuneable Xray source such as only exists at synchrotrons sources like

the NSLS.

Our lab has solved several structures using MAD

but at first this did not seem to be the best approach to

take for Hatl. One factor influencing the success ofMAD

is being able to incorporate sufficient anomalously

scattering atoms into the protein. An ideal method to do

this is to take advantage ofprotein chemistry and prepare

protein in which the sulphur atom in each methionine

residue is replaced by selenium. This can be done fairly

easily by making protein in bacteria and growing the

bacteria on a medium that contains selenomethionine

instead of methionine. It usually takes a ratio of 1

methionine for every 100 or so protein residues to give

enough anomalous signal to successfldly determine a

MAD structure. However, Hatl has only 2 methionines

for 320 residues, putting us well below the typical 1 in

100 mark. Therefore we made several attempts to prepare

derivative crystals to try solving the structure by MIR,

but in most cases the crystals either did not diffract as

strongly or were clearly non-isomorphous with native

crystals. We therefore reconsidered using the MAD

approach (and given the type of protein we were working

on there were lots of jokes about “MAD HATters”). We

went ahead and prepared Selenomethionine-Hatl crystals

but to try to increase the chance of success we attempted

a variation on the MAD approach. We prepared crystals

of a methyl-mercury derivative of SelenomethionineHatl, which although not isomorphous with

underivatized protein, did contain more anomalously

2-20

scattering atoms. We then planned to collect a four

wavelength MAD data set, collecting data sets at the

absorption edges of the Selenium and mercury atoms (2

for Se, 1 for Hg) plus a remote wavelength.

We took these crystals to the NSLS in Feb. 1998

and collected a four wavelength MAD data set using a

crystal of methylmercury-selenomethionine-Hatl plus a

“typical” three wavelength MAD data set using a crystal

of plain selenomethionine-Hat 1. We collected the data

on beamline Xl 2C using a CCD detector which gave

excellent sensitivi~ in measurements ofX-ray data. Being

able to measure accurately small differences in the X-ray

data is important for the MAD technique. As things

turned out we were able to solve the structure using the

“typical” three wavelength MAD data set (based on Se

atoms alone). In part we were fortunate that both

methionine residues in Hatl are buried in the core of the

protein and are well ordered in the structure. The second

factor in our favour was that we were able to collect high

quality data sets using the CCD detector and measure

the very small differences produced the two selenium

atoms. This is, to our knowledge, the lowest selenium

content (1 per 160 residues) ever used to solve a structure,

but we were still able to produce high quality electron

density maps, making interpretation much easier. We later

used the four wavelength data set to calculate a map but

there were no clearly discernible improvements over the

map using phases from selenium alone. Another

innovation that was available to us was the program

SOLW, which automatically locates heavy atom positions

and calculates phases. This enabled us to calculate an

electron density map within only three to four hours of

completing the data collection. This almost instant

feedback gave us a better assessment of the level of success

of our experiment allowing us to make better use of our

data collection time and return to Utah, sleepy but happy

MAD hatters.

The structure of the Hatl -acetyl CoenzymeA

complex has given us a wealth of information about how

this enzyme, and other related histone acetyltransferases

such as Gcn5, fimction. Using the structure we have been

able to propose a model for how Hatl binds to a particular

histone and places a specific Iysine residue within the

active site for modification. The structure will play a key

role in fhture structural and biochemical studies aimed

at understanding this important group of enzymes. ■

REFERENCE

R.N. Dutnall, S.T. Tafrov, R. Sternglanz,and V.

Ramakrishnan, “Structure of the histone acetyltransferase

Hatl: a paradigm for the GCN5-related Nacetykransferase superfamily”, Cell 94, 427-38 (1 998).

. .

—.. >- ., —
ChemicalDifferencesinSubchondralOsteoarthritisBone

ObservedwithSynchrotronsInfraredMicrospectroscopy

L.M.Millerand M.R.Chance

(De artment of Physiology and Biophysics,Albert Einstein College of Medicine)

D. ~amerman

(Department of Medicine, Division of Geriatrics,Montefiore Medical Center)

C.S.Car[son

(Department of Veterinary Diagnostic Medicine, College of Veterinary Medicine,

University of Minnesota)

Infrared spectroscopy at the NSLS has grown

substantially over the last several years as increased use of

the existing bean-dines has led to construction of new

facilities. The use of microscopy to study biological

structure is one of the main goals of the new station at

U2B, which is operated by the Albert Einstein College of

Medicine as an NIH Resource Center. The study of bone

structure and fimction is one of the main projects of the

Center, and this article describes some of the progress

using synchrotrons methods of the NSLS.

Osteoarthritis is the leading cause of disability

among people over 65 years old and affects approximately

40 million people in the United StatesIll. It is generally

considered a disease of the cartilage. However, it has

recently been suggested that the health and integri~ of

the articular cartilage is dependent upon the mechanical

properties of the underlying subchondral bone (Figure

B-2), where stiffened subchondral bone may lead to the

that has been made so far in understandhg bone dkease breakdown of articular cartilage121.

joint,car~lage

in

1,20

0.00

Figure B-2. (Left) Schematic drawing of the proximal

end of a monkey tibia.

(Right) Optical and infrared images of normal (top)

and osteoarthritis subchondral bone. both

carbonate/protein and phosphate to protein ratios

are higher for osteoarthritis bone than normal bone.

Samples were 5 pm-thick sections of monkey tibia

mounted between KBrwindows. Data were collected

on Beamline UIOB with a SPecta Tech k us infrared

microscope and a Cu-doped Ge detector (Infrared

Labs). Infrared maps are collected in transmission

mode, 128 scans per point, 4 crnl resolution. The redundant apertures are set at 15pm and sequential spectra

are collected in 40pm steps. Data analysis begins by performing a baseline correction on each spectrum. Then

the following peaks are integrated to determine protein and mineral concentrations: Amide I (1700-1600 crnl,

phosphate (650-500 cm’), and carbonate (905-825 cm’). The crystal size/perfection is determined by dividing

the amount of stoichiometric phosphate (603 Crnl) by non-stoichiometric phosphate (563 cm-l).

2-21
400

300

‘ h

F1

200

&QL.--l

Carbonate / Phosphate

Carbonate / Protein

:~

Figure B-3. (Clockwise from top left) Frequency distributions for phosphate/protein, carbonate/protein,

crystallinity, and carbonate/phosphate ratios from 5 histologically normal monkey samples (10 infrared maps)

as compared to and 2 monkeys with severe osteoarthritis (7 infrared maps). Mineral/protein ratios and

carbonate content are significantly higher in osteoarthritis bone than normal bone. Average crystal size/

perfection is broadly distributed and not significantly different between normal and osteoarthritis monkeys.

Data are expressed as ratios to account for small variations in sample thicknesses.

—.—

Osteoarthritis joints display significant thickening We are addressing this hypothesis by examining the

of the subchondral bone. To date, the basis for chemical composition of subchondral bone using

subchondral bone thickening is unknown. But, an

extensive study ofcynomolgus monkeys has demonstrated

that this thickening precedes the development ofarticukw

lesions131. In addition, there appears to be a threshold

subchondral bone thickness, below which articular

cartilage lesions are extremely rare. Because of the

inherent difflcul~ in studying the eady stages of the

disease in humans, the use ofan appropriate animal model

is important. We hope that using the cynomolgus monkey

model to examine all ages and stages of the disease will

help shed light on the comparable human condition.

The mechanical properties ofsubchondral bone are

dependent upon its chemical structure. Modifications in

the chemical composition of bone can ailect properties

such as its strength, rigidiy density, and flexibility. Thus,

we hypothesize that the bone matrix composition and/or

bone mineral content and crystallinity are modified in

~itu in a specific manner as a function of subchondral

bone thickness.

synchrotrons infrared microspectroscopy. Infrared

spectroscopy is an analytical technique that is sensitive to

the chemical components in bone; a spectrum of infrared

light is absorbed differently depending on the protein

(primarily collagen) and mineral (hydroxyapatite) content

and composition. More specifically this technique can

be used to determine (1) protein structure and

concentration, and (2) mineral concentration,

crystallinity, and content (e.g. phosphate, acid phosphate,

carbonate). The infrared crystallinity results are wellcorrelated to hydroxyapatite crystal size and perfection as

determined by x-ray powder diffraction. If infrared light

is put through a microscope (equipped with special

infrared optics), then infrared spectra can be collected on

micron-sized regions of bone in situ and compared to

visible images of the same region. Thus, we can examine

the chemical composition of subchondral bone as a

fimction of (a) age, (b) position in the subchondral plate,

and (c) thickness of the subchondral plate and compare

2-22
these results as a function of severity of the disease.

Inherently the long wavelengths of infrared light limit

the spatial resolution achievable with this technique. Our

preliminary results show that substantial changes in

chemical composition occur within 20 ym of new bone

growth14’j]. This type of spatial resolution can only be

achieved with a synchrotrons infrared source. The National

Synchrotrons Light Source at Brookhaven National

Laboratory provides a source of broadband infrared light

that is 1000 times brighter than a conventional infrared

source. This permitting rapid data collection at the

highest spatial resolution possible (3-5 pm).la

Using synchrotrons infrared microspectroscopy we

have compared the chemical composition ofsubchondral

bone in situ in histologically normal versus osteoarthritis

monkey tibias. Specifically, we have analyzed the protein,

phosphate, and carbonate concentrations and bone

crystallinity throughout the subchondral bone as a

flmction ofdisease severity Figure B-2 illustrates mineral/

protein infrared maps from the subchondral bone of

normal (top) and osteoarthritis (bottom) monkeys. As

can be seen, both the phosphate/protein and carbonate/

protein ratios are higher in the osteoarthritis bone. The

results from this single sample were confirmed by

examining five radiographically normal monkeys and two

monkeys with severe osteoarthritis (as defined by

considerable fibrillation and clefing of the joint carriage.)

REFERENCES

[1]

[2]

[3]

[4]

[5]

[6]

This analysis totals approximately 3000 infrared spectra

for each disease state. Frequency distributions were

calculated for normal bone versus osteoarthritis bone and

can be seen in Figure B-3. Wriance analysis (ANOVA)

demonstrates that these both the phosphate/protein and

carbonate/protein distributions are significantly different

for normal versus osteoarthritis bone, where the

osteoarthritis bone is more mineralized than the normal

bone.

Analysis of the carbonate/phosphate ratio (Figure

B-3) also demonstrates that the carbonate content is

significantly higher in osteoarthritis bone than normal

bone. High carbonate content often correlates with low

average crystal size, since carbonate substitution into the

hydro~apatite lattice is usually limited to the surface of

hydroxyapatite crystals. However, we find that the average

crystal size/perfection are broadly distributed in both

normal and osteoarthritis bone, but are not significantly

different between the normal and disease states.

These results support our hypothesis that chemical

composition changes occur in the subchondral bone in

osteoarthritis. Since subchondral bone composition

ai%ectsboth the mechanical and physiological properties

of bone, differences between histologically normal versus

osteoarthritis monkeys may provide insight into the

chemical basis for subchondral bone thickening and

articular cartilage breakdown in osteoarthritis. ■

Control, C. f. D. Mm-b. Mortal. WHY. Rep. 43,433-438 (1990).

E.L. Radin, and R.M. Rose, Clin. Orthop; 213,34-40 (1986).

C.S. Carlson, R.F. Loeser, C.B. Purser, J.F. Gardin, and C.P. Jerome, 1 Bone Minez Res. 11,1209-1217

(1996).

L.M. Miller, C.S. Carlson, G.L. Carr, and M.R. Chance, Cellular and Molecular Biolo~ 44, 117-127

(1998).

L.M. Miller, C.S. Carlson, G.L. Carr, G.P. Williams, and M.R. Chance, SPIE 3153,141-148 (1997).

G.L. Carr, J.A. Reffner, and G.P. Williams, Rev. Sci. Instx 66,1490-1492 (1995).

I

1:I

1

2-23
CrystalStructureof a HepatitisDeltaVirusRibozyme

Revealsa BuriedActiveSiteCleftReminiscentProtein

Enzymes

A.R.Ferre-D’Amareand J.A.Doudna

(YaleUniversity)

The hepatitis delta virus (HDV) ribozyme is the

only catalytic RNA known to be required for the viability

of a human pathogen. This self-cleaving RNA is

remarkable for its high stability, its limited requirement

for divalent cations, and its fmt rate. The HDV ribozyme

is fully active in condkions, such as 8 molar urea, under

which most RNAs and proteins are denatured and

strongly inactivated. Because of the negatively charged

phosphodiester backbone of RNA, most catalytic RNAs

depend on divalent cations to fold into their active

conformations. The HDV ribozyme is the f~test natural

self-cleaving RNA that has been characterized. Even in

very low concentrations of a variety of divalent cations, it

.——

...

.. . . . —.—.

Figure B-4. Ribbon and stick

representation of the HDV ribozymeU1A RBD complex structure. The protein

moiety lies at the bottom of the figure,

far away from the active site residues

that surround the 51terminus of the RNA.

The five helical or base-paired segments

are labeled P1 through P4 and P1.1.

2-24

can cleave itself at .1/second, which is two orders of

magnitude faster than a typical self-cleaving RNA, and

approaches the rate of some protein enzymes[ ll.

In order to gain structural insight into the unique

catalytic prowess of this RNA, we had to obtain welldiffracting crystals. Good crystals of tightly folded RNAs

are notoriously difficult to obtain, presumably because

the surface of these molecules is dominated by a periodic

array of phosphates. This might allow neighboring

molecules to pack subtly out of register in the crystal,

resulting in poor order. To overcome this problem, we

engineered a solvent-exposed, functionally and

structurally dispensable stem-loop of the HDV ribozyme

into a high-aflhity binding site for the small, basic RNAbinding domain (RBD) of the UIA protein. We expected

the complex between the 72 nucleotide RNA and the

UIA protein RBD to produce better crystals than the

“naked” RNA, because the complex not only has a

negatively and positively charged ends, but has the wide

varie~ ofsurface iimctional groups of the protein available

for making crystal contacts.

Our best crystals of an HDV ribozyme-UIA RBD

complex diffracted X-rays to beyond 2.2 A resolution.

We solved the structure by crystallizing RNA-protein

complexes in which the merhionines of the protein moiety

had been biosynthetically substituted with

selenomethionine. We then carried out a mukiwavelength

anomalous diffraction (MAD) experiment around the

selenium absorption edge at NSLS Beamline X4A, with

help from Drs. C. Ogata and D. Cook. The phases thus

obtained produced a good electron density map, and the

resulting atomic model has now been refined against

diffraction data extending to 2.3 ~ resolution[zl. Use of

the RNA-binding protein “crystallization module” might

be a powerful general technique, not only for obtaining

high quality crystals of large RNAs, but also for

determining their structures by MAD.

Our crystal structure revealed that the HDV

ribozyme adopts a compact, highly convoluted fold in

which five helical segments are linked by five strand

crossovers; a connectivi~ that can be described as a “nested

double pseudoknot” (Figure B-4). This fold buries the
..........- . ~ .... ... ....— 

. .. .

Figure B-5. Solvent accessible surface

representation approximately in the same

orientation as Figure B-4. The atoms of the 5’-

most ribose are shown as red spheres. The

active site lies in the cleft behind this sugar.

I

i

i

active site at the bottom of a deep, solvent-inaccessible t

clefi, in which various base and backbone functional

!

groups appear to be poised to achieve catalysis (Figure

B-5). Interpretation ofpreviouslypublished biochemical

results from other workers in light of the structure suggests

that the complex fold of the HDV ribozyme is at least in

part responsible for the remarkable stability of this RNA.

No tightly bound metal ions were found in the electron

dens~y maps. This is consistent with published

biochemical data, and indicates that nature can achieve

intimate packing of negatively charged RNA without

recourse to tight metal ion chelation131.

The HDVribozyme is the first catalytic RNA whose

ground state structure demonstrates an active site preorganized for catalysis. The three-dimensional structure

of this remarkable ribozyme constitutes the starting point

for fimher biochemical, biophysical and pharmacological

investigations into its mode of action both in vitro and in

the life cycle of the virus in the human liver. ■

REFERENCES

[1] M.D. Been and G.S. Wlckham. “Self-cleaving ribozymes of hepatitis delta virus RNA”, Euz J Biochem 247,

741-753 (1997).

[2] A.R. Ferre-D’Amare, K. Zhou, and J.A

Nature 395,567-574 (1998).

[3] A.R. Ferre-D’Amare and J.A. Doudna.

Biopbys. Bionzo[ec. Struct. In press.

Doudna. “Crystal structure of a hepatitis delta virus ribozyme”,

“RNA folds: insights from recent crystal structures”, A.v.zu. Rev.

2-25
HowSosActivatesRas: The CrystalStructureofthe RasSosComplexat 2.8 AResolution

P.A.Boriack-Sjodin,S.M.Margarit,D.BarSagi, and J. Kuriyan

(RockefellerUniversity)

The Ras proteins are structurally conserved guanine

nucleotide binding proteins that are involved in

intracellular pathways controlling cell proliferation and

differentiation11’21.When bound to GTE Ras is “on” and

is able to transmit the cellular signal initiated by Iigand

binding to receptor tyrosine kinases. When bound to

GDl? Ras is “off and is unable to propagate the cellular

signal. The intrinsic rates of GTP hydrolysis and

nucleotide dksocation from Ras are low, therefore, two

classes of proteins regulate the nucleotide-bound state of

Ras: GTPase activating proteins catalyze the hydrolysis

of GTP to GDP, turning Ras “off”, while guanine

nucleotide exchange factors facilitate the exchange of

GDP for GTE switching Ras “on”. Although many

biochemical studies have been done on Ras exchange

factors, the mechanism for exchange was largely unknown

due to the lack of structural information.

The X-ray crystal structure of Ras complexed to the

exchange factor Son of Sevenless (Sos) was recently

determined (Figure B-6) using multiple isomorphous

replacement methods. Data used to solve the structure

were collected at beamline X25 at the National

Synchrotrons Light Source at Brookhaven National

Laboratories using the Brandeis B4 2x2 module CCD

detector. The structure provides the first glimpse of how

Ras exchange factors fimction to (1) remove nucleotide

from Ras and (2) allow nucleotide to rebind to Ras.

The structure reveals that Sos interacts extensively

—— . ..

- Gtermlnus

Figure B-6.The complex of H-Raswith the exchange factor region of human Sosl. The N-terminal domain

of Sos (residues 568 to 741) is blue; the C-terminal catalytic domain (residues 752 to 1044) is green; the

Switch 1 and Switch 2 segments and the P-loop region of Ras (as defined in the text) are orange and red,

respectively. Conserved regions (SCRS)among Ras family exchange factors shaded cyan12,31.Disordered

residues of Sos are shown as dotted lines.

2-26
. .. __ .

with Ras to exclude nucleotide and magnesium ion and

stabilizes Ras in the nucleotide-free state. Residues 25-40

of Ras (the Switch 1 region), which normally form part

of the nucleotide binding pocket, are completely removed

from the nucleotide binding site. Confirmational changes

in residues 57-75 of Ras (tie Switch 2 region) result the

occlusion of the magnesium binding site of Ras by Ala

59 (Figure B-7). Sos also introduces a hydrophobic

residue (Leu 938) into the magnesium binding pocket,

further changing the electrostatic environment to one

unsuitable for a divalent ion. Residues which normally

coordinate the nucleotide (Lys 16 and Gly 60) are in

alternate hydrogen bonding interactions and Sos

introduces an acidic residue (Glu 942) into the ~-

phosphate binding site, fbrther disrupting the binding

site of the nucleotide. Importantly the complex leaves

the guanine base and ribose binding sites unobstructed,

thus providing a mechanism for the rebinding of

nucleotides to Ras to complete the exchange reaction.

This structure was recently published in Nature:

1?A. Boriack-Sjodin, S.M. Margarit, D. Bar Sagi, and J.

Kuriyan, “Structural basis for the activation of Ras by

So<, Nature 394,337-343 (1998). ■

REFERENCES

[1] H.R. Bourne, D.A. Sanders, and F. McCormick, “The GTPase superfamily conserved structure and molecular

mechanism”, Nature 349, 117-127 (1991).

[2] M.S. Boguski and F. McCormick, “Proteins regulating Ras and its relatives”, Nature 366,643-654 (1993).

[3] C.-C. Lai, M. Boguski, D. Broek, and S. Powers, “Influence of guanine nucleotides on complex formation

between Ras and Cdc25 proteins”, A401ec. Cell. Biol. 13, 1345-1352 (1993).

[4] E.F. Psi, et al. “Refined crystal structure of the triphosphate conformation of H-ras p21 at 1.35 ~ resolution:

implications for the mechanism of GTP hydrolysis”, Eik?BOJ 9,2351-2359 (1990).

b HeIlx(iH

f

rE!!@l d Bl”w$%

1-

Figure B-7.A schematic of the differences in the Switch 2 regions of a) Ras-GTPanalogue (5P21)141

and b) Ras-Sos.Selected polar interactions are shown as dashed lines, hydrophobic interactions

are shown as solid arcs.

2-27
Structureofthe HIVgp120 EnvelopeGlycoproteinin

ComplexwithCD4anda NeutralizingHumanAntibody

P.D.Kwong(ColumbiaUniversit )

R.Wyatt and J. Sodroski (Dana-?arber Cancer Institute)

W.A.Hendrickson (ColumbiaU.and the Howard Hughes MedicalInstitute)

As the 20th century draws to a close, the human

immunodeficiency virus (HIV) continues to spread,

having recently surpassed both malaria and tuberculosis

as the Ieadlng infectious disease killer. Since 1983, when

HIV was first discovered, the UNAIDS organization

estimates that over 40 million people have been infected

of which ~most 1.5 million have died. Despite global

awareness and recent therapeutic advances, the only hope

for containment in many countries lies in the

development of a vaccine. In spite of enormous effort,

all such vaccine candidates have thus fa met with ftilure.

HIV is an enveloped virus, which establishes a

persistent infection in its human hosts. Although

neutralizing antibodies are generated, HIV eludes the

immune system. Thk ability of HIV to evade the immune

system is the basis of both the well noted vaccine ftilures

as well as of the ability of HIV to establish a persistent

infection. Over a period of years, the constant battle

with the virus impairs the immune system enough to allow

opportunistic infections to kill the human host.

The HIV lipid envelope, which is derived from the

membrane of the host cell, hides most of the infectious

virus particle from immune surveillance. Only two viral

proteins protrude beyond the protective lipid bilayer, the

exterior envelope glycoprotein, gp120, and its membranespanning partner, gp41. Of these, gp120 appears to

occlude much of the gp41 ectodomain and is the target

of virtually all neutralizing antibodies.

The exposure of gp120 on the virion surface is a

fictional consequence of its central role in virus-cell

entry. The gp 120 glycoprotein binds sequentially to the

CD4 glycoprotein and a chemokine receptor on the

surface of specific cells of the immune system, and then

in concert with gp41 orchestrates a fusion of the viral

and cellular membranes. This fusion is critical for the

introduction of HIV’s genetic material into the target

cell.

Because of the pivotal role of gp120 in receptor

binding and interactions with neutralizing antibodies, we

undertook an investigation of its atomic structure.

The size of gp120 as well as its extensive

glycosylation and expression in eukaryotic cells limited

2-28

the choice of high resolution structural techniques to Xray crystallography. X-ray crystallography in turn depends

on obtaining well ordered crystals of the molecule of

interest. For gp120, this proved to be extraordinarily

dii%cl-dt.

It was apparent from functional and sequence

analyses that many of the same mechanisms that HIV

uses to avoid specific protein: protein contacts in eluding

the immune system, would also stymie attempts at forcing

gp120 into the specific protein:protein lattice interactions

required to produce a well ordered crystal.

To surmount these dificukies, we used a procedure,

which we term variational crystallization, that focuses on

protein modification to enhance the overall probability

of producing crystals. Variational crystallization takes

advantage of the ability of molecular biology to provide

almost limitless variation in the protein of interest. To

guide our efforts, we also derived the theoretical

underpinnings for an approximate probability theory,

based on the comparison of crystallization probabilities

before and after a modifying procedureI1l.

This combination of probability analysis and

variational crystallization produced very small crystals

from four different gp120 crystallization variants, in six

different crystallization conditions. Because the larger

crystals necessary for high resolution structural analysis

are often dlfflcult and time-consuming to grow, we used

the NSLS bean-dine X4A, to shortcut the process. The

intense X4A x-rays, several orders of magnitude stronger

than standard laboratory sources, enabled us to directly

assay the suitabili~ of the very small initial crystals for

structural analysis. Of the six, only one proved sufficiently

well-ordered for firther study. This crystallization variant

was composed of a ternary complex of core gp120 (gp120

with deletions at the N and C termini as well as at two

internal variable loops), the N terminal two domains of

CD4, and the antigen binding fragment of the

neutralizing human antibody, 17b.

Small needle-shaped crystak, 5-10 pm in crosssection, could readily be grown. These were used to screen

for appropriate cryocrystallography conditions and heavy

atom derivatives. Despite several months of concentrated
effort, only five larger crystals, with

cross-sections of /50 pM, could be

grown. Nonetheless, use of the NSLS

X4A beamline made possible the

collection of a native and three

derivative data sets. The structure was

solved to 2.5 ~, a resolution sufficient

to decipher the gp120 atomic structure

(Figure B-8).

Analysis of this structure revealed

the detailed features of a cavity-laden

CD4-gp120 interface, highlighted by

an extraordinary 150 ~3 cavity which

reached from the pivotal Phe 43 residue

of CD4 into the heart of gp120. Also

revealed were a conserved binding site

for the chemokine receptor, evidence for

a confirmational change upon CD4

binding, and the nature of a CD4-

induced antibody epitope[zl. In

addition, epitope maps in conduction

with the crystal analysis defined the

antigenic structure of gp120 and

specific mechanisms of immune

evasion131. These included multiply

redundant mechanisms of steric

hindrance and confirmational

occlusion as well as a completely

unanticipated, immunologically “silent”

face masked by carbohydrate.

Whereas previous attempts to

devise an HIVvaccine relied on indirect

hints and clues, our results visualize

gp120 at atomic resolution.

Understanding the structural basis for

the remarkable ability of HIV to elude

w

pe

Figure B-8. Structure of the gp120 ternary complex shown in its

biological context. The center of the figure depicts the gp120

ternary complex in ribbon representation, with core gp120 (red)

caught in the act of binding to the CD4 receptor (yellow) by the

neutralizing antibody, 17b (heavy chain, blue; light chain purple).

The pivotal Phe 43 residue CD4 is also shown, at the nexus of

the gp120-CD4 interface. The target cell membrane (cyan),

domains 3 and 4 of CD4 (yellow ovals), chemokine receptor

(green), viral spike and virion (pink) are also shown for reference.

the immune response should assist in the design of a for understanding the biology of HIV entry into cells,

vaccine. Our results thus provide not only a fr~ework but also a guide ii attempts IO intervene. ■”

REFERENCES

[1] P.D. Kwong, R. Wyatt, E. Desjardins, J. Robinson, J.S. Culp, B.D. Hellmig, R.W. Sweet, J. Sodroski, and

W.A. Hendrickson, ” Probability analysis of variational crystallization and its application to gp120, the exterior

envelope glycoprotein of type 1 human immunodeficiency virus (HIV-l)”, J. Biol. Cbem. in press.

[2] l?D. Kwong, R. Wyatt, J. Robinson, R.W. Sweet, J. Sodroski, and W.A. Hendrickson, “Structure of an HIV

gp120 envelope glycoprotein in complex with the CD4 receptor and a neutralizing human antibody”, Nature

393,648-650 (1998).

[3] R. Wyatt, I?D. Kwong, E. Desjardins, R.W Sweet, J. Robinson, WA. Hendrickson, and J. Sodroski, “The

antigenic strucure of the HIV gp120 envelope glycoprotein”, Nature 393,705-711 (1998).

2-29
StructuralBasisforthe Interactionof RaswithRalGDS

L.Huang, F.Hofer,G.S.Martin, and S.-H.Kim

(U.of California at Berkeley)

Ras is central within a web of signaling circuits, thus

understanding the basis for Ras control is key to

unraveling the principles of signal transduction. Indeed,

rm is the most prevalent of all the oncogenes isolated from

human tumors. Mutationally activated Ras plays a role

in 900/oof pancreatic cancers, 500io of colon cancers, and

25’% of lung cancers.

Ras and a large faily of related GTPase.s function

as molecular switches that control a variety of signaling

pathways that regulate cell growth, motility, intracellular

transport, and dKferentiation. Interaction of the GTPase

with its effecters is dependent on binding of GTP.

Binding of GTP to human Ras results in major

confirmational changes in two highly conserved regions:

switch I and switch II.

The Ras protein signals to a number of distinct

pathways by interacting with diverse downstream

effecters. Among the effecters of Ras are the Raf kinase

and RalGDS, a guanine nucleotide dissociation stimulator

specific for Ral (Ras like GTPase). Ral may regulate

Cdc42, which plays a role in the actin cytoskeletin

organization. Ral also signals to Phospholipase D

pathway. Despite the absence of significant sequence

similarities, both effecters bind directly to Ras, but with

different specificities. The solution of the Ras/effecter

complex would lay a foundation for understanding Ras

signaling, and thus the role of malfimctioning Ras in

oncogenesis.

The X-ray data taken at the BNL beam line X12B

and X25 enabled us to solve the structure of the complex

between Ras(E3 lK) and the Ras-interacting domain

(RID) of RalGDS in the presence of bound nonhydrolyzable GTP to a resolution of 2.1 ~ l]l. The small

crystals of the complex dKfracts only weakly at home

source, which is not sufficient to determine the precise

side chain interactions in the complex. Access to the high

beam intensi~ of beam line X25 was mandatory in order

to determine its structure to such a high resolution.

This structure reveals that the ~-sheet of the RID

joins the switch I region of Ras to form an extended antiparallel ~-sheet with a topology similar to that found in

the Ras homologue Rap-Raf complex. In addition, the

overall structure of RalGDS-RID is similar to that of the

Ras-binding domain (RBD) of Raf and ubiquitin.

However, the side chain interactions at the joining

junctions of the two interacting systems, the electrostatic

complementarily at the interface, and the relative

orientation of the two binding domains are distinctly

different. Furthermore, in the case of the Ras-RID

complex a second RID molecule also interacts with a

different part of the Ras molecule, the switch II region.

These findings account for the cross-talk between Ras

and Ral pathways. Additionally comparison with the

RaplA/Raf-RBD structure enabled us, for the first time,

to explain the multiplicity and specificity of Ras signaling

at an atomic level. It also helps to distill the common

structural motif underlying protein-protein interaction

in the signal transduction process.

The mechanism by which RalGDS is activated by

Ras is implied by the observation that the interaction with

Ras perturbs the structure of RalGDS-RID, but not Ras

itself The free RalGDS-RID was solved by the MAD

method with data taken at beam line X4A using a

selenomethionine mutant protein crysta1121. This

confirmational change might activate the catalytic

domain of RalGDS structurally, which in turn would

activate Ral.

The structural characterization of the Ras/effecter

interface will assist in the rational design of small drug

molecules capable of disrupting this interface, thereby

halting the oncogenic effect of the constitutively activated

Ras. Furthermore, the discovery of this interaction motif

will aid in recognizing other pairs of signal transduction

proteins that may interact via these mechanisms. ■

2-30

.. .. ,

.> —

. .

----- —
.. .... ... . . ..

c

b.

RID(2)

Figure B-9. Ribbon representation of the complex between RalGDS-RID and Ras(E31K).

(a) Front view of the complex

(b) a different view of the complex.

Rasmolecules are in purple (Rasl ) and brown (Ras2),and RID molecules are in cyan (RID1) and green

(RID2). The switch I region (residues 30-37) is colored yeHow, while the switch H region (residues 60-

76) is colored blue. Non-hydrolyzable GTP (GMPPNP) and magnesium are drawn in ball-and-stick

representation.

[1] L. Huang, F. Hofer, G.S. Martin, and S.-H. Kim, Nature Strut. Biol. 5,422-426 (1998).

[2] L. Huang, X. Weng, F. Hofer, G.S. Martin, and S.-H,. Kim, Nature Strut. Biol. A, 609-615 (1997).

2-31
Structureofthe LargeRibosomalSubunitfrom

FLmtu%rnorfuiat 5.5 AResolution

B.Nenad, P.Nissen,P.B.Moore and T.A.Steitz

(YaleUniversity) -

The ribosome plays a pivotal role in the process of

protein synthesis. Ribosomes mediate the interaction

between mRNA and tRNA, and catalyze peptide-bond

formation. Protein synthesis is one of the most studied

cellular processes. Intense research over the past 30 years

led to many important discoveries regarding sequences

of ribosomal components, folding of the rRIW.s, spatial

proximity of ribosomal proteins, and overall shape of the

ribosome[l’2’3’ 41. Structural information about the nature

ofprotein-nucleic acid interactions in the ribosomes and

the structure of the entire organelle is a prerequisite for a

mechanistic analysis. Undoubtedly thk structure also will

reveal fimdamental architectural principles that govern

the assembly and maintain the stability of all

ribonucleoproteins. The progress on the research of

ribosomes is reviewed periodically in book form [5>6’7’81.

The general interest has shified from investigations of

the biochemical properties of the ribosomes to highresolution studies of their structure and fimction.

Prokaryotic ribosomes (7oS) are composed of two

subunits and have a molecular weight of roughly 2.5x106.

Each of the subunits is a complex of ribosomal RNA

(rRNA) and proteins. The small subunit (30S) contains

a single 16S rRNA molecule and 21 different proteins,

while the large subunit (50S) contains two rRNA

molecules and 32 different proteinstgl. The 50S subunit

has a molecular weight of about 1.5x10G Daltons and

catalyzes peptide bond formation, possibly functioning

as a ribozyme[l”l. Eukaryotic ribosomes are similar

structurally, but they are significantly bigger and more

complicated[lll. Although the research on which we are

embarked focuses on the large subunit from an

archebacterial ribosome, there is no reason to believe that

bacterial and eukaryotic ribosomes are fimdamentally

different1121,and many of the conclusions are likely to be

transferable.

We have generated X-ray crystallographic electron

density maps of the large ribosomal subunit from

HabarcuLz marismortuiat various resolutions up to 5.5A,

having measured data from crystals that diffract to 3A

resolution. Initial steps in the solving of this structure

demanded a marriage of two techniques, electron

microscopy and X-ray diffraction. We were able to place

a 20~ resolution, three-dimensional model of the 50S

subunit determined by EM methods into the crystal unit

cell. To accomplish this required that we had measured

the lowest-angle X-ray diffraction data from the crystals,

in the 80-20~ range, which often are ignored by

crystallographers. This provided initial phases for low

resolution reflections. Using these EM-derived phases,

we were able to use difference-Fourier electron-density

maps to locate the high-occupancy sites in heavy atomderivatized crystals. This allowed us to initiate the process

of heavy-atom refinement, leading to our first

interpretable electron density map of the 50S subunit.

The map at 9A resolution revealed long, continuous, but

branched features whose shape, diameter and righthanded twist are consistent with segments of double

helical RNA that crisscross the subunitI’31.

High-resolution structure determination of the large

ribosomal subunit will be initiated using

crystallographically determined phases calculated at 5 .5A

resolution by multiple isomorphous replacement and

anomalous scattering (MIRAS) methods. Electrondensity maps calculated using these phases begin to unveil

the molecular architecture that underlies this large,

ribonucleoprotein complex. First glimpses of the 7.0~

resolution map show ribbons of electron density

corresponding to the RNA backbone, punctuated at

regular intervals by bumps arising from the phosphates

(Figure B-10). Some of the proteins can be distinguished

clearly from RNA at this resolution. Thus, we believe

that a critical step has been taken on the path leading to

an electron-density map of the large ribosomai subunit

that can be interpreted in atomic detail.

X-ray crystallographic data collection for this project

represents a significant technical challenge which, it

appears, can be met by the facilities at NSLS. All the

data collection to date has been done at NSLS beamlines

X12C, X12B, and X25. For this purpose, numerous

adjustments and modifications have been provided by

the helpful staff at these beamlines. Initial heavy-atom

data were taken at bean-dineX12C with the Brandeis fourmodule CCD-based detector. Using a MAR300 imagingplate detector on beam line X12B we have been able to

collect excellent 3.8A resolution data. We hope that in

the fhture, when some addkional modifications will be

made, it will be possible to collect data to the diffraction

limit of the crystals. ■

2-32
. . . . .. . ... . . ..

Figure B-10: Resultsfrom the study of the 50S ribosomal subunit from Huloarculamarisn?orfui. Preliminary electrondensity maps at 7A resolution are shown and compared to the previously published 9A resolution map1131.

REFERENCES

[1]

[2]

[3]

[4]

[51

[6]

[71

[8]

[91

[10]

[11]

[12]

[13]

H.F. Noller, Am.m.Rev.Biocbem.53,119 (1984).

J.A. Lake, Annu. Rev.Biochem.54,507 (1985).

A. Yonath, (1992). Ann. Rev.Biopbys.Biomol.Struct.21,77 (1992). Z.H. Zhou, S.J. Macnab, J. Jakana, L.R. Scott, W.

Chiu, and F.J. Rixon, Proc. Natl. Acad. Sci. USA 95:2778 (1998).

J. Frank, CWZ Opin. Struct.Biol. 7(2), 266 (1997).

B. Harde.q, and G. Kramer, Structure, Function, and Genetics of Ribosomes, Springer-Verlag, New York (1986).

W.E. Hill, A. Dahlberg, RA. Garrett, l?B. Moore, D. Schlesinger, andJ.R Warner,The Ribosome. Structure, Function,

and Evolution. American Socierv for Microbiolo gy Washington, D.C. (1990).

KH. Nlerhaus,F.Franceschi,A.R Subramanian,VA Erdmann, and B. Wkrmann-Llebold, TheTranslational Atmatatus.

Plenum Press, New York (1993).

A.T. Matheson, J.E Davies, N? Dennis, and W.E. Hill, Frontiersin Zamkztion.Biochw. CellBiol.73, 739 (1995).

B. Wktmann-Liebold, Ribosomal oroteins: their structure and evolution, in Structure, Function, and Genetics of

Ribosomes, B. Hardeq & G. Kramer, Editors. Springer-Verlag New York,. pp. 326 (1986). I.G. Wool, Annn. Rev.

Biocbem.48,719 (1979).

H.F. Noller, V HoEarth, and L. Zimniak, Science256, 1416 (1992).

I.G WOO1,Y.Endo, Y.-L. Chan, and A. Gluck, “Structure, function and evolution of mammalian ribosomes”, in ~

Ribosome. Structure, Function and Evolution, W.E. Hill, A. Dahlberg, R.A. Garrett, I?B. Moore, D. Schlesinger &J.R.

Warner, Editors. American Society for Microbiology Washington, D.C. pp. 203. (1990).

I.G. WooI,The biflmctional nature of ribosomalproteinsand speculationson their origins,inTheTmnslationdAD oaratus,

K.H. Nlerhaus, F. Franceschi, A.R. Subramanian, V.A. Erdmann & B. Wktmann-Llebold, Editors. Plenum Press,New

York. pp. 727 (1993).

N. Ban, B. Freeborn, 1?Nksen, 1?Penczek, R.A. Grassucci, R. Sweet,J. Frank, I?B. Moore, I?B., T.A. Steitz, Cell 93(7),

1105-1115 (1998).

2-33
ChemistryofS02 and OrganosulfurMoleculeson Metal

and OxideSurfaces:Unravelingthe Mysteriesbehind

CatalystPoisoningand Desulfurization

J.A.Rodri uez,J. Hrbek,T.Jirsak,J. Hanson and S.Chaturvedi (BNL)

J.L.Brito($enezuelan Institute of ScientificResearch, IVIC)

Sulfi-m dioxide is one of the major air pollutants

released to the atmosphere as a result of volcanic activity

and the combustion of fuels in power plants, factories,

houses and transportation. On the other hand,

organosulfim molecules are common impurities in oilderived feedstocks and poison many metaUoxide catalysts

used in commercial processes. Millions of dollars are lost

every year due to the negative effects ofsulfi.u poisoning.

In rhe Catalysis Group at the Chemistry Department of

the effects of sulfur on the structural, electronic and

chemical properties of metal and oxide surfaces. This type

of knowledge is necessary when designing catalysts that

have a high efficiency for the destruction or removal of

sulfur-containing molecules (DeSOx and

hydrodesulfurization processes), or when choosing

catalysts that have a low sensitivity to sulfur poisoning.

The research projects make extensive use of the unique

facilities available at.the NSLS for surface and materials

Brookhaven National Laboratory, experiments are being characterization.

carried out to obtain a fimdamental understanding of

>

.=

co

c

ar —-z

u

n

1

—

r 1 I 1 I I 1 I

SOJRU(OOI) ,...?...,

- s2p S04 SJs +o

[“””””; :!... s03

hv = 260 eV

,... !..:02

Anneal 350 K

. .

Anneal 260 K

Anneal 160 K

:::

:::

::

:::

:::

:::

:::

:::

:::

:::

:::

:::

:::

:::

multilayer 100 K

I I I 1 1 t

72 170 168 166 164 162 160

Binding Energy (eV)

Figure C-1. S2p photoelectron spectra

taken after annealing a Ru(OO1)

surface saturated with SOZfrom 100

to 160,260 and 350 K.

2-34
.

The chemistry of sulfur dioxide on Pt(l 11),[11

Rh(l 11),121RU(001),131 and Mo(l 10)[4] was examined

at temperatures between 100 and 500 K. In

experiments performed at beamlhe U7A, several sulfur

species with distinct electronic properties were

identified (for example, see Figure C-l). On all the

metals, S02 dissociates (S02, + S. + 20,) or

transforms into S03 and S04 sp~cies. No evidence was

found for the existence of SO as a stable product. The

reactivity of the metals increases following the

sequence: Mo c Ru < Rh Pt. It was found that

adsorption geometries in which SOZ is di-coordkated

via 0,0 or S,0 are the most probable precursors for

dissociation.

Metal-metal bonding can have a drastic impact

on the chemical ai%nity of a metal for SOZ and other

sulfur-containing molecules.11’2’5’aA Sn/Pt(l 11) alloy

is much less reactive towards S02 (Figure C-2),

HZS, S2, and thiophene than polycrystalline tin or

clean Pt(l 11) .111 The electronic perturbations that

accompany the formation of Pt-Sn bonds reduce the

electron-donor ability of Pt and Sn, and both metals

are not able to respond in an effective way to the

presence of molecules like S02 or HZS.1]’51Among the

common site blockers (Cu, Ag, Au, Al, Zn, Sri), tin is

the best choice for reducing the sensitivity of Pt

reforming catalysts to sulfur poisoning.11’51In a similar

way, Pd/Rh automotive exhaust catalysts can have a

good catalytic activity and be more tolerant to the

presence ofsulfur-containing molecules in the gasoline

than pure Pd catalysts.121A Pd monolayer supported

on Rh(l 11) is less chemically active than pure Pd or

Rh(l 11) for the dissociation of SOZ or rhiophene.121A

very large drop in the reactivity of Pd can be expected

when this metal is bonded to s,p or early-transition

metals.121 All these results together indicate that

bimetallic bonding can be a useful “tool” for increasing

the sulfur tolerance of Pt and Pd based cata.lysts.11’2’51

On the other hand, in hydrodesulfhrization processes

metal-metal bonding can be usefi.d for enhancing the

activity of Me-based catalysts in the removal or

transformation of organosulfur molecuks.[d

Since most poisoned catalyst are expensive, there

is a need to reactivate them. Reaction with oxygen (SWfi~

a?

+02W+S02 is a promising route for regenerating

pure oxide cat’ ysts. The process is carried out under

pressures of oxygen (0.2-2 atm) that are not compatible

with most of the techniques currently used in surface

science. One can study it using x-ray absorption nearedge spectroscopy (xANES) and x-ray diffraction

(XRD).18’71 Investigations at beamline X7B have

established the feasibility of conducting subminute,

(J3xJ3)R30°-WPt(lll) es.= 0.33 ML

Figure C-2. (top) Structural geometry for a (43x

43)R30° -Sn/Pt(lll) surface alloy. The The dark

and white circles represent Sn and Pt atoms,

respectWely. The Sn atoms are present only in

the top layer and protrude 0.22 A from the plane

of Pt atoms (from ref. [7]).

(bottom) Total sulfur uptake for the adsorption

of S02 on polycrystalline tin, Ft(l 11) and a a (J3

x ~3)R30° -Sn/Pt(l 11) alloy.

Sulk Uptake 0.4-

300-310 K

S03 -

~“ -

:0.2 -

5

:

s

r- 0.1-

0.0

0 2 4 6 6 10

S02Exposure(L)

2-35
..

., 0 ,. <

—..—–— ——ti —

Figure C-3. Time-resolved x-ray powder diffraction patterns for the regeneration of sulfided

NiMoOQ. The sample was sent in an open capillary exposed to air and heated from 25 to 650 “C.

Heating rate = 1.2 OC/min.

2c3

time-resolved XRD experiments under a wide variety of

temperatures and pressure conditions (-1 90 ‘C < T <

9000C; Ps 45 atm).[’ol This unique approach has been

used to study the regeneration of poisoned oxide

catalysts. [8’91A typical case is shown in Figure C-3. Afier

exposing a nickel molybdate (FTMoOJ) to HZS, one sees

the formation of metal sulfides and sulfates that change

the x-ray diffraction pattern of the system. [s’glIn the

presence of Oz this “mixture” is stable up to 250 “C

when reaction begins.191As the temperature is raised several

intermediates are observed, and at .4000C the diffraction

lines for pure NiMoOA appear. At 480 ‘C only the XRD

pattern of NiMoOA is seen.181Results of time-resolved

XRD and XANES indicate that reaction with oxygen at

high temperature is very effective for removing sulfim from

poisoned NiMoOA, ZnO, NiO and M003 catalysts. ■

Thziresearchwassuj.portedby the USDepartment ofEnergy

Division of Chemical Sciences, Ofice of Basic Energy

Sciences.

REFERENCES

[1] J.A. Rodriguez, T. Jirsak, S. Chaturvedi and J. Hrbek, J Am. Cbem. Sot., 120,11149, (1998).

[2] J.A. Rodriguez, T. Jirsak and S. Chaturvedi, J Cbem. Ply., 110, in press, (1999).

[3] T. Jirsak, J.A. Rodriguez, S. Chaturvedi, andJ. Hrbek, Suqf Sci., 418,8, (1998).

[4] T. Jirsak, J.A. Rodriguez and J. Hrbek, Surjf Sci., submitted.

[5] J.A.ROdr@zS.Chaturvecli, T.JirSak,andJ. Hrbek, J Chem. My., 109,4052, (1998).

[6] M. Kuhn, J.A. Rodriguez and J. Hrbek, Smjf Sci., 365,53, (1996).

[7] S.H. overbuy, D.R. Mdlim M.T. Pa.ffett and B.E. Keel, Surjf Sci., 254,45, (1991).

[8] S. Chaturvedi, J:A. Rodriguez and J.L. Brito, Catal. Lett., 51,85, (1998).

[91 J.A.ROdrigu=,s.Chxurvd J.C.Hanson, and J.L. Brito, J Pbys. Cbem. B, in press.

[10] 1?Norby and J.C. Hanson, Catal Xday, 39,301, (1998).

2-36
UsingX-Ray “Vision”to UnderstandSelf-Assembly

P.Fenter (ANL),F.Schreiber(MP1-Stuttgart),A.Eberhardt (LANL),

T.Y.B.Leun (U.Illinois,Urbana-Champaign),

L.Berman b NL-NSLS),M.Bed k (Northwestern U.and ANL),

G.Stoles (PrincetonU.),and P.? isenberger (ColumbiaU.)

INTRODUCTION

The concept of “self-assembly” (SA) is derived from

biological systems and can be defined as a process bywhich

molecules having many internal degrees of freedom are

able to form ordered supermolecukw structures utilizing

weak interactions such as van derWaals forces or hydrogen

bonding 1’1.Monolayers of~l-thiols grown onAu(l 11)

surfaces are special among the many self-assembling

systems because this system is widely considered as

applications. In this system the gold-sulfhr bond is strong

enough to anchor the molecules to the surface, yet at the

same time this interaction leaves suf%cient lateral mobility

to allow the inter-chain van der Waals interaction to drive

the system toward the formation of a stable well-ordered

monolayer. Here we review some of the phenomena that

we have uncovered using x-ray scattering techniques to

study the growth of decanethiol (Cl O) on Au(l 11)

surfaces from the vapor phase (for details of sample

prototypical and has many potential technical preparation, etc., see references 12’3’41).

100

0

Figure C-4. The coveragetemperature (Q,T) phase

diagram of CIO/Au(lll)

derived by GIXD (reprinted

from Schreiber et al., 1998).

The phases include the striped

(S), the intermediate (1P),the

C(4X2) (C) and the melted (L)

phases, respectively (a

schematic of each phase is also

shown). The vertical lines

indicate the nominal coverages

of the striped phase (0.27ML),

the nucleation of the C(4X2)

phase (0.47ML), and saturation

of the C(4X2)phase (1ML).

I

s

I

,

I

a 1 I

a

I

1

0.0 0.2 0.4 0.6 0.8 1.0

coverage

2-37 I
PHASE BEHAVIOR OF SAMS

The first complexi~that must be overcome is to

understand the different equilibrium structures that are

present during growth. Early growth studies have

interpreted SAM growth as a continuous process by which

the alkyl chains within the monolayer collectively

transform from a disordered to an ordered configuration[5].

Instead, through a combination of X-ray, He atom

difiiaction and scanning tunneling microscopy it has been

shown that there are a number of dktinct phases present

during the growth process 13’Q.In addition to the densely

packed “standing up” C(4X2) phase at saturation coverage

(G= 1 ML = 4.6x10’4 molecules/cm2), at low coverages a

lying down “striped” phase (0 = 0.27 ML) has been

observed. By mapping out the temperature and coverage

dependence of these two ordered phases using grazing

incidence x-ray diffraction (GELD), we have delineated

131the equilibrium phase behavior of this system (shown

in Figure C-4). In addition to these two ordered phases

there are at least two other disort&redphases. There is an

“intermediate” phase which is found at coverages

intermediate between the C(4X2) and the striped phases

(forT < 15”C, with a nominal coverage of @ = 0.47 ML),

and a melted phase which apparently exists at all coverages

for sufficiently elevated temperatures. Thus, at

equilibrium, the growth proceeds primarily through the

coexistence of these distinct phase.s131.

A remarkable feature is that while a complete

monolayer melts at .90°C, at @. 0.5 ML the SAM melts

at - 150C (even though both phases are chemisorbed!).

This dependence ofT~ with@ is one of the essential keys

to understanding the SAM’s ability to assemble into highly

ordered structures131. When growing in the presence of

the melted phase (T > 15”C) the order in the SAM (as

measured by the average domain size) is substrate limited

which is suggestive of significant diffhsivity and Ostwald

ripening of the growing islands. At lower temperatures

(<15°C) the final SAM is significantly less ordered and

the domain size evolution during growth is consistent

with a fixed number of islands suggesting a loss of

difkivi~ at these temperatures[3].

THE HEADGROUP-SUBSTRATE

INTERFACE STRUCTURE AT THE

BURIED INTERFACE

How can we understand the combination of high

thermal stability coupled with an ability to assemble at,

and even behw, room temperature? This issue is closely

related to the nature of the S-Au bond. While the vast

majority ofstudks on these systems assume that the sulfhr

., . . .

-. . —-—..— --——-–L_—_ —._. .._—>

./’;

- —h —.——

(A)

L . . . . . . . . . . .

2 : .*:::f ....

...............

........

.......

......

..... .... .......

.... ...

...

.......

.... .........

... .......

- 1.6 :::

~~ -.

........

> 1.2

~!;::::m. ~:

0.8 :

.......

......... ...

...............

...........

I I I

0.5 1 1.5 2 2.5

x (A)

(B)

R

Figure C-5. (A)$ map of the two sulfur head-group positions at heights of z, = 2.21*0.05 A (green), and

~= 2.97*0.05 A (blue) with respect to the underlying substrate lattice as derived from the X5W data for

O= 1.OML.The large circles denote the Au substrate lattice sites. (B)A schematic of the derived %ulfurdimer’ structure, in which only one of the two head-groups interacts directly with the substrate (green

circle). The hydrocarbon chains are schematically shown as “R (adapted from Fenter et al., 1998).

2-38
head roup bonds to the Au surface in an hexagonal

43~3R30° mesh with a S-S spacing of 5 ~ [~, our 2D

crystallography results found that while the chain-chain

spacing was indeed .5 ~, the sulfur headgroups were

instead arranged as sulflu dimers with a S-S spacing of

-2,2 A [*J.

To resolve the ensuing controversy, we performed

X-ray standing wave (XSW) measurements to directly

probe the S/Auinterface structure for this system121.XSW

is one of the few techniques which can directly and

quantitatively probe a buried interface structure

containing a low Z element such as sulfhr by probing its

XSW induced photoelectron yield near a substrate Bragg

condkion. The resuhs (summarized in Figure C5) reveal

a highly detailed picture of the S-Au interface structure

and directly contradict the widely assumed hexagonal S

mesh. We find that the two distinct S headgroup locations

within the unit mesh each have a distinct height and lateral

position121. By combining these results with the

information derived with GIXIY81, we find that the S

dimer is bound to the Au substrate through only one of

the two S atoms with the presumed S-S bond being

inclined by 19° k 2° with respect surface plane. The

derived Au-S-S angle is consistent with the tetrahedral

angle and therefore provides a natural context in which

to understand the S-Au interface structure. The existence

of a sulfur div.wrspecies (which presumably interacts more

weakly with a gold surface than a sulfur monomer)

provides a simple yet plausible explanation for the

observation of both a melted phase and significant surface

diffusivity for these chemisorbed species at temperatures

aslowas 15”C.

10-1

10-2

10-3

104

1 0 10 20 30 40 50 60 70 80

Irnphgement Rate (LLs~ Temperature (“C)

Physisorption Chemisorption Physisorption 8iRMei:::~ Chemisorption

Figure C-6. The C(4X2)growth rate is plotted as a function of impingement rate for two representative

temperatures, and as a function of temperature for two impingement rates (reprinted from Eberhardt

et al., 1998). At 40°C the dependence is linear, but at 5° C the growth rate increases quadratically

with “the impingement rate. .Also shown is a schematic of the-uni- and hi-molecular-adsorption

processes.

2-39
ADSORPTION MECHANISMS

IN SELF-ASSEMBLY

In this system, SA proceeds in a two-step fahion12’31,

of which the second step is associated with the formation

of the C(4X2) phase and the final “assembly” of the

monolayer. We have made use of the simple

proportionality between the GIXD integrated intensity

and the coverage of a particular phase (the C(4X2) phase)

to follow the growth kinetics in situ and in real-time, as a

fimction of the thiol impingement rate and the substrate

temperature[~l. The data (Figure C-6) clearly show that

there are two distinct adsorption processes, each having a

distinct dependence upon temperature and pressure.

From the decrease of the growth rate vs. increasing

temperature in both processes, we can dkectly conclude

that the molecules adsorb as a physisorbed precursor phase

and thermalize before either chemisorbing or desorbing

from the surface (i.e., physisorption mediated

chemisorption)

A unique feature of these data is that while the high

temperature process varies linearly with the impingement

rate, the low temperature process varies quadraticalb with

this quanti@41. While a linear variation is ubiquitous in

surface adsorption and can be understood

phenomenologically as the result of a uni-molecular

process (i.e., each molecule adsorbs or desorbs

independently of orher molecules), the quadratic variation

can be understood as an associative adsorption process,

whereby the rate-limiting step is a bimo.h-ukzr reaction in

the physisorption well:

2 R-SH(p) + R-S-S-R(c) + Hz,

where “p” and “c” denote physisorbed and chemisorbed

species, respectively. This bimolecular adsorption process

is very unusual and may ultimately be the result of the

peculiar adsorption energetic of this systemlgl.

CONCLUSIONS

X-ray scattering techniques have allowed us to

unravel many of the molecular-level aspects of SA of Cl O

on Au(l 11). We conclude that the growth of this system

can be understood in terms of its phase behavior, bonding,

and adsorption mechanisms, and the complexity of this

system is not a direct result of the molecular structure

(e.g., as a result of chain entanglement), although chain

entanglement is expected to be important for longer

aliphatic molecules (e.g., polymer brushes). In work

presently in progress[g], we are testing our level of

understanding of the SA process by probing the behavior

of molecules that have two headgroups (e. g.,

hexanedirhiol) and by investigating the influence of the

molecular backbone rigidity. H

The work described here WB perjormed at the X1OB and

X24A beandines. We thank SteveBennett (X1OB), Baoshan

Zbang (2Y1OB)andBarry Kzriin &24A) fir tbeiraxsistance

during the measurements.

REFERENCES

[1]

[2]

[3]

[4]

[51

[6]

[71

[8]

[91

[91

G.M. Whitesides, J.l? Mathias and C.T. Seto, Science, 254, 1312, (1991).

I! Fenter et al., Surf Sci., 412,213-235, (1998).

F. Schreiber et al., Pbys. Rev., B 57, 12476, (1998).

A. Eberhardt, I? Fenter and I? Eisenberger, Surjf Sci. Letts., 397, L285, (1998).

M. Grunze, Pbysica Scrzpta,T49, 711-717, (1993).

N.C. Camillone III et al., J Cbem. I%ys., 101,11031, (1994).

A. U1man, Cbem. Rev., 96, 1533, (1996).

1? Fenter, A. Eberhardt and 1? Eisenberger, Science, 266, 1216, (1994).

D.J. Lavrich, S.M. Wetterer, S.L. Bernasek and G. Stoles, J Pbys. Cbem., B 102,3456-3465, (1998).

T.Y. Becky Leung, Ph.D. Thesis, Princeton Universi~ (1998); see the following web page for

more information: www.princeton.edul+ gscoles.

2-40
I

IonicStatesofSmallMoleculesInvestigatedby

VibrationallyResolvedCore-levelPhotoelectron

Spectroscopy

U.Her enhahn, A.Rudel,E.E.Rennie, K.Maier,B.Kempgens, H;M.Koppe,

and A.h . Bradshaw

(Fritz-Haber-lnstitute,Berlin,Germany)

Upon photoionization of a small molecule in the

gas-phase, the excitation of one or several vibrational

degrees of freedom is common. This occurs because the

potential energy curve of the molecular ionic state is

different from that of the neutral ground state. Since the

photoionization process corresponds to a szdk!enchange

between the two states, the atomic core has no time to

adiabatically respond to the change in conditions and is

thus left in a state with potential energy. The ground state

configurations of small molecules are usually well known

and it is therefore possible to draw conclusions as to the

nature of the excited state. This is especially true for the

case of inner-shell ionization. However, the ability to

record vibrationally resolved electron spectra at photon

energies sufficient to ionize an inner shell requires very

good monochromatization of the incident light. In the

last few years we have recorded core-level photoelectron

spectra of several closed shell molecules at the XIB

beamline11-31.

A good example of the determination of the ionic

geometry in a closed-shell molecule is provided by the

C 1s ionization spectrum of ethane (C,HG). Two

vibrational progressions are visible in the C 1s

photoelectron spectrum of CZHG(Figure C-7). The first

one, with vibrational energies around 400 meV, is typical

for the photoionization of all small hydrocarbons and

pertains to the totally symmetric C-H stretching

vibrations. In terms of molecular geometries, excitation

200

1400

~

1200

: 1000

g

~ 800

.-

: 600

z 400

200

I I I

I

I I I I

I

1 I 1 I

I

1 I .: I 1 t

~; I

CZH6C 1S-l

1!

Bending ~

– hv = 309 e~ vibration

.,

.

1 8 I

_hv = 309 eV

I I I

16.0 16.5 17.0 17.5

Kinetic energy (eV)

Figure C-7. C 1s photoelectron

spectra of ethane and deuterated

ethane measured with 309 eV

photon energy at beamline Xl B.

The results of a least-squares fit

assuming the excitation of only two

normal vibrational modes have

been included. The dashed lines

represent the individual vibrational

states, while the full line through

the data points represents the fit

result after summation and

convolution with the instrument

profiles.

2-41
1500

500

400:

3000

1000

0

21.5 22.0 22.5 23.0 23.5 24.0

A

t

k

L

k?????%

J

...””...”” {~.. ...

,.. ,.

,.. “..

,.. ...

...

~U.

22.5 23.0 23.5 24.0 24.5 25.0

kinetic energy (eV)

Figure C-8. Core Ievelphotoelectron spectrum ofgaseous NO

recorded at beamline Xl B. Preliminary results from a leastsquares fitting procedure are shown as dotted lines.

of this mode means that the C-H bond length shortens of up )

C-C-H bond angle along with a change in CH bond length. Quantitatively, vibrational

energies of 176 *5 meV were found for this

bendng mode for erhane and 130 *1O meV

fof deuterated ethane. The C-H stretch was

found to be 407 +5 meV and the C-D stretch

tobe291 *1O meV. The changes in C-H bond

length and C-C-H bond angle are 0.036 ~ and

2.1°, respectively assuming a delocalized core

hole[q.

Molecular Species with an unpaired

electron determine an important part of the

chemistry of the atmosphere despite their

generally low concentration. AS a step towards

the spectroscopic characterisation of these

systems, we have recently measured inner-shell

photoelectron spectra of the open-shell

molecules Oz and NO. Upon removal of an

inner-shell electron, both of these molecules,

will, in principle, show a photoelectron line

split into two components by the exchange

interaction between the unpaired electrons.

The high-resolution photoelectron spectra of

these systems can therefore give information

on the influence of this spin-dependent force

on the binding state of the molecular ions in

play.

Turning to open shell molecules, we note

that in the ground state configuration NO has

an unpaired electron in the 27corbital. Together

with the spin 1/2 of an inner-shell hole, the

molecular states 111 and 311 are thus formed.

These states can be easily distinguished afier

ionization of an N 1s electron: our value for

the exchange splitting is 1.40(1) eV

(Figure C-8). Both states show a similar

vibrational progression, in which excitations

two vibrational quanta can be seen. The

upon removal of the C 1s core electron. The second mode,

with vibrational energies around 180 meV, was at first

assigned to a totally symmetric C-C stretching vibration

by several groups141. However, calculations of the

vibrational excitation probabilities have yielded the first

evidence that another mode, namely an umbrella-like

bending vibration of the hydrogens attached to the site

of the core-hole, might play a stronger role than the

movement of the two methyl groups against each other[51.

By studying isotonically substituted ethane, C2DG, in

parallel with CZHG, we have found that the frequency

shift observed for the mode in question matches that of

a C-H bending vibration, but not that of a CH3-CH3

stretching vibration. That is, the molecule changes its

vibrational energy from a preliminary analysis is around

240 meV for bo;h spin sta;es. This is-similar to the value

of 241 meV found for the N2 N ls+n * excited neutral

state[sl and is much smaller than the valueof314(4) meV

measured for inner-shell ionized Nz. A close similarity

between NO and n“-excited N, is expected from the

Z+ 1 model. Less evident are the differences in exchange

splitting, which can be seen by comparing the N 1s

ionization spectrum with the O 1s spectrum. The triplet

and singlet components of NO O ls-l overlap each other

and the singlet peak can be seen as a shoulder about

0.48 eV away from the larger triplet peak. This splitting

is, to our knowledge, resolved here for the first time and

was earlier predicted to have a smaller value by theory

2-42
The authors of [~ give values of 1.48 eV at the N-edge

and 70 meV at the O-edge. A plausible explanation in

chemical terms seems to be possible in this case As oxygen

has a higher electronegativity than nitrogen, the charge

densi~ of the bonding orbitals is stronger on the O side.

Therefore, the anti-bondinglone Z* electron preferentially

adheres to the N side and causes a stronger exchange

interaction with a lone core electron at the same site.

However relaxation, i.e. the reaction of the molecular

charge cloud to the core hole creation, seems to

substantially influence the charge distribution. Otherwise,

the failure of theory to reproduce the splitting

quantitatively would not be explainable.

The inner-shell photoelectron spectrum of Oz shows

an easily observable separation into the

O ls-l ‘X and 42 states (Figure C-9). An analysis of both

lines reveals fhrther differences. Although vibrational

components cannot be resolved for both of these lines, a

significantly larger width of the 22 component compared

to the 4Z is clearly observed. A least squares fit results in a

profile for the 4Z line which hardly shows any vibrational

excitation. Interestingly, the 22 line has vibrational

components with a significantly larger spacing, 170(20)

meV compared to 110(20) meV for the 4X and larger

excitation probability as well. One is therefore led to

conclude that an ion with a stronger force constant and

smaller bond-length is formed in the case of doublet

ionized 02+ compared to quartet 02+. This change in

molecuku- potential is solely brought about by the different

coupling between the lone inner-shell electron and the

high-spin coupled ln~ open valence shell. The high

brightness of the XIB undulator has proved to be crucial

in measuring high resolution core-level spectra of small

molecuks with high sensitivi~. H

REFERENCES

[1] B. Kempgens, K. Maier, H. M. Koppe, M. N. Piancastelli, M. Neeb, and A. M. Bradshaw, Pbys. Rev. Lett., 79,

998, (1997).

[2] B. Kempgens, H. Koppel, A. Kivimiiki, M. Neeb, L. S. Cederbaum, and A. M. Bradshaw, Pbys. Rev.

Lett,, 79,3617, (1997).

[3] A. Kivim3ki, K. Maier, U. Hergenhahn, M. N. Piancastelli, B. Kempgens, A. Rudel, and A. M. Bradshaw,

Phys. Rev. Lett., 81,301, (199$.

[4] H.M. Koppe etaL, NSLSAnnua/ReporG (1996); S. J. Osborne et a~J Chem. Pbys., 106,1661, (1997).

[51 T. D. Thomas, L. J. sae~re, S. L. Sorensen, ~d S. Svensson, J Cbem. PLy~.,109,1041, (1998).

[6] E. E. Rennie, H. M. Koppe, B. Kempgens, U. Hergenhahn, A. Kivimii.ki, K. Maier, M. Neeb, A.

Rudel, and A. M. Bradshaw, J Pbys. B, submitted, (1998).

[7] J. Muller and H.f¥, in: Proceedhuzs of a NATO Advanced Studv Institute on Molecular Ions, edited

by J. Berkowitz and K.-O. Groeneveld, Plenum Press, New York, Kos, Greece, B90, p. 221, (1980).

4

Figure C-9. O 1s photoelectron 23

spectrum of oxygen recorded at C

beamline Xl B.Open dots are the 3

data points, the solid line is the $

result of a least-squares fit for the JJJ2

total profile, while the dotted lines .=

are results for the constituent m

components before convolution gl

with the apparatus profile

function.

o

10 13

ld~tic ener~ (eV)
— ————.

X-ray Scatteringfroma SolubleMonolayer

at the Water-HexaneInterface

M.L.Schlossman,Z.Zhang, D.M.Mitrinovicand S.M.Williams

(U. of Illinois,Physics and Chemistry Department)

Z.~H;)ang

Measurements of the microscopic structure of liquid

interfaces or surfactant assemblies at these interfaces have

milked primarily one of two geometries: (1) macroscopic,

single liquid-vapv interfaces at which the tail groups of

surfactanrs are exposed to the vapor, and (2) multiple,

microscopic liquid-liquid interfaces existing within

surfactant solutions. A macroscopic single liquid-vapor

interface is oriented by gravity and, in turn, orients

surfactants supported on its surface. This allows for

detailed structural measurements using, for example,

either x-ray or neutron reflectivity or x-ray grazing

incidence diffraction. However, surfactants at liquidliquid interfaces in solution are in a chemical environment

typically used for either man-made or biological

applications. Recent efforts have combined the

advantages of these two geometries in a third geometry, a

macroscopic single liquid-liquid interfacel*-51. In

particular, our ability to flatten otherwise very curved

interfaces allows x-ray surface scattering techniques to be

used in the study of a wide range of liquid-liquid

interracial phenomena.

Here, we describe an x-ray surface scattering study

of the structure of a monolayer of soluble surfactants at

the water–hexane interface. The few available

thermodynamic or spectroscopic measurements indicate

that soluble and insoluble amphiphilic monolayer at

water-oil interfaces are more loosely packed than the

corresponding monolayer at the water-vapor

interfaceIG’7’81. In particular, monolayer formed from

surfactants soluble in the oil phase are expected to be

disordered and in a liquid or gas phase at liquid-liquid

interfaces[sl. Contrary to this expectation, we find that

soluble monolayer can form solid monolayer phases at

the water-oil interface. In addition, the system described

below exhibits a solid to gas phase monolayer transition

at this interface. Comparison to a similar transition at

the liquid-vapor interface indicates that the solvent acts

to disorder the solid monolayer at the liquid-liquid

interface at a lower temperature.

Monolayer of F(CFZ)IO(CHZ)ZOH (denoted here

as FCIZOH) self-assemble from a solution (2x10-3 mol/

kg) in hexane onto the solution-water interface(g’ ‘O].

I I t i

r=l

‘%\. uE.L.li

Figure C-10. X-ray reflectivity from the

water-( hexane solution of

F(CF2)10(CHJ,0H)interface at T=32”C,

triangles; T=48°C, circles; pure waterhexane interface at T=32”C, open

squares. Inset is a cartoon of the solid

surfactant monolayer that forms at

T=32”C. Also indicated are the x-rays

reflecting off the top and bottom of the

monolayer. The constructive

interference of these x-rays is

responsible for the increase in

reflectivity.

o 0.1 0.2 0.3 0.4

Q, [A-’]

2-44
a) 1 -0 ● -

m ●

~ 0.8 - Mo%o!fyer ●

■

~ 0.6

\\

●

heating

●

CD

g 0.4 cooiing ■●0

c ■ O

~ 0.2 ■ Gaseous

.-

60

~ Monoiayer

u) ●0 9

1 t 1 I I

20.0 25.0 30.0 35.0 40.0 45.0 50.0

Temperature (1’C)

Figure C-11. Surface coverage of the Iowertemperature solid monolayer

phase on a heating-cooling cycle through the solid-gas monolayer

transition of F(CFJ10(CHJ20Hat the water-(hexane solution) interface.

Figure C-10 illustrates x-ray reflectiviV measurements

at T=32.00 (*0.03)”C from the monolayer at the water–

(hexane solution) interface (plotted as a fi.mction of the

wave vector transfer normal to the interface,

Q= (4dA)sin(@, where A= 0.0825*0.0002 nm is the

x-ray wavelength for these measurements and cx is the

reflection angle measured from the plane of the interface).

Also shown are measurements from the pure water-hexane

interface at the same temperature and measurements from

the water-(hexane solution) interface at T=48.00°C. The

enhanced reflectivity at higher Q from the water–(hexane

solution) interface at T=32.00”C is due to a constructive

interference of x-rays reflected from the top of the

fluorinated monolayer with x-rays reflected from the

bottom of the monolayer. The reflectivity from the water-

(hexane solution) interface at T=48.00”C is nearly

identical to the measurements from the pure water-hexane

interface and indicates that most of the FCIZOH

molecules have desorbed from the interface at this

temperature[ll].

These data can be analyzed by using a generai

expression, derived from the first Born approximation

for x-ray scattering, that relates the reflectivi~ to the

electron density gradient normal to the interface,

~~pe @ (averaged over the interracial plane), and

~ written as [14

+

WzL. 1 d{Pe (z))

2

dz~- exp(iQ# R~QJ =

‘Pew (1)

where APt,bk = p,,bU&.@,w– p,,bU&.P~ and R&~ is *e

Fresnel reflectivity predicted for an‘“iI eal, smooth and flat

interface1131. The layer of FCIZOH is modeled simply as

a thin slab of higher electron density sandwiched between

two bulk liquids. The interfaces of the top and bottom

of this slab are roughened by thermal capillary waves,

characterized by the roughness parameter, C. The

reflectivi~ calculated from Eq. (1) using the slab model

for the electron densi~ is fit to the data to yield values

for the three fitting pararneterx the slab thickness L .

1.24 A0.03 nm, O= 0.36~ 0.02 nm, and the fluorinated

slab electron density (normahzed to p bxkwd,e)P~ 1.90 *

0.04 (Figyre C-10) 11’1.

Our measurement of the electron density of the

monolayer at T=32.00”C, pf= 1.90 k .0.04, corresponds

to a mass density of 2.19 * 0.05 g/cm3. This agrees with

the density of bulk solid J-‘fluoroalkane phases

(e.g., for n-C,OF1,) which have a densi~ of either

2.23 g/cm3 for the monoclinic crystal phase or 2.16 g/

cm3 for the rhombohedrai rotator solid phase 1141.These

measurements exclude the possibili~ that the FC120H

monolayer at the water-hexane interface is in a liquid

monolayer phase (bulk liquid fluoroalkanes have a mass

densi~ of approximately 1.7 g/ems) 114-16.

2-45
A similar analysis of the data from the water–(hexane

solution) interface at T=48.00”C indicates that a

conservative upper limit to the surface coverage of

FC,20H is approximately 1.5?40 ‘l]]. The transition from

the solid FCIZOH monolayer to this gaseous monolayer

at higher temperature can be studied by measuring

reflectivity as a finction of temperature. Figure C-11

illustrates the first heating-cooling cycle through this

transition. We believe that the transition region represents

an interface with coexisting solid and gas monolayer

phases. This is consistent with enhanced off-specular

diffuse scattering that we measured in this transition

region (not shown) [l’1. Accordingly the reflectivity has

been interpreted to yield the surface coverage of the lower

temperature solid phase monolayer. Preliminary data

indkate that the hysteresis in Figure C-11 is reduced

with fimher heating-cooling cycles through the transition

temperature.

An important feature of studk.s of the liquid-liquid

interface is the ability to characterize the role of the upper

phase on the structural order within, for example,

monolayer at the interface. To gain some insight into

the role of the upper-phase hexane on the ordering of the

low temperature FCIZOH solid phase monolayer, we

studied a similar transition in FCIZOH monolayer

supported on the water-vapor interface. The FCIZOH

monolayer was spread in the crystalline island phase at

an inverse density of 0.4 nm2/molecule. Since the

crystalline unit cell size is 0.29 nm2/molecule there is

excess area at the interface that allows the monolayer to

undergo a transition to a liquid or gaseous disordered

phase. X-ray grazing incidence diffraction measurements

(not shown) indicate that a solid to gas (or, possibly liquid)

monolayer phase transition occurs between 58.8°C and

62.09”C, slightly more than 20”C higher than the solidgas transition in the FCIZOH monolayer at the water–

(hexane solution) interface[’11. Therefore, the presence of

the hexane solvent acts to disorder the solid monolayer at

a lower temperature. ■

This work wm supported by the donors of The PetroLeum

ResearchFund administered by theACS, the UIC Campus

ResearchBoard andtheNSFDivision of~atetiak Research.

REFERENCES

[1] L.’T. Lee, D. Langevin, and B. Farnoux, l%ys. Rev. Lett. 67,2678, (1991).

[2] J.S. Phipps, R.M. Richardson, T Cosgrove, and A. Eaglesham, Langmui~ 9,3530, (1993).

[3] B.R. McCla.in, et al., Pbys. Rev. Lett. 72,246, (1994).

[4] M.L. Schlossman, et al., Rev. Sci. Instrum. 68,4372, (1997).

[5] S.M. Williams, Z. Zhang, D. Mitrinovic, Z. Huang, and M.L. Schlossman, in preparation, (1998).

[6] B.Y. Yue, C.M. Jackson, J.A.G. Taylor, J. Mingins, and B.A. Pethica, j Chern. Sot. Faracihy172,2685,

(1976).

[71 M.C. Messmer, J.C. Conboy and G.L. Richmond, J. Am. Cbem. SOC.,117,8039, (1995).

[8] G.L. Richmond, Ana$tical Chemistry 69, 536A, (1997).

[91 Y. Hayami, A. Uemura, N. lkeda, M. ~atono, and K Motomura, J coil. ht. Sci. 172,142, (1995).

[10] T. Takiue, et al., J Pbys. Cbem. 100,20122, (1996).

[11] Z. Zhang, D.M. Mitrinovic, S.M. Wdliams, Z. Huang, and M.L. Schlossman,J Cbenz. Pbys., in press (1999).

[12] IX. Pershan, Faz Dfic. Cbem. SOL-.89,231, (1990).

[13] M. Born, and E. WOIL Princ@les of Optics, (Pergamon Press, Ofiord, 1980).

[14] H. Schwickert, G. Strobl, and M. Kimmig, J Cbem. Phys. 95,2800, (1991).

[15] PCR catalog (Gainesville, FL).

[16] H.W. Starkweather, Macromolmda 19,1131, (1986).

[17] D.M. Mitrinovic, M. Li, Z. Huang, and M.L. Schlossman, work in progress, (1999).

2-46
GEcM@G’/KcALSamvaz$$’

ChemicalAnalysisofImpactMaterialon a DustCollector

Flownonthe MIRSpaceStation

G.J. Flynn(SUNY-Plattsburgh)

S.R.Sutton (TheUniversityof Chica o)

F.Horz (NASAJohnson Space Center7

Low density silica aerogel collectors have been flown surface, a 10 micrometer diameter particle may stop as

on earth-orbiting satellites to collect samples of earth- deep as 1 centimeter below the surface, with a typical

orbital debris and interplanetary dust in order to depth of .o.5 centimeters.

characterize the flux and types of small particles in the Previously, chemical characterization of these

.-

near-earth environment. This effort has

three objectives:

1)

2)

3)

to determine the relative

contributions of man-made orbital

debris and interplanetary dust to

the flux,

the chemical analysis of the manmade debris to infer the sources of

the most abundant types of

particles which may be hazardous

to earth-orbiting spacecraft, and,

the chemical analysis of

interplanetary dust particles which

have never resided in the

stratosphere as a monitor of

possible stratospheric

contamination of the interplanetary

dust particles collected by NASA

from the earth’s stratosphere.

High-velocity (km/see) particles

penetrate the aerogel, leaving a coneshaped damage track, sometimes having

a surviving particle at the end (as shown

in Figure G-1). In 20 mg/cc density

aerogel a hypervelocity particle will

typically produce a track whose length is

about 1000 times the diameter of the

particle. Thus, a 10 micrometer diameter

particle will stop in a distance of about 1

centimeter. Depending on the entry angle

of the particle relative to the aerogel

‘ Figure G-1. Image of a high-velocity particle captured

in low-density silica aerogel.

2-47
captured particles has required their

removal from the aerogel. The

penetration depth of the analysis

electron beam in instruments such as

electron microprobe is inadequate

for the analysis of particles buried

millimeters to centimeters beneath

the surface of the aerogel. However,

high-energy x-rays are not readily

absorbed, and the inherent limitation

on in-situ analysis ofparricles beneath

the aerogel surface results from the

absorption of the fluorescence x-rays.

We have developed an in situ analysis

rechniqueI*l, performing x-ray

fluorescence elemental analysis using

the X-Ray Microprobe on Beamline

X26A of the National Synchrotrons

Light Source, to characterize the

heavy elements in particles at depths

of up to several centimeters in low

density aerogels. The aerogel is

composed mostly of Si, but trace

amounts of Ti, Fe, Cu, and Zn are

also present. Thus, the composition

Figure G-2. X-ray fluorescence spectrum of a patilcle captured in

aerogel exposed for 18 months on the MIR SpaceStation. This particle

contains Fe,Ni, Cr and possibly Mn, in roughly chondritic proportions,

indicating it is an interplanetary dust particle rather than orbital

debris.

of particles or their residue is inferred by observing

significant excesses in these elements over the signal from

adjacent regions of the aerogel.

The X-Ray Microprobe on Beamline X26A (and

previously on Beamline X26C) has been used for the

chemical analysis of interplanetary dust particles collected

by NASA stratospheric sampling aircraft for the past

decade[’1. The chemical compositions of more than 200

interplanetary dust particles have been measured, and

these provide a basis for comparison with particles

captured in earth orbit. The most abundant type of

interplanetary dust collected from the Earth’s stratosphere

is similar in chemical composition to the chondritic

meteorites. Chondritic material has an Fe/Ni ratio of

about 17, quite distinct from the much higher Fe/Ni ratio

in terrestrial surface rocks. We use this Fe/Ni ratio to

identifj likely interplanetary dust particles. This

identification is not perfect, since stainless steel orbital

debris could also have high NL Some types of orbital

debris, such as Ti-rich paint flakes, can also be identified

on the basis of their chemical composition.

Thus far, we have examined five pieces of aerogel,

each having a surface area of about 1” by 2“, exposed for

18 months on the MIR Space Station. Two contained a

series of parallel tracks, several having particles at the end,

indicating a “swarm” of particles struck the aerogel

simultaneously. AIl 14 of the tracks in these two swarms

2-48

contained Fe residue, either distributed along the track

or in particles at the end of the track. In three cases we

also detected Ni in the residue or particles, with an Fe/Ni

ratio similar to the chondritic meteorites. The largest of

these particles, several micrometers in size, had detectable

Fe, Nl, Cr, and possibly Mn, present in roughly chondritic

proportions (Figure G-2). This composition provides

an almost certain identification of this particle, and the

other particles in this swarm, as extraterrestrial. Further

analysis of these swarm particles is in progress.

We ako analyzed an apparent particle at the end of

a track not associated with a swarm. No elements were

detected in this particle. Because this particle was several

millimeters below the aerogel surface, Ca was the lightest

element we would expect to detect. The apparent particle

might simply be compacted aerogel at the end of the track,

or it might be composed predominately of Si (which

cannot be detected because of the Si signal from the

aerogel) or of elements lighter than Ca.

Other impacting material produces shallow pits in

the aerogel, sometimes with debris from the impacting

particle on the bottom or walls of the pit. The residue in

these pits was also characterized using the X-Ray

Microprobe. We examined three aerogel pieces which

contained pits. One pit showed K and Cain the bottom,

consistent with the impact of human waste. Examination

of two other pits showed no element enhancements,
suggesting that either the impactor consisted

predominately of low-Z material (lower than Al), which

we cannot detect with the X-Ray Microprobe, or silicon,

or that little residue from the impacting particle was

retained in the these pits.

This in situ analysis of particles captured in

aerogel also serves to develop and demonstrate analytical

techniques that will be important for NASA’s upcoming

ST~UST mission. ST~UST, which is scheduled

for launching in February 1999, carries a large aerogel

collector that will fly through the dust cloud of Comet

Wild-2, with a relative velocity of about 6 krrdsec,

collecting more than 1000 cometary dust particles larger

than 10 micrometers in size. The rear surface of the

aerogel will be exposed during the cruise-phase of the

ST~UST mission in an effort to collect hundreds of

0.5 micrometer size interstellar dust grains. The

STDUST aerogel collector is scheduled to return to

Earth in 2006. Because the removal ofindividual particles

from the aerogel would be tedious, and would leave open

the possibility of contamination during extraction, insitu particle characterization, using and X-ray Microprobe,

is likely to be an important part of the preliminary

characterization of these particles. ■

REFERENCES

[1] G. J. Flynn , S. R. Sutton, and F. Horz, “h Situ Chemical Analysis of Extraterrestrial Material Captured in

Aerogel”, Lunar& Planeta ry Science XXVII, Lunar and Planetary Institute, Houston, TX, 369-370 (1996).

[2] S. R. Sutton and G. J. Flynn, “Stratospheric Particles: Synchrotrons X-Ray Fluorescence determination of

Trace Element Contents”, Proceedings of the Eighteenth Lunar and Planetary Science Conference, Cambridge

University Press, 607-614 (1988).

Figure G-3. IDP (-10 mm) collected from the stratosphere

showing the aggregated, porous texture (NASA/JPL/Caltech).

2-49
ComparativeRheologyofMantlePhases

J. Chen and D.J.Weidner

(Centerfor High Pressure Research, SUNYat Stony Brook)

The mineralo~ of the Earth’s mantle changes with

depth owing to pressure induced phase transformations.

Olivine, pyroxene and garnet are expected to be the stable

minerals in the upper 400 km of the mantle; garnet,

wadsleyite and ringwoodlte likely dominate the region

form 400 - 700 km depth; and perovskite and

ferropericlase are the stable phases at depths greater than

700 km. Theological properties of the reverent minerals

are important for defining dynamic earth phenomena

such as mantle convection and the origin of deep

earthquakes. Using a newly developed in-situ high

pressure x-ray diffraction technique at X17BI]’21, we have

measured theological properties of the predominant

mantle phases at elevated pressure(to 20 GPa) and

temperature (to 1300K).

Stress held in the powdered sample is measured as a

fimction ofpre-ssure, temperature and time by monitoring

the x-ray diffraction line profile. The line broadening is

generally caused by either elastic strain or small grain

si~e[3Al

B’= [K(l/2)Jc /(Psin8J]2 + [2EE]2

where B represents the line breadth (refers to fill width

at halfmaximum of a gaussian profile in our experiments),

K’is the Scherrer constant, b is Planck’s constant, c is the

veloci~ of light, P is the average crystallite size, 200 is the

f~ed scattering angle, e is the upper limit ofstrain (refers

to elastic shear strain in our experiments), and E is the xray photon energy. Product of the aggregate Young’s

modulus of the mineral and the measured strain derived

from above expression yields the deviatoric stress

supported by the sample.

The experiments are conducted in the multi-anvil

high pressure apparatus, SAM85[5]. Deviatoric stress is

generated through the interaction of individual grains of

the sample. Stress relaxation measurements are

,. —

6

Load (GPa)

O 5 10 +constant P at -10 GPa +

u

Q(021)

❑(101)

0(131)

A(112)

0(021)

El(lol)

e(131)

A(112)

6

4

Load (GPa)

O 5 10 +-constant Pat -10 GPa +

u

.=@-, Q%

$

* anhydrous p

:

9

i

l&%%8~ ~

t’

i ❑(310)

25°C 400”C 600”C 0(112)

~w ~el$~

--~

hydrous D

❑(310)

% 0(112)

;

o

0 1 0 1“ 2“

Time (X103s)

u

01230123

Time (x103 s)

Figure G-4. Differential stress in anhydrous and

hydrous olivine as a function of load pressure Figure G-5. Differential stress in anhydrous and

followed by heating at the constant load. Different hydrous wadsleyite as a function of load

symbols represent the stress derived from different pressure followed by heating at the constant

diffraction lines. The bars show average errors for load. The bars show average errors for each

each data set. Data of single crystal San Carlos data set.

olivine measured at room pressure by Evans and

Goetze (1979) are superposed as solid squares with

the olivine data for comparison.

2-50
Load (GPa)

o 10 20 <— constant pressure at -20 GPa ●

6

5

1

0

4

!I ❑

(Mg,Fe)Si03 o (020)

!2 ,.’’-”-iiijiij -$ , q+ggf&@j )

Perovskite ❑(112)

o

A (200)

- -[ 2

0

1’ -%

,

#

?

!!

25 “C 400 “c 600 “C 800 “C

o 1 0 1 0 1 234

Time (X103 see)

Figure G-6. Differential stress in perovskite as a function of load pressure followed

by heating at the constant load.

accomplished by observing the decay of stress-induced the anhydrous phase drops by 39’%0. Upon heating to

diffraction-peak broadening as a fi.mction of time and

temperature. The minerals we have studied are olivine,

wadsleyite, ringwoodite, garnet, perovskite and periclase.

Hydrous phases of olivine, wadsleyite, ringwoodite are

also studied to investigate the water weakening on the

theological properties of minerals in the mantle. The

experiments are carried out by first compressing the

sample at room temperature, then stepping up and

holding the temperature at desired interval for the stress

relaxation measurements.

Figure G-4 illustrates the experimental result on

anhydrous and hydrous olivine. The deviatoric stress in

both anhydrous and hydrous phases increases with applied

pressure at room temperature until the room-temperature

yield strength is reached. The stress in the hydrous phase

saturates at a lower level than that in the anhydrous phase,

which shows that the hydrous phase is weaker at room

temperature. At an applied pressure of 10 GPa the yield

strength of the hydrous a is about 28% less than that of

the anhydrous phase. When the samples are heated up

to 4000C, thermal yielding results in significant stress

drop in the both phases. The hydrous cx shows again

weaker behavior than the anhydrous phase, and the yield

strength of the hydrous ~ drops by 62% while that of

600°C, the yield strength of the anhydrous a drops fiu-ther

to about the same strength level of hydrous phase, and

the hydrous phie does not show any obvious decrease in

yield strength. The anhydrous olivine shows stress

relaxation as a fimction of time at temperatures of 400”C

and 600°C. Yield strength data from single crystal San

Cados olivine at room pressure by Evans and GoetzeI~

are superposed on the figure showing that our date agree

well with theirs at low temperature.

In contrast to olivine, its higher pressure - deeper

depth phases, wadsleyite and ringwoodite, are much

stronger than olivine and similar to each other.

Furthermore, water only slightly weakens wadsleyite and

ringwoodite while weakens olivine dramatically. Figure

G-5 shows the result of wadsleyite.

The theological proper~ of garnet is comparable

to wadsleyite and ringwoodke, and periclase is as weak as

olivine. Standing out of all these phases, perovskite is by

fa the strongest phase. In the range of investigation,

temperature doesn’t result in any significant stress drop

as seen in the other phases. It only changes the relaxation

rate. The stress at 800°C remains as high as 75°A of that

at room temperature at 20 GPa (Figure G-6).

2-51
—

Figure G-7 shows a summary of the stress capaci~

of the predominant mantle phases at the indicated

temperatures. The temperature-depth profile of thk figure

is similar to that expected in a subduction zone where

cold material is sinking and where deep earthquakes occur

(to depths of 700 km). The general conclusion is that

olivine and periclase are by far the weakest phases, with

majorite, wadsleyite, and ringwoodite of comparable, but

intermediate strength, and perovskite is significantly the

strongest of all. The experiments represent the first high

REFERENCES

temperature measurement of the theological properties

of most of these materials. The results suggest that the

bimodal distribution of earthquake activity with depth

and the cessation of earthquakes at 700 km is simply a

reflection of the strength dependence and stress relaxation

character of the stable phases and thus does not require

different triggering mechanism for earthquakes above and

below 400 km. The experimental observations are also

consistent with a significant viscosity increase at the upper

mantle-lower mantle boundary. ■

[1] D. J. Weidner, Y. Wmg and M. T. Vaughan, “Yield strength at high pressure and temperature”, Geophys. Res.

Lett. 21,753-756 (1994).

[2] J. Chen, T. Inoue, D. J. Weidner, Y. Wu and M. T. Vaughan, “Strength and water weakening of mantle

minerals, olivine, wadsleyite and ringwoodke”, Geo@ys. Res. Lett. 25,575-578, 1103-1104 (1998).

[31 F. W. Wlllem,”~ an~ysis ofx-ray diffraction line profiles using standard deviation as a measure of breadth”,

Brit. J /@i. Phys. 16, 323(1965).

[4] L. Gerward, S. Morup, H. Topsoe, “Particle size and strain broadening in energy-dispersive x-ray powder

patterns”, J Appl. Phys. 47,822 (1976).

[51 D. J. Weidner, M. T. Vaughan, J. Ko, Y. Wang, X. Liu, A. Yeganeh-Haeri, R. E. Pacalo and Y. Zhao,

“Characterization of stress, pressure, and temperature in SAM85, a DL4 type high pressure apparatus”, in

Hi~h-Pressure Research: Atmkation to Earth and Phnetarv Sciences, edked by Syono, Y. and M. H. Manghnani.

pp. 13-17, Tokyo/AGU, Wahington, D. C., Terra Scientific (1992).

[6] B. Evans and C. Goetze, “The temperature variation of hardness of olivine and its implication for polycrystalline

yield stress”, J Geophys. Res. 84,5505-5524 (1979).

25 600°C

r===zzl ‘oooc

Figure G-Z Shear strength of predominant mantle phases at indicated temperature. The depth represents

where the minerals are stable in the earth. 01: olivine, ~: wadsleyite, % ringwoodite, Mj/Py majorite

pyrope (1:1) garnet, Pv: perovskite.

2-52
IroninMartianMeteorites:Microanalysisof Fe3+/ZFeby

SynchrotronsMicroXANES(SmX)as IndicatorsofVariabie

OxygenFugacity

J.S.Delaney (De t. of GeologicalSciences,Rut ers University)

S.R.Sutton (Dep.r of GeophysicalSciences 8 C! RS,Universityof Chicago)

M.D.Dyar (Dept.of Geology, Mt.HolyokeCollege)

Igneous rocks from Mars are believed to be sampled

by SNC or martian meteorites. Martian magmatism is

inferred to have produced basaltic and more evolved

magmas from a peridotitic mantle[l’zl. These rare

meteorites cannot be realistically sampled for destructive

measurements of Fe3’/ZFe(Fe2++Fe3+)which is used as a

proxy for the oxygen budget of the planet, so that

nondestructive microanalysis is essential for improved

understanding of this important parameter. Wriation of

oxygen fugacity (fOz), causes compositional diversity

among terrestrial magmas13’41and the ratio F&/(F~+F#)

is used as an monitor of oxygen iigacity, particularly

when applied to coexisting minerals. Ultimately Fe3+/

(Fe2’+Fe3+) provides a fundamental constraint on the

abundance oxygen, this most abundant element

(volumetrically) in any crust and mantle of all the rocky

planets. The few reliable measurements of F~/(Fd+F#)

in Martian meteorites were done on bulk samples and

are difficult to apply to the crystallization hktory of the

rocks because weathering effects complicate the resuhx151.

Partitioning data for Fe*+ and Fe3+among the coexisting

minerals are needed to determine fugacity sensitive

magmatic equilibria for Martian rocks. Here we provide

in situ microanalyse-s of F&/(Fd’+Fe3’) using the XANES

microprobe at X26A for minerals in eight meteorites that

may be used to estimate oxygen fhgacity in Martian crustal

rocks. The data are comparable with those from terrestrial

rocks buffered at the quartz-magnetite-fayalke and nickel

- nickel oxide reactions and are dktinct from products of

asteroidal magmatism buffered by iron-wustite

reactionIG’7’81.The results indkate that the crust of Mars

is relatively oxidized and comparable with that of the

Earth. The results reflect Martian magmatism, shock

effects and probably hydrothermal activity.

To document oxygen fugacity related equilibria

among coexisting minerals, Fe%/ZFe data for each mineral

being considered must be acquired at metrologically

constrained locations on mineral grains. Nhety three

spectra of the Fe K-absorption edge (Figure G-8) were

acquired using Synchrotrons microXANES (SmX)

spectroscopy for 12x1 5 micrometer areas on coexisting

olivine, pyroxene, plagioclase/maskelynite, oxides, and

carbonate in petrographic thin sections of eight Martian

meteorites: ALH77005, ALH84001, Chassigny,

EET79001, LEW88516, Nakhla, Shergottyand Zagami.

The spectra were processed to extract quantitative

estimates of F#/ZFe. Sm measurements were made using

the X-ray fluorescence microprobe facility (beamline

X26A) at the National Synchrotrons Light Source (NSLS), “

Brookhaven National Laboratory. The spatial resolution

2.0-

1“”~

I

i

1.8-

i

I

1.6-

g

1.2- E

—

0.0-

-10 -5 0 5 1015 2025 30 35

AeV(rel.NMNHmagnetiteFe-edge)

Figure G-8. Representative synchrotrons

microXANES spectra of the Fe-K edge in: two

olivines from LEW88516, pyroxene fro m

ALH77005 and Zagami, feldspar and oxide from

Zagami. All spectra are normalized to Intensity

=3D 1.0 at +40eV but are displaced vertically

for clarity. The line at AeV=3D0 represents the

magnetite pre-edge having Fe3+/XFe=3D0.667.

2-53
of SmX permits microanalysis to be made avoiding oxide

inclusions in many minerals that confound bulk analytical

determinations of Fe3+/ZFe.The energy shifts of a preedge feature in the Fe K-absorption spectra area function

of oxidation state[gl and were calibrated against the

Fe3+/ZFevalues in standard minerals[]ol. SmX spectra of

a broad range of rock- forming minerals from terrestrial

rocks that were independently analyzed by either

Mossbauer or wet chemical techniquesIl*’121were also used

to test the consistence of the results. The grain size of

these meteorites is in the sub-millimeter range, so the

spatial resolution of SmX permits variation of F&+/ZFe

to be detected within mineral grains.

Resuks: Every mineral shows variation of Fe3+/ZFe

from meteorite to meteorite and within a single meteorite.

Fe3+/ZFe is lowest in olivine and highest in feldspathic

phases (Figure G-9 - Table)

OLIVINE

Meteorites ALH77005,LEW88516 and Chassigny

all contain significant olivine. (Our EET79001 is from a

basaltic Iithology B with no olivine). Olivine is generally

not a host for F# so Fc%/ZFe values of O are normal.

Colorless olivine in these meteorites contains Fe?+/ZFe

less 0.02. Olivine in ALH77005 and LEW88516 is both

colorless and brown as a result of shock induced

modifications121. Brown olivine has values of Fe3+/ZFeup

to 0.12 in ALH77005 and 0.26inLEW88516 in which

very deeply colored healed fractures through the grains

have the highest values. Mossbauer analysis 13 of Fe3+/

ZFe in bulk olivine from ALH77005 gave 0.045, and

probably represents the average of the microscale

variabili~ seen. In Chassigny, olivine F#/XFe varies from

0 to 0.16 but does not correlate with color variations.

The range observed is consistent with recent TEM

observations of exsolved Iamellae containing iron, oxides

in Chassigny olivine1141.

PYROXENE

I?yroxene is present in all the Martian meteorites

and is the most useful mineral for examining the variation

of Fe3+lZFe with f02. In general, pyroxene in the

Iherzolitic meteorites has lower Fe3+/ZFe than in the

basaltic meteorites (Figure G-9). Fe3+/XFe in two

pyroxene species in ALHA77005 varies (0.09-o.3) and

may correlate with variations of Ti, Al and Cr and the

pyroxene species (pigeonite or augite), but insufl-icient

Fe3+/XFeanalyses are currently available to confirm these

correlations. The pyroxenites examined, Naklda (augite)

and ALH84001 (orthopyroxene), have similar Fe3+/ZFe

values (0.09 - 0. 14) to the Iherzolitic samples. The

observed values are, however, comparable with the lower

part of the Fe3+/ZFerange measured in mantle peridotites

2-54

and pyroxenites on Earth[’l. The observed values are

typical for terrestrial orthopyroxenes (.0.1) and lower than

those of clinopyroxene equilibrated at the quartzmagnetite-fayalite buffer curve.

In Naklda, spectra of several grains and a traverse

across a single grain of augite revealed homogeneous Fe3+/

ZFe (0.09), similar to the bulk meteorite value1151,except

where the analysis included a micrometer scale oxide

inclusion has higher Fe3+/ZFe (O.16). Analyses that

overlapped grain boundaries in Nakhla showed elevated

Fe3+/ZFe (0.30): The basaltic meteorites, Shergot~ and

Zagami, and the basaltic lithology B of EET79001 have

high Fe3+/ZFe (0.2 - 0.3) consistent with their having

crystallized at or above the QFM bufferllG1.Variations of

Fe3+/ZFein both Zagami and Shergotry may reflect steric

differences between coexisting pigeonite and augite in

these meteorites, but may also suggest that pigeonite has

variable F.#+/ZFe in both meteorites. Eucritic pigeonite,

from asteroidal basalrs, is dominated by Fe*+ as expected

from the inferred oxygen fugacity at or below the ironwiistite buffer.

FELDSPAR

The Iherzolitic meteorites ALH77005 and

LEW88516 and the basaltic lithology of EET79001 have

relatively constant Fe3+/EFe (-0.31) in feldspar. The

basaltic meteorites, Shergotty and Zagami, however, are

more oxidized with Fe3+/ZFe .0.48. The increase of

oxidation ratio in pyroxene from the Iherzolitic to basaltic

meteorites is repeated in feldspar data. Compositional

differences between the maskelynite in EET79001

Iithology B and that of the basaltic meteorites suggest

that the coupled substitution Na+Si =3D Ca+Al may

have altered the abundance of sites most compatible with

Fe3+(Al) and Fe*+(Ca) in plagioclase and that the feldspar

results may reflect crystal chemical controls in addition

to oxygen fugacity effects. Insufficient spectra are

presently available to test this possibility and to document

compositional variation within individual meteorites.

OTHER MINERALS

Oxide spectra from Nakhla suggest F&/XFe values

of 0.4 -0.5 similar to the previous calculated resuks1171.

The low intensity of the pre-edges of the Fe-XANES

spectra suggest that the oxide minerals have little

tetrahedrally coordinated Fe. The oxide minerals maybe

exsolved ilmenite-hematite solid solutions. Iddingsite

spectra from Naklda appear to be dominated by this oxde

and give F#/ZFe of 0.45. A preliminary calcite spectrum

for ALH84001 suggests Fe3+/ZFe at 0.14. Discussion:

There are three independent processes that may have

controlled the Fe3+/EFe of the Martian meteorites: (1)

oxidation caused by magmatism in a relatively oxidized
magmatic system. (2) hydrothermal alteration and (3)

shock induced effects. Detailed Fe3+/ZFemeasurements

on coexisting phases and correlation of the oxidation

state results with other microanalytical and

crystallographic data will be needed to dktinguish among

these processes.

The general trend of increasing Fe3+/ZFefrom the

peridotitic samples to the basaltic samples suggests that

magmatism on Mars became more oxidized as it evolved

(again comparable to much terrestrial magmatism) and

is consistent with the presence on the modern Martian

surface of abundant ferric oxide minerals1181. Highly

fractionated silicates discovered by Pathfinder/Sojourner

at Sagan Memorial Station on Mars 1 should have high

Fe3’ in pyroxene and feldspar and we anticipate that SmX

measurements on returned samples, when available, will

confirm this prediction. It is unlikely that magmatism is

the only contributor to the range of oxidation in the

Martian suite. Shergotty and Zagami are young and may

have erupted on a (partially) dewatered planet. The mantle

from which they were extracted may well have been wet

and capable of oxidizing the magmas. Old meteorites such

asALH84001 sample Iirhologies may have formed when

Mars had extant surface water and hence had a

significantly wetter mantle. The role of water in the

formation, dehydrogenation and metasomatism of

peridotitic and pyroxenitic rocks in the terrestrial mantle

is increasingly recognized1191and is an important target

for Martian studies. The roles of both hydrothermal

activity and shock modification of Fe3+/ZFe may be

important. Both ALH77005 andLEW88516 experienced

major shock events that generated abundant defects in

the olivine.

The textures observed in olivine of these lherzolites

are consistent with post shock annealing seen in

experimental charges[zol.The brown color in this olivine

may result from light scattering from the defects, oxidation

of the defects, or both. The Martian atmosphere is oxygen

poor (pOz- 10-6) so any shock induced oxidation

probably involved orher oxygen bearing species- perhaps

atmospheric COZ. Water present in the Martian crust

when ALH77005 was shocked may provide an alternate

oxidizing agent. The time of oxidation is, however,

uncertain. The presence of significant amounts of water

in the Martian crust make hydrothermal processing of

some crustal rocks seem very likely. In ALH77005,

crystalline feldspar rims replacing the shock produced

maskelynite glass, strongly implies a period of extended

subsolidus hearing of this rock during which hydrothermal

interactions might have occurred. In LEW885 16, the

presence of deeply colored, healed fractures in olivine

requires more localized oxidation processes than in

ALH77005 and suggests that the olivine was first shocked,

and then oxidized during a hydrothermal recrystallization

event caused by the flux of an oxidizing agent through

cracks. The absence of tight temperature constraints and

of data for the coexisting magmas and fluids that

equilibrated with the Martian meteorites prevents the

Figure G-9. (Table) Synchrotrons microXANES analyses of Fe3+/ZFein minerals from Martian meteorites.

Meteorite Olivine Pyroxene Feldspar Oxide Others

Shergotty n.p. 0.28 & 0.05 0.47 * 0.10 na

Zagami n.p. 0.212 f 0.08 0.49 A 0.08 na

(0.171 * 0.04)

Nakhla na 0.09 * 0.01 clean na 0.49 lddingsite

‘0.17 -0.35’ cloudy 0.42 * 0.05

Chassigny 0.06-0.16 0.35 na na

ALH77005 O -0.05 clean 0.09-0.30 0.32 na

0.12 brown

EET79001 na 0.27 -0.3 0.32 * 0.05 na

LEW88516 O -0.03 clean na 0.30 * 0.07 na

0.11-0.26 brown

ALH84001 na 0.14 & 0.01 na na cc 0.14

n.p.=not present, na=not analyzed

,.

2-55
determination ofF#/XFe partition coe%cients from the

present results. However, the data confirm the general

trends of partitioning for ferric and ferrous in terrestrial

magmatic systems and-appear to be consistent with

oxygen figacities ranging from below the buffer curve

quartz- fayalite-magnetite to about that of the nickelnickel oxide buffer. These data provide the first

metrologically constrained sampling of Fe3+/EFefrom any

meteorite parent body. They differ from bulk

REFERENCES

[1]

[2]

[3]

[4]

[51

[6]

[71

[8]

[91

[10]

[11]

[12]

[13]

[14]

[15]

[lq

[17]

[18]

[19]

[20]

measurements of Fe3+/XFe as the dii%culties caused by

contaminants such as weathering products and

micrometer scale inclusions are easily excluded. The

results for the Martian suite are generally consistent with

the formation of these rocks in a very “terrestrial”, i.e.

oxidized, setting. The range of Fe3+lZFe seen is

comparable to that seen in many mantle and eruptive

rocks on Earth. Martian samples are much more oxidized

than lunar, basaltic achondrite and most chondritic

meteorites. ■

R. Rieder et al. “The chemical composition of martian soil and rocks returned by the mobile alpha proton xray spectrometer: preliminary results from the X-ray data”, Science 278, 1771-1774 (1997).

H. Y. McSween, Jr. et al. “Petrogenetic relationship benveen Allan Hills 77005 and other achondrites”, Earth

Pkmet. Sci. Lett. 45,275-284 (1979).

D. C. Presnall, “The join forterite-dlopside-iron oxide and its bearing on the cryrallization of basaltic and

ukramafic magmas”, Amez J. Sci. 264,753-809 (1966).

E. F. Osborn, “Role of oxygen figacity in the crystallization and differentiation of basaltic magma”, Amez J.

SCi.257,609-647 (1959).

T. C. Solberg and R. G.Burns, “Iron Mossbauer spectral study of weathered Antarctic and SNC meteorites”,

Proc.Lunar Planet Sci. ConE 19th, 313-322 (1989).

E. Stolper, “Experimental petrology of eucritic meteorites”, Geocbim. Cosmocbim. Acts 41,587-611 (1977).

M. D. Dyar, A. V. McGuire, and R. D. Ziegler, “Redox equilibria and crystal chemistry of coexisting

minerals from spinel Iherzolite mantle xenoliths”, Amez Mineralog 74,969-980 (1989).

A.V. McGuire, M. D. Dyar, and K. A. Ward, “Neglected Fe{+3+}/Fe{+2+} ratios - a study of Fe{+3+) content

of megacrysts from alkali basalts”, Geolo~ 17, 687-690 (1989).

G. A.Waychunas, M. J. Apted, and G. E. Brown, Jr., “X-ray K-edge absorption spectra of Fe minerals and

model compounds: near-edge structure”, Ply. Cbem. Minerak 10, 1-9 (1983).

S. Bajt, S.R. Sutton, andJ.S. Delaney “Microanalysis ofiron oxidation states in silicates and oxides using x-ray

absorption near edge structure (XANES)”, Geochim. Cosmochim. Acts 58,5209-5214 (1994).

J.S. Delaney S. Bajt, S.R. Sutton, and M.D.Dyar, in Mineral Spectrosco~v : A Tribute to Roger G Burns. (Eds:

Dyar,MD; McCammon,C; Schaefer,MW) 165-171 Geochemical Society Special Publication, 5. Elsevier, New

York, 1996).

J. S. Delaney M. D.Dyar, S.R. Sutton, and S. Bajt, “Redox ratios with relevant resolution: solving an old

problem by using the synchrotrons microXANES probe”, Geolo~ 26, 139-142 (1998).

R. Ostertag, G. Amthauer, H. Rager, and H. Y. Mcsween, Jr., “Fe3+in shocked olivine crystals of the ALHA

77005 meteorite”, Earth Pkznet. Sci. Lett. 67, 162-166 (1984).

A. Greshake, T. Stephan, and D.Rest, “Symplectic exsolutions in olivine from the Martian meteorite Chassigny

evidence for slow cooling under highly oxidizing conditions”, Lunar Planet. Sci. XXIX, Abstract CD-ROM#

1069 (1998).

G. T. Prior, “The meteoritic stones of El Nakhla El Baharia (Egypt)”, Mineral. Msg. XVI, 274-281 (1912).

E. Stolper, and H. Y. Mcsvveen, Jr., “Petrology and origin of the shergottite meteorites”, Geocbim. C’osmocbim.

Acts 43, 1475-1498 (1979).

T. E.Bunch and A. M. Reid, “The nakhlites - I. Petrography and mineral chemistry”, Meteoritic 10,303-315

(1975).

S. F. Hviid et al., “Magnetic properties experiments on the Mars Pathfinder lande~ preliminary results”,

Science 278, 1768-1770 (1997).

M. D.Dyar et al., in: Mineral Soectroscorw : a tribute to Roger Burns (eds. M. D. Dyar, C. McCammon and

M. W. Schaefer), pp. 289-304. (Geochemical Society Special Publications, 5, Elsevier, 1996).

J. F. Bauer, “Experimental shock metamorphism of mono and polycrystalline olivine:A comparative study”,

Proc.Lunar Planet Sci. Conf. 10th, 2573-2596 (1979).

2-56
FirstXAFSMeasurementson FerrousChloride

HydrothermalSolutionsusinga NovelDiamondAnvilCelI

R.A.Ma anovic (SouthwestMissouriState University)

A.J. Anc?erson (St.FrancisXavier University)

W.A.Bassett (CornellUniversity)

l-MingChou (U.S.Geolo ical Survey)

G.Shea-McCarthy(U.of l!!hicago)

The decrease in density, viscosi~, and dielectric

constant of water with temperature signals that

appreciable changes take place in its structure under suband supercritical conditions. Very little is known about

how such changes in the physical properties of water, in

going from ambient to supercriticd conditions, influence

the nature of short-ranged interactions between solvated

ions. Determination of the structure and speciation of

complex ions in hydrothermal solutions under controlled

thermodynamic conditions is an essential step in

developing theoretical basis of electrolytes

beyond the Debye-Hiickel theory. Systems

such as iron(II) chloride aqueous solutions

have a two-fold interest for us: 1) Current

theories of the molecular electronic

structure and metal-ligand interactions for

first-row transition metal ions are among

the most developedfll and thus offer an

opportunity for development of an

extensive knowledge base of such

electrolytes, and, 2) they have direct

relevance to studies in hydrothermal

geochemistry[z ’31.

Conventional metal autoclaves

have proven restrictive for studies on

dissolved salts in supercritical water

because of the severe corrosion problems

caused by such fluids. The hydrothermal

diamond anvil cell developed by Bassett et

tZ1.[41 offers a much more suitable

alternative because corrosion problems can

be greatly minimized while control over

pressure, temperature, and concentration

can be substantially enhanced. However,

x-ray absorption experiments have been

limited to the higher photon energies (>

15 kev) because of the attenuation of the

beam by the diamonds. We have developed

a new diamond anvil cell suitable for

making x-ray absorption studies of first row transition

metal ions in supercritical aqueous solutions. Each

diamond has been laser drilled to within 150 micrometers

of the anvil face, minimizing the loss of x-ray intensity

due to absorption and scatter by diamond. We have for

the first time measured Fe K-edge X-ray Absorption Fine

Structure wS) spectra from 2m Fe(II)Cl~NaC1/H20

solutions, at temperatures ranging from 25-500”C and

pressures estimated up to 200 MPa, using the microprobe

capabilities of beam line X26A. The capabilities of the

Th

Molybdenum~fi

HeaterWires .

J

a

CeramicCement

d

4

etmocmples

3

,18VAC

%i$Rer I ‘-7’eam

*

---T- I-7-’-’

TungstenCarbideSeats

Figure G-10. Schematic diagram of the hydrothermal diamond

anvil cell used for our XAFS experiments. Each diamond has

been laser drilled to within 150 urn of the anvil face. The seats

containing the diamond anvils are mounted on an upper and

lower platen, which are drawn together by three screws.

2-57
— .

new diamond anvil cell were demonstrated more fidly in

a prewous XAFS study made on zinc chloride aqueous

solutions, at beam line B-2 of the Cornell High Energy

Synchrotrons Source (CHESS), at temperatures ranging

from 25-6500C and pressures up to 800 MPa. The

solution samples were placed inside a volume defined by

a 0.5 mm hole, of a 0.13 mm thick rhenium gasket, and

the opposing diamond anvil culet faces pressing against

the hole. The measurements were made in transmission

mode, using conventional gas ionization chambers. The

incident x-ray beam was focused using the Kirkpatrick/

Baez mirrors to approximately 13 micrometer spot size.

Selective tilting of the cell by 0.1-0.2 degrees relative to

the x-ray beam caused the diffraction peaks resulting from

the diamonds to shift in photon energy between

individual spectra. In thk way, spectral refinement can

be accomplished by replacement of a region contaminated

by a peak in one scan by an uncontaminated region from

another scan.

Studies of this system were largely motivated by our

earlier studies on the structure of iron(II) complexes in

saline fluid inclusions in quartz found in a pegmatite dyke

intruding into granr.dites of the Saxon Grarmlite Massifi

Germany15’. Results from fitting of the Fe K-edge spectra

measured at different temperatures, where the pressure

varied according to the equilibrium liquid-vapor

coexistence, indicate that the iron(II) ion is predominantly

octahedrally hydrated from 250C to 1000C. From 2000C

to 5000C, there appears to be a stable mixture of chloro

iron(II) complexes in the fluid, with the average Iigand

coordination number being 3.5. The results from a

preliminary analysis of the XAFS spectra measured from

2m Fe(II)CIZ/l lwt?lo NaC1/HzO solutions under similar

pressure and temperature conditions are in qualitative

agreement with our results for the fluid inclusions. This

is despite the fact that the iron concentration in the fluid

inclusions is considerably lower (up to several thousand

ppm) than in the solutions. In addition, the Clconcentration of the liquid phase of each inclusion

undergoes a gradual increase with temperature due to the

progressive dissolution of its constituent halite phase

@aCl), which is typically completely dissolved at about

2600C. There is a progressive and very similar slight

change with temperature, from 2000C to 5000C, in the

near edge region of the spectra measured from either the

inclusions or the 2m Fe(H)Clz/ 11 wtYo NaC1/H20

solution. This may result from the structural symmetry

of the iron chloro complexes undergoing small changes

with temperature. Our XAFS experiments on zinc and

iron in solutions using the HDAC, including on the 2m

Fe(II)C12/1 lwt?40 NaC1/HzO system, demonstrate that

this is a very usefid tool which can be used to constrain

the thermodynamic variables and thereby help establish

a base of knowledge to more fully understand, for

a

1.0- 1.0

T=4K10C

p = 0.75 z

P - 15’3MPa .%

.~

*

~

g

s 0.5 -

2

.= 0.5 gl

1 >

G

L

m F%+ lwt”A w.a+!-$0

o

0.0 1

7CO0 7203 ? 74C0 7ew 0,0I_]

Energy (e~

o

R (A)

Figure G-II. Fe K-edge XAFS spectrum measured Figure G-12. The magnitude of the Fourier

from a 2m Fe(Il)Clz/ll wt% NaC1/HzO solution at transforms (IT) of the extended XAFS data (blue

400”C and about 150 Mpa of pressure. The large line), isolated from the spectrum shown in Figure

peaks occur as a result of diffraction of the incident G-11, and of the fit (red line) of this data, made

x-ray beam from the diamond anvils of the cell. using FEFF6.

2nF~+11wt%WCi+~0

T=4CO%

p = 0.75

P -150 MPa

— data

— fit

2 d

2-58
example, reaction kinetics in fluid-rock interactions.

When used in conjunction with similar experiments

carried out on naturally occurring fluid inclusions, the

knowledge ofspeciation and structure ofmetal complexes

REFERENCES

!

,

at elevated temperatures and pressures gained from such

experiments should prove to be very usefid for increasing

our understanding of the transport and deposition of

elements under ore-forming, hydrothermal conditions. ■

[1] C.J. Ballhausen, Molecular Electronic Structures of Transition Metal Complexes, (McGraw-Hill, New York,

1979).

[2] H.L. Barnes, in Geochemistry ofHydrorhermal Ore Deposits, H.L. Barnes, ed. (Wiley New York, 1979) 404. ~

[3] D. Crerar, S. Wood, S. Brantley and A. Bocarsly Can. M..neral 23,333 (1985).

[4] WA. Bassett, A.H. Shen, M. Bucknam, and I-M. Chou, Rev. Sci. Imti 64, 2340 (1993).

[5] R.A. Maymovk A.J. Anderson, and S. Bajt, -1 l%ys. WF.’.WZce7, C2-1029 (1997).

1

2-59
—

QUantif@ngMagmtk DomainCorrelationsinMuRilayer

Films

Y.U.ldzerda, V.Chakarian, and J.W.Freeland

(Naval Research Laboratory)

ABSTRACT

The vertical correlation of magnetic domains in a

Co/Cr/Co magnetic trilayer is statistically quantified as a

fimction of applied magnetic field. These measurements

used in conjunction with determinations of the indhridual

layer magnetometry curves identifies the presence ofboth

interlayer anti-ferromagnetic exchange coupling and

ferromagnetic dipolar coupling for different regions

within the trilayer.

The spin conductance of a magnetic heterostructure

is controlled by the relative orientation of the magnetic

moment dhections of the component layers on a locaI

scale (within a few spin mean-free-paths) II]. Any

meaningful comparison between the measured and

calculated spin-conductances for multilayer structures

requires a quantitative description of the field dependence

of the magnetic domain correlations taken vertically

between the layers. The correlation between magnetic

domains can be statistically quantified by measuring the

magnetic field dependence of the X-ray resonance

magnetic scattering (XRMS)12-51. XRMS is the angle

dependent specular reflectance of circular polarized sofi

x-rays whose energy is tuned to the absorption energy of

a magnetic element present in the mukilayer.

The specular scattered intensity of a resonant sofi

x-ray is a fimction of the incident angIe of the sofi x-ray,

9, and the magnetic configuration of the multilayer

(which is dependent on the applied magnetic field

history). For a single film with magnetic domains large

compared to the photon coherence length, the reflected

intensity, I(f3,B), is given by

I(i,B) = ~~(i) x~(B) (la)

k

where k denotes a particular magnetic domain type within

the film, 1~the scattered intensity from that domain, and

x~is the fraction of the film in the kIhdomain type. (Note

that ~A(B) = 1 at any field value.) For a film which

k

has only two possible magnetic domains (lefl and right),

eq. (la) becomes

I(i3,B) = I+(6)X ‘(B) + I ‘(8)X ‘(B) (lb)

Eq. (la) can also apply to a muhilayer film, but

now k denotes a particular configuration of the magnetic

moment orientations for each magnetic layer taken

vertically along the multilayer. 1~is the scattered intensity

from that moment configuration and x~is the fraction of

the mukilayer in that particular configuration.[d Similarly

extending eq. (1 b) to a magnetic film system consisting

of two layers, each with two possible magnetic domain

directions, the total scattered intensity becomes

I(6B) =12$ +$~ += + I~xz (2)

where x: and x%re the fractions of the film with the

magnetic domains of the top and bottom film aligned

with each other (correlated) and x= and X$ are the

fractions of the film anti-aligned to each other (anticorrelated). It k these four magnetic field dependent

fractions which will ultimately express the vertical

correlation of magnetic domains in the trilayer.

To experimentally realize only these 4 magnetic

domain configurations, a magnetic structure with a strong

uniaxial magnetic anisotropy is utilized. To accomplish

this, a single crystal Co (50A)/Cr (35A) /Co (50A) trilayer

is deposited on an epitaxially grown ZnSe(OO 1) substrate.

To stabilize the bcc Co structure, a seed layer of 5 ~ of

bcc Fe is first deposited on the ZnSe. The specular

reflected intensity is measured using a Si photodiode

2-60
I

located at an angle 20 to the incident beam direction (q

to the film plane). The 75?40 circular polarized sofi x-ray

is tuned to the Co L~ edge (778 e~, corresponding to

the maximum in the Co absorption curve.

To quanti$ the magnetic domain configuration

fractions x~(B), the applied field dependence of the

scattered intensity is measured. But, as indkated in Eq.

(la), the contributions to the total scattered intensity

depend separately on the applied magnetic field and on

the incidence angle. This latter angular dependence is

demonstrated in the top panel of Figure M-1, where the

log of the specular scattered intensities for negative helicity

light and the resulting asymmetry (P - 1-) /(P + 1-) are

shown for the sample filly magnetized by an applied field

of+ 120 Oe (P) and -120 Oe (l-). Displayed with these

angle dependent reflectance curves are a subset of the field

dependent reflected intensity curves recorded at the

reported incidence angles (shown in the 8 curves at the

bottom of Figure M-l). Due to the changing

contribution of the scattering intensities 1#3) these curves

are markedly different.

The obvious variation in these curves belies a hidden

similari~. In eq. (2), the dependence on the applied

magnetic field is contained only in the four configuration

fractions, %(B), whereas the angular dependence is derived

solely~m the four prefactor terms F@), l= (@, ~ (@,

and l’+(g) which each remain constant for a fixed incident

angle. Therefore, the large variations observed in the field

scans taken at different incident angles, results only from

a variation of these four multiplicative constants.

Actually only two of these prefi-ictors are unknown.

In the top panel of Figure M-1, we show the

Figure M-1.

(Top Panel)

Scattered intensity

for circular

polarized soft xrays near the Co

L~edge (778 eV)

for trilayer fully

magnetized in

either direction.

Also shown is the

normalized

asymmetry.

(Bottom Panel)

Eight magnetic

field dependent

specular intensity

spectra acquired

at the indicated

incidence angle

for circular

polarized soft xrays near the Co

L~edge (778 eV).

10-3

L I

, 1 I I 1 I

0.4

\

\

\

\

5 10 15 20 25 30

kadent Angle (deg.)

_ 7.8° -8.0°

-1oo 0 100-100 0 100-100 0 100-100 0 100

Applied Magnetic Field (Oe)

2-61
,.. .

,.

experimentally determined values for the angle

dependence of the scattered intensity when the film is

completely magnetized to saturation in the positive

[x= =1 and I@)= 12@)] or negative [x:=1 and 1-(6)

=~~ (o)] field direction. utilizingthe many field

dependent scans, an iterative, least-squares best-fit

pr~cedure can be applied to determine the-two remaining

unknown intensi~ factors, which are different constants

for each angle, and the four co~figuration fractions,

X2(B) X=(B), ~<B), and X+(B), which must be the

same for ALL scans. In this way, the fraction of the film

with a particular magnetic domain configuration can be

uniquely determined.

The validi~ of this procedure can be checked by

comparing measured magnetometry loops with calculated

magnetometry loops derived from the four extracted

domain configuration fractions by noting that the

moment of the bottom layer, M~omo~, is given by

MBO170M = M, (x: –x:) (3)

wherexr ( x:) is the fraction of the bottom magnetic

layer with moment along (opposed to) the applied field

direction. This can be rewritten in terms of t~ fou~

configuration+ fractions by noting that X7 =X+ + x+

+

and X, c X7 + X- (and similarly for the top magnetic

layer).

In the top panel of Figure M-2 is shown both the

normalized total moment hysteresis curve (measured by

vibrating sample magnetometry) as well as the normalized

hysteresis curve of just the bottom layer. We have directly

measured the hysteretic behavior of the bottom film by

measuring the element specific hysteresis curve in

absorption of the strongly coupled Fe seed layer used as a

template to establish the bcc growth of Co. Superimposed

over these curves are the calculated hysteresis loops as

determined from the four extracted configur~tion

fractions and eq. (3). The agreement is nearly exact, giving

confidence in the extraction of the film fractions.

For spin-conductance applications, it is the relative .-

orientation of the magnetic moments within a domain

which gives rise to the resistance variation (aligned for

low resistance, anti-ahgned for high resistance). Therefore,

the correlation function representing the fraction of the

film which is aligned, , minus the Fraction of the film

anti-ahgned, , is amore useful quanti~ to examine. This

quanti~ is plotted in the middle panel of Figure M-2.

From Figure M-2, it is clear that the Co/Cr/Co

film never reac~es a fully anti-aligned configuration. The

field value where the correlation is m-ost negative

corresponds to the peak in the magneto-resistance since

it is at this point that the two magnetic layers are most

anti-aligned and the trilayer has the highest resistance.

This correlation fimction can be used in conjunction with

measured transport curves to extract the coefficient of

magnetoresistance171 or for a detailed comparison with

theory. It can also be used to identifi and quantify the

interlayer coupling mechanisms present in this mukilayer.

In the abse~ce of any type of interactions between

the magnetic layers, the purely random distribution of

magnetic domains will still result in a statistical probability

that two vertically offset regions of different magnetic

layers within the rnultilayer ~re aligned with each other.

For two non-interacting independent films, the predicted

fraction of the film in a particular configuration, ~I(B),

can be calculated as simply the product of the individual

domain fractions of each laye~ (i.e., keeping with the

previous notation ~~= X1+ x Xz+, and similarly for

each of the other configurations). Since, as shown in

Fignre M-2, the individual layer fractions can be extracted

fr~m either the magnetometry data or the measured twolayer configuration fractions themselves, a correlation

function for two non-interacting films can be separately

constructed for comparison with the derived correlation

flmction of Figure M-2. By comparing the calculated

non-interacting films correlation function to the extracted

correlation function, we can imply the presence of

coupling between the magnetic layers and even ascertain

the sign of the coupling. -

This comparison is performed in the bottom panel

of Figure M-2 where is shown the bottom film hysteresis

curv;, the extracted correlation function, and the

difference between the extracted correlation function and

the calculated correlation ii.mction for non-interacting

films, each for only the increasing field leg of the hysteresis

loop. This difference is just the remainder of the

correlation function caused by coupling between the

films[s]. As the field is increased, the extracted correlation

function is reduced while the bottom film hysteresis loop

shows that the bottom film is still near saturation. Since

the coupling-derived remainder of the correlation

function remains zero, as it must if either film is at

saturation, the initial reduction in the extracted correlation

fimction would occur regardless of the presence or absence

of any interaction between the films. As the field is

increased fiuther, the coupling-derived remainder of the

correlation fimction remains near zero until a significant

number of magnetic domains have begun to for-m in the

bottom film. At this point the coupling-derived

remainder of the correlation fi.mction becomes non-zero

and positive, indicating that a significant fraction of the

film-is interacting and that the-magnetic domains are

preferentially aligned to those domains directly opposite

them in the adjacent layer, probably from dipolar

coupling. At higher applied fields, this predominant

ferromagnetic interaction is replaced by an anti2-62
I

ferromagnetic coupling indicating that the majority of

the sample is now dominated by an anti-ferromagnetic

interlayer coupling mechanism.

Of the various formulations for describing the

magnetic domains with this trilayer system, it is the final

coupling-derived remainder of the correlation fimction

associated with interacting films which probes the

fundamentally significant behavior of the magnetic films

by identi~lng and quanti~ing the type and strength of

the intedayer coupling mechanisms. ■

This work supported by the ojlce of iVaval Research.

EC. permanent adh!ressEtec Systems,Inc. Hayward C21.

JWF wm an IWL/iVRCpostdoctora[ fil[ow; permanent

addressArgonne iVationa! Laboratory Argonne, IL.

REFERENCES

[1] I? Bruno and C. Chappert, Phys. Rev. Lett. 67,

1602 (1991).

[2] K. Namikawa, et al, J. Phys. Sot. Jap. 54,4099

(1985).

[3] C.-C. Kao, et al, Phys. Rev. B (RC) 50, 9599

(1994).

[4] J. M. Tonnerre, et al, , Phys. Rev. Lett. 75,740

(1995]=) 75,740 (1995).

[51 ~ Chkian, eta~, J. Magn. Magn. Mater. 165,

52 (1997).

[6] Here we have ignored intra-domain scattering-or

scattering from domain walls.

[7] Y U. I~rda, eta-l, J. Appl. Phys. 76,6525 (1994).

[8] Domain correlations may occur for non-interacting

films if growth non-uniformities propogate vertically

through a structure, acting as magnetic domain

nucleation sites.

I I I 1

1.0 - ~ Total

A

-------- -----

c 0.5-

.$

~ 0.0-

E

-1,0 :

------Decreasing ~ — Increasing

I I I I I

I I I I

1.0 -

--”--%._...--

............

--------

~ ....

“~ 05 -

------Extracted ‘....

5 ;

Correlation ‘.... ;

k

...

G 0.0

“g ● coupling

i 0.0 ~

-----

Remainder ...

G 4.5 -

z

E

- -0.5 0

— BottomLayer 3

8 Hysteresis

-1,0l——

~

. -1.0

~

100

Magnetic Field (se)

Figure M-2.

(Top Panel) Normalized

magnetometry loops for

the total moment and only

the bottom film (the Fe

hysteresis loop).

Superimposed is the

calculated hysteresis loops

from the least-squares

best-fit extraction of the

configuration fractions (see

text).

(Middle Panel) The

extracted correlation

function (as defined in the

text) for increasing (solid)

and decreasing (dashed)

field.

(Bottom Panel) The

bottom layer hysteresis

behavior (solid line), the

extracted correlation

function (dashed line), and

the coupling-derived

remainder of the

correlation function (dots)

of the Co/Cr/Co trilayer as

a function of increasing

field.

2-63
. — —— ————— . --—.

OrientationalCorrelationsinLiquid

RevealedByPolarization-Analyzed

Scattering

CrystallinePhases

ResonantX-Ray

R.Pindak (BellLaboratories, LucentTechnologies)

P.Mach (Universityof Minnesota)

A.-M.Levelut(Univ.Paris-Sud,France)

P.Barois(Centrede Recherche Paul Pascal, U.Bordeaux, France)

C.C.Huan (Universityof Minnesota),

L.-Furenlid7NSLS;current address U.of Arizona))

The existence of a helical symmetry axis is

widespread in systems exhibiting liquid crystalline

order, especially in systems comprised of chiral

molecules. Because these systems usually lack

three-dimensional positional order, the helical

symmetry axis cannot be observed using

conventional x-ray scattering. It is well known

that in crystalline systems, resonant x-ray

scattering can be used to observe such “hidden”

SymmetriesI’]. In our recent research at NSLS,

we demonstrated that polarization-analyzed

resonant scattering could also be applied to

observe the “hidden” helical symmetry axis in

liquid crystals[zl. Since the nature of the helical

ordering impacts the electro-optic response of the

liquid crystal phase, it is a crucial structural feature

to establish.

The liquid crystal systems which we studied

are the chkal smectic-C (SmC*) phases. In these

phases, the molecules form a stack of fluid-like

layers. Wkhin each layer, the molecules, on

average, tilt in the same dkection. Moreover, the

local symmetry environment is consistent with a

hindered rotation of the molecules about their

long axes resulting in a spontaneous local

polarization parallel to the layer plane and

perpendicular to the tilt plane (Figure M-3). The

different SmC* phases are distinguished by

different interlayer sequence-s of changes in the

molecular tilt direction. This interlayer

orientational order of the molecular tilt varies

from the molecules in each layer being tilted in

the same direction to the molecules in alternate

layers being tilted in opposite directions. Since

this intedayer orientational order also applies to

the local spontaneous polarization direction, the

electro-optic response of the phases varies,

#

lfl

Figure M-3. (Top) Chemical structure of the sulfurcontaining thiobenzoate liquid crystal compound studied.

(Bottom) Schematic diagram illustrating the structure of

the SmC~lz*Phase.The red arrows indicate the direction of

the molecular tilt while the blue arrows indicate the

direction of the local spontaneous polarization.

2-64
Figure M-4. Diffraction peaks observed in the range

1.2< Q/~< 2.2 plotted as a function of the energy

above the resonance energy EO.The half and quarter

order resonant peaks vanish off-resonance.

phase of the scattered x-rays depend on the orientation

of the local environment of the scattering sulfur atom,

and therefore, helical modulation of the orientational

order can result in diffraction peaks forbidden in

convention diffraction. Moreover, the polarization state

of the diffracted x-rays can differ from that of the incident

x-rays. Dmitrienko calculated the tensorial atomic

scattering factor for a crystal with a 41 helical symmetry

axis[d. We extended Dmitrienko’s analysis to the 4-layer

helical structure of the SmCEIz* phase and found that his

results also apply; namely, for as-polarized incident x-ray

beam, a structure with a 4, helical symmetry axis should

produce s-polarized half-order peaks and p-polarized

quarter-order peaks.

The existence of quarter and half order resonant

peaks for the SmC~u* phase with the 4-layer helical pitch

is shown in Figure M4. Taking the scattering wavevector

normal to the layers to be Qz and the wavevector

associated with the layering to be q=2n/d, the scattered

intensity is plotted as a fhnction of both C&/~ and as a

function of the energy departure of the incident x-rays

from the resonant energy, Eo. It is evident that when (EEo) >20 e~ only the integer order ~/~ = 2.0 peak

remains withh the range of wavevectors probed.

To measure the polarization state of the scattered

x-rays, we used a pyrolytic graphke (PG) analyzing crystal.

At the suli%r resonant energy, the 2(3 Bragg angle for PG

is close to 90° so rotating the analyzing crystal about the

2-65
axis of the x-ray beam through the angle, ~, , will

diffract most of the beam if the beam is polarized

perpendicular to the PG diffraction plane, but will

cMF.ractnearly zero beam if polarized parallel to this

plane. The top plot in Figure M-5 illustrates this for

the incident bti. The incident beam was a-polarized

and was polarized perpendicular to the PG diffraction

plane when X== + 90° giving maxima in the diffracted

intensity. We applied a similar polarization analysis to

the resonant peaks in the SmC~12* phase (lower three

plots in Figure M-5) by rotating the analyzer crystal

about the diffracted beam. For the half order peak,

the diffracted beam was a-polarized, same as the

incident beam, giving x, maxima at k 90°. On the

other hand, for the two quarter order peaks, the

diffracted beam was n-polarimd so the maximum in

X, occurs at 0° as predicted by the tensor analysis for

the 41 helical symmetry.

In summary, we showed that polarizationanalyzed resonant x-ray scattering provides a valuable

and unique probe of the orientational correlations that

occur in liquid crystalline systems. These orientation

correlations can be studied from Angstrom to micron

length scales. The observed polarizations agree with a

clock-model of the SmC* phases, and unambiguously

rule out other proposals made to date for these

structures. ■

REFERENCES

[1]

[2]

[3]

[4]

[51

[6]

2-66

D. H. Templeton and L. K Templeton, Acts

Cryst. A42, 478 (1986); L. K Templeton and

D. H. Templeton,Acta Cgut. A44, 1045 (1988).

I? Mach, R. Pindak, A.-M. Levelut, 1? Barois,

H. T. Nguyen, C. C. Huaug, and L. Furer&d,

l%ys. Rev. -Lett. 81, 1015 (1998).

H. T. Nguyen, J. C. Rouillon, 1? Cluzeau, G.

Sigaud, C. Destrade, and N. Isaert, Lig. Cryst

17,571 (1994).

M. Cepic and B. Zeks, Mol. Cryst. Liq. Cyst.

263,61 (1995); V. L. Lorman, Mol Cry~t.Liq.

Cryst. 262, 437 (1995); A. Roy and N.

Madhusudana, Europbys. Lett. 36,221 (1996).

A. Fukuda, Y. Ttishi, T. Isozaki, K Ishikawa,

and H. Takezoe,J Matez Cbem. 4,997 (1994)

and references cited in this review.

V E. Dmitrienko, Acts C@t. A39, 29 (1983).

1

0

Incident X-Ray Beam

1 I

. ——— .

8

!3

ti

(D

(n

N

o

0

[’ smcFp* Qz/Qo = 1.50

.*m: 0- polarized I

%CF12* Qz/QO = 1.75

ti4 -

a)

;3 -

\

Cn

22 -

z

;1 -

Y

o

-90 -45 0 45 90

Xa (deg.)

Figure M-5. Upper Plot Intensity diffracted

by the PG polarization anaiyzer as it was

rotated through an angie, x,, around the

incidentx-raybeam. Thisscan wastaken at

an energy where the PG 213Braggangie =

90°. Lower ThreePlots These plots, taken at

the suifur K-edge energy, show the intensity

diffracted by the PG polarization anaiyzer as

it was rotated about the resonant diffracted

x-ray beam for the quarter and haif order

peaks in Figure M-4.
SurfaceandBulkElectronicStructureinWideBandGap

NitrideSemiconductors

K.E.Smith

(Department of Physics, Boston University)

INTRODUCTION

Wide band gap nitride semiconductors are the focus

of intense scientific scrutiny due to their numerous

potential applications in optoelectronic and high

temperature devices.lll However, our understanding of

the basic physics of these materials lags f-u behind our

ability to make simple electronic devices from them. If

wide band gap nitride semiconductors are to achieve their

full technological potential then we must have as deep an

understanding of their jimahmental properties as exists

for Si and III-V electronic materials. We have begun a

program aimed at understanding both the basic electronic

structure of a variety of wide band gap nitride

semiconductors, and also the electronic structure of metal

and non-metal ovedayers on these nitrides. We use a

unique combination of photon and electron

spectroscopes in this effort, and our experiments are

primarily performed on NSLS bearnlines U4A and XIB.

EXPERIMENTAL TECHNIQUES

Four complimentary spectroscopic probes of

electronic structure in solids are utilized in this program

angle resolved photoemission spectroscopy (ARP) and sofi

x-ray emission spectroscopy (SXE) being the primary

tools, and soft x-ray absorption spectroscopy (SXA) and

inverse photoemission spectroscopy (IPS) being secondary

tools. ARP is a well established technique that allows us

to measure the band dispersion of both bulk and surface

states in solids. However, the short mean free path of

electrons in solids leads to a very high surface sensitivi~

for N, which requires that the surface of the sample

under consideration be atomically clean and well ordered.

In contrast, as a photon in/photon out spectroscopy SXE

is a bulk probe. SXE measures the element- and sitespecific density of states resolved into its orbital angular

momentum components. A renaissance in SXE is

presently underway due to two factors: i) the combined

use of grazing incidence diffraction gratings to disperse

the x-ray emission and a wide area x-ray detector to

measure the emission, that can be moved under vacuum

to remain at the focal point of the gratings for all energies,

and ii) the use of high intensity monochromatic

synchrotrons radiation as the excitation source.1241 The

former allows energy resolution comparable to that of

conventional photoemission to be obtained, while the

latter allows the selective excitation of individual core levels

in multi-element systems. An added feature of our SXE

spectrometer is the abili~ to be used as a high energy

inverse photoemission spectrometer, since the physical

process leading to inverse photoemission is similar to that

leading to electron-excited SXE.15’ q. In a collaboration

with Dr. Peter Johnson from BNL Physics, we also have

used his dedicated IPS instrument in this program.

Finally we also have used SXA spectroscopy which gives

complimentary information concerning the empty

densiV of state.s.[~

RESULTS

Among the highlights of our nitride research program

thus far are:

●

●

●

●

●

●

The firstfillmeasurement of the bulk valence band

dispersion of wurtzite GaN;

The definitive observation and characterization of

surface states on GaN(OOOl);

The commissioning of a new high resolution x-ray

emission spectrometer on XIB, and its use to measure

the eienrentaliy resolved valence band electronic

structure in GaN, AIN, AIXGal-XN, and GaNxAsl-X

The direct measurement of shallow core level

hybridization in semiconductors;

The measurement of ek?mental~ resolved band gap

evolution in AIXGal-XN

A measurement of the dispersion of conduction band

states using inverse photoemission spectroscopy.

i) Bulk Band Dr3prsion in GaiV The fi.dl bulk

band dispersion of the occupied valence states in n-type

wurtzite GaN was measured for the first time.[s”1 Figure

1 shows a series of photoemission spectra where states

along the GM direction in the bulk Brillouin zone are

being probed. The rich set of spectra in Figure M-6 are

representative of those measured in other directions, and

indicative of the high quality of the surfaces being studied.

SinceAIU? is a surface sensitive technique, the bulk band

2-67
—

N

o

9

I.!.l. !.!.l. !.l.l.l.l. l.w

12 10 S (j 4 ~ o

BindingEner=g (eV) relative to VBM

Figure M-6.

(3,hv(eV)

lsO, 55

16”,54

14”,53

12”,52

100,51.5

so, 51

6°,50.5

4°,50

0°,50

L I I 1 I I I I I I I I I I I I 4

r K hI r A

Figure M-7.

structure cannot be measured wzkmthe surface is

atomically clean andwell-ordered.ll”’ ]]l Achieving

a reproducible method of cleaning the film

surfaces was a prerequisite to all our ARP

experiments. The method we used was repeated

cycles of N2 sputtering followed by annealing in

UHV Bermudez recently published an exhaustive

comparison of the various methods of cleaning

GaN surfaces, and found this to be one of the

best approaches.[”1 The spectra in Figure M-6

and those obtained for the other high symmetry

directions of the zone can be used to generate the

measured bulk band structure. This is shown in

Figure M-7, with the data points corresponding

to the experimentally measured structure.[gl Also

shown in Figure M-7 as solid lines are the results

of an LDA calculation by Rubio et al[]3] Aside

from the non-dispersive state at the top of the

valence band, the agreement between this

calculation and the measurement is good, in terms

of both variation in band width and band

velocities. The non-dispersive state near the

valence band maximum that we have observed

can be conclusively identified as a surface state,

as is discussed below.

ii) Bulk DensiV of States izz GaN, AIN

and ReLztedAlbys: The last NO years saw the

commissioning of our new high resolution x-ray

emission spectrometer on XIB. Our first

experiments involved studying the bulk electronic

structure of GaN thin flms.[8’141 Figure M-8a

shows both the SXE spectrum for the radiative

decay of the valence band into a N Is hole (N K

emission), and the SXA spectrum for excitation

of N IS electrons into the empty conduction band

(N K absorption). In the SXE spectrum, the N

Iscore state is excited by 430 eV photons. Details

of how the emission and absorption spectra are

placed on a common binding energy scale relative

to the VBM can be found elsewhere.1141The N K

emission spectrum reflects the valence band N

2p PDOS. Figure M-8b shows both the SXE

spectrum for the radiative decay of the states near

and in the valence band into a Ga 2p~,zhole (Ga

Lzemission), and the SXA spectrum for excitation

of Ga 2p~,zelectrons into the empty conduction

band (Ga L absorption). Here, emission from N

2p states is dipole forbidden, and the spectrum

reflects the Ga 4s PDOS of the valence band, and

the Ga 3d shallow core state. Also shown in

Figure M-8 are the results of an LDA calculation

of the PDOS for wurtzite GaN.1151 Here we have

2-68
(a)

J

, t I I ! d

Energy Relative to VRM (eV)

(b)

I 8 1 1 1 t

Ga L~emission ~ GaL-absorption

,.

,.

; #-

-::,

.:.. :,-

-..“ /’

%’

.,. :: “’lb/

., :. :,, .

:: # .

;-., :;

...-” ;,“..,

i

...........~..> ‘ .... .....

\;s;

t

:

I

:; unoccupied

,, \ ,1 GaPDOS occupied; \ \

Ga PDOS ;

.i!‘~ ‘%..JO.8eV/l ev)

, ,.-., ; t

1.8eVll.~/?V) ’11 ; ,. ~

,.,

;:

,. ,! i,

~“ :=.: ;%/ ‘-. . ................................... ....................................

Figure M-8.

Energy Relative to VRM (eV)

convoluted the theoretical DOS by Lorentzians to significantly different. (Fortunately the bulk states

simulate the core-hole lifetime broadening and by

Gaussians to simulate the instrumental broadening. The

agreement between the calculated and measured PDOS

for the valence and conduction bands is very good. The

ability to study nitride alloy systems without worrying

about cleaning their surfaces (and maintaining

stoichiometry) is a particularly notable feature of SXE.

Our results from theAIXGal-XN alloy system are presented

in Figure M-9.tlG’1~ Here we have been able to measure

the e[ernental~ reso[vedpDOS for the entire alloy system,

thus allowing us to determine the evolution of the band

gap as fimction of elemental concentration. Figure M-9

shows the dominant N 2P contribution to the valence

band, i.e. these spectra result from the transition of N 2P

valence electrons into N Is holes. These spectra

reveal that there is no bulk band gap bowing in this

alloy system.

iii) Su@ace Ehctronic Structure of GaIV:

As noted earlier, there is a state visible at the top of

the valence band in the experimental band structure

of Figure M-7 Aat does not correspond to any bulk

state. Using the linearly polarized nature of

synchrotrons radiation, we have definitively

identified this state as a surface state with Spz

character. The state is destroyed by adsorption of

activated H2, and by exposure of the surface to 02

or by ion bombardment. These measurements are

performed on n-type GaN films grown by MBE.

Recently we have found that despite identical

surface cleaning of the films, the electronic structure

of GaN surfaces grown by MOCVD on SiC are

measured by ARP are the same between the MOCVD

and MBE samples.) Figure M-10 shows the

experimentally measured surface band structure for

MOCVD-grown GaN surfaces cleaned in exact~rhe same

manner we cleaned the MBE films. For clarity, only the

surface related states are plotted in Figure M-10, but the

contrast with our results for MBE films presented in

Figure M-7 is dramatic. Instead of a spatially localized

state (and hence non-dkpersive in k-space) at the valence

band maximum, we find two highly dispersive states, one

of which disperses throughout almost the entire valence

band. The most obvious explanation for the different

results from MBE and MOCVD films whose surfaces

were cleaned in the identical manner is that the suface.s

m

s.-

-0

.-2

4

6

8

I

I ‘A I

10! ..,....,....,....1.. , . . . . . . . . . . ..’1 I

2.0 1.5 1.0 0.5 0

b (D.,)

0.5 1.0

Figure M-9.

1.5 2.0

EF

VBM

,

,

,>
BndiugEuergy (eV) rddire to AIN Y6M

Figure M-10.

have different terminations or polaitim.Ig>12’18-211Both

types of surface were atomically clean (as measured using

Auger electron spectroscopy) and displayed sharp (1x 1)

low energy electron diffraction (LEED) patterns

indicating identical surface symmetries. However, it is

likely that the termination of the surfaces is different.

iv) Conduction Band Dispersion i% GaN:

While soft x-ray absorption can measure the PDOS of

the conduction band, inverse photoemission spectroscopy

is required to measure the dfi-ersion of the empty states.

We began a collaboration with Peter Johnson from BNL

Physics to use his high resolution inverse photoemission

spectrometer.[nl Our first experiments were on MBEgrown n-type GaN. We found that there are no

unoccupied surface states. [n] Furthermore, we found that

the conduction band states differ significantly from free

electron states up to 20 eV above E~. Since the free

electron final state assumption is used to generate the

measured band structure (Figure M-1 O) from the ARP

spectra, this is an important observation. However, higher

photon energies were used in the band mapping, so we

are satisfied the free electron final state approximation is

appropriate in this case.

We have embarked on a multi-technique study of

the electronic structure of wide band gap nitride

semiconductors that employs heavily the facilities of the

NSLS. This research has lead to significant progress in

understanding both the surface and bulk electronic

structure in simple nitrides, and in more complex alloys.

Future research will be directed towards the electronic

structure of overlayers and interfaces in such systems.

Thiswork wasperformedby theElectronic Structure Group,

Department ofPhysics, Boston University: Yu-Cbang Chao,

Laurent D&, Sarnjeet Dhesi, Cristian Stagarescu,James

Dowries, and Philip Ryan. The inverse photoemission

qeriments were perj$ormedin colkzboration with Tonics

VaL%and Peter Johnsonfrom the Dpartment of Physics,

Brookhaven iVational Laboratory. Some of the SXE

eqeriments are perjormed in collaboration with Jinghua

Guo andJosephNordgrmfiom UppsakzUniversity. Samples

areproviakd /y TheotLmeMoustakmfrom Boston Universiy,

Robert Davis from North Carolina State University,

Thorvald Anderson j$om Chalmers Universi~, and Jim

Edgarsfiom IGm.sasState University.

Ourresearcb issuppotied~ theNSFund2rDMR-9501174

and our SE spectrometer kfinded ~ the USARO under

DAAH04-95-0014.

.

2-70
REFERENCES

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

[10]

[11]

[12]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

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J. Nordgren, G. Bray S. Cramm, R. Nyhohn, J.-E. Rubensson, and N. Wassdahl, Rev Sci. Inst. 60, 1690

(1989).

J. Nordgren and R. Nyhohn, Nucl. Inst. Methods A 246,242 (1986).

N.V Smith and D.P. Woodruff, Prog. Surf Sci. 21,295 (1986).

F.J. Himpsel, 1 Phys. Chem. Solids 49,3 (1988).

J. Stohr, NEXAFS Spectroscopy (Springer, Berlin, 1992).

K.E. Smith, S.S. Dhesi, L.-C. Duda, C.B. Stagarescu, J.H. Guo, J.Nordgren, R. Singh, andT.D. Moustakas,

Mat. Res. Sot. Proc. 449,787 (1997).

S.S. Dhesi, C.B. Stagarescu, K.E. Smith, D. Doppalapudi, R. Singh, andT.D. Moustakas, Phys. Rev. B 56,

10271 (1997).

Angle Resolved Photoemission, edited by S.D. Kevan (Elsevier, Amsterdam, 1991).

K.E. Smith and S.D. Kevan, Prog. Solid State Chem. 21,49 (1991).

VM. Berrnudez, D.D. Koleske, and A.E. Wickenden, Appl. Surf Sci. 126,69 (1998).

A. Rubio, J.L. Corkill, M.L. Cohen, E.L. Shirley, and S.G. Louie, Physical Review B (Condensed Matter)

48, 11810 (1993).

C.B. Stagarescu, L.-C. Duda, K.E. Smith, J.H. Guo, J. Nordgren, R. Singh, and T.D. Moustakas, Phys.

Rev. B 54, 17335 (1996).

Y-N. Xu and W.Y. Ching, Phys. Rev. B 48,4335 (1993).

L.-C. Duda, C.B. Stagarescu, J. Dowries, K.E. Smith, D. Korakakis, T.D. Moustakas, J. Guo, and J..

Nordgren, Phys. Rev. B 58,1928 (1998).

K.E. Smith, et al., 1 We. Sci. Technol. B 16,2250 (1998).

A.R. Smith, R.M. Feenstra, D.W. Greve, M.S. Shin, M. Skowronski, J. Neugebauer, and J.E. Northrup,

Appl.Phys.Lett.72,2114 (1998).

M.M. Sung, J. Ahn, V Bykoy J.W. Rabalais, D.D. Koleske, andA.E. Wickenden, Phys. Rev. B 54,14652

(1996).

A.R, Smith, R.M. Feenstra, D.W. Greve, J. Neugebauer, and J.E. Northrup, Phys. Rev. Lett. 79, 3934

(1997).

K. Rapcewicz, M. Buongiorno Nardelli, and J. Bernholc, Physical Review B (Condensed Matter) 56,

R12725 (1997).

RD. Johnson, S.L. Hulbert, R.F. Garrett, and M.R. Howells, Review of Scientific Instruments 57, 1324

(1986).

T. Valla, RD. Johnson, S.S. Dhesi, K.E. Smith, T. Moustakas, and E.L. Shirley, Phys. Rev. B (in press)

(1998).

2-71
X-ray DiffractionStudieson LevitatedLiquids

S.Krishnan

(Containerless Research, Inc.)

S. Anselland David L.Price

(Argonne National Laboratory)

Liquid structure measurements are important in

advancing condensed matter theory, in developing

predictive models, and in establishing structure-propertyprocess relationships in high temperature materials

sciences. For example, the differences between the

structures of the liquid and crystalline phases of the same

composition can influence the nucleation kinetics and

solidification paths.

The maj_orexperimental difflcukies encountered in

obtaining structural data on liquids at temperatures above

about 10OOK are, (i) reactions of the specimens with

container walls, and (ii) influence of the containers on

the structural measurements. Recently a number of

research groupsf]~l have attempted to overcome these

problems by employing levitation techniques in

conjunction with X-ray scattering to study the structural

properties of liquids. These groups have employed tonical

nozzle levitation (CNL) 11*21and electromagnetic levitation

techniques13’41to suspend 3-6 mm dk.rneter droplets in

X-ray synchrotrons sources and have conducted X-ray

scattering and EXAFS measurements to obtain structural

data on liquids. Several key advantages of these methods

include the elimination of container interactions and

container-derived impurities, rapid access to high

temperatures, localized heating conditions, and lastly

access to the supercooled (metastable) liquid. We have

used the CNL method extensively to investigate the

structure of a number of liquids15-101in their normal and

supercooled states in a series of experiments conducted

at the NSLS. These prior studk.s include a description of

the techniquesI1l, and structure measurements on liquid

Si [j], Al,03 [a, boron171, YzO~ 181,CogoPd20[g],Ni ‘md

‘zr[lol.

This article highlights a few recent results obtained

on levitated liquids that were obtained with the use of

conical nozzle levitation (CNL). These experiments were

conducted at the X25 beamline at the National

Synchrotrons Light Source (NSLS) at the Brookhaven

National Laboratory. The CNL apparatus consisted of a

gas flow system which delivered the levitation gas (inert

gases like argon) into a plenum chamber from which the

gas flowed out through a divergent nozzle. Small (2-4

2-72

mm diameter) spheres of the specimen materials could

be levitated stably in the nozzle. The specimens were

then be laser-heated, melted and levitated for long

durations of up to several hours. The complete CNL

system was integrated with a with a Huber model 6-circle,

X-ray diffractometer.

The CNL system was enclosed in an

environmentally-controlled chamber with suitable ports

for laser heating, pyrometry, sample injection and retrieval,

and pressure measurements. The upper part of the

chamber was a 9 inch diameter sphere. Two beryllium

windows were included in this section; the first was a

small window for the incident X-ray beam which was

placed at the end of a radial tube port. The second window

was curved and subtended approximately 120° around

the nominal specimen position at the center of the

chamber. This window extended about 5° below the

normal levitation height of the specimen to enable

transmission of the dkect X-ray beam. The specimens

were heated with the aid of a 270 watt COZ laser.

Temperature measurements were obtained with two

pyrometers whose operating wavelengths were 0.65 pm

and 1-2.5 ~m, respectively. Precise sample positioning

was achieved with a 3-axis motorized translator assembly

and a phosphor screen to observe the shadow of the

specimen in the X-ray beam. Specimen materials could

be levitated, heated, melted and positioned stably over

durations of up to 3 hours, which were suficient for the

X-ray diffraction studies.

Scattered X-rays were detected using a solid-state

detector with 300 eV resolution over a 20 angular range

of 10-1100. Diffraction data on liquids were obtained

over a momentum transfer (Q = 4~sin ((3)/1) range of

1.2-13 ~-*” The measured intensity, I (2(3 ,E), for an

incident X-ray energy E is given by

I (20, E) = I $E) [A,$ (2EI, E)oP(2e)oIa~(Q) + l~~”’h]

+IP(E) [A,,, (2e, E’)o I inC(Q’)+ I ~s ‘“’(Q) ] (1)

.

—. = —_————.——— .
where:

lP(E)=intensi~ of the main beam at the energy E,

IX(Q) = the coherent or incoherent

scattering intensity

A,,,(2fJE) = attenuation coeilicient,

I*~s(Q) = the coherent or incoherent

multiple scattering,

P(2e,E) = polarization factor

E’= E + A = E/(1 - 0.00392Esin2(0)), and

Q = 1.014E sin(e), where Qis

measured in ~-1 and E in keV.

This equation was used as the basis of the correction

procedure which employed a Monte Carlo simulation of

the experimental geometry that was then back refined

against the measured data. The corrections were

implemented through a two-stage refinement procedure:

the first stage refined instrumental parameters, including

photon density profile and detector efficiency derived

from a statistical average of all the data sets obtained in

the experimental run cycle, and specimen parameters

including sample position in the beam, sample radius,

and density. In the second stage, individual runs were

analyzed using fwed instrumental and variable sample

parameters. Form factors were obtained from Bare, et

al,I*ll; the temperature dependence of the form factors

The data analysis procedure directly yields the xray weighted average structure factor S(Q). From the

S(Q), the radial distribution fimction, G(r), is given by

9-

G(r) -1= 1

2X Zp=

J Q( S(Q -1) sin ~dQ (2)

o

where p. is the number of atoms per unit volume. This

inverse Fourier transform method employs the maximum

entropy criterion 1131where G(r) is constrained to one at

large r. Vidues of the number density, p=, was either

estimated or obtained from literature data.

In this article, we will present structural results

(obtained at the X25 bearnline) on liquid silicon[jl and

boron{71 in the normal and supercooled liquid states.

Figure M-n shows the X-ray weighted average structure

factors S(Q) for liquid Si at temperatures of 1542,1603,

and 1829K. The melting point of Si is 1688K, so that

the first and second measurements correspond to the

supercooled liquid state. The S(Q) shows a main peak

with a pronounced shoulder on the high-Q side in

addition to a second peak. Figure M-12 (Table) lists the

locations of the peaks in the S(CJ for liquid Si. The

significant effect of supercooling is to move the first peak

was obtained f~om Ref. 12: and shoulder

1.5

1

o

-0.5

-1

I

o 2 4 6 8

Q (A-l)

Figure M-11. Total structure factor, S(Q) for liquid Si at three

specimen temperatures of 1542, 1603, and 1829K. The melting

point of Si is 1688K. The S(Q)curves have been shifted for clarity.

to a Q value that is about 8’% greater at

1542K than at 1829K. Pair correlations

fimctions g(r) were obtained from the S(Q)

using a maximum entropy method1]31and

are given in Figure M-13. Supercooling

results in a significant sharpening of the

first peak and a reduction in the

coordination number from 6.4 to 5.6. A

systematic decrease of 2?40in the position

of the first peak is observed with

supercooling, as given in Figure M-12.

The stable liquid shows a shoulder on the

high-r side of the first peak, which splits

into a double shoulder upon supercooling.

The present results for liquid Si above the

melting point were found to be in good

agreement with the prior measurements

of W=eda, et a11141and in fair agreement

with the d iYzz%”oMDsimulations of Stich,

etal.[151.The decrease in the first peak ,

maximum and the first shell coordination

with supercooling is consistent with the

MD simulations of Angell and BorickI1a.

Further discussion of the structural

/

measurements and a discussion of results

obtained on liquid Si results can be found

in a recent publication151.

2-73
.’

Figure M-12 (Table ). Structural results for liquid Si and B; S(Q),g(r), ahd coordination (C)

s(Q) g(r)

Temp Q, hump Q, r, subl sub2 rz Cn

(K)

~.l ~.l ~., AA A A atoms

*0.03 *().03 *0.03 *().()3 *0.05 *0.5

Silicon (m.~ 16881Q

Si 1542 2.65 3.65 5.65 2.41 3.28. 3.98 5.22 5.6

Si 1603 2.70 3.60 5.70 2.42 3.27 3.95 5.22 5.6

Si 1829 2.45 3.55 5.45 2.46 3.45 5.20 6.4

Si [15] 1800 2.63 3.55 5.68 2.46 3.64 5.64 6.2

Boron (m.~. 23601Q

B 2600 2.50 4.40 1.76 3.15 5.8

B 2400 2.50 4.45 1.78 3.16 5.8

B 2090 2.45 4.35 1.78 3.15 6.2

B [17] 1.71 3.18 6.0

The crystalline forms of boron embody some of the absence of a low Qpeak near 1 ~-1 in the S(Q) [see ref 7]

most complex crystal structures for a pure element. The does not provide conclusive proof of the existence of B,,

cx-rhombohedral, ~-rhombohedral and tetragonal

crystalline forms have a very large number of atoms per

unit cell, and are dominated by the B ,Z icosahedron

structural unit. Based on surface tension, entropy of

melting and stability data, it was speculated that these

icosahedrons may survive upon melting. Because of the

very high reactivity of boron at high temperature, the

liquid phase had never been studied prior to the present

work which employed levitation to access the liquid phase.

Figure M-14 shows the pair correlation fimction, g(r),

for liquid boron at temperatures of 2600, 2400, and

2090K [~. The melting point of boron is 2360K. The

positions of the peaks in the g(r) are not significantly

tiected by temperature, although there is a sharpening

of the second and third peaks upon supercooling and an

increase in the first shell coordination (Figure M-12).

The liquid g(r) compares well with those predicted in a

recent A initio MD stud~]’l. The liquid g(r) is also similar

to the g(r) for the different crystalline forms, but the

.—

icosahedral units. Nevertheless, the first direct

measurement of the structure of liquid B shows that the

short-range structure is remarkably similar to the

crystalline and amorphous solid forms, with little change

in bond lengths but a broadening of the first coordination

shell, preserving the coordination number around a value

of 6. The present study shows that boron is unique among

covalently-bonded solids in undergoing an insulator to

metal transition on melting with small volume expansion

and little change in the short-range structure. ■

This work was supported by the US Department of Energy

SBIR Contract number DE-FG02--94ER81732 and by

Division of Materials Sciences, O@e of Basic Energy

Sciences,unakr Contiact W-31 -109-ENG-.38. The authors

thank DE Lenny Berman of NSLS for his he~ with the

eqeriments. The National SynchrotronsLight Source at

BrookhavenNationalLaboratory ksupportedby theDivision

of Materiah Sciencesand Chemical Sciences of the DOE.

2-74
..

REFERENCES

[1] S. Krkhnan, J. J. Felten, J. E. Rix, J. K. R Weber, 1? C. Nordine, S. Ansell, M. A. Beno, and D. L. Price, Rev.

Sci. Instrum., 68,3512 (1997).

[2] C. Landron, X. Launay J. C. Rifflet, 1? Echegut, Y. Auger, D. Ruffier, J. 1? Coutures, M. Lemonier, M.

Gailhanou, M. Bessiere, D. Bazin, H. Dexpert, iVuciear Imtruments and MetbosA in PhysicsResearchB., 124,

627 (1997).

[3] G. Jacobs,LEgry, K. M~er, D. Plamek J.Rake,andR Frahm, Rev. Sci. Instrurn., 67,3683 (1996).

[4] D. Herlach, Private Communication, 1998.

[5] S. Ansell, S. Krishnm, J. J. Felten, and D. L. Price, -1 l%ys. Cond. Matt., 10, L73(1998).

[6] S. Ansell, S. Krkhnan, J. K. R. Weber, J. J. Felten, 1?C. Nordine, M. A. Beno, M-L. Saboungi, and D. L. Price,

Phys, Rev. LeG 78,464 (1997).

[7] S.~lshnan, S.~sell, J. J. Felten, K. J. Volin, ~dD. L. Price, PLys. Rm. Leti.,8l576(l998).

[8] S. fiishnm, S.hsell, mdD. L. Price, JAm. Ceram. Soc.,81 (7),l967(l998).

[9] S. filshn~, S.~sell, and D. L.price, in Press, proc. of fieTenh International Conference on fiquidad

Amorphous Metals, Dortmund, Germany 1998.

[10] S. Ansell, S, Krkhnan and D. L. Price, Submitted for publication to I%@. Rev. Lett.

[11] J. Bare, M. Roteta, J. M. Fernandez-Vies, and F. Salvat, Radiat. Pbys. C.bem., 44,531 (1994).

[12] J. Chihara, J l%ys. 1? Met. I%ys., 17,295 (1987).

[13] A. K. Soper, Inst. Pbys. Cor$Proc.R.Sot.,97,711 (1989).

[14] Y Wiseda, K. Shinoda, K. Sugiyama, and S. Tidceda, Jpn. J Appl. Pbys., 34,4124 (1995).

[15] I. Stich, R. Car, and M. Parrinello, Ply. Rev. Lett., 63,2240 (1989).

[16] C. A. Angell and S. Borick, Submitted for publication to~ Pt5ys.Cond. Matt., 1998.

[17] N. Wst, S. Bernard, and G. Zerah, Ply. Rev. B., 52,4123 (1995).

4.5 ~ ,

I I

4

3.5

3

2.5

2

1.5

1

0.5

0

-.—. -

0246810

r, A

2

1.5

1

0.5

0

-0.5

-1

0 2 4 6 8 10

r (A)

Figure M-13. Radial distributionfunction, g(r)for liquid Figure M-14. Radial distribution function, g(r)for liquid

Si at three specimen temperatures of 1542, 1603, Bat three specimen temperatures of 2600,2400, and

and 1829K computed using the maximum-entropy 2090K computed using the maximum-entropy Fourier

Fourier transform method. The melting point of Si is transform method. The melting point of B is 2360K.

1688K, The g(r) curves have been shifted for clarity. The g(r) curves have been shifted for clarity.

2-75

1
.- -. —

DirectObservationof Chargeand OrbitalOrderingin

Manganites

M.v.Zimmerman, J.P.Hill,Doon Gibbs,M.Blume (BNLPhysicsDept.)

Y.Murakami (Photon Facto~ Japan)

Y.Tomioka (JointResearch enter for Atom Technolom [JRCATkJa~an)

Y.Tokura (Universityof Tokyo,Japan)

Understanding the origins of high-Tc

superconductivity and colossal magnetoresistence are

among the most intensely studied issues of physics

research today. Intriguingly, both phenomena appear in

perovskite-~e transition metal oxides, which share the

common characteristic that the electrons are neither

localized nor completely delocalized, but behave in an

intermediate fashion. These materials are known as

strongly correlated electron systems and it is believed that

their unusual properties result from these correlations.

The doped manganites are one class of materials

where such behavior can be investigated. The manganites

are fundamentally interesting because the four main

characteristics of strongly correlated systems, the spin,

charge, orbital and lattice degrees of freedom, are all

● Nhl(4+)

/

Mll(3+)

Figure M-15. Pattern of charge and

orbital ordering in PrO~CaOdMnO~.

present. In addition, members ofthis class exhibit colossal

magnetoresistance phenomena, in which the measured

magnetoresistance can change by 6-8 orders of magnitude

in an applied magnetic field. This has attracted

considerable attention because of possible applications

in the magnetic recording industry and elsewhere.

Here, we briefly report our results on Prl-XCaXMnO~

forx=O.4, and illustrate the use ofresonant x-ray scattering

techniques to probe the orbital and charge degrees of

freedom directly. This is a new development in the field

which holds enormous promise for helping to understand

the unusual behavior exhibited by manganites. For

PrO,GCaOiMnO~the spin ordering occurs at 170 K, while

the charge and orbital ordering occurs at a significantly

higher temperature of about 240 K. In these experiments,

we have been able to observe critical fluctuations of both

the orbital and charge order at temperatures above the

phase transition. We have discovered that, while the two

order parameters have the same temperature dependence

below the phase transition, they exhibit very different

behaviors above. Specifically the charge order fluctuations

have a longer length scale than the orbital order

fluctuations, for a given temperature. This in turn suggests

that it is the charge order that is driving this phase

transition, which is an important insight.

The charge ordering The charge ordering in these

systems manifests itself in an alternating pattern of Mn3’/

Mn4+valences as shown in Figure M-15. Associated with

this ordering pattern is a lattice distortion which has been

studied in detail in related systems by neutron and electron

diffraction[]l. Direct information concerned with the

valence of the Mn-atoms is gained by resonant X-ray

diffraction via the anomalous dispersion of the Mn3+ and

Mn4+ scattering factors. The slight difference in the Mn3+

and Mn4+ absorption energies leads to an anomaly in the

scattered peak intensity at the charge order supedattice

peak when the incident photon energy is tuned to the

manganese K absorption edgeE21.

Orbital ordering in these systems refers to the long

ranged orientation of the occupied Mn 3d orbitals in a

periodic pattern. In a first approximation, the electronic

configuration of Mn3+ in this compound is (t2~3,e~l).The

tz~-electrons are localized, while the e~-electrons are more

2-76
delocalized, and they occupy either (3z2-r’) or (x’-y’)-type

orbitals. It is the e~ orbitals, present only on the Mn3+

ions, which order periodically (Figure M-15). Very

recently it has been demonstrated that it is possible to

probe this ordering of the orbitals by means of resonant

X-ray scattering12’31.The asphericity of the atomic electron

density leads to the observation of forbidden reflections

and a dramatic enhancement of the scattered intensity

results when the incident photon energy is tuned to the

Mn-resonance energy. Two characteristics of the orbital

ordering superstructure reflection are that the polarization

of the incident beam is rotated from o to n and that the

intensi~ depends on the azimuthal angle according to

I(+) K sin’(~). This latter behavior is in distinct contrast

to the azimuthal dependence of a regular Bragg ‘peak,

which is independent of @ These features of the scattering

allow one to identi~ peaks arising from orbital order

unambiguously[’~ 31.

One of the most fascinating issues to be probed

concerns the interaction between the charge and orbital

ordering. In particular, it is not clear whether the two

sublattices order independently, or if one drives the other.

We have investigated the critical temperature range of

the charge and orbitally ordered regime by means of

resonant x-ray scattering, in order to gain insight into

this question.

The experiments were performed at bedlneM2C

at the National Synchrotrons Light Source. The bea.rnline

is equipped with a focusing toroidal mirror and a Ge(l 11)

double monochromator with an energy resolution of

about 5 eV. The polarization of the scattered beam was

analyzed with a CU(220) analyzer crystal. A single crystal

of PrO~CaO~MnO~ was cooled with a standard dkplex

.,

refrigerator.

Because the charge and orbital order have different

periodicity, they give rise to superlattice peaks at different

positions in reciprocal space, and the two types of order

may be studied independently. The charge ordering was

measured in a G-G scattering geometry at the (O 3 O)

superstructure reflection and the orbital order at the

(O 2.5 O) superstructure reflection in a a-n geometry. In

this notation the fundamental Bragg reflections occur at

(O 2n O), where n is an integer. Figure M-16 shows the

peak intensities and full width at half maximum of the

charge and orbital ordering plotted versus temperature.

The intensities show a sharp drop at T=240 K for both

the charge- and the orbital ordering peaks, consistent with

a first order transition. A few degrees above the transition

temperature, fluctuations are observed at both the charge

and orbital order positions. Remarkably, as seen from the

peak width, shown in the bottom part of Figure M-16,

the inverse correlation length for the orbitally ordered

phase increases significantly faster with increasing

I

1

10’

10° -0000000000

.*0

c1

-1

s 10 %

~

?33 E 10-2 -

b ❑°000

z @n 00 0

,0-3 : 0

10-4

0.06 -

(-J05 0 Charge o + o

❑ Orbital a + n

~ 0.04 -

!

5 0.03

.—

= 0.02 - f I

Oos G

0.01 . ❑ 000000000000 d

o

200 220 240 260 280

Temperature (K)

Figure M-16. Comparison of the peak intensity

(top) and the peak width (bottom) of the

charge peak (O3 O)(blue circles) measured in

a a-a geometry and the orbital order peak (O

2.5 O) (red squares) measured in a o-n

geometry.

temperature than that of the charge order. This behavior

.

indicates that the charge order is better established at a

given temperature than the orbital order, suggesting that

a charge ordered phase is a prerequisite for orbital

ordering. In particular, these results imply that it is the

charge order which drives the phase transition. While

more detailed investigations are still required, these results

‘%oextremelyinteresting and beautifidly demonstrate the

power of this new technique for the study of charge and

orbital degrees of freedom, opening a new window on

these intriguing and complex systems.=

REFERENCES

[1] E.O. Wollan and W.C. Koehler, F’lgw.Rev. 100,

545, (1955).

[2] Y. Murakami, H. Kawada, H. Kawata, M. Tmaka,

T. Arima, Y. Morimoto and Y. Tokura, l%ys. Rev.

Lett. 80,1932, (1998).

[3] Y. Murakani, J.I? Hill, Doon Gibbs, M. Blume,

I. Koyarna, M. Taaka, H. Kawata, T. Arima, Y.

Tokura, K. Hirota and Y. Endoh, l%ys. Rev. Lett.

81,582, (1998).

2-77
TheLEGSCollaboration- X5

The Laser Electron Gamma Source facility (LEGS)

provides intense, polarized, monochromatic y-ray beams

by Compton backscattering laser light from relativistic

electrons circulating in the X-Ray storage ring of the

National Synchrotrons Light Source at Brookhaven

National Laboratory. Such a beam has a high degree of

polarization (typically .90Yo) with very low background

and the energies of the photons are well determined by

measuring the loss of energy of the struck electrons(tl ?40).

Photon energies up to 333 MeV can be obtained with

the present laser shining on 2.58 GeV electrons. With a

new frequency-quadrupled laser that is now installed and

2.8 GeVstored electrons, photon energies up to 470 MeV

have been obtained.

The LEGS faciliV and collaboration continue to be

in a time of transition with activity on several fronts. The

final paper describing the Compton and pion

photoproduction experiments L7 and L8 is nearly

complete. In addition, the first experimental

determination of Sn, the backward spin-polarizability, was

extracted from thk data and published last year. Analysis

continues of the first data taken with the SAW (Spin

ASYmmetry) detector array, experiment L1O. In all

instances, we have found good agreement between the

experimental data and Monte Carlo simulation. Over the

last year, the laser hutch has undergone a major

renovation, and preparations are nearing completion for

the first measurement of the GDH sum rule.

Development work on the SPHICE (Strongly Polarized

Hydrogen ICE) target is going quite well. The group is

preparing to provide the first target as soon as the inbeam cryostat arrives from France and is installed. This

should happen spring 1999. A mukipole analysis of our

L1 and L3 photodisintegration of deuterium data

published this year, suggests that the inclusion of meson

exchange currents in current models maybe incomplete.

COMPTON SCATTERING FROM

THE PROTON: L7 / L8

The first phase of LEGS culminated in a pair of

experiments, L7 and L8, designed to measure the electric

quadruple component in the N+A transition (EMR).

Concurrent measurements were made of the p~y~z and

~~y ‘channels. These data formed the basis for the first

simultaneous multipole analysis of both Compton

scattering and n-production. The use of the two new

constraints from Compton scattering resulted in sizeable

alterations to several multiples and has provided a new

high precision determination of the EMR, -3.0% t 0.3

(stat+sys) t 0.2(model)I’l.

This simultaneous multipole analysis also led to the

first experimental determination of the backward spinpokwizability, 6Z . The proton’s lowest order scattering

response is freed by its static properties of mass, charge,

magnetic moment and spin. The Ieadlng corrections to

thispointscartering arise from the dynamic rearrangement

of constituent charges and spins within the proton, and

are expressed in terms of Jixpoiarizabiiities. Four of these

are the result of the interaction of the photon with the

constituent spins and thus are sensitive to the proton’s

spin structure. The first determination of a particular

linear combination of these spin po~arizabi[ities that

characterizes backward scattering was extracted from the

analysis of LEGS Compton scattering data. The value of

6Z = 27.7 * 2.3 (stat+sys) +2.8 / -2.4 (model) is

significantly dXferent from current theoretical estimates,

and indicates an appreciable contribution from the

proton’s spin-structure. Both of these results have gone

to press in the last year[zl, and the final paper describing

the fi.dldetails of the pair of experiments will be submitted

soon.

COMPTON SCATTERING FROM

THE NEUTRON: LIO

A measurement of Compton scattering and TCOproduction from quasi-free neutrons in a liquid deuterium

target ran through July of 1997. The Compton data will

provide a new extraction of the neutron polarizabilities.

This requires accurate knowledge of the neutron photopion multiples below 2n-threshold (309 MeV). Prior to

this measurement, there was no no-production data at all

below 300 MeV

This experiment was the first to use the SASY

detector array. This large solid-angle calorimeter is

2-78
designed for efficient detection of neutral particles (y, n,

no), In the first phase, three major calorimetry subsystems

were implemented. The XTW Box, consisting of 396

optically isolated NaI crystals, covers the fill azimuthal

range for photons in the range 45°<0<135°, providing

reasonable energy and position resolution. At forward

angles, a 30 cm thick wall of plastic scintillators provides

detection of the forward-going hadrons. The wall is

roughly 400/0ei%cient for the detection of neutrons. This

plastic wall is backed by a 10 inch thick array of 176 lead

glass erenkov detectors, providing forward angle coverage

for photons from no decay.

The analysis of this data is in progress. We find good

agreement between the experimental data and results fi-om

Monte Carlo simulation of the array. Most notably the

experimental reconstruction of the no invariant agrees

quite well with Monte Carlo results for both the case of

two photons in theXTfi Box and the case of one photon

in the XT& Box and one in the lead glass array. The

separation of Compton and no events is consistent with

the separation achievable in Monte Carlo.

GDH AND FORWARD

SPIN-POLARIZABILITY

The LEGS SPIN Collaboration (I-SC) is preparing

a series of double-polarization experiments (beam and

target) designed to study the helici~ structure of the

nucleon. Among other things, we will evaluate large

portions of the spin-polarizability and GDH (Gerasimov,

Drell, Hearn) sum rules. This work requires the

development ofanewpolarizedHD ice target (SI?HICE),

an upgrade of the laser system to increase the energy range

of LEGS, and additional detector components to be

integrated with SAW.

SPHICEO

There have been three major target production runs

with the BNL dilution refrigerator and 17 Tesla magnet

system presently stationed in Syracuse. Full size (3 cm

dia. x 5 cm long) HD targets with over 50’%0 H

polarization have been produced and successfully

extracted from the dilution refrigerator. After the first

round of experiments has been completed, the SPHICE

target factory (the dilution refrigerator and magnet system

and its ancillary equipment) will be moved from Syracuse

to BNL and recommissioned in the new lab adjacent to

the LEGS beam line. This required some building

modifications to safely accommodate all of the equipment.

The dilution refrigerator-and-superconducting

magnet system has been designed with the potential of

manufacturing three targets simultaneously, with a. 100/0

increase in elapsed time. Work will focus on developing

this capability and on optimizing deuteron polarization.

As many as four sets of three SPHICE targets could

be produced annually ifsuflicient cryogens are available.

To facilitate this a helium liquefier has been obtained from

the University of Virginia. The use of this liquefier,

together with a recovery system for helium gas, will reduce

cyrogen costs in subsequent years by a factor of five.

There are four main advantages to the new HD

targets that can potentially lead to significant

enhancements to several key experiments:

1.

2.

3.

4.

Conventionally dynam-id~-polarized ammonia or

butynol targets are diluted with significant quantities

of other unpolarized or even worse, partially polarized

background nuclei. Except for 5% aluminum added

for its thermal properties, the HD targets are

undiluted. The figure of merit of a polarized target is

defined as the length of time required to attain a

desired level of statistical accuracy. This varies with

the square of the target dilution. SPHICE targets are

at least a factor of three better than conventional

proton targets and more that a factor of 30 better for

neutrons.

The small dilutions have an added consequence.

Because the backgrounds are small (or nonexistent)

it is possible to make absolute cross section

measurements. There are essentially no data from

direct measurements of absolute cross sections made

with conventional polarized targets.

Polarized neutron and proton measurements can be

carried out simultaneously, which is significant for

the control ofsystematic uncertainties in cases where

proton-neutron comparisons are important.

The HD targets have true frozen-qin. They are not

dynamically polarized during the ‘experiment. This

fact, together with spin-relaxation times on the order

of months, permits the target manufacturing facili~

to be separated from the experimental hall by any

arbitrary distance (e.g. Syracuse to BNL).

THENEW LASER

The laser upgrade has been completed. The new

frequency-quadrupled Neodymium-Yttrium-LithiumFluoride (Nd-YLF) ring-laser system has been installed

side by side with the Argon-Ion laser. This new laser, in

combination with a recent increase of the electron storage

ring energy to 2.8 GeV, increases the maximum photon

energy at LEGS to 470 MeV. The first 470 MeV beam

was taken in the experimental hall April of 1998.

SASY

Early measurements of the GDH sum rule will be

performed using an aerogel Cerenkov veto surrounding

2-79
the target. This will allow rejection of electron

backgrounds online and permit a measurement of the

total reaction cross section before we have the tracking

and complete separation of channels. This aerogel veto is

under construction and will soon be in place for the first

double-polarization experiments.

THE TIME PROJECTION CHAMBER

(TPC) FOR SASY

Work has begun on the construction of a central

drift chamber to expand SASYS capabilities for charged

particles (p, m+,m-). Final design and engineering work

has begun, and construction of several components is

taking place at institutions in the LEGS Spin

Collaboration (LSC). Construction of the gas handling

and monitoring system is almost complete. A prototype

of the TPC trigger scintillator has been constructed and

successfidly tested. The design has been completed for

the superconducting solenoid that will house the TPC

within the SASY calorimeter and potential manufacturers

have been contacted. The magnet and cryostat will be

purchased in FY 1999 by collaborators with finds from

the National Science Foundation (NSF), and the steel

yoke will be constructed at BNL. A nitrogen laser system

to calibrate the TPC has been purchased and is being

tested by collaborators.

DEUTERIUM PHOTODISINTEGRATION

MULTIPOLE ANALYSIS

A fi.dl microscopic model for ll~~p~n requires a

unitary coupled-channel treatment of the NN and NA

interactions, and several sophisticated calculations have

been developed in recent years. Characteristic of these

calculations is a discrepancy in the cross section that grows

with energy above about 250 MeV creating a “dip” in the

predicted 90° cross section that is absent from the data.

A detailed comparison of the calculations of’wilhelm and

Arenhovel with the LEGS data at 300 MeV shows that

while the predicted cross section with photon polarization

parallel to the reaction plane, o,,, is in reasonable

agreement with the data, the cross section in perpendicuku

polarization kinematics, 01, is predicted to be too high at

forward and backward angles and too low at 90°.131

h experimental mukipole decomposition of this

reaction would be an extremely useful tool in analyzing

the successes and shortcomings of theoretical calculations.

This has not previously been attempted, mainly because

of the ambiguities that result from combining

measurements from different experiments with different

systematic uncertainties. This situation has been changed

by the recent availability of a precision data set from LEGS

which reports both cross sections and beam asymmetries

covering the energy region of the A resonance.

We have made the first multipole decomposition of

the ll~ypjn reaction141. We have included electric and ----

magnetic dipole and quadruple photons in the initial

state and ail possible relative p-n angular momenta in the

final state. This produces a multipole expansion

containing 22 complex amplitudes. Since the data lie

mainly below the 27c threshold where the inelasticities in

most partial waves are small, we invoke Watson’s theorem

to specifi the phases. According to this theorem, the

multipole phases in this energy region should equal those

found in np scattering. This leaves 22 magnitudes to

determine from the data. To ensure that the fitted

multiples vary smoothly with energy, the energy

dependence for each mukipole is assumed to vary, at most,

quadratically.

Since &e fit is underdetermined with only two out

of a total of 22 observable available, the result is

necessarily model dependent. Nevertheless, a physically

meaningful fit was produced with 8 multiples

determined by 11 par~eters. A measure of the overall

quality of the fit is seen by examining the difference

between the data and the fit for the 204 sum and

difference cross section data points. The standard

deviation for this distribution is 0.20 Lb/sr. This is quite

comparable to the average statistical experimental

uncertainty of 0.13 pb/sr. Using the complete covariance

matrix to compute the uncertainties on the fit, the angle

integrated total cross sections are determined to about

+().3~~ (statisti~).

Solutions of equivalent quality can be obtained with

divers parametersers and we have examined the mukipole

decom-positions of a wide variety. In all cases, the par~lel

cross s~ction is dominated by electric multiples and the

forward/backward asymmetry that charac~erizes the

angular dependence of the G,,data is produced by E20E1

interference. In contrast, the perpendicular cross sections

are dominated by magnetic multiples, and a spurious

90° “dip” in the al predictions that characterize all recent

coupled-channels calculations can be reproduced by

changing the M2 strength distribution in our fit.

While the Wilhelm and Arenhovel calculations are

in good agreement with the electric-multipole-dominated

all data, they predict a shape for the magnetic-dominated

OL distribution that is clearly inconsistent with the

measurements. We speculate that this rather unusual

situation could be caused by an incomplete treatment of

MEC which afFects primarily the magnetic transitions

where the hadronic currents are important. This has been

found to be the case in recent coupled-channel

calculations including pion retardation ‘effects[5]. It is

2-80
,

clearly desirable to fi.mher reduce the ambiguities in the sensitive to nuclear potentials and currents. The beammultipole decomposition. For this, other polarization target double-polarization experiments using SPHICE

observable are required, and many are expected to be and SASY should change this situation dramatically. ■

[1] The LEGS Collaboration, Pbys. Rev. Letts., 79,4337 (1997). BNL-64382.

[2] The LEGS Collaboration, Z’hys.Rev. Letzx., 80,4382, (1998). BNL-65060.

[3] LEGS Collaboration, .Wys. Rev., C52, R455, (1995).

[4] C. S. Whisnant, W. K. Mize, D. Pomar4de, and A. Sandorfi, l%ys. Rev., 58,289, (1998).

[51 M. Schwamb, H. Arenhovel, 1?Wilhelm, and T.H. Wllbois, Nucl Pbys., A631, 583c, (1998).

2-81
SoftX-RaySpeckleandSurfaceMorphology

S.Eisebitt,A.Karl,R.Scherer, and W.Eberhardt

(Institut fur Festkor erforschung)

M.Adamcyk,C.~icoll,T. Pmnington, and T.Tiedje

(U.of BritishColumbia, Advanced Materials and Process Engineering Lab.and

Department of Physics and Astronomy)

When coherent light scatters from a random surfice, In the visible photon energy range, coherent light

the intensity of the scattered light can exhibit a scattering has been successfidly used for some time to

pronounced random interference effect known as speckle. study the dynamical properties of liquids and surface

The speckle pattern contains information on the adsorbed species[l]. Some experiments have been carried

particular configuration of the surface structure. This is out using hard X-rays in transmission[zl or reflection13-51.

in contrast to the scattering of incoherent light which With measurements at the NSLS Xl B beamline, we have

measures statistical averages of the surface structure only. recently demonstrated the feasibility of speckle

The time dependence of the speckle is the basis for the experiments using soft x-rayslGl. In contrast to hard xtechnique known as dynamic light scattering, which can rays, the soft x-ray range has the advantage that the

provide information on surface diffusion and other reflection coefficients of the samples are much higher. As

dynamical effects in equilibrium systems. The spatial a result, a wider range of scattering geometries is accessible

resolution for the structural information is limited by the while surface sensitivity is still retained.

wavelength of the Iighc shorter wavelengths improve Here, we report on the measurement of sofi x-ray

resolution.

. .

---- — . ,. ——. ——.-.———.——.. —

Figure T-1. AFM image of lnP islands on InP.The height scale is in Um. Only an area corresponding to the

footprint of the synchrotrons radiation in the speckle experiment is shown. Top: Original Image. Bottom:

One island has been erased (arrows) in order to simulate the effects of a change in the surface morphology

on the speckle.

2-82
speckle patterns from InP islands grown on InP with an

InAs wetting layer. Numerical simulations of the partially

coherent scattering have been carried out according to

Huygens-Fresnel scattering theory in the Fraunhofer

approximation, in order to understand the observed

speckle patterns. The experiments were carried out at the

XIB undulator beamline. To increase the lateral coherence

length of the incident X-ray beam, the synchrotrons

radiation was apertured using a 20 ~m pinhole. To ensure

a sharp illuminated area on the sample, the downstream

pinhole to sample distance was kept small (3 cm). The

angle of incidence of the synchrotrons beam on the sample

can be varied, here we present data for 7.4I’ angle of

incidence using 266 eV radiation. A movable position

sensitive soft x-ray detector was placed typically 54 cm

away from the sample. The detector is a microchannel

plate stack with a 2D spatially resolving resistive anode

readout. The active area is composed of 1024 x 1024

pixels, which are 40pm x 20 Lm in size.

The sample investigated consists of InP islands

grown on InP by solid source molecular beam epitaxy.

The surface morphology was investigated by RHEED and

laser light scattering during growth and ex situ by atomic

force microscopy (AFM). An AFM image of the InP

islands is presented in Figure T-1. The image has been

clipped with an elliptical pupil function in order to show

the footprint of the incident soft x-rays on the sample.

The surface morphology as measured by AFM has been

used to simulate the speckle pattern. Details of the

calculations are reported elsewhere171. Intuitively, the

calculation can be envisioned in terms of summing the

complex phase factors arising from the path difference

between each point on the sample and the considered

pixel on the detector. The finite lateral coherence length

was determined by the simulation of measured Fraunhofer

diffraction rings and taken into account in the speckle

simulations. At the present stage, calculations were carried

out assuming infinite longitudinal coherence, although

we expect the longitudinal coherence length to be

The measured speckle pattern of the InP sample

using 266 eV photons along with the simulations are

presented in Figure T-2. As indicated by the momentum

transfer scales, the images were recorded/calculated

symmetrically around the specular beam. For comparison,

all three results are plotted on the same logarithmic

colorscale, which is set by the dynamic range of the

measured data. In order to study the effects of the beam

coherence, the simulation in the middle panel includes

the finite lateral coherence, while the simulation in the

top panel assumes infinite coherence lengths.

-1.tl -05 0.0 0.5 1,0

0“ (@’}

10

5

da

5

-5

●1o

R

3

2

I

9

2

1

0

-1.0 -0.5 0.0 a5 I.O

Q/Jw-’)

Figure T-2. 2D Speckle images from the sample

shown in Figure 1 (top). The glancing angle of

incidence is 7.4°,the photon energy is 266 eV.

The intensity is represented on a logarithmic

colormap. From top to bottom: simulation

assuming perfect coherence, simulation

including a lateral coherence length of 20 pm,

experimental data.

2-83
The simulations reproduce the main features in the

experimental data. The overall elongated shape of the

intensity and the size of the speckles agree with the

experiment. Of course, quantitative agreement of the

speckle structure cannot be expected, as the AFM and

speckle experiments are likely to probe different sample

areas. As expected, the simulations illustrate that a

reduction in the coherence of the synchrotrons radiation

results in a loss of contrast. With regard to the dynamic

range, the agreement between experimental data and the

simulation inchdng the lateral coherence is good, but

not perfect. We ascribe this discrepancy mainly to the

influence of the longitudhxd coherence, which is of the

order of the maximum path difference between light

beams scattered from either end of the illuminated region

on the sample.

The distribution of the simulated x-ray scattering is

tilted with respect to the flame ofrhe image. Thk is caused

by the orientation of the InP islands on the sample. In

Figure T-1 (top), the islands are elongated and are aligned

with rhe [100] crystal dkection on the substrate. The

orientation of the islands creates the preferential scattering

responsible for the tilt in the image. We observe a tilt in

the same direction but with a smaller slope in the

experimental data (especially when analyzing images at

larger ~ (not shown)) , which indicates that the

alignment of the sample crystal axes was slightly off with

respect to the plane of incidence.

The effect of a change in the surface morphology

on the speckle pattern was evaluated by erasing one InP

island from the AFM image used to simulate the

scattering. The missing island is indicated by an arrow

on both images in Figure T-1. The scattering simulation

was computed with the modKied AFM image and the

resulting speckle pattern was subtracted from the original

simulation. The absolute value of the difference image is

shown in Figure T-3 using the same logarithmic gray

scale as in Figure T-2. There is a clear difference between

REFERENCES

I

. ,-

-1.0 -0.5 0.0 0.5 1.0

QI{m-g)

Figure T-3. Absolute value of the difference in the

partially coherent speckle simulations for the two

different surfaces shown in Figure T-1 top/bottom.

-< — ——.

the two simulated speckle patterns, indicating that the

soft x-ray speckle experiment is promising for-the study

of system dynamics. There are about 20 islands in the

original AFM image which are responsible for the

scattering. The removal of one island should therefore

decrease the scattering by about 5?40which is consistent

with the difference image in Figure T-3: at the specular

position, the intensity difference is about 1.3 orders of

magnitude (i.e. a factor of 20) smaller than the intensity

of the scattering. With a fast detector, which measures

the intensity at one point only studies of the dynamics at

surfaces or buried structures will become possible. ■

[1]

[2]

[3]

[4]

[51

[6]

[71

2-84

See e.g. Laser speckie and rekztedphenomen~ Ed.J.C. Dainty, (Springer, Berlin, 1984).

S. Brauer, G.B. Stephenson, M. Sutton, R. Bruning, E. Dufresne, S.G.J. Mochrie, G. Griibel,

J. Als-Nielsen, and D. Abernathy Pbys. Rev. Lett., 74,2010, (1995).

Z.H. Cai, B. Lai, W.B. Yun, I. McNulty, K.G. Huang, and TX? Russell, Pkys. Rev. Lett.,

73,82, (1994).

M. Sutton, S.G.J. Mochrie, T. Greyrag, S.E. Nagler, L.E. Berman, G.A. Heald, and G.B. Stephenson,

Nature, 352, (1991).

J.L. Libbert, R. Pindak, S.B. Dierker, and I.K. Robinson, I%ys. Rev. B, 56,6454, (1997).

S. Ekebitt, A. Karl, R. Scherer, W. Eberhardt, M. Adamcyk, T. Tiedje, and C. Pistonesi,

Synch. Rad News 11, No. 5, p. 15, (1998).

M. Adamcyk, T. Tiedje, S. Eisebitt, A. Karl, R. Scherer, W. Eberhardt, Proceedings of the 26th

Conference on the Physics and Chemistry of Semiconductor Interfaces, to be published (1999).
A NewMethodfor Examiningthe Dynamicsof

Macromoicules:Time-resolvedSynchrotrons

X-ray “Footprinting”

M.Chance, M.Brenowitz, M.Sullivan, B.Sclavi,S.Maleknia, and C.Ralston (Center for

SynchrotronsBiosciences, Department of Physiology and Biophysics and Department of

Biochemistry,Albert Einstein College of Medicine of Yeshiva U.,and NSLS)

A new method of determining structure is under

development at the National Synchrotrons Light Source

(NSLS) called synchrotrons x-ray foootprinting. The goal

is to probe the confirmational dynamics and tertiary

structure changes of proteins and nucleic acids with

millisecond time resolution. This activity is being

undertaken by the Albert Einstein College of Medicine

and funded by NIH as a Biotechnology Resource Center.

The technique of synchrotrons x-ray footprinting is a

melding of stopped-flow mixing technolo~ and radiolytic

chemistry using a high flux x-ray source. Radiolysis

generates ●OH according to equation 1:

As photons interact with water and generate a water ion

and an electron. The ionized water molecules react with

water to produce ●OH according to the reaction outlined

in eq. (l). The kinetics and dose of “OH and its use in

footprinting studies has been extensively reviewed[’”1.

The prediction underlying synchrotrons x-ray

footprinting is that irradiation of solutions by high flux

“white light” x-ray beams at National Synchrotrons Light

Source (NSLS) beamline X9A yields sufficient

concentrations of “OH so that footprinting studies of

nucleic acids and proteins can be conducted with

millisecond exposures to the x-ray beam. Figure T-4

h H,O shows the flux emanating from a bending magnet port

HZO + HZO’ + e-~v+ H,O+ + ●OH + e-,,- (1) (impinging on a sample typical for a synchrotrons

footprinting experiment) at the NSLS when the ring

~

~ 2.5

s

-0

c

r%

$

Y

j 0.5

~

g

o

E

0.0

5 10 15 20 25 30

Photon Energy (ke~

Figure T-4. Photon flux intercepted by a l-mm pathlength sample of -10 microliters (3-4 mm diameter) at

beamline X9A, National Synchrotrons Light Source. Beam energy of 2.54 GeV, 250 mA beam current. The

figure indicates the front-end flux available for the specified geometry, the flux absorbed by the beamline

optics incident on a typical sample, the flux passing through and absorbed by the sample.

2-85
-. —

Figure T-5: Secondary structure of the

Tefrahymena ribozyme and rate

constants for folding of 22 separate

regions of the ribozyme that were

determined by x-ray footprinting.

Regions that fold on similar

timescales are highlighted in the

same color. P5c, the first region to

fold, is highlighted in green.

Immediately after, 7 regions within

the P4-P6 domain fold

simultaneously (orange).

Subsequently, P2 and P9 make

contacts (purple) with the pre-formed

P4-P6 scaffold. After several minutes,

protections appear in the P3 and P7

domains indicating formation of the

native, active structure (yellow).

energy is 2.54 GeV, as a function of energy. Thking into RNA molecules fold into their native conformation has

account losses due to the current bean-dine X9A optics, received much attention. Early investigations into the

which consist of two Be windows (254p and 500 pj and

an M window (2OOp), gives the flux incident on a typical

10 microliter sample as a fimction of energy. We can also

calculate the transmitted flux subsequent to the l-mm

water path, the difference between the two curves is of

course the absorbed dose. Note that total absorbance is

small, thus the dose is homogeneously delivered through

the l-mm path.

Our first “proof of principle” of the method

consisted of an analysis of the foldlng of an RNA catalyst,

the Ztrahymena ribozymeE31. During the folding of both

proteins and RNA, dramatic changes in solvent

accessibility occur. The conformation changes of RNAs

in fict, can limit the speed of chemical reactions carried

out by RNA catalysts131.As a result, the process by which

folding of tRNA established approximate timescales for

the formation of secondary (10-4- 10-5 s) and tertiary

interactions (10-2 -10-1 s), with reorganization of incorrect

secondary structure occurring more slowly (O.1- 1 S)[4].

Recent work has shown that folding of large RNAs is

more complex, involving multiple pathways15’Gl.Individual

domains ofan RNA may format rates that differ by orders

of magnitude, with some transitions requiring minutes

to reach completion. Our synchrotrons footprinting

method, with the abiliiy to monitor changes in the solvent

accessibility throughout the RNA and monitor processes

occurring from milliseconds to minutes, is ideally suited

to investigate the complex folding of large RNAs.

The 385 nt. ribozyme derived from the li%rahymena

group I intron (Figure T-5) folds into a well-defined

2-86
tertiary structure in the presence of M~, which is

required for activity141.Biochemical and genetic methods

have identified at least three domains of tertiary structure

that, when separated, can re-associate to form the active

ribozyme. A 160 nt domain containing paired regions

P4-P6 folds independendY17’81,and its structure has been

determined by x-ray crystallography 171. The

M#dependent folding kinetics of the ribozyme were

quantitated by determining the changes in solvent

accessibility of individual sites as a function of time afier

the addition of magnesium ions. A powerfi.d advantage

of the footprinting method is that changes in protection

in sites throughout the ribozyme can be monitored in a

single experiment. Figure T-5 summarizes the kinetic

determinations of folding for 22 separate regions of the

ribozyme that show significant changes in protection upon

addition ofM~. The rapidly protected sites corresponded

to nucleotides that are excluded from solvent by folding

of the P4-P6 domain upon itself the tertiary interactions

within the domain are established in a concerted manner

at a rate of about 1 S-l at 42 “C (colored in orange). A

subset of nucleotides in P5c (Figure T-5) were protected

about twice as rapidly as other regions in the P4-P6

domain (colored in green). This region is a M~-rich

subdomain suggesting that formation ofa “metal ion core”

REFERENCES

[1]

[2]

[31

[4]

[51

[6]

[71

[8]

[91

[10]

in P5a-P5c could serve as a nucleation site for additional

tertiary structure formation. Other regions highlighted

in Figure T-5 show that tertiary contacts with the other

domains of the ribozyme occur more slowly (colored in

purple).

These synchrotrons footprinting results yield a

complete kinetic ‘map’ for the folding of the ribozyme

allowing detailed questions about the folding mechanism

to be answered for this and other large RNAs. The

methods used for analysis of RNA structure are

immediately translatable into examining the evolving

protections that occur upon binding of proteins to both

DNA and RNA, and experiments to probe such

interactions in real time are underway. The footprinting

of proteins, to examine the time-resolved changes in

protection of a protein molecule, either in a folding

reaction or in macromolecular assembly processes, is also

being addressed through synchrotrons applications.

Although detailed discussion of the technical challenges

of these applications are beyond the scope of this article,

the modification of proteins by hydroxyl radical occurs

on timesca.les equivalent to those of nucleic acid cleavage,

use of advanced analytical techniques, like mass

spectrometry can monitor these modifications and

provide new probes of macromolecular structure[~’lol. H

B. Sclavi, S. Woodson, M. Sullivan, M.R. Chance, and M. Brenowitz, J A&l Biol., 266,144, (1997),

and B. Sclavi, M. Sullivan, M. Chance, M. Brenowitz, and S.A. Woodson, Science, 279, 1940, (1998).

M.R. Chance, B. Sclavi, S.A.Woodson, and M. Brenowitz, Structure, 5,865, (1997) and B. Sclavi,

S. Woodson, M. Sullivan, M. Chance, M. Brenowitz, Metboak in Enzymology 295,379, (1998).

T.R. Cech and D. Herschlag, lWcleicAcia3 andMolecuLm Biolo~,

edited by F. Eckstein and D. M. J. LUey 10, 1, (1996).

D.E. Draper, Nature Struct. Biol, 3,397, (199G).

IT Zarrinkar, and J.R. Wdliamson, Science, 265,918, (1994).

N? Zarrinkar, and J.R. Williamson, Nature .%uct. Biol, 3,432, (1996).

J.H. Cate, A.R Gooding, E. Podell, K. Zhou, B.L. Golden, C.E. Kundrot, T.R. Cech,

and J.A. Doudna, Science, 273, 1678, (1996).

F.L. Murphy and T.R. Cech, Biochemistry, 32,5291, (1993).

S.D. Maleknia, and M.R. Chance, Proceeding of the 46A Annual Conference on

Mass S~ectromet rv and Allied ToDics,Orkmdo, Florida, p. 972, (1998).

S.D. Maleknia, S. Goldsmith, S. Vorobiev, S.C. Almo, M.R. Chance, and K.M. Downard, Proceedimzs of the

4@ ~nu~ Conference on Mms Spectromet — rv and Allied ToDics, Orlando, Florida, p. 973 (1998).

2-87
High-ResolutionX-Ray Fluorescence

Spectroscopy at X25: Whereare the Electrons?

Whoare the Ligands?

U.Bergmann, P.Glatzeland S.P.Cramer

(Lawrence Berkeley National Laboratory and U.of California at Davis)

A newly designed multi-crystal X-ray spectrometer

is described and applications in the field of X-ray

fluorescence spectroscopy are discussed. The instrument

is based on 8-spheri~y curved crystals aligned in the

Rowland geometry (see schematic setup in Figure T-6).

Each crystal has three degrees of freedom for adjustment,

Bragg angle, azimuthal angle and distance to the source

and detector. The design is very flexible and crystals of

different size and ben~ng radius can be employed. If all

crystals have the same dkmmce to the source scans can be

facilitated by moving the motorized spectrometer table

to change al_lBragg ~gles simuhaneo~sly.

Currenrly eight 8.9 cm diameter Si (4,4,0) crystals

bent to 86 cm radius are employed. At Bragg angles close

to backscattering a solid angle of 1/180 of the total 4TCsr

can be captured-with sub e~ energy resolution. To avoid

intensi~- losses due to absorption on the long paths

between source crystals and detector, a He-filled bag that

encloses the entire beam path is inserted. An instrument

combining such a large solid angle with high energy

resolution is ideally suited for analysis of weak quasi

isotropic signals. Among the many possible applications

the technique of K~ fluorescence spectroscopy is

illustrated with two examples.

WHERE ARE THE ELECTRONS?

It has been shown that the main lines of the K~

fluorescence (3p+ 1s transition) in transition metals are

strongly influenced in shape as well as energy by the

number of unpaired 3d electrons. Hence K~ spectra give

an excellent signature of the oxidation and/or spin state.

Due to their variety of oxidation states, transition metals

play an important role in catalytic processes. Obviously

the knowledge the oxidation state is of fundamental

importance for the understanding of these processes.

One predominant example of a catalytic process in

nature is the oxidation of water in photosystem II, a

mechanism responsible for essentially all the oxygen in

our atmosphere. The catalytic center for this process is a

cluster containing 4 Mn atoms. The oxygen is released

. .’

. . .

Detector A

/w //

/

SR beam

~ ‘Pectiometer

Figure T-6. Schematic setup of the spectrometer geometry. All eight crystals are aligned to form

identical symmetric triangles of source point, crystal and detector. Energy scans can be performed

by moving the spectrometer table and the detector (twice as much) in the vertical.

2-88
afier the fourth step in the so called Kok cycle, in each of

which a visible light photon had been absorbed.

In collaboration with the Penner-Hahn, Christou

and Armstrong Groups, high resolution Mn K~ X-ray

fluorescence spectra have been recorded on the darkadapted S1 state and the hydroquinone-reduced of

photosystem II (21.By comparison of the K~ chemical

shiiis with those of appropriate model compounds, the

S, state is found to contain equal amounts of Mn(III)

and Mn(IV). In the hydroquinone-reduced sample, a

significant fraction of the Mn is reduced to Mn(II), and

the results are compatible with models involving

conversion of Mn(III)2Mn(IV)z to Mn(II)zMn(IV)z

clusters.

In a collaboration with the Klein Group at Calvin

Lab, we have then studied the evolution of the Mn

oxidation states through different S-states in the Kok cycle.

Our preliminary findings are consistent with the Berkeley

model of Mn(II,III,IV) for SO, Mn(IIIz,IVz) for S1 and

Mn(III,VI~) for both S, and S~ states 13’41.

WHO ARE THE LIGANDS?

Besides the work on the very dilute protein samples,

the large solid angle combined with the high incident

flux at X25 enabled us to systematically study much

weaker K~ emission features appeaing at higher emission

energies (see Figure T-7). These transitions result from

valence orbitals close to the Fermi level and, in some cases,

even ligand orbitals. In particular we studied the so called

“interatomic” or “crossover” x-ray transitions of ligand

(N, O, F) 2s to metal (Mn) 1s 151,also known as K~”.

The energy of the Kfl” feature is very distinct even

for Iigands of neighboring Z, resulting in shifis of order 5

eV. It can therefore be used to identi~ the type of ligand.

Furthermore, for a variety of oxygen ligated Mn

compounds, the intensity of the K~ transition is found

to decrease exponentially with increasing Mn-O. The

normalized KY intensity can be used to predict distances

to .0.1 ~. The result demonstrates the potential of this

technique as a new alternative to tell not only who but

also where the Iigands are. H

REFERENCES

[1] U. Bergmann and S. 1? Cramer, SPIE Proceedings, 3448,198-210 (1998).

[2] U. Bergmann et al., J l%y-r. Cbem. B, 102/42, 8350-8352 (1998).

[3] J. Me.ssinger et al., Proceeding of the XL Int. Corwress on Photosynthesis 1998, edited by J. Garab, Kluwer

Academic Pub., The Netherlands, in press.

[4] R. M. Cinco et al., Proceedimzs of the XL Int. Corwress on Photosvnrhesis 1998, edited by J. &rab, Kluwer

Academic Pub., The Netherlands, in press.

[51 U. Bergmann et al., G7em. I%ys. Lett., accepted.

I

~n

I I I I I I

valence

levels T

3p

2p

z

Kb,,

.g ;1s :

:“:

::

::

g Ka,

x15 ::

:::!

Il!J-.:l.~ )3” :; :’.

:,:: ,Kb” ;: x 500

:;.. . .

;: !,

K02 Kb’ : ;

,., .

. . .

::

;: . .

..”‘. . . . . .

.. ,, :

.,”. .....

...

-----

.........................................

Kb

,.

..-..J...,..-, .. l,,

5880 5900 5920 6480 6520 6560

Energy[eVl

Figure T-7. K-emission

spectrum of MnFz. The Ka

spectrum was simulated

using the known Ka/K~

integrated intensity ratio of

-7.7. The main K~ lines are

split by the 3p-3d exchange

interaction into a Kp13peak

and a K~ feature. These are

shown magnified by a factor

15 (dashed line). The much

weaker K~z~ and K~”

features which are not

visible in the main figure are

shown magnified by a factor

500 (dotted line).

2-89
—.——— ——...—— .— -.—..——

NewlyCommissioned3-30eV UndulatorBeamlineU13UB

S.L.Hulbert(NSLS),A.V.Fedorov,T.Valla,and P.D.Johnson (BNLPhysics)

The low-K (undulator regime) output of the

insertion devices on both NSLS storage rings is essentially

“third generation”, by being nearly dKfraction-limited in

one direction (vertical). As such, they represent an

important and unique component of the synchrotrons

radiation facilities available in the U.S. The NSLS

undulator sources are U5U and U13U in the VUV

photon energy range and Xl and X13 in the sofi x-ray

range.

The brightness (flux per unit phase space) of the

U13U undulator in the photon energy range covered by

values of the magnetic strength parameter K, for which

the fundamental photon energy spans the 3 to 30 eV

range. Note that the brightness of the undulator output

is three orders of magnitude greater than a VUV bending

magnet.

In terms of flux, the U13U undulator produces

fundamental output greater than 2 x 1015 photons/see/

0.1 ?40bandwidth/Amp in the 3-30 eV photon energy

range. This range of fimdamental photon energies hvl is

readily achieved by changing the magnetic strength K

from 4.7 to 1.4. The radiation is directed into a narrow

the U13UB beamline, 3 to 30 ev is shown in Figure T- spatial cone, e.g. the 1-O opening angle is 210 prad at

10. This figure plots the spectral brightness for seven hvl = 15 eV.

NSLS U13U on—axis brightness

g 10’7

J

I

Figure T-10. On-axis spectral brightness (flux per unit phase space) of the U13U undulator for seven values of the

magnetic strength parameter K(proportional to the product of magnetic field strength and spatial period) spanning

the photon energy range covered by the U13UB beamline, 3 to 30 eV. The highest brightness curve at each

photon energy is associated with output at the fundamental wavelength. The underlying peaks are higher

harmonics (n> =2) associated with higher Kvalues which, for non-zero-emittance electron beams, appear at all

integer multiples of the fundamental wavelength. Note that the brightness of the fundamental is three orders

of magnitude greater than a VUV bending magnet.

2.0 ‘ “7 ‘,;4

::

-.

-.

.-

.. I

-. I

.

.

.

. 8

--

-. :

. .

. .

;

++. .

5 10 15 20 25 30

Photon energy [eV]

2-90
This article focuses on the new U13UB beamline,

which has been in operation since June 1998. The

properties of the U13U source and the U13UB bearnline

are provided, followed by a general overview of the

scientific opportunities which we envision for this

bean-dine, Finally a descriptive overview of two angleresolved photoemission endstations destined for use at

U13UB is given, including a sampling of the first

experiments, which are ongoing.

COMPARISON WITH BENDING

MAGNET SOURCE

In order to justi~ the use of a unique resource such

as the U13U insertion device, is it necessary to show that

a NSLS VUV bending magnet beamline could not

produce the desired flux density at the sample. The flux

output of 1 prad horizontal of an NSLS VUV bending

magnet is approximately 1 x 1013 photons/see/

O.lYobandwidth/Amp, and the vertical opening angle of

radiation in the 3-30eV photon energy range is 5-1o mrad.

In order to ;ompete with U13U in terms of raw flux, a

bending magnet bearnline must collect a large horizontal

fan, e.g. NSLSU11 collects 55 mrad in the horizontal

plane.

However, such a beamline is saddled with problems

related to the large phase space area of the bending magnet

source (horizontally, vertically, and in depth). Clever.

optical designs, such as the modified Wadsworth

monochromator at UI 1, provide fairly good energy

resolution, but at the expense of providing a rather large

focal “spot” (1 mm). The transverse (horizontal and

vertical) phase space volume of the U13U radiation is on

the order of 250 to 500 times smaller than thatofU11,

which enables U13U to provide significantly higher flux

density at the sample.

From this discussion, it is clear that the experiments

which will benefit the most from the high brightness

undulator beam at U13UB are those for which flux

density on the sample defines the figure of merit. This

class of experiments includes all of angle-resolved

photoemission spectroscopy (ARPES), for example, since

the electron energy analyzer in these experiments can

accept emission from only a finite area on the sample.

Further, as the energy resolution of these analyzers is

improved, the size of this acceptance spot decreases

dramatically.

U13UB BEAMLINE DESCRIPTION

Beamline U13UB is one of three branch beamlines

which share the output of the U13U NdFeB hybrid

wiggler/undulator (0.5 z K c 7.6) insertion device

on the VUV Ring. The other two branches are U13UA,

a focused white light bearnline, and U13UC, a coherent

optics characterization beamline. Figure T-11 is an

elevation layout drawing of the U13UB bearnline, which

was constructed by McPherson, Inc. of Chelmsford, MA.

The U13UB bearnline is separated from the U13U

centerline by a horizontally-deflecting (12° grazing angle

of incidence) v~iable-radius (50m c R < 200m) integrallywater-cooled spherical mirror (MOB), which collects 1.66

mrad and focuses on the exit slit of the U13UB

monochromator. The!’ MOB mirror material is glidcop

(ceramic copper alloy) explosion-bonded to a stainless

steel substrate. The second optical element is a verticallySAMPLE v

GRATINGSJ

Figure T-11. Elevation layout view of the U13UB high resolution VUV spectroscopy beamline,

showing the paths of the monochromatic (lower) and white-light (upper) branches.

2-91
deflecting (7° angle of incidence — nearly normal

incidence) integrally-water-cooled spherical (R= 1.9m)

mirror (M 1B), which collects 2.4 mrad and focuses (with

.15:1 demagnifkation) on the entrance slit (SOB) of the

monochromator. The large total output power (287W

at K = 8, 500MA ring current) and significant output

power densities (up to 32.5W/mrad2 at K = 8, 500MA

ring current) require water cooling of MOB, MIB, and

SOB. Owing to its nearly normal incidence geometry, the

lion’s share of the source power is absorbed by the MIB

mirror. The M 1B mirror is a one-inch thick piece of

CVD SiC and is integrally water cooled: finite element

calculations show that the temperature rise, stress, and

resulting deformation are well within the mechanical

limits of this material (in fact they are all small).

The U13UB beamline features a Normal Incidence

Monochromator (NIM) in which a spherical (R= 3m)

grating is used in fixed included angle geometry. The

grating chamber houses two gratings on a rotating

turret with detents to select either of the two gratings

in situ. These two gratings (1200 and 2400 line/mm

groove densities), and the -3m entrance and exit

armlengths in this monochromator, produce >10,000

spectral resolving power in overlapping photon energy

ranges spanning 3 eV to 30 eV. The entire grating housing

moves, under interferometric control, along the angle

bisector between the entrance and exit beams, in order to

track the photon energy-dependent focus of the diffracted

exit beam. The grating angle scanning motion is provided

bya DC servo system, also under interferometric control.

The variable radius of the MOB mirror can be used to

correct for the photon-energy-dependent astigmatism of

the NIM as it scans through the 3-30 eV range.

OVERVIEW OF SCIENTIFIC OPPORTUNITIES

USING BEAMLINE U13UB

Several types of scientific programs could be

expected to benefit greatly by instrumenting the U13U

wiggler for high resolution VUV work in the 3 to 30 eV

range. Perhaps the most obvious application in solid state

physics is ultra-high resolution angle resolved

photoemission. In cases where the states of interest lie

100

0

-1oo

-400

-503

-600

i,. ,. ... ~..,-. . . . ,., :- . . ., +., .,,, A-, . ..+... .“. ,,.

-— . ... .

-12 -lo 4

Polar Angle (deg)

Figure T-12. ARPESintensity plot of the Mo(110) surface recorded along the ~ - ~ line of the surface

Brillouin zone at 70°K. Inset “fixed-mode-spectrum of the region around k, (marked with box).

2-92
near the Fermi level, self-energy corrections are small, and

reductions in the photon energy spread will significantly

enhance the experiments. High TC superconductors and

heavy fermion systems are examples of such problems.

In addition, surface photo-voltage measurements,

chemical dynamics applications, and photoelectron

spectromicroscopy are all experiments for which spatial

flux density is the relevant figure of merit, and could

therefore be expected to be well matched to the U13UB

beamline.

The section of beam pipe located vertically above

the NIM beamline (see Figure T-11) houses relay optics

which will provide a time-delayed (or advanced) white

light beam, the focus of which will be collinear and

coincident with that of the NIM bearnLne, for the purpose

of pump-probe experiments. This capability is expected

to be central to a large fraction of the biology experiments

planned for U13UB.

ANGLE-RESOLVED PHOTOEMISSION

ENDSTATIONS AND EXPERIMENTS

Angle-resolved photoemission, developed in the

seventies, still represents the premier tool available for

the study of the momentum dependence of the electronic

structure in solids. Here the energy of the emitted

photoelectron is measured as a fi-mction of the angle of

emission. Combined with beamlines such as U13UB, a

whole range of new electron spectrometers is expected to

lead to a resurgence of activity in this area. By

multiplexing in energy and angle, these new instruments

allow a considerable reduction in data acquisition times.

At the same time, they offer extremely high energy and

momentum resolution. With these improvements,

ARPES maybe used to obtain direct access to the real

and imaginary components of the electron self energy, a

measure of the interaction of an electron or hole with its

environment.

Two instruments are scheduled to exploit the high

photon fluxes available from U13UB. The first is a 200

mm radius Scienta SES200 analyzer that has recently been

commissioned in the group of Peter Johnson (Physics -

BNL) and the second is a Gamma Data 50 mm radius

spectrometer currently being constructed by Eric Jensen

(Brandeis U.) and Kevin Smith (Boston U.).

Initial experiments using the SES200 have already

been completed. An example is presented in Figure T12, which shows a measurement of the dispersion of an

electronic band in the vicinity of the surface of

molybdenumI1l. Shown in more detail in the insert, the

spectra clearly show a slight change in the rate of

dispersion and a rapid narrowing of the band in the

vicinity of the Fermi level. These changes are directly

attributable to the interaction of the electrons with the

lattice vibrations or phonons in this system.

(a) Photoemission,hv = 21.4 eV

I I I I I

high k km

zn

F1

I

Figure T-13. Three-dimensional

photoemission map of KO,~MoO~,

showing two parallel bands

dispersing toward the Fermi level.

0:2 - 0.3 0.4

Electron Momentum along IX (A-l)

2-93
Another example of the use of high momentum

resolution is shown in Figure t-13. Here are shown the

results of a study of the blue bronze, KO,JMoO~, which is

a quasi-one-dimensional system having two chains per

unit cel1121.The valence electrons in this system form a

charge density wave that results in a metal-semiconductor

transition at 180”K. This study, carried out in

collaboration with the Boston University Electronic

Structure Group (K. Smith et al), was able for the first

time to clearly resolve two bands reflecting the interaction

between the chains, as shown in Figure T-13.

Furthermore, a detailed study of the temperature

dependence of the wavevectors associated with these two

bands provided a direct connection between the electronic

structure and the temperature dependence observed for

the wavevector of the charge density wave in this system.

As a final example of the new possibilities in ARPES,

we show the results of a detailed temperature dependent

study of optimally doped Bi2Sr2CaCu208 (BSCCO)131.

These studies have found evidence for the opening of a

gap in the speccral response with the onset of long range

coherence at the superconducting transition temperature

T=. Figure T-14 shows the emission from a region of

momentum space when the sample is in the

superconducting state. The “airplane wing” section

corresponds to the superconducting paired electrons.

Figure T-15 shows temperature dependent “angle

integrated” spectra obtained from images such as those

shown in Figure T-14.

Figure T-1 5 shows that the sharp feature

immediately below the Fermi level characterizing the

superconducting state appears in the spectra even above

the transition temperature TC, 91 ‘K, and that it remains

at constant bindhg energy at all temperatures. Further,

the spectra show that the intensi~ of this feature changes

continuously on passing through TC. This latter

observation is surprising because within the framework

of a mean field or BCS model, if the sharp peak reflects

the super fluid density, it should disappear at T= and,

further, the separation between it and the Fermi level

should dkappear. However, the authors of the study

Fedorov, et a~, noted that at the transition temperature,

a dip rapidly develops in the spectra immediately beyond

the sharp peak. By fitting the angle-resolved data collected

within an angle of 0.5°, Fedorov, et d. were able to show

that the development of this dip maybe associated with

the opening of a gap at the Fermi level, reflecting the

onset of long range phase coherence as defined by the

transition temperature TC. The latter development

represents the extension of the pseudogap, which is

reported to exist above T= up to 130K in the optimally

doped materials, to all states in the system. H

2-94

. .-

. . ,. -. ,.

.. <+,. .,

- SK==’

?

t)

. am

Figure T-14 (Spectral density plot of optimallydoped Bi,Sr,CaCu,O, recorded in the r M

direction of the Brillouin zone with the sample

temperature held at 46”K. The incident photon

energy is 21.2 eV. The most intense emission is

indicated in red.

The U13UB beamline wasassembkd installed leak tested

and mechanically debugged by the technical members of the

NSLSExperimentai SystemsGroup, especial~ Gay Nintzel

and Dennis Carlson. The beandine components were

positionedly theNSL.SSurvq Zam, headdby R. Scheuere~

to such aprecision thatgettz”ngundukztor light to the sample

was easy. All of the U13 UB beamline components were

desi~ed andfibricated by McPherson, Inc. of Chelm#ord

MA, including alignment of the NIM gratings and

inteferometez
1-

1 1

,

I I I I I

Figure T-15. Angle-integratedphotoemission

spectra of optimally-doped Bi2SrzCaCuz08

recorded as a function of temperature and

integrated along the r Mlineofthe Brillouin

zone. The different temperatures are

indicated.

REFERENCES

[1] T. Valla, A. Federov, I? D. Johnson, and S. L. Hulbert,’’Many-body Effects in Angle-resolved Photoemission:

Quasiparticle Energy and Lifetime of the Mo(11O) Surface State”, F’hys.Reu. Lett., submhed (1999).

[2] A. Federov, S. A. Brazovskii, V N. Muthukumar, I? D. Johnson, J. Xue, L.-C. Duda, K. E. Smith, W. H.

McCarroll, M. Greenblatt, and S. L. Hulbert, “Photoemission Study of the Charge Densi~ Wave Transition

in the Quasi-one Dimensional Conductor ~.~MoO~”, Pbys. Rev. Lett., submitted (1999).

[31 A. Y Fedorov, T. Villa, i? D. Johnson, Q. Li, G. D. Gu, N. Koshizuka, “Temperature Dependent Photoemission

Studies of Optimally Doped Bi,Sr,CaCu,08”, Pbys. Rev. Len., 82,2179, (1999).

K

I

2-95

,

I

I
AGeneralSolutionto the DiffractionPhase Problem

inSystemswithTwo-DimensionalPeriodicity

Y.Yacob (Racah Institute of Ph sits, Hebrew U)

R.Pinda; , R.MacHarrieand L.Jfeiffer,

(BellLaboratories, LucentTechnologies)

R.Clarke (RandallLaboratory of Physics,U.of Michigan)

L.Berman (NSLS)

Material systems periodic in two dimensions and

aperiodic in the third (2D crystals) are very interesting

scientifically and often very important technologically.

Crystal surfaces, crystals with epitaxially grown layers of

another material, and interfaces, are all 2D crystals. They

are scientifically interesting because physical and chemical

phenomena at suri%ces and interfaces are often different

from those in the bulk, and are technologically relevant

because many devices depend for their performance on

material interfaces. Systems with an interkce between a

crystal and an amorphous material (e.g., Si and its oxide)

are not ideal 2D crystals. However in the region of the

interface, they do have partial two-dimensional

periodicity. Finally self-organized systems on crystalline

surfaces are also 2D crystals and are currently of great

interest both scientifically and technologically. Knowing

the structure of these systems is crucial to understanding

their properties and to the development of new processing

techniques and devices.

V3rious x-ray methods have been used to investigate

the structure of 2D crystak. These include reflectivi~

and diffuse scattering 1,21, high resolution x-ray

difFraction131,Multiple diffraction141and standing wavesL51.

In ail these methods, the structure cannot be directly

determined. Instead it is necessary to first guess a structural

model and then refine its parameters to obtain best fit

with experiment. A step in overcoming this difficulty has

been the development of a method to determine the layer

structure using anomalous reflectivity[q.

In this paper we present a new x-ray method to

determine directly the atomic structure of 2D crystals.

We have successfully tested the method both in

f

reflected

beam

n

GaAs

Figure T-16: Schematic diagram of the experiment. The sample consists of a GaAs crystal cleaved

along the [110] plane. 4 monolayer of AIAs and 20 monolayer of GaAs were grown epitaxially on

its surface. Two samples were prepared, with and without a 2000A gold overlayer. The gold film

was used in order to measure the phase derivative along the Bragg rods as described previouslyl’’al.

. .,

. ..’ .“ .,’; ,’

.—

2-96
simulations and in actual experiments. Using this method,

we can determine the structure dkectly without the need

to presuppose a structural model. As in all direct methods

we measure not only the amplitude of the scattering factor

but also its phase. The method we developed is general

but it will be easier to explain using an example, shown

in Figure T-16.

We consider a material system composed ofa threedimensional semi-infinite crystal with a known structure

and a 2D crystal with an unknown structure. By

definition, the 2D crystal is the difference between the

whole system and the ideal 3D semi-infinite crystal. In

our example, the 3D crystal is GaAs, extending all the

way to the sample surface. The unknown 2D crystal is a

few monolayer ofepitaxialAL4s and its electron densi~

is equal to the difference between the electron density of

the ideal GaAs and that of the AlAs. Notice that if the

GaAs is distorted relative to the ideal structure the

difference will also show up in the 2D crystal representing

the epitaxial AL% and its interface with the GaAs.

The 3D crystal defines a 2D grid on planes parallel

to its surface. At first we assume that the 2D crystal is

periodic with respect to this grid. The complex scattering

factor of the semi-infinite substrate crystal S(kJ is wel.ldefined because its structure is known. However, the

scattering factor of the 2D crystal D(k), which will

contribute to the scattering intensity along the Bragg rods,

is not known. What is dhectly measured is the absolute

value of the total scattering factor ITl which is the absolute

value of the complex sum of the two. We now consider

two points along a Bragg rod at a small separation Akz

from each other. Then,

(1)

S(kz + Akz) + D(kZ +Akz)

Here, ~(kZ ) is the unknown phase of T and &@kz is

the derivative of this phase along the Bragg rod. Notice

that these equations cannot be solved for the complex

scattering factor of the unknown crystal, D(k) because

~(kz) is not known. We have recently developed, and

experimentally demonstrated, a method to measure the

phase derivative ~@3kz along the Bragg rods17’81.In

principle one could integrate the measured phase

derivative in order to obtain the phase itself. The problem

is that even a small amount of noise in the experimental

data produces large errors in the phase, rendering the

method useless. It was therefore necessary to find a way

to use the phase derivative dhecdy without the need to

integrate.

In Eqs. 1 and 2 we have assumed that the real-space zero

reference point of the x-ray dielectric fimction is at the

sample surface. If this reference point is shified in the z

direction by ZO,Eqs. 1 and 2 will have the form:

S(kz)eik’% + D(/cZ)eikz%= l~(~Z)leip(k’)eikZz”

S(kz + Akz)ei(kz+Mz)’” + D(kz + Akz )ei(~z+~z)%

= T(kZ + AkZ )leiI~(~ZJ+~9/a~~~* lei(~Z+~Z)%

We now find a ZOvalue such that

~– = l~(kZ) – ~(kZ + Akz)l

(3)

(4)

(5)

has a minimum. Here ~(kz ) = D(kZ )ei~’a . Notice

t~at in this case the complex numbers ~(kz ) and

~~+~ have the same argument. If ~– is at its

minimal value, its~bsolute value will be in general small

compared to AS and AT and can therefore be

neglected. Then the absolute value of the difference

between Eqs. 3 and 4 has the form:

S(kZ + AkZ)ei&ZzO –S(kZ) =

llT(kz +AkZ)le i&p I akzzikzeiAkZZ.

-lT(kZ)ll (6)

Notice that here all the values except for zfiare known. So

thk equation can be used to determine z;. We can now

use the ratio between Eqs. 3 and 4 to determine ~.

Where,

~ = D(kZ)eikz% s D(kZ + AkZ)ei(kz+Nz)% (8)

This procedure provides D(k) for all relevant Bragg rods

in reciprocal space. Back-Fourier transforming it in threedimensions into real space, provides the 3D real space

dielectric fimction E(~,z). Here ~ is the position vector

in the 2D unit cell and z is the distance in the direction

normal to the plane of the 2D crystal.

It turns out that in many systems the value of ZOcan

be estimated without measuring d~ /dk, along the Bragg

rods. In systems where the thickness of the unknown 2D

structure is small compared to its distance from the crystal

surface, 20 is approximately equal to this distance. In this

case Eq. 6 can be used to determine d~ /~kz and Eq. 7

to determine the value of D.

The method we developed is also applicable if the

unknown 2D system is not fidly periodic with respect to

the 2D grid. It can be shown that in this case the exact

same procedure provides an average complex dielectric

function &(j5, 2)

2-97
1 &(f3>Z)=~~&(f3+Rj>Z) (9)

j

Here, ~ is~ position vector in the substrate-defined 2D

unit cell; ~ is the 2D position of the jthunit cell, z is

the distance from the nominal interface and the sum is

carried over ail 2D unit cells.

We have demonstrated this method experimentally

using the system shown in Figure T-16. The diffraction

profiles were measured along one Bragg rod from

[-5 -1 1] to [1 5 1]. The data were then analyzed using

the method discussed above, resulting in the complex

scattering factor along the Bragg rod. This was then backFourier transformed in one dimension resulting in the Al

density as a fimction of the distance from the crystal

In Figure T-17 we show the AI concentration as a

fimction of the distance from the surface. The top curve

represents the Al concentration obtained from simulated

diffraction data calculated for the nominal sample used

in the experiment. We included in this data noise and

background typical of those we have in our experiments.

The results are shown in curve (c). Each peak in the figure

represents one monolayer. The distance between

monolayer is 2A, namely we have atomic resolution.

Notice that the analysis indeed faithfldly reproduces the

initial structure.

Curves 2a and 2b represent the structure obtained

from the analysis of the experimental data. Note that Al

is present not only in the 4 monolayer that were intended

as the AlAs 2D crystal, but also there is some Al

concentration in one or two addkional monolayer which

surface. were intended to be pure GaAs. On the other hand the

I

1 I 1

3.0 -

2.5 -

-7

.=

5

a 2.0

.=>

g

p

; 1.5 -

.+- 0

mL

~ 1.0

0

K

o

: 0.5 -

0.0 -

c

--A.

I

I

I

a

\ 1

‘1

1 1 I I ! I I

o 20 40 60 80

distance from surface [A]

Figure T-17. Al concentration as a function of distance

from the sample surface. (a) and (b)- experimental results

of two different samples. (c) The structure reconstructed

from simulated data. All the results shown here were

obtained without using the phase derivative along the Bragg

rods.

2-98

structure of the cleaved crystal seen on

the right of theAIAs layer has hardly been

aKected. It is also interesting to notice

that the number of GaAs monolayer

above the AIAs layer is different in the

two samples in spite of th; fact that the

two samples were grown simultaneously

but at two different places in the growth

chamber.

It should be emphasized that the

results shown in Figure T-17 are from

analyzing just one Bragg rod.

Determining the complex scattering

factor along all the relevant Bragg rods

and back Fourier transforming the results

in 3D will provide the positions of the

various atoms in the 2D-unit-cell as a

function of the distance from the surface.

In conclusion, we have

demonstrated a method to

experimentally determine the complex

scattering factor along the Bragg rods of

a 2D crystal. We have shown that using

this data we can determine the structure

of the 2D crystal by back-Fourier

transforming the results. We expect that

this method will be useful in the

investigation of crystal surface structures,

interfaces between a crystal and

epitaxially grown layers, crystal-melt and

crystal-solution, and self-ordered systems

grown on a crystalline surface. The

method can also be also used to

investigate structural phase transitions at

surfaces and interfaces. ■
REFERENCES

[1]

[2]

[31

[4]

[51

[6]

[71

[8]

S,K. Sinha, M.K. Sanyal, S.K. Satija, C.F. Majkrzak, D.A. Neumann, H. Homma, S. Szpala, A. Gibaud, and

H. Morkoc, Pbysic4 B198, 72, (1994).

l?F. Miceli, Semiconductor Interfaces, Microstructure and Devices: Properties and Applications, edited by

Z.C. Feng, IOP Publishing, Bristol UK, p. 87, (1993).

I.K. Robinson and D.J. Tweet, Reports on Pro~eu in I%ysicsj55,599, (1992).

S.L. Morelhao and L.l? Cardoso, J ofAppl Pbys., 73, 4218, (1993).

J. Zegenhagen, Surjace Science Reports, 18,199, (1993).

M. K. Sanyal, S. K. Sinha, A. Gibaud, et al., Zuroykysic$ Letters, 21,691, (1993).

Y. Yacoby Solid State Comm., 91,529, (1994).

H. Bakes, Y. Yacoby R. Pindak, R. Clarke, L. Pfeiffer, and L. Berman, Pbys. Rev. Letten, 79,1285, (1997).

..

.

.

.-

2-99

●

30.4

=0,2

~

s 000

32

Thets(degrees) 32,25 -
-.

John B.Parke

SUNYat Stony Brook

NSLSUsers’Executive Committee Chairman

The NSLS users held their Annual Users’ Meeting

on Tuesday May 19, 1998 at Brookhaven National

Laboratory (BNL). It allowed many users to meet the

new BNL contractor, Brookhaven Science Associates

(BSA), for the first time, obtain the latest news from the

Department of Energy (DOE), and review and celebrate

scientific accomplishments. On the Monday and

Wednesday bracketing this meeting, users attended a total

of six workshops.

The meeting began with an extended introduction

by Peter Paul, BNL Deputy Director for Science &

Technology. John Marburger, Director of BNL then

elaborated on the-se remarks, pointing out that users of

the facilities at BNL are its primary customers and

summarizing some of the trauma which resulted in the

termination of the AUI contract to operate BNL and the

succe.ssfid bid by BSA. He indicated a willingness to

represent the interests of users in Wmhlngton DC, and

particularly the need to improve infrastructure and user

support.

The subject of the meeting then turned to science.

Larry Carr of the NSLS gave a presentation entitled

“Infrared at the NSLS - A Long Wavelength Probe of

Smali Things on Short Time Scaies”. Larry described

the facilities at U121R along with @ctra showing the

performance advantage over conventional sources. The

signal throughput for small samples exceeded that

obtained with the spectrometer’s internal source (a high

pressure mercury arc lamp) by more than 2 orders of

magnitude in the far infrared. Spectra down to 1 cm-l

were shown, includlng an observation of enhanced signal

at 1.4 cm-l (42 GHz).

Cev Noyan of the T.J. Watson Research Center of

IBM described the “Determination of Mechanical

Properties of Thin Film Interfaces with X-Ray

Microdiffraction” at the X20A beamline. The (buried)

interfaces between polycrystalline Al, Cu and W thinfilm features and their substrate (single crystal Si) were

characterized using the Si (OO4) reflection. Topographic

images of the Si around and under the metallization

I

John Marburger, New Director

of Brookhaven National

Laboratory, updating users on

recent changes at BNL and its

new manager, Brookhaven

Science Associates.

3-2
,

1

i

features were constructed, showing that a fidly elastic Barbara Illman (University of Wisconsin, USDA/

“mosaic” structure develops in the Si under the thin film

features.

The first speaker after the morning break was

Michael Hart, Chairman of the NSLS. He pointed out

the positive light in which the NSLS was painted by the

recent BESAC review and that the FY99 presidential

budget includes an increase for support of users of some

5.2Y0. He cautioned, however, that these increases might

prove illusory Michael Hart also pointed out the dramatic

increase in the number of life science users over the past

5 years and the expectation that they will soon constitute

the largest user group at the NSLS.

Some of the concerns with fimding by the U. S.

Department of Energy (DOE) were addressed by Robert

Marianelli, Director of the Division of Chemical Sciences

for the Office of Basic Energy Sciences (BES). He assured

the users of the importance of basic science to the mission

of the DOE. The BES program contributes 2 billion

dollars per year, or 17’%0of all federal finding for the

physical sciences. In response to questions regarding the

budget negotiation process, he agreed that it is every

citizen’s right to make their elected representatives aware

FS Forest Products Lab) next described part of her research

program at beamlines X26A and X27. With the

microprobe at X26A, she and collaborators are employing

new, non-destructive synchrotrons tecluiques for detecting

iron and manganese oxidation states in wood to study

biochemical mechanisms of fimgal decay. She and Betsy

Dowd (NSLS) work at X27 to develop novel synchrotrons

techniques for element mapping in 3-dimensional images

of preservative-treated wood.

In the time remaining in the morning session the

users had an opportunity to thank representatives from

NSLS staff and BNL Plant Engineering who worked to

repair power cables responsible for a shutdown in

December 1997. The repair to the NSLS were so well

managed that most users dld not know there had been a

major power ftilure until the User Meeting.

The Scientific Highlight speech was given directly

after lunch. NobelistJames Warson, President of the Cold

Spring Harbor Laboratory, presented a retrospective of

hk lif<s work “From the Double Helii to the Human

Genome Project”. This was followed by a presentation

by Wayne Hendrickson of Columbia University/HHMI.

of decisions which adversely affect their interests. In collaboration with researchers from Dana-Farber

Left to right, NSLSAnnuai Users’ Meeting Organizing Committee: John Hili(BNL Physics),Harald Ade (NCSU),

Nancye Wright (NSE), Eiaine DiMasi (BNL Physics),Linda Feierabend (NSLS)and John Parise (SUNYat Stony

Brook).

,.

,

3-3 ,
Cancer Institute, SmithKline Beecham Pharmaceuticals,

and Tdane UniversiT Medical Center, they were able to

obtain small crystals of the HIV-1 gp 120 envelope

glycoprotein in complex with the CD4 receptor and a

neutralizing human antibody. The crystals were needles

of only 30-40 microns in cross-section, and required the

intense synchrotrons radiation on NSLS beandine X4A

for data collection. They were able to solve the structure

at 2.5 ~ resolution. The structure reveals the details of

the CD4-gp 120 interface, a conserved binding site for

the chemokine receptor, evidence for a confirmational

change upon CD4 binding, the nature ofa CD4-induced

antibody epitope, and specific mechanisms for immune

evasion. The results provide a framework for

understanding the complex biology of HIV entry into

cells and should guide efforts at intervention.

Ian Robinson of the Physics Department, Universi~

of Illinois, Urbana spoke about grazing X-rays and

electrochemical interfaces. The examples presented

included the electrochemical oxidation of copper,

specifically at the Cu(l11) surface. Structural studies of

the native oxide formed in air show an epitaxial film of

CU20 (cuprite) which gradually thickens over several

hours following electropolishing. Both hexagonal

orientations of the interface form simultaneously with

equal proportions. The situation is very ddlerent in acidic

solution, where the oxidation and reduction can be driven

by an external potential. There, only one epitaxial

orientation of the film is found to

grow thick; the other orientation

forms, but always remains a single

monolayer in thickness.

Peter D. Johnson of the

BNL Physics Department gave a

talk on recent advances in High

Resolution Photoemission applied

to the study of low dimensional

oxides, in particular the High T=

superconducting materials. New

developments in instrumentation

now allow the energy and angular

distributions of the photoelectrons

to be measured in parallel, and

with much higher energy

resolution than in earlier studies.

The Keynote Address was

delivered by Dr. Ernest J: Moniz,

Under Secretary of Energy at the

US Department of Energy. Given

the recent history of BNL, his

opinions were of interest to an

audience beyond the users of the

NSLS and the numbers of people in the auditorium

swelled during his presentation. Dr. Moniz began by

commenting that BNL is regarded as amongst the best

of the research laboratories in the country and that the

new BNL management team lead by Dr. John Marburger

is “hitting the ground running”. He also emphasized

that the recent Birgeneau report, which emphasized the

growing importance of the four DOE synchrotrons in

the nation’s research programs, praised the NSLS for the

number of users served and its education and outreach to

new users.

Other important parts of the meeting included the

reception the evening before the meeting, poster sessions,

a barbeque luncheon outdoors under a tent and an

equipment exhibit attended by 17 vendors. All were held

in Berkner Hall and all were popular with the users. The

election of three new members to the User Executive

Committee took place during the Annual Meeting John

Hill (BNL Physics Department), Carol Hirschmugl (U.

of Wisconsin), and Lka Kelly (U. of Maryland) were

elected as general members, and the UEC chose Barbara

Illman to be its Vice-Chair (Chair-Elect). The Annual

Meeting was capped off that evening by a banquet at the

Port Jefferson Country Club which overlooks the Long

Island Sound. ■

Left to right: John Parise (SUNY at Stony Brook), current NSLS User

Executive Committee Chairman; Carl Zimba (NIST); and Joel Brock

(Cornell U.)former UECChairman, between User Meeting sessions.

3-4
Usin Powder Data to Solve

CrysFal Structures

David Cox

Peter Stephens

(SUNY@Stony Brook)

This workshop, held on May 18,1998 at the Annual

NSLS Users’ Meeting, was motivated by the recent rapid

advances in the application of powder diffraction

techniques to the ab initio solution of unknown

structures. In contrast to the well-known Rietveld method

for structure refinement, this is a relatively new application

which has been driven mainly by the development of highresolution synchrotrons x-ray techniques, especially for

framework structures such as zeolites, fullerene derivatives

and other molecular compounds, and small organic

molecules of pharmaceutical significance. The roughly

80 attendees were treated to a state-of-the-art exposition

by an international cast of speakers from the USA and

Europe, where much of the cutting-edge work in this

field is currently taking place.

Afier Henk Schenk (U. ofAmsterdam) started the

proceedings with an introduction to the use of direct

methods for structure solution from powder data, zeolites

took center stage with talks by Lynne McCusker (ETH,

Zurich) about her structural “toolbox” and two new tools

for solving zeolite structures, texture and structure

envelopes, and Ralf Grosse-Kunst_leve @.le U.) on a third

new tool, which allows usefi.dcrystal chemical idormation

to be incorporated via Fourier recycling and a search for

unique topologies (the “FOCUS” method). John Newsam

(Molecular Simulations Corp.) described some successfid

approaches to structure determination based on model

construction and simulated annealing, and Dick Harlow

(DuPont Corp.) closed out the morning session with an

update on the $1000 “DuPont Challenge”, to be awarded

to the first person to solve the structure of HAIF4 (an

intermediate product in the industrial synthesis of AIF~

catalysts) from powder data collected at the NSLS. No

winner has yet been announced!

Molecular and organic compounds were the focus

of the afternoon talks, led off by Ken Shankland ,’

(Rutherford Appleton Lab.) with a description of real- ~

space techniques that are suitable for organic molecules,

including examples of structures solved by simulated

annealing and genetic algorithms. Jim Kaduk (Amoco

Corp.) discussed the structure solution of several

moderately large organic molecules using more

conventional techniques, whale Robert Dinnebier (U. of

Bayreuth) compared standard tools (such as direct

methods) and some unconventional algorithms, including

extended use of chemical constraints and rigid bodies,

grid searches, and the use of pseudo-atoms for compact

units such as phenyl rings to a variety of structure

solutions.

Peter Stephens (SUNY, Stony Brook) discussed

several aspects ofline.shape modelling, inch.dng a newlYdeveloped algorithm for handhng anisotropic broadening

due to lattice strains, and in the final talk, Bob Von Dreele t

(Los Alarnos National Lab.) described some first attempts j

at protein crystallography with powder samples, in which

with appropriate constraints he was able to refine the

structure of whale myoglobin (1401 atoms in a 65,OOO

~ 3 unit cell!) from high-resolution data taken at the ~

NSLS.

On this impressive note, Peter Stephens closed the

meeting by urging the audience to make more use of the

several high-resolution synchrotrons powder instruments ,.

available, and to apply these powerfid new tools for

ab initio structure solution to more complex materials of

scientific and commercial interest.

The success of the workshop was in no small part

due to the support of the following sponsors whose

generosiV is gratefidly acknowledged: the International

Cemre for Diffraction Data, Air Products, Amoco,

Chevron, Clariant, Mobil, UO~ SUNY X3B1 Powder

Diffraction Facility, X7A PRT. H ‘1

‘

(,
. .... . .. .. . , .: ,.,-;,.’ , “ ., . . .’.. ,. ; ,,-

:. ,

. . -t:. “.. .“ ,“.

,—-———. ..—.-.—.——— (

h Situ Surface I

Manipulation 3

Ian Robinson I

(Universityof Illinois@ Urbana) I

-. —..—---——..— -A

A workshop on in situ manipulation of surfaces

using X-Ray diffraction methods was held in conjunction

with the Annual NSLS Users’ Meeting on Wednesday,

May 20, 1998 from 9:OOam to 5:30pm. The workshop’s

emphasis was the structure and properties of surfaces and

interfaces in their working environments. An exciting

and stimulating series of talks was presented, covering a

wide range of physics, chemistry and materials topics that

have been addressed by experiments at NSLS. Viuable

support for the meeting came from the Users’ Executive

Committee. The attendance varied from 25 to 50 as

participants selected parts of the program of interest to

them.

Bill Elliot from the University of Missouri spoke

about growth morphology of Ag during homoepitaqz

where he reported roughness exponents at different

growth temperatures. Hubert Zajonz from the BNL

Physics Department and Odlle Robach of the University

of Illinois compared their heteroepitaxial deposition

systems, Cu on Ru(OOO1) and Ni on Ag(OOl). New and

unique unit-cell structures are stabilized by epitaxial forces

in the thin-film state.

Joel Brock of Cornell University presented his new

results on the nucleation and ordering kinetics of Cu films

electrochemically deposited on Pt(l 11). His group used

a periodic drive of the applied potential to attain good

statistics with excellent temporal resolution. Mary Ryan

and Jia Wang of the BNL Department of Applied Science

then presented their respective structural studies of the

passive oxide film formed on iron and the T1-Br

coadsorbate on Au(l 11). In both cases, the chemical

complexi~ of these highly relevant compound systems

was impressive, and structural details down to the oxygen

site occupation and the Au displacements were discovered.

After an outdoor barbecue lunch, Ken EvansLutterodt of LucentTechnologies talked about a new kind

of order detected in very thin SiOz layers on Si, an

interface of great importance to the semiconductor

industry. A discussion broke out concerning the different

aspects of structure probed by reflectivity and truncation

rod measurements. This theme was developed i%rther

by Pulak Dutta of Northwestern University who spoke

about self-assembled and Langmuir monolayer on Si

substrates. Elaine DiMasi of BNL Physics followed with

animated results ofsurface segregation in liquid Hg alloys,

which showed very different temperature dependence

from pure Hg. Then Mike Bedzyk, also of Northwestern

University, introduced the standing-wave technique with

its in situ applications to the interface between calcite

and water.

Art Baddorf of ORNL introduced his original ideas

about dynamic Smoluchowski smoothing of surfaces and

its coupling to surface vibrations. High-frequency optic

modes lead to transient structures containing paired atoms

(just like in a reconstruction) whose electronic response

drives a bigger relaxation than in ideal non-vibrating

surfaces. The final speaker of the day was Joe Woicik of

NIST, who captured some overflow audience from the

already closed EXAFS workshop for his presentation on

EXAFS and diffraction determinations of InGaAs

interatomic spacings. H

3-6
Crystallography Under

High Pressure: %echniques

for Everyone

Jiuhua Chen

(SUNY@Stony Brook)

Synchrotrons radiation has greatly benefited high

pressure research. A high pressure apparatus has either a

very small amount of sample or a large amount of pressure

medium surrounding the sample; therefore, in situ high

pressure studies with x-rays have a great demand for

synchrotrons radiation. This workshop was held on May

20, 1998, in conjunction with the NSLS Users’ Meeting

and co-sponsored by the Center for High Pressure

Research (CHiPR). In this one-day workshop, the most

recent technological developments and scientific research

with synchrotrons radiation under high pressure were

reviewed. Ten invited speakers presented the latest high

pressure techniques and research at the NSLS,APS, ESRF,

SPring-8 and PF.

After a brief introduction by Jiuhua Chen

(workshop organizer, SUNY at Stony Brook), Donald

Weidner (Director, CHiPR, SUNY at Stony Brook) and

Russell Hemeley (CHiPR, Carnegie Institute at

Washingron) reviewed the research activities of the largevolume press (LW) and the diamond anvil cell (DAC) at

the NSLS, respectively. Many pioneer developments of

methodology and technology for LW and DAC, such as

theological measurement, uniform laser heating and

translating imaging plate system, were presented. A

comprehensive HP system includhg both LVP and DAC

is emerging at the NSLS. The studies have a very

important impact in understanding the interior of the

earth as well as some other aspects of physics and material

science.

In the late morning session, two special topic talks

on ultrasonic measurement of sound velocities with LW

and x-ray spectroscopy with DAC were given by Robert

C. Liebermann (CHiPR, SUNY at Stony Brook) and

Jean-Pascal Rueff (NSLS). Asimukaneous measurement

of ultrasonic sound velocity and x-ray diffraction has been

achieved for the first time at the X17B 1 beamline. This

development opens new opportunities for establishing

absolute pressure scales. Spectroscopic techniques,

including inelastic scattering, x-ray absorption and

emission, with a Be-gasket DAC provide valuable

information for understanding the electronic structures

of materials under Klgh pressure. A general dkcussion

on Rietveld refinement with energy dispersive powder

diffraction data using synchrotrons radiation light source,

as well as a neutron “heavy” source, was given by Robert

B. Von Dreele (Los Alamos National Laboratory), and

some pioneer trials of LaBeil fit and Rierveld fit for high-

-pressurediffraction data collected at the NSLS were also

discussed.

The afiernoon sessions focused on the reports of

high pressure research from the third-generation

synchrotrons radiation facilities. Francesco Serte (ESRF) \

presented the development of inelastic x-ray scattering

measurements in the .20 KeV energy region with energy

resolutions tunable in 1.5-7 meV range. Thk technique

overcomes the’ kinematic limitations of the traditional

neutron inelastic scattering system and favors high-

-pressure experiments with small samples. An overview

of the high pressure research at the ESRF was given by $

Daniel Hausermann. The high pressure cell has been a

I

widely accessed tool at the ESRF. In the past year, about

one thkd of the over 20 optimized bea.mhnes have been

used to carry out the high pressure experiments. The 12-

second cycle “Fastscan” imaging plate detector enhanced

the capabilities of LVP and laser-heating DAC.

Combining an 1P detector and a background-subtraction

technique, which was initiated at CHiPR, reaction and

synthesis kinetics was studied using the LW. Osamu

,
. . . . _—

Shimomura (SPring-8) introduced the recent high

pressure research in Japan (both Photon Factory and

SPring-8). The result of spinel - perovskite+perclase phase

boundary study using the double-stage large-volume

apparatus, SPEED 1500, was published as the first

research paper of the SPring-8 facility. The press offers

the highest pressure so far reached in an LVP in

conjunction with synchrotrons radiation.

The high-pressure research at GeoSoilEnviroCARS

was reviewed by Yanbin Wang (APS). Both the DAC

and LW systems at the APS have been complemented

based on the success of CHiPR at the NSLS. HPCAT is

a proposed integrated high-pressure facility at the APS.

David Mao (CHiPR, Carnegie Institute at Washington)

described the beamline design which will integrate the

well established HP x-ray diffraction programs and the

new frontiers in HP x-ray spectroscopy. H

Biologicaland Environmental

Applications

Barbara Illman

(Universityof Wkconsin)

-1

Biological and environmental sciences are

increasingly using synchrotrons techniques in diverse areas

of research. A workshop on biology and environmental

applications was held on May 18, 1998 in conjunction

with the 1998 Annual NSLS Users’ Meeting. This

workshop included research conducted on a variety of Xray and VUV beamlines at NSLS. Speakers dkcussed

current and future developments in X-ray computed

microtomography, EXAFS, microXANES, STXM, sofi

x-ray microscopy, fluorescence spectroscopy, and x-ray

crystallography for studies in molecular and

developmental biology, human pathology, bioremediation

of toxic wastes, impact of toxins on ecosystem dynamics,

plant pathology, and forest ecology. James Penner-Hahn

(U. of Michigan) presented research on spatial and

temporal imaging of Zn speciation during development

of fish eggs using microXANES. Paul Bertsch (U. of

Georgia) presented research on the distribution and

chemical speciation of metals and metalloids in

environmental samples by micro X-ray fluorescence and

micro X-ray absorption spectroscopes. Mark Chance

(Albert Einstein COIL of Med.) described the use of

synchrotrons X-radiation for studies on the structural

3-8

biology of RNA folding. Cathryn Lawson (BNL Biology)

told of protein crystallography to unlock the secrets of

the tick-borne pathogen that causes lime disease. Don

Huber (Purdue U.) told how microXANES was used in

monitoring oxidative reactions to determine basic

mechanisms of plant pathogenesis. Ulrich Neuhaeusler

(SUNY at Stony Brook) summarized the soft X-ray

spectromicroscopy research at XIA, including studies of

hydrated colloidal systems. Formation of a PRT for the

recently developed X-ray microtomography beamline at

NSLS was described by Barbara Illman (U. of Wisconsin,

Forest Products Laboratory). Two speakers gave talks for

this workshop and for the workshop on Applications of

Infrared Synchrotrons Radiation. George Flynn

questioned the potential of organic-carbon-based

molecules on extraterrestrial samples using FTIR and

STXM measurements. Lisa Miller (Albert Einstein Coil.

of Med.) presented applications of synchrotrons infrared

microspectroscopy to the study of biological cells and

tissues. The talks in this workshop represented

synchrotron-based research that is making an impact on

the biological and environmental sciences. 9
I

r

XANESand NEXAFS

Spectroscope :Theory

,and Applicat?Ions

L

Boyan Boyanov

(North Carolina State University)

As x-ray absorption spectroscopy (X&3) matures as

an analytical technique, more emphasis is placed on

understanding and quantifying the fine structure in the

near-edge region of the absorption spectrum. This year’s

workshop, which is the continuation of a series of XAS

Workshops held at the NSLS Users’ Meeting, reviewed

recent progress in theoretical, acquisition, and analysis

techniques, and facilities development at NSLS. More

than 80 people attended the workshop.

The current state of the full multiple-scattering

(FMS) technique for calculating XANES spectra was

reviewed by Bruce Ravel from the National Institute of

Standards and Technology (NIST). Bruce gave attendees

an overview of the development goals and capabilities of

FEFF8. Examples covered ranged from fairly routine

simulations of the near-edge structure of ~CrOA, to

difficult and time-consuming calculations for diamond.

The factors affecting the precision and difficulty of the

calculation, as well as the advantages and disadvantages

of the FMS method in comparison to molecular orbital

approaches, were dkcussed.

Stephen Wasserman from the Advanced Photon

Source (APS/ANL) described the application ofprinciple

component analysis (PCA) for chemical speciation using

XAS. Steve’s presentation included many useful tips on

practical issues, particularly on the difficult problem of

deciding how many components describe the data in

sufficient detail. The main advantages of the PCA method

are that it provides an estimate of the number of distinct

species observed in a series of measurements even when

detailed analysis is not possible, and the abil@ to test

whether a model compound is a constituent of the system

being examined, without the need to know the other

species present.

The present status of the Dow/NIST materials

characterization facility at beamline U7A was reviewed

by Daniel Fischer from NIST. The facility enables

experimenters to perform new soft-x-ray materials science

to study the chemical nature of diverse materials. Practical

industrial problems currently being investigated include

model catalyst systems, polymer surfaces and their

interfaces, hard disk lubricant chemistry, self assembled

monolayer, and high T= superconducting tapes.

Stephen Urquhart from North Carolina State

University (NCSU) discussed the use of XAS for the

characterization of polymer systems. Stephen’s talk

explored the chemical information content of polymer

NEXAFS spectra and the use of molecular models for

the interpretation of the relationships between polymer

structure-and x-ray absorption spect~a. He examined the

significant perturbations of high~resolution spectra caused

by electronic delocalization, and showed how the

chemical sensitivi~ of NEXAFS can be utilized to perform

chemical microanalysis of real-life polymers.

The final talk was given by Angelika Osanna from

SUNYStony Brook, who described the use of image stacks

at beamline XIA to obtain images of sub-100 nm

resolution of polymer and biological systems. Angelika

gave a real-time demonstration of the acquisition and

analysis sofhvare developed by Chris Jacobsen (also from

Stony Brook), and described ongoing efforts to extend

an existing database of amino acid spectra to oxygen and

nitrogen edges. ,

The workshop concluded with a discussion by the

participants of some outstanding issues faced by

researchers in the field. The discussion covered a wide .,

range of topics such as: the ability of self-consistent

calculations to minimize the need of ad hoc adjustments

I

I

3-9
to important model parameters; the widespread need for temperature dependence of near-edge spectra (or the lack

reference libraries, particularly of polymers and amino thereof); and the dependence of the detailed shape of

acids; the limited applicability of the widely used soft x-ray near-edge spectra on the experimental setup,

“gaussian+arctan” deconvolution of near-edge structure, particularly when electron or fluorescence detection is

particularly in inorganic systems where effects are ofien used, and its implications for the ability to quantitatively

very long-range in nature; factors that determine the analyze such spectra. ■

I Infrared Synchroiron I Radiation and Applications

~ Lawrence Carr I

: (Brookhaven National Laboratory, NSLS)~

This workshop was held on May 18, 1998 at the

NSLS and attended by approximately 60 people from

more than 25 different institutions. Gvvyn Williams

(NSL.S) began by reviewing the special characteristics of

infrared synchrotrons radiation (IRSR), the performance

advantages of the NSLS VUV Ring, and the bean-dines

specifically built to utilize this radiation. Presently two

IR beamlines are operational, and a third (for

microspectroscopy) is very near completion. The

remaining three IR beamlines have all delivered “first

light” and beam distribution systems are being

constructed. Wayne McKinney (Lawrence Berkeley

National Laboratory) described the design and

performance of their recently completed IR bearnline at

theALS, along with their successful effort to reduce noise.

A microspectrometer endstation is operational and already

in use for the study of micro-organisms related to

bioremediation. The high brightness of synchrotrons

radiation enables various measurement methods, such as

ellipsometry, to be applied to small specimens. Alex

Witdin and collaborators from the Max Planck Institute

(Stuttgart, Germany) have developed a custom

ellipsometer for use in the far infrared, and have studied

the “pseudo-gap” behavior in the c-axis response of small

high-TC oxide crystals. Grazing incidence reflectionabsorption spectroscopy is another method that benefits

from high brightness. Carol Hirschmugl (U. ofWkconsin

- Milwaukee) reviewed the grazing incidence technique

available at NSLS bearnline U41R and described two areas

. .

.,. —

3-1o

of active research; the study ofabsorbates on noble metals

and thin oxide films on various transition metal surfaces.

In the former case, additional insight has been gained

into the interaction between various types of absorbates

and the conduction electrons in the metal. Perhaps the

best illustration of high brightness synchrotrons infrared

enabling an existing, wide-spread measurement method

is microspectroscopy. John Reffner, former director of

research at Spectra-Tech, Inc. reviewed microspectrometer

instrumentation and pointed out areas where

improvements were still available in conjunction with the

synchrotrons IR source. He remarked that a reduction in

detector area could provide better signal-to-noise. One

of the earliest examples of microsampling with infrared

synchrotrons radiation was the work by Rus Hemley and

co-workers from the Geophysical Laboratory (Carnegie

Institution of Washington). Their program makes use of

an IR microscope-style optical system for probing

materials inside ultra-high pressure diamond anvil cells.

This group continues to investigate hydrogen at high

pressure and low temperature for evidence of metallic

behavior, as well as other “simple” materials such as ice,

for which a new quantum ordered phase has been

discovered. IR microsampling and chemical identification

of extraterrestrial samples was described by George Flynn

(SUNYat Plattsburgh). Interplanetary particles, collected

from the Earth’s upper atmosphere or extracted from

meteorites found on the surface, are typically

heterogeneous. Flynn’s group uses two different NSLS
I

I

x-ray beamlines for elemental and some chemical

mapping, as well as the infrared microspectrometer at

U41R for complete chemical identification. The latter

allows the identification of both mineral phases and the

presence of both simple and more complex (e.g. polycyclic

aromatic hydrocarbons) organic compounds. Lisa Miller

of the Albert Einstein College of Medicine presented two

examples of how synchrotrons infrared microspectroscopy

can be used to the study biological cells and tissues. In

her work on diseased bone (e.g. osteoarthritis),

microtomed sections of bone tissue are examined for

both protein and mineral content. By using an extrinsic

photoconductive detector such as Ge:Cu, the

microspectroscopy can be readily extended down to 400

cm-l. Thus, bone mineralization can be tracked through

both carbonate and phosphate vibrational features, and

differences between normal and diseased bone are spatially

resolved. The effect of typical cosmetic treatments on

the properties ofhuman hair were also shown. This work,

by J.-L. Bantignies (ELF Atochem), shows how IR

microspectroscopy can be used to image hair structures

(e.g., the cortex and medulla) and detect variations in

the water content as a fimction of hair treatment. The

last two presentations addressed applications of the puked

nature of synchrotrons raiation to the field of time-resolved

spectroscopy. Most synchrotrons sources produce light in

pulses shorter than Ins in duration. DavidThnner (U. of

Florida) discussed the U121R bearnline at the NSLS and

the synchronizedTixapphire Iasersystem that can be used

to perform pump-probe spectroscopy. A time resolution

of better than lns has been achieved. Initial

measurements on semiconductors and superconductors

were described, as well as several candidate experimental

systems. Richard Palmer (Duke U.) described an

interesting time-resolved measurement system proposed

for the Duke storage ring based FEL. Time-resolved

spectroscopy could be performed in a manner similar to

that being performed at the NSLS, namely pump-probe

spectroscopy using a synchronized laser as the excitation

source. I

[

)

3-11

\

i

,

t.

i

,

i

(

,

,

i


..—.

.

.. ’-., \

,,

Stephen Warner

VUV Ring Manager

Figure 1 shows the breakdown of the VUV Ring

operating statistics for the Fiscal Year 1997. The monthly

breakdown of most significant operational performance

statistics are presented in Figures 2 through 6. The

operational statistics continue to show improvement

above the record year of FY 1996. The fraction of the

time during the year resulting in unscheduled downtime

was only 1.5°/0. The probability that beam was not

available when it was scheduled for operations was only

2.38Y0. However the total beam time actually delivered

to the users was 6 hours greater than was scheduled, or

100. 1’% of scheduled. This resulted from the early return

from maintenance and a reduction in accelerator study

hours actually used. The accelerator performance

continued to improve with higher injection rates and

longer beam lifetimes. Injections are now routinely done

in less than 3 minutes with the average approaching 2

minutes. The beam lifetime had been lower due to higher

vacuum resulting from the two openings of the ring

during the year and due to vacuum leaks. However, from

August through the end of the year the lifetime has

exceeded the pre-shutdown values by about 8Y0. This

was achieved despite the new gas load introduced by the

new U121R mirror being inserted into the ring vacuum

chamber and a leak in the front-ends of two beam ports.

To help reduce the impact of these new gas loads, a new

beam scrubbing shifi (vacuum chamber conditioning

shift) was introduced during the owl shifi (0:00 to 08:00)

of the two day study period that occurs once a month.

This shift helps desorb the gas that was introduced by

these new sources more rapidly than would occur during

normal operations and helps reduce the base pressure of

the ring.

The major improvement to the VUV Ring during

this fiscal year occurred during the winter shutdown when

another large aperture beam port was installed for the

U21R beamline. The ceramic gap just after this beam

chamber had started to leak during the fdl 1996 and was

also replaced during the winter shutdown of the ring.

Despite the increased work load from the ceramic gap

replacement, the effective planning of the Mechanical

Group allowed the ring to be brought on four days early

4-2

and scrubbing of the vacuum with beam to take place

during the three day holiday weekend. This allowed

operations to begin on schedule but with longer beam

lifetime resulting from the reduced vacuum pressure.

During the spring, a front-end valve started leaking in

the half of the ring opened during the winter shutdown.

This valve was replaced during the May shutdown

requiring the same half of the vacuum chamber to be

vented again. Recovery to pre-shutdown values of the

beam lifetime required about the same integrated current

as the winter shutdown, but since this vacuum work had

not been anticipated, much of the beam scrubbing had

to be done during operations.

Other improvements in the ring resulted from

changes in the damping of higher order mode of the main

RF cavity and other changes in this RF control system.

Testing began on the implementation of a fast RF

feedback system on the main RF system. This system

should suppress the noise introduced by that RF system

on the beam and it appeared to work quite well when

operated by itself. However, when the bunch lengthening

RF system was also working the beam showed increased

fluctuations and will require more work to allow these

two systems to work together. Other improvements were

in the dkgnostics of the electron and photon beams. New

extended dynamic range Beam Position Monitor (BPM)

receivers were installed on aIl of the ring’s pickups. This

will allow measurements of the beam position down to

lower values of current. This of little concern for normal

operating currents but will help better understand the

electron beam model for the ring by allowing

measurements at low beam current. A new fmt turn-toturn BPM measurement system was prototype and the

full system should be operational in FY 1998. This BPM

will allow modeling of the non-linear properties of the

electron beam. Other diagnostic improvements that are

planned will help understand the fist beam fluctuations

and how to reduce their impact on the users.

The long awaited improvement in the VUV

radiation shielding did not take place during FY 1997, as

it was originally planned. This was due to the difficulty

in findhg suppliers of the heavy concrete shielding blocks.
However, this supply difflcul~ has been overcome and

the shielding is planned to be installed around half of the

ring during the winter 1997-1998 shutdown. Once the

improvement in the radiation levels in that half of the

ring is measured the remainder of the shielding will be

scheduled for a fi.nure shutdown. When the radiation

shielding has been installed new studies of the Top-Off

Method of Injection (TOMI) will be performed, in order

to demonstrate that TOMI offers the users the ultimate

improvement in beam stability over long time periods

both from the source and the optics points ofview. TOMI

will also eliminate the age old conflict between longer

beam lifetime and higher brightness of the photon beam.

To insure that the frequent injection pulses are not seen

by the users, new shorter pulse kickers will be installed in

FY 1998 to allow the injected beam to be added to the

stored beam with minimum disturbance to the stored

beam.

During the next fiscal year studies will be carried

out to increase the operating beam energy of the VW

Ring. This will continue the improvement in beam

lifetime that has dominated the past improvements. In

addition, studies are being carried out to develop methods

of providing for real-time variation of the undulator gaps

in the ring. Although this is common place on the high

energy rings, the lower energy of the VUV Ring makes

the impact of these gap changes more significant for the

other users. The initial studies to control the orbit and

betatron tunes proved insui%cient and addition correction

of horizontal-vertical coupling effects also will have to be

compensated. ■

Figure 1: The breakdown of

the VUV Ring usage based on

total time (not scheduled

time) for FY 1998.

VUVRing Time Usage

Unsched.O s. (1.86%)

Unsched.Downtime?13.39%)1

.Ops. (66.39%)

I

FY 1998 Ring Performance Statistics

Ave. fill Current: 830 mA

Ave. Charge Rate: 251 mA/min

Ave. Lifetime at 500 mA: 283 min

Total user integrated current:

3033 A-Hrs (126 A-days)

Total hours of operation: 5978 hours

Average operating currenti 507 mA

4-3
.“

— —.— —-——

VW Ring

Performance

FY 1998

350

300

250

200

150

100

50

0

800

~ 600

L

w

:400

E

200

0

Ott Dec Feb Apr Jun Aug

Figure 3: The total integrated current for

the VUV Ring accumulated each month.

Ott Dec Feb Apr Jun Aug

Figure 5: The VUV Ring vacuum pressure at

500 mA beam current averaged over each

month.

Ott Dec Feb Apr JLM Aug

Fkure 2: The VUV Rirwziniection charge

ra~e average over all fill; in ‘each month.

1

Ott Dec Feb Apr JLM Aug

Figure4 The injection current averaged over

al~fills in a month for the VUV Ring.

400

300

200

100

0

Ott Dec Feb Apr JLUI Aug

Figure 6: The VUV Ring exponential beam

lifetime at 500 mA beam current (seven

bunch operation only) averaged over each

month.

4-4
VUVSTORAGERINGPARAMETERSAOFNOVEMBER1998

Normal Operating Energy

Peak Operating Current (multibunch ops.)

Circumference

Number of Beam Ports on Dipoles

Number of Insertion Devices

Maximum Length of Insertion Devices

IJEJ

B(p)

Electron Orbital Period

Damping Times

Lifetime @ 200 mA with 52 MHz

(with 211 MHz Bunch Lengthening)

Lattice Structure (Chasman-Ch’een)

Number of Superperiods

Magnet Complement

Nominal Tunes (VX,VJ

Momentum Compaction

RF Frequency

Radiated Power

RF Peak Voltage with 52 MHz (with 211 MHz)

lesign RF Power with 52 MHz (with 211 MHz)

Synchrotrons Tune (vJ

Natural Energy Spread (o,/E)

Bunch Length (20)

(21 ~, with 211 MHz Bunch Lengthening)

Number of RF Buckets

Typical Bunch Mode

Horizontal Damped Emittance (E.J

Vertical Damped Emittance (sJ

Power per Horizontal Milliradian (1A)

0.808 GeV

1.0 amp (1.06 x 10’2e-)

51.0 meters

17

2

-2.25 meters

19.9 ~ (622 eV)

1.41 Tesla (1.91 meters)

170.2 nanoseconds

ZX=TY=13 msec; 7, = 7 msec

360 min

(590 rein)

Separated Function, Quad, Doublets

4

{

8 Bending (1.5 meters each)

24 Quadruple (0.3 meters each)

12 Sextupole (0.2 meters each)

3.14, 1.26

0.0235

52.886 l/11-lz

20.4 kW/amp of Beam

80 kV (20kV)

50 kW (10 kW)

0.0018

5.0 x 104, lb< 20 mA

9.7 cm (lb< 20 mA)

(36 cm)

9

7

1.62 x 10-7, meter-radian

23.5 x 10-’0 meter-radian (4.0x 109 in normal ops.)*

3.2 Watts

ArcSource Parameters

Betatron Function (ftX,pJ 1.18 to 2.25 m, 10.26 to 14.21 m

Dispersion Function (?lX,TLJ 0.500 to 0.062 m, 0.743 to 0.093 m

ax, = -p’ J2 -0.046 to 1.087,3.18 to -0.96

Yxy‘0 +%,yk,y 0.738 to 0.970 m-l, 1.083 to 0.135 m-l

Source Size (oX, o; 536 to 568 pm, >60 to >70 ~m (170-200pm in normal ops.)’

Source Divergence (OX,OJ 686 to 373 prad, 19.5 to 6.9 prad (55-20 prad in normal ops.)

— I Insertion Device Parameters I

Betatron Function (PX,PJ 11.1 m, 5.84 m

Source Size (OX,OJ 1240 pm, >45 pm (220pm in normal ops.)’

Source Divergence (tsX,OJ 112 prad, >7.7 prad (22 prad in normal ops.)’ *

SYis adjustable

4-5
\ ;“—z—–:;–—-:: ,‘ \

,/ ,

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,,‘

,, ,/‘

,:

f+,; ,/ ,J ,, ‘, ,

—— ‘F’. ,-

,’ ‘

/’“\ ‘$, “ ‘-

. —--:-k-~’iiY-i?IN.G :

Roger Klaffky

X-RayRingManager

During the November 18-23, 1997, 2.8 GeV

operations period and thoughout the December

shutdown, there was continued progress towards

completion of 2.8 GeV beamline shieldlng. Before the

March/April 2.8 GeV operations period, studies shifis

were set aside so that all lines could be approved for

operation.

There was a considerable amount of work

performed on various NSLS systems during the December

1997 shutdown. A primary aluminum water system heat

exchanger was replaced and a plugged high pressure

copper water system heat exchanger was disassembled and

cleaned. The aluminum water system control valve was

rebuilt and the the three deionizer systems were relocated

to make them more accessible. Additional 1 inch diameter

experimental water spigots were installed at several

locations on the X-ray floor. The X-Ray Ring RIA and

RIB interlock chains were physically separated in new

conduits running around the ring. The Critical Device

Overtemperature System (CDOS) was installed in the

Control Room and the installation of Klixon temperature

sensors at the output of existing Proteus flow meters

continued. The CDOS will dump X-ray beam if the

cooling water temperatures from critical ring components

(aluminum chamber, crotch, front end components, etc)

exceed specified setpoints. Presently there are interlocks

that will dump the ring if the global aluminum

temperature exceeds 105° F or if the power supply water

exceeds 115° F. Towards the goal of438 mA operation at

2.584 GeV, new Be windows were installed on X3B,

X16A, X16B, X16C, X18A, X18B, X20B, X22B, X27A

and X27C. There were three Be windows that still needed

to be replaced: Xl OB, Xl 1A, and X22C. New safety

shutters rated for operation up to 500 mA were installed

in the X21 and X25 frontends. The final requirement

remaining for high current operation was that a simulation

.

.—.

X-Ray Ring TimeUsage

-w mm%]

120

100

80

60

40

20

n

- ‘Ott’ Dec “Feb Apr Jun Aug

The breakdown of the X-Ray Ring usage based The total integrated current for the X-Ray Ring

on total time (not scheduled time) for FY 1998. accumulated each month for FY 1998.

4-6
and testing be completed to confirm a lifetime projection

for the 10 degree crotch assembly. In preparation for the

Spring 1998 shutdown, a 1.5 foot deep hole was cut

through the X-ray Ring shield wall for the installation of

a transmission line for a new RF cavity. The new hole

was required because the RF 1 and RF2 cavities have to

be split to provide room for the possible fkure installation

of another IVUN.

During the Spring 1998 shutdown, anew all-copper

cavity was installed replacing the existing RF2 cavity.

This system is unique, having two 125 kW amplifiers

driving a hybrid combiner capable of supplying in excess

of 160 kW to the cavity and beam. The original cavity

and drive loop limited this power to 100 kW. Anew allcopper drive loop with improved cooling and a refined

window design was also installed and tested to 150 kW

continuous input power. Prior to installation the cavity

underwent extensive testing in the NSLS RF test room.

The cavity was baked and achieved a pressure of

lxIO-J Torr while being powered to 60 kW. The new

window was tested at power levels of 120-150kW.

Running at 150 kW will supply another 60 kW to the

beam and allow the system to run more reliably at 35o

rnA with three transmitters if one system trips. The cavity

has also run to 65 kW, and when in operation will increase

the total voltage gradient to the beam, improving

reliabili~ when operating at 2.8 GeV. The new cavity

has improved cooling and superior internal surfaces which

will result in better vacuum afier conditioning. All higher

harmonic modes were damped with antennae to levels

lower than the other RF cavities. The RF resonant

frequency was successfidly corrected by replacing the large

Helicoflex vacuum seal with a larger cross-section seal.

Another major task planned for the Spring 1998

shutdown was the installation of the new Oxford

Instruments X17 superconducting wiggler. In preparation

for the wiggler, a loading dock was installed outside the

present location of the X17 refrigerator for the delivery

of 500 liter dewars. Double doors were installed. Duct

work was removed to make room for wiggler power

supplies. Before the Spring shutdown, a raised steel floor

was installed for the power supplies and water cooling

will be hooked up to these supplies. The new wiggler

installation had to be delayed due to problems

encountered during acceptance tests at BNL. Two specific

issues were identified as the new wiggler was being

prepared for cold tests. The first problem was a leak

between the helium and nitrogen vessels in the wiggler.

The other defect was an electrical short. Both of these

discoveries were cause for rejection. After consultation

with the manufacturer, a series of electrical checks was

performed in an attempt to pinpoint the electrical short

and to determine if the two defects were related. At that

point all agreed that repairs on site at BNL were not

feasible and arrangements were made to ship the wiggler

back to the UK for fhrther evaluation and repair.

The X17 straight section chamber downstream of

the wiggler was replaced during the Spring shutdown

because a water-to-vacuum leak had developed in the

cooling channel in the horizontal “speed bump”, which

protects X17 front end components from excessive

thermal loading. The leak first started November 21,

1997, and climbed into the 5x1 0-7 Torr region in

December 1997. When the water pumps were turned

back on at the end of December, a large leak opened up.

In order to resume operations on schedule in January,

the chamber was baked out and a pump installed on the

water channel to keep it evacuated during ring operation.

Because there was no water cooling, the wiggler had to

be turned off until after the chamber replacement

occurred.

The beryllium window replacement program, which

was begun in the Winter 96 shutdown, was completed

during the Spring shutdown. During this time, the

upstream-most beryllium windows in beamlines X-1OB,

Xl lAandX22C were replaced, bringing the total number

of beamlines upgraded to 38. Consequently all NSLS

X-ray bearnlines became compatible with ring operation

up to and includlng 438 mAmps at 2.584 GeV or 300

mAmps at 2.8 GeV.

There were a number of interlock tasks completed

during the Spring 98 shutdown. The X14A beandine

security system was converted from a Phase I system to a

PhaseII modular system and a Phase II system was

installed on the newX14B beamhne. Fast valve electronics

were installed for the X1O, X13, X14, X15, X16, and

X23 front ends. To render these systems operational,

their logic systems will be modified (so the X-ray Ring

will dump if they trip) or molybdenum fist valve blades

will be installed. The installation of cables for the Critical

Device Overtemperature System (CDOS) took place

bringing this system closer to completion. X-ray Ring

tunnel emergency stops were inspected and rewired where

required.

A number of electrical power distribution tasks were

also completed during this shutdown. A power panel

(SP8) inside the ring was moved to a more accessible

location. When the last panel is moved during the

upcoming Wkter shutdown, all power panels inside the

ring will have been relocated. Emergency power was

hooked up to X-ray Wand Booster micros, to back up

the existing UPS systems, and to the Biology Cold Rooms.

The deionizer pumps for the NSLS machine water

systems were moved to a more accessible location. New

4-7
—.

. —..—— ———- .-— —-.— _

hosing and proteus units were installed on different watercooled X-ray Ring components, as a part of the

maintenance program.

After the Spring shutdown, commissioning of the

X-Ray Ring went smoothly. The new RF system

parameters were adjusted to restore routine injection to

350 mA. The X17 Active Interlock syrem was recertified

for the new X17 chamber PUES downstream of the

wiggler. The chamber conditioned rapidly with the

wiggler at 4.7 T=la.

To track the horizontal motion of the X-ray ring

chambers, sensor stands will be installed and data acquired

during operations from high sensitivity LWT probes

.’

mounted on the stands at various PUE locations.

Ultimately, data acquired from the horizontal sensors

measuring the ring chamber motion at each of the 48

PUES during X-ray fills, will be input to the digital

feedback system to correct for this motion. Carbon fiber

tubes for the sensor stands arrived in March 1998.

Prototype stands were built and tested for thermal

stabiliqc

Studies of the low emittance lattice indicated that

addkional sextupole strength was required to operate with

the low emittance lattice at 2.8 GeV. Operations with

the low emittance lattice commenced on September 1998

at 2.584 GeV. ■

4-8
X-RAYSTORAGERINGPARAMETERSAOFSEPTEMBER1,1998

Normal Operating Energies

Maximum Operating Current

Lifetime

Circumference

Number of Beam Ports on Dipoles

Number of Insetilon Devices

Maximum Length of Insertion Devices

IJEJ at 1.25/1.36 T

%JEJ at 5.0 T (W)

B(p)

Electron Orbital Period

Damping Times

Touschek (0.25A)

Lattice Structure (Chasman-Green)

Number of Superperiods

Magnet Complement

32 Sextupole

Nominal Tunes (VX,VJ

Momentum Compa&lon

RF Frequency

Radiated Power for Bending Magnets

RF Peak Voltage

Design RF Power

v, (Synchrotrons Tune)

Natural Energy Spread (cr,/E)

Natural Bunch Length (20)

Number of RF Buckets

Typical Bunch Mode

Horizontal Damped Emittance (EJ

Vertical Damped Emittance (EJ

Power per Horizontal Milliradian (0.25A)

2.584 GeV/2.800 GeV

0.35/0.25 (1012 e-)

-20 hours

170.1 meters

30

5

<4.50 meters

2.23 ~ (5.6 keV)/1.75 A (7.1 keV)

0.56 ~ (22.2 keV)/O.48 ~ (26.1 keV)

1.25/1.36 Tesla (6.875 meters)

567.2 nanoseconds

TX=rY=6 msec; z,= 3 mseclq = ~Y=4 msec; r. =2 msec

>22 hrs (v~~= 804 kV)/ 57 hrs. (1120 kV)

Separated Function, Quad Triplets

8

{

16 Bending (2:7 meters each)

40 Quadruple (0.45 meters each)

16 Quadruple (0.80 meters each)

(0.20 meters each)

9.15,6.20

0.0056/0.0062

52.88 MHz

144/198 kW (0.25A)

804/1 120 kV

400 kW

0.003

8.6 X 104/9.2 X 104

10.5 cm

30

25

7.2 x 108/7.8x 108 meter-radian

7.2 x 1011/7.8x 1011 meter-radian

23/32

ArcSource Parameters m

Betatron Function (~,,~~ 1.0 to 3.8 m, 7.9 to 26.5 m

Dispersion Function (rIX,?l.J 0.47 to -0.11,-0.39 to 0.22

a = -p’ ,,42 -0.49 to 1.62, -3.4 to 4.5

I’x,y=r~ +%,J%,Y 0.952 to 0.962 m-’, 0.81 to 0.52 m-’

Source Size (OX,OJ 371 to 612 pm, 27 to 53 pm

Source Divergence (OX,OJ 476 to 324 prad, 9 to 7 prad

4

,

Insertion Device Parameters ,

Betatron Function (& ~J 1.60 m, 0.35 m

Source Divergence (OX,o; 260 prad, 35 prad

4-9
,.

Roger Klaffky

Beamline Technical Liaison

VUV BEAMLINES

There were a number of technical VUV beamline

improvements during FY 1998. In preparation for the

start of user operations on the U2B beamline, an infrared

microscope was purchased which, when utilizing the

NSLS as a source, will perform with a 1000-fold

improvement over the commercial instrument.

Recommissioning of the U3A beamline continued

with special emphasis on the beam requirements for

Advanced X-ray Astrophysics Facility (AXAF) X-ray

mirror reflectivity calibrations in the 1000-2000 eV

energy range. These requirements include adequate

stability for arcsecond alignment, a sharp beam profile,

less than 0.1 ‘Yobeam impurity and adequate flux for

energies up to 2000 eV. Monochromator upgrades

continued with implementation of lookup table based

tracking of monochromator crystal elements. Periodic

error corrections for both crystal rotary tables were

calibrated and energy scanning algorithms based on

lookup table tracking were defined, debugged and

implemented in a LabView monochromator control

program. Adequate tracking was demonstrated using

Na-~ alumina crystals for the 800-2100 eV range. Scraper

slits were installed downstream of the horizontallyfocusing mirror to achieve a sufilciently sharp beam

profile. The stabili~, alignment characteristics, spectral

purity, and flux characteristics for the beam in the 1-2

keV range were determined to be adequate for the AXAF

calibration program.

Design of the U3B diagnostic beamline was

completed and bids were received for fabrication and

polishing of the critical water-cooled mirror. Construction

was underway on the mirror vacuum chamber and

beamline support structure. The U3B beamline will

provide a previously unavailable energy measurement

capabili~ for the electron beam in the VUV storage ring.

.—--- .. .

, ,,/ ‘

On U3C a four-reflection high order trap (HOT)

developed by Hettrick Scientific was tested in order to

reduce photons outside the desired bandwidth to less than

1‘XOfor instrument calibration. This system has six sets

of traps covering different spectral regions up to 540 eV,

and provides beam purities greater than 99’%0below 250

eV. A HOT optimized for U3C was designed with the

intention of installing it in FY99.

As part of the DOE Facilities Initiative, spherical

gratings and a moveable slit will be added to the U4A

beamline, replacing toroidal gratings and freed exit slits.

The ARP chamber will be fitted with a sample transfer

and load lock system. Plans for these improvements were

finalized with installation expected in FY99.

In order to complete construction of the U7A soft

X-ray materials characterization facility, the former facility

was completely dismantled and reconstructed. The new

facili~ incorporates a refocusing mirror (commissioned

in FY98) which produces a sub-millimeter spot at the

sample position. The refocusing mirror also provides a

rapid means of switching the sofi X-ray beam from the

U7A monochromator between the surface science end

station and the materials end station. Also, a sample

manipulator and preparation/load lock chamber were

installed which allow rapid sample entry as well as catalyst

calcining and pretreating under atmospheric pressures.

The new sample manipulator allows multiple (3o) samples

to run in an automated fmhion.

The U9A NSLS storage ring vacuum R&D

beamline was completed in FY98. Photon-stimulated

resorption measurements were carried out on various

vacuum surfaces, includlng KEK B-factory chambers.

To optimize signals on the U9B fluorescence

spectrometer, an xyz sample positioning system was

installed with more than 1 cm travel in each direction.

Also, a new photomultiplier was installed to detect the

4-1o
intensity of light passing through the samples that are

being simultaneously monitored for fluorescence. The

process of upgrading the data acquisition system was

underway with the purchase of new control sof%vare for

the multiparameter analyzer.

The U1OA infrared beandine neared completion

with the installation of the front end mirror box and a

diamond window to separate the UHVfront end vacuum

from the rough vacuum ( or purge gas) used in the

instruments. The Bruker IFS66v/S infrared Fourier

transform vacuum interferometer was installed on the

U1OA beamline. Two reflectance units have been built

for the interfere- meter. The first allows the use of the

detector area inside the spectrometer. The second unit

employs a single reflection whereby light from the sample

is collected by a large mirror and then focused into an

external detector. This arrangement is used almost

exclusively for large, liquid-helium cooled detectors which

must be located outside of the spectrometer.

The U11 beamline was used for photoionization

mas spectrometry (I?IMS), high resolution angle-resolved

photoemission spectroscopy and absorption spectroscopy

of gases. The biology chamber quartz lens used to collect

fluorescence and focus it onto the entrance slit of an

emission monochromator was replaced by a custom-built

off-axis toroidal mirror, thereby extending the wavelength

range and improving efficiency by eliminating chromatic

aberration. Also, a 1.5 Tesla room temperature

electromagnet with optical access through the iron pole

pieces was in the process of being fit to operate atU11

for magnetic circular dichroism experiments.

During FY 98 all major components for the U12A

IRbeamline were procurred with installation of the optical

components and completion of the beamline vacuum

envelope expected by the end of 1998. Final alignment

and commissioning is slated for early in 1999.

The U13UB beamline is devoted to W/VUV

spectroscopy in the 5-30eV range. The U13 undulator/

wiggler source can be directed to either: (1) a focused

white light branch with variable ( O-1Ons) delay, or (2) a

high resolution (hv/Ahv > 104) monochromatic branch.

The monochromatic branch, which contains the bulk of

the mechanical and optical components of the entire

beamline, became fully operational in June 1998.

During FY98 the U15 bean-dine was used primarily

for studies of soft X-ray excited luminescence in doped

nanocrystals. To conduct these studies changes were made

to the U15 main chamber, and pumping systems. The

TGM monochromator motor control unit was

recommissioned. The U16B beamline was restored to an

operating condkion and made available to General Users

during FY98.

X-RAY BEAMLINES

The first tests of a new XIA scanning transmission

X-ray microscope were carried out in FY98. This

microscope has kinematic mounts for exchange of its

optics, and a motorized detector platform to allow rapid

exchange between different detectors, and positioning of

configured detectors by taking scanned images of detector

alignment. In its first test, these capabilities were used to

demonstrate (in collaboration with Denis Joyeux of

Institut d’Optique and Francois Polack ofLURE, France)

Nomarski phase contrast in a scanning microscope. The

successfid test of the basic components of the microscope

paves the way for implementation of the system in a sealed

chamber for spectromicroscopy at the nitrogen and

o~gen edges.

On the XIB bearnline, new refocusing optics were

installed and aligned. These changes should facilitate

experiments requiring high brightness such as those using

the soft X-ray spectrometers.

On the X3 beamline there were a number of

upgrades. The X3 beamline equipment protection

interlock was modified to include a front valve which

was previously unprotected. The X3A1 cryogenic system

was repaired to eliminate helium leaks and modified to

allow continuous operation during recharge. A new

1000x1OOO element CCD detector was installed in May

1998 which can be used on both the Al and A2 stations.

Progress was made in writing new diffractometer-control

sofiware in coordination with APS staff.

An Raxis-IV imaging plate detector was put into

operation on the X4A bean-dine during FY98. The

automation of the scanner resulted in a large improvement

for users. A further improvement will be made in 1999

when a CCD detector is installed to reduce the

turnaround time between exposures. On the X4C

bean-dine 1.5 horizontal mradians of beam was focussed

into 0.42 mm(FWHM) on the experimental table. An

ADSC single cell CCD detector system was purchased

and integrated with Windows driven PC sofhvare and

preliminary debugging of the motion control system took

place.

Further progress occured in FY98 towards running

strongly polarized hydrogen-deuteride ice (SPHICE)

targets at the X5 LEGS bearnline. There were 3 major

target production runs with the BNL dilution refrigerator

and 17 Tesla magnet system presently at Syracuse

University. Full size (3cm dia. x 5 cm long) HD targets

with over 50% H polarization were produced and

successfidly extracted from the dilution refrigerator. Afier

the first round of experiments has been completed, the

SPHICE target factory will be moved to the NSLS and

recommissioned in a new lab adjacent to the LEGS

4-11

I

i
—. ,. .—

beamline. To facilitate the production of SPHICE targets

a helium liquefier was obtained from the University of

Virginia. Work also took place on the construction of a

central drifi chamber to expand the spin assymetry(SASY)

calorimeter capabilities for charged particles (p,ti, m).

Final design and engineering work began and

construction of several components was underway at

several of the LEGS collaborating institutions. A

proto~e of the time projecton chamber (TPC) trigger

scintillator was constructed and successfully tested. A

major beamline upgrade was implemented providing a

new front-end transport system capable of switching

benveen an existing Ar- Ion laser and a new frequencyquadrupled Neodymium-Yttrium-Fluoride(Nd-YLF)

ring-laser system. The combination of this new ring laser

and the recent increase in the storage ring energy to 2.8

GeV has increased LEGS gamma-ray energies to 470

MeV. The first 470 MeV beam was observed in April

1998.

Stimulated by an effort to develop a facility to

perform time-resolved in-situ measurements of

catalytically-active materials, several changes were

implemented at X7B during FY98. An externally

exhausting fume hood was installed to vent both the

hutch and a commercial gas cylinder cabinet, in order to

satisfy safety standards for gas flow and reactivity

experiments. To reduce heat loading of the

monochromator crystal, graphke wtiers were inserted in

the beam-defining slit package located upstream of the

premirror position. A new portable detector/sample trolley

system was designed and constructed. The heart of the

sytem is a MAR 345 automated detector system based

on image plate technology. The system makes it possible

to adjust the sample to detector sparation over more than

a meter with 50 micron accuracy. The detector system

can also be moved above and below the plane of the

incident beam by 30 degrees with 0.01 degree accuracy.

The entire assembly sits on a kindmatic mounting system

that makes alignment of the detector system simple and

reproducible. Finally, A Labview based NSLS DAC

beamline control system was implemented during the

second half of FY98.

Operations expanded on beandine as it became a

dedicated station for X-ray footprinting. A dedicated

stopped-flow mixing device was constructed and put into

operation. This device enabled experiments on a 10-20

millisecond or longer timescales. The efficiency of

operation of the X9B X-ray spectroscopy bearrdine was

enhanced with software and hardware advances in

beamline control. There were improvements to the

AUTOFIT1.2 package which allows tue use of advanced

ab initio XAS codes by users understanding structural

analysis.

4-12

At X1OA and X1OB a new two-dimensional CCD

detector(Bruker Smart 1500) was purchased to enhance

real time measurements of small-angle and wide-angle

scattering. A new data acquisition and analyzing system

was also scheduled for installation. A Siemens FSD

scintillation counter was also purchased for use at Xl OA

and Xl OB. This detector handles count rates up to 10

counts per second, permitting some experiments to be

performed without attenuation. A new oven was

constructed for polymer stretching in order to investigate

the deformation process of polymers at elevated

temperatures. Conversion of the VAX beamline control

system to a LINUX system was also underway.

There were a number of upgrades and replacements

on the Xl 1A beamline in the past year. The operating

system on ail the PRT computers was upgraded and a

macro command utility was added to the data collection

software to allow automatic data collection as a fimction

of sample position, temperature, etc. The 13-element

Canberra detector was serviced to optimize its

performance. Commissioning and testing of a sagittal

focussing system continued. Anew computer controlled

slit assembly was installed. A new collimating mirror

was received and found to meet specifications when

measured at the BNL Instrumentation Division. Design

of a mirror support mechanism began.

The X13A SGM instrument was commissioned

with an existing grating. Two new gratings were procured

to make use of the EPW for magnetic spectroscopy

development. A new crystal monochromator was

developed for X13B for use with the IVUN and EPW.

A new beryllium window with two ports was

installed at Xl 5A to provide a 5 inch wide white beam

with a 1 mm thick aluminum filter for diffractionenhanced imaging (DEI), and a 1 inch wide white beam

for X-ray standing wave (XSW) experiments. The hutch

and bean-dine were reshielded for 2.8 GeV operation. A

rail system was installed under the XSW chamber to

facilitate switching from the XSWmode to the DEI mode.

At Xl 5B design, construction, and full

commissioning of a new room-pressure sample chamber

and hutch box took place. The upgraded chamber, which

complements the existing high vacuum( 106 - 10-g Torr)

and ultra-high-vacuum (10-10 - 10-12 Torr) chambers,

allows transmission or fluorescence X-ray absorption

measurements in air or controlled atmosphere at room

or cryogenic ( S 10 K) temperatures.

At X17B 1, the beamline control system was

upgraded by replacing the old V24X computer with a PC

Linux platform running a standard sofmare, SPEC. A

2048 by 2048 real-time CCD detector with 65 micron

resolution was used scattering experiments using high

energy X-rays of up to 90 keV.
Anew optical lab for pressure measurement was set

up near the Xl 7C beamline. It will develop into a new

Raman spectroscopy experimental lab in the future. A

new electric discharge drilling machine was set up in the

lab to enable users to drill rhenium gaskets for the

diamond anvil cell. A new Dell XPS R 400 workstation

1 was acquired for data analysis by users. In the future this

computer will replace the micro VAX beamline control

computer.

I At X18B the experimental hutch was enlarged and

cable feedthroughs installed to permit the use of a larger

array of experimental equipment, inch.dng solid state

I detectors. An additional fluorescent screen was installed

in the beampipe to facilitate alignment. The data

collection software was upgraded. A small device was

fabricated to collect a small part of the incident

monochromatic beam and reflect from a standard metal

sample to provide a reference spectra for thick or

supported samples used for fluorescence XAS.

The most significant bean-dine upgrade at X19A

was the replacement of the damaged zerodur mirror with

a new silicon mirror. A factor of 10 improvement in

throughput resulted with a significant decrease in the

focused beam size. Additional diagnostics were installed

for alignment purposes. At X19C an analyzer axis for

the detector arm was designed and implemented. This

enables detailed analysis of harmonic contamination on

white beam tomographs.

On the X20 beamlines filtering transformers were

installed for the protection fo the more control electronics

and beamline equipment safety systems. AISO, new

stepping motor controllers were installed for hutch and

diffractometer motors. Unshielded ribbon cables were

replaced with shielded ones and capacitance filtering was

installed on the E500 sustem for the new controllers. At

X20B New Focus Picomotors and a controller were

purchased for the tilt and bend of the monochtomator

crystal. Design of a vertical focussing mirror began. It

will intercept approximately 2mm of the beam and give

a 50 micron vertical FWHM spot at the sample position.

The mirror should provide a factor of 13 increase in

brightness and eliminate harmonic contamination. AII

IBM RS/6000 Model 590 computer was installed and

upgraded to AIX Version 4.2. This will serve as a fwtdata analysis machine, primarily for the in-situ phase

transformation studies done in real time at X20C.

AtX21 commissioning and operation of a 7-element

analyzer took place.

In addition to normal maintenance at the X22

bearnlines, there were a number of upgrades. At X22A a

new Pt-coated Si focussing mirror was installed. Also,

Soiler slits were upgraded for electrochemistry

experiments. At X22B a new Pt-coated Si focussing

mirror was also installed, the liquid surface spectrometer

was upgraded and a new U~ chamber for liquid metal

surface studies was completed: At X22C a new Pt-coated

Si focussing mirror was returned to the manufacturer for

repolishing because its roughness exceeded specifications.

An azimuthal rotation stage was fabricated for use on the

Franke-Heydrich spectrometer in studies of resonant

orbital ordering.

At X23A2 an energy discriminating SiLi

fluorescence detector was installed. ASO, the data

acquisition system was converted to a LabView based

system to record DAFS data.

At2C23B problems with the collimating mirror were

settled and the bea.rnline operated with good flux and

excellent energy resolution. This allowed minor problems

with the monochromator to be uncovered and f~ed. The

beamline computer was upgraded to a Power Macintosh

to increase the speed and to take advantage of the fidl

capabilities of the NSLS-DAC software.

At X24A a new UHV chamber for PRT members

and general users was brought into operation. The

chamber will have a hemispherical analyzer and precision

manipulator for surface science experiments.

Modifications were made to the downstream optical slit

assembly to permit the use of a feedback control of the

X-ray beam position over a limited range at the

experiment. The position control is desirable for

experiments such as EXAFS measurements or electron

spectroscopy.

New toroidal collimating and focussing mirrors were

received which should improve resolution at X24C by at

least a factor of two and increase flux at energies above

1000 eV The new mirrors will replace old paraboloidal

mirrors that had an effective roughness of 3 nm rms and

a figure slope error of about 20 microradians rms. The

surface roughness of the new mirrors is 0.5 nm rms or

less, and the slope errors are within 4 microradians of

circular.

A new front end safety shutter was installed to

permit X25 to operate at currents in excess of 350 mA (at

2.584 GeV).

At the X27A X-ray Computed Microtomography

bearnline, the computational speed of the reconstruction

algorifhm was improved by more than 10 times in FY

98. Implementation of a parallelized Pentium farm

provided another factor of 8 or better improvement in

reconstruction speed. More alignment and data

acquisition functions were automated in 1998 for user-

-friendly operations. Multilayers in the X27A

monochromator were replaced, as well as the Be window

on the output port of the monochromator. ■

4-13


ErikD.Johnson

DUV-FELProject Manager

It is certainly no secret that the activi~ at the source

development laboratory has become the Deep Ultraviolet Free Electron Laser (D W-FEL). Adopted as one

of four BNL initiatives, the D W-FEL has been the focus

of considerable activity in the last year. The objective of

the program is to provide a sound technological

foundation for sources and science that will lead to the

next generation of synchrotrons radiation based research.

BNL shares the view with many other laboratories that

these machines will be Free Electron Lasers, and that

getting to short wavelengths will require single pass

configurations.

The BNL effort has, from its inception, held the

view that to be usefid experimental tools these machines

must wed the best aspects of solid state lasers with

accelerator technology. The source must have the

characteristics of stability and optical quality people have

come to expect in laser technology, while operating at

wavelengths that are only readily accessible using

accelerator based amplifiers. The High Gain Harmonic

Generation (HGHG) approach proposed by Yu et al. is

the central concept for the DW-FEL.

A photon beam from a solid state laser is made to

couple with an electron beam in a short “energy

Photo A: @’emleft to right) RichardHeese,ErikJohnson and Bill Gravesreveal

the secretlocation of i!heDUV_FELi

5-2
modulation” undulator. This introduces an energy

modulation in the electron bunch that is converted to a

spatial modulation in a magnetic dispersion section. The

electron beam thus has a micro-bunching imposed on it

which has characteristics related to the seed laser. A second

longer “amplification” undulator is used to produce

coherent radiation at either the fundamental (same

wavelength”as the laser and microbunching) or a higher

harmonic (shorter wavelength than the seed laser). In

the HGHG scheme, the stability properties of the laser

(central wavelength, bandwidth, pulse length) are

translated into the FEL output, while the accelerator

effectively acts as an (optical) dispersion-free harmonic

generator and amplifier. In principle the scheme provides

exactly what we desire in a fourth generation source. In

practice, this all has to be proved experimentally which

is one of the main goals of the DW-FEL project.

To make this project possible, several years ago the

NSLS collected together an assortment of recovered

equipment that could be used to assemble the experiment.

The Source Development Laboratory (building 729)

houses the Iinac from the x-ray lithography project, and

a long undulator (NISUS) originally built for dkected

energy weapons research. For our D W-FEL project,

the Iinac must become a high brightness machine with a

photocathode gun as an electron source. To operate in

HGHG mode the DW-FEL needs a flexible laser system

not only to drive the gun, but to provide the seed beam

for the FEL. The demands on the laser are sufficiently

stringent that it was built specifically for this application.

The transformation of the linac from a ring injector

to an FEL driver has been guided during the last year by

Richard Heese and Bill Graves, and accomplished by a

great deal of hard work from people all over the NSLS.

This activity includes some ftirly basic infrastructure as

well as the novel technical developments one might

anticipate in such an endeavor. For example, precise

temperature control of the Iinac is required. In fact it

runs at 450C, while accessory cooling for power supplies

must be provided. The design of this system was

performed by the NSLS utilities group and installation

was accomplished with Plant Engineering personnel (see

Photo B).

To get its “Ckderella” treatment in moving from

ring injector to FEL driver, the Iinac had to be totally

reconfigured. This included the installation of a

photocathode gun by Xijie Wang based on his work at

theAcceleratorTat Facili~. Another major improvement

is the addition of a pulse compression chicane system

developed by Bill Graves to increase the peak current of

the electron beam, which will significantly improve the

FEL performance. This involves an enormous amount

Photo B: Some of the people responsible

for the installation and operation of the

process water system for the DUV-FEL.

Clockwisefrom Iejl, Mike Ponficiello and

John Fogus (Plant Engineering), Mike

Schwartz, Ron Beauman, and Lenny

Santangelo (NSLSUtilities).

5-3
. —.————— —.. —. . .

Photo C:Part of the crew responsible

for the mechanica/ design and

installation of the DUV-FEL Iinac

system. Fromfront on the left of the

beam dump, Mike Radulescu, Mal

Tardd, and John Skaritka. Working

from back tofronf on fherightside of

the beam dump, Pete DeToll, Chris

Stelmach, Bob Scheuerer and Skip

Thomas. Working /@tto right infronf,

J@Aspenleifec Dick Wiseman (hand

on transit), Mike Caruso and Bill

Bambina. In back (/@tto right) Sal

Pjerov, Peter Gross and Roger

Hubbard.

of mechanical work in design, fabrication and installation. in the deep ultra-violet. Apart from the technological

Only a handfid of the pe~ple who have worked on the

machine thus far were available for the picture given here

(Photo C).

A key element of our project is the integration of

laser science into the FEL. Lou DiMauro from the BNL

Chemistry Department has been leading this effort for

the DUV-FEL. The laser we selected is a Titanium

Sapphire system with a regenerative amplifier. It is a

chkped puke amplification system that produces adequate

power for running the photocathode gun and for seeding

the FEL. The chirped puke can in principle be used to

produce a chirped pulse amplified (CPA) FEL.

Simulations show that pukes the order of 10 femtoseconds

can be generated with puke energies of nearly a millijoules

developm~nt of the laser syst~m, extensions oflaser b~ed

science now practiced in the laboratory need to work their

way into the machine and the science it is intended to

serve. This has been part of our project philosophy from

the start, and we expect it to be important in making

FEEs genuinely usefil for research. Pa~t of the team

working with Lou on the laser systems is shown in

Photo D.

Of course once you have brought the components

together, you have to connect them, condition them, and

make them work. Reconfiguring the linac has been as

much an electronics and control task as a mechanical task.

During the past year, the linac computer control system

was entirely revamped to use the same type ofsofhvare as

PhotoD: fart of the laser

developmentgroup in thelaser

lab (clockwisefrom /q?) Brian

Sheehy (Chemistry), Todd

Clatterbuck (SUNY SB), Paul

Montanez (NSLS),and on the

wallpaperhereforthejlrst time

(virtual) Lou DiMauro

[Chemistry).

5-4
Photo E:Some of thepeople who

make the lina~ goj Clockwise

from left lim Garrison, Jefi

Rothman, Richard Heese, Bill

Graves, Charles Nielson, Kate

Feng-Bem?anand BoyzieSingh.

the NSLS machines. The electrical systems have been

brought up to current codes, and extensive modifications

to the low level RF drive system and interlocks were

performed to enhance their reliability. Finding and fting

each bug as it crops up is a demandhg task that requires

perseverance and experience. Fortunately the NSLS has

broad experience in this area as exemplified by the people

in Photo E. At the time of writing, the system has been

powertid up and high power RF conditioning of the

accelerating sections has been started.

During the next year, the plans include bringing

the Iinac into fill operation, and preparing our undulator

for conducting the first FEL experiments with the DUVFEL. Initially we will start running as a self amplified

spontaneous emission (SASE) FEL in the visible. In this

mode, a high quality electron beam passes through the

undulator and starts up from noise. From an

experimenter’s viewpoint, what you get is essentially loud

noise at the end, but it is a stringent test of the electron

beam quality and is less complex to operate than a seeded

beam FEL. As technological achievements allow, we will

move as rapidly as possible to seeded beam operation and

to shorter wavelengths.

The development of Fourth Generation Sources is

becoming an important priority for the DOE. Many of

the proposed experiments nation wide, inchdng parts

of the DW-FEL, are being conducted in collaboration

with scientists from universities and other national

laboratories. The DW-FEL project has progressed to a

state of development where it will be the focus of major

activi~ in this area over the next several years, and we

hope, in establishing the basis for future source technology

and science. H

m n &, d

oB

* ... =

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m

lb El

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Mapof theSDL,marked with the locations ofphotos

taken. (Athrough E).

5-5 >

I
I1an13en-Zvi #

ATF Head

The interest in Free-Electron Lasers operating in

very short wavelengths, down to hard x-rays, is growing.

A key aspect of the mission of Brookhaven National

Laboratory (BNL) is to construct, operate and use large

facilities for the breadth of scientific disciplines supported

by the Department of Energy. An important component

of the success of BNL comes from innovative accelerator

R&D, since new accelerator technologies hold the key to

new achievements in applications and user facilities. We

are now facing the emergence of a new technology very

high-brightness electron beams. This technology has far-

-reaching implications for x-ray sources and other

applications.

Part of the NSLS’ mission is to develop radiation

sources for the future. The NSLS has been the first light

source to pursue the development of Free-Electron Lasers

(FEL.s) as the next generation synchrotrons light sources.

BNL has been a leader in the national effort on FEL

development, hosting the workshops “Prospects of a 1 ~

FEL” in 1990 and “Towards Short Wavelength FELs” in

1993, as well as developing its Conceptual Design Report

and pursuing subsequent efforts to develop a national

collaboration in the field. In the past decade, the NSLS

made significant contributions to the science of FELs

suchas the theories on Universal Scaling of exponential

regime FELs in 3-D, the High-Gain Harmonic

Generation and beam conditioning. Experimentally we

have led in the development of record high-brightness

electron beams and methods of measurements of these

and the shortest wavelength measurement of Self

Amplified Spontaneous Emission (SASE).

The NW-S developed a vision of the next generation

of light sources and is assembling the beam physics and

technology to make this happen. Emphasizing single-pass

FEL amplifiers, which have advantages over oscillators in

the short wavelength regime where cavity mirrors are

unavailable, the NSLS developed the High-Gain

Harmonic-Generation (HGHG) FEL approach as a the

best strategy to build a high quality short wavelength FEL.

High-brightness electron beam R&D was undertaken in

a major way, since this is the key to achieving short5-6

wavelength FELs as well as other significant applications,

such as linear colliders, laser accelerators and more. The

BNLAcceleratorTat Facility (ATF) is the proving ground

for these advances.

What is the ATF? First and foremost, it is a user

facility for accelerator and beam physicists, operated by

the NSLS and the BNL Center for Accelerator Physics.

There is no other proposal-driven, peer-reviewed facili~

like the ATF that is dedicated for long range R&D in

accelerator and beam physics.

The ATF has a unique combination of a highbrightness electron beam, synchronized-high-power lasers,

a well-equipped 3 bearnline experiment hall, and advanced

diagnostics and control systems. The ATF’s program in

RF guns is recognized internationally. With its

synchronized lasers and electron beams of unprecedented

brightness, the ATF is an ideal site for R&D on advanced

accelerator concepts, FELs, femtosecond X-ray sources

and similar topics. These tools have been crucial to recent

ATF record achievements: the measurement of Self

Amplified Spontaneous Emission (SASE) at 1 pm and

0.63 pm, and laser acceleration by the Inverse Cerenkov

and Inverse FEL mechanisms.

The generation and acceleration of very high

brightness electron beams is a key technology for short

wavelength FELs as well as other applications, including

linear colliders, Compton backscattering for the

production of femtosecond x-rays, laser accelerators and

more. A high brightness means that the electron bunch

has a high density in 6-D phase space. To achieve high

brightness beams, it is necessary to do the following I)

Master the production of such beams in special electron

guns. 2) Develop diagnostics that provide information

of the 6-D distribution of electron bunches on subpicosecond time scales. 3) Control the 6-D distribution

of the bunch in various ways. 4) Accelerate the electrons

to high energies without diluting the brightness.

NSLS scientists working at the ATF measured the

slice emittance of a 10 ps electron bunch with a 1 ps

resolution, achieved a record high 6-D electron phasespace density and directly measured electron bunching
on an optical scale. Another diagnostic under

development at the ATF is tomographic analysis of the

distribution of electrons in transverse phase space. The

next step is to pursue non-linear emittance compensation.

Laser photocathode RF guns have provided a major

impro~ement in the bri~htness, which was further

enhanced by the introduction of (linear) emittance

compensation. The dream ofanother major improvement

by the introduction of non-linear corrections has been

brought within reach by the development of the sliceemittance diagnostic and phase space tomography.

Key to our plans is the development of subharmonically seeded FELs in which harmonic generation

converts a laser seed to much shorter wavelength radiation.

A proof-of-principle High-Gain Harmoni~-Generation

(HGHG) FEL experiment is now being executed at the

ATF in the infrared using a COZ laser seed. Both the

SASE and HGHG work will be extended into the VUV

at the Source Development Laboratory (SDL), using the

NISUS wiggler.

Anot~& feature, made necessary by the low energy,

is the use of a very short period undulator. It is clear that

to make use of lower emittance electron beams short

period undulatory must be developed. The SAE

measurement at the ATF was made with an undulator

built by MIT with a period of 8.8 mm. Another

undulator, with the same period but using a

superconducting magnet, was developed by the NSLS.

These are the shortest period undulatory in actual use

anywhere.

Using the MIT microundulator and theATF beam,

scientist from the ATF, MIT and LBL measured for the

first time spectral spikes in the spontaneous emission of

fluctuations in the incoherent radiation carry information

about longitudinal and transverse phase space of the beam.

Measurements in other fields that have been recently

completed at the ATF include work by Russian scientists

on an ultra-high precision single-shot beam position

monitors. The monitors demonstrated two axis beam

position measurement to a resolution of150 nm for a

0.5 nC beam pulse. Scientists led by BNI-?s AGS

department and Instrumentation Division have

demonstrated an optical ultra-fast particle detector.

Scientists from Columbia and Yale started measurements

of a novel dielectric wake field accelerator.

The ATF and the NSLS are in the center of the

national effort to develop short wavelength FELs, and

effort that at this time encompasses also SSRL, APS,

TJNAF and universities. Whenever possible, we have

collaborated with other laboratories, as exemplified by

the highly successftd “Next Generation PhotoCathode RF

Gun” developed with WAC and UCLA, the SASE and

HGHG experiments at the ATF being developed with

ANL using a wiggler from Cornell, as well as collaboration

with industry. In the near future, an exciting new

experiment is being proposed for the ATF. This is the

VISA experiment (short for Visible SASE). It is planned

as a collaboration ofBNL (NSLS), UCLA, SLAC (SSRL),

LLNL and LANL. In this experiment a four meter long

wiggler with a period of 1.8 cm will be installed early

1999 at the ATF to produce SASE to saturation at visible

wavelengths. This experiment is considered by SSRL as

an important milestone on the way to a hard x-ray FEL.

Following the experiment at the ATF, the wiggler will be

increased in length to six meters and installed at the SDL

to extend the experiment to the VUV at about 100 nm.H

the microundulator~ These fund~enral shot noise-driven

5-7
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Frank Terrano ~-”

NSLS

Assistant to Chairman

WORK PLANNING AND

CONTROL SYSTEM

FY 1998 was a year of change at BNL as well as at

the NSLS. Not so much a physical change as a cultural

one. Along with the new Brookhaven Science Associates

(BSA) management of BNL, there came an increased

emphasis on elevating the awareness of safety and

environmental protection throughout the Laboratory.

Along with the heightened awareness came new and more

formalized systems and procedures, designed to ensure

only the highest standards are maintained in these areas.

The NSLS, with its community of two and one half

thousand users doing research at the facility annually has

always maintained the utmost concern for individual

safety and the environment, and continues to be in the

forefront when addressing these issues. In the early part

of FY 1998 the NSLS agreed to take on a pilot program

for the (BNL) Laboratory which entailed the development

of a Work Planning and Control System with its primary

focus on improving control over the external work coming

into the facility. The system was designed to provide a

consistent method for identi$ing and analyzing job

hazards, planning work, and coordinating job activities

through the issuance ofWork Permits for all external work

coming into the NSLS. The pilot program met with great

success, largely through the efforts of NSLS Building

Manager, Mike Kelly and NSLS ES&H OMcer, Tom

Dickinson. By April 1998 the pilot was concluded and

by July the rest of the Laboratory was on the new Work

Planning and Control System. The process worked so

well that its scope has been expanded to now include a

review of all internal work performed by NSLS technical

stfi, with work permits to be issued as required via an

internal review process. Mike Kelly has assumed the

responsibilities of Work Control Manager for the overall

program at the NSLS.

5-8

SPACE MODIFICATIONS

In response to the increasing need for Iaboratoryl

setup areas at the NSLS, room 1-110 (contiguous to the

NSLS Green-Chasman Library), formerly used as a

storage space has been reconfigured. During the fall of

1998, modifications were completed which converted the

space into three separate laboratory/setup areas. Located

adjacent to the experimental floor, the space is now much

better utilized and provides some needed relief for our

users. Additional storage has been made available in the

basement of building #535 (connected to the

experimental floor by tunnel) to accommodate the

equipment and materials previously stored in room 1-

110. Renovations to the new NSLS vacuum technician

lab, occupying additional space recently acquired by the

NSLS, together with the new interlock technician lab

were completed in the fall of 1998. Both areas are in new

locations in the lower level of building #535, connected

by tunnel to the NSLS experimental floor, and are

designed to provide improved workspaces as well as

enhanced working conditions for the technicians. The

actual move of both groups is planned to take place shortly

after the December 1998 shutdown.

EXPERIMENTAL FLOOR

LIGHTING

The new mercury vapor lighting fixtures to be

installed around the X-ray and VW Rings have been

purchased and are in house. Having previously tested the

new lighting in several locations around the rings, we

found user opinions to be more favorable towards the

new whiter “daylight” illumination than the dimmer

“yellowish” light cast by the existing sodium lamps. There

will also be some reconfiguration of the lighting plan to

take better advantage the f~ture locations with regard to

the working areas around the experimental floor.

Installation is planned to take place after the December

1998 shutdown. ❑

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Users’Executive Committee

The Users’ Executive Committee (UEC) provides for organized discussions among the user

community, NSLS administration, and laboratory directorate. It aims to communicate current and

future needs, concerns, trends within the user community to NSLS staff and management, and to

disseminate to the users information about NSLS and BNL plans. Members were:

Chairperson: John Parise, SUNY@ Stony Brook

Vice-Chairperson: Barbara Illman, USDA/FS Forest Products Laboratory

Past-Chairperson: Joel D. Brock, Cornell University

Secretary Paul Stevens, Exxon Research & Engineering Co.

General Members John Hill (BNL-Physics), Carol Hirschmugl (U. of Wisconsin),

Lisa Kelly (U. of Maryland Baltimore County)

NSM User Adminktrato~ Eva Rothman, Ex-Officio

Beamline Support/R&D Head: Erik Johnson, Ex-Officio

Special Interest Group Representatives

Special Interest groups in areas of common concern communicate with NSLS

management through the UEC. Group representatives were:

Biological Scattering, Diffraction Malcolm Capel, BNL-Biology

Imaging George Cody, Carnegie Inst. of Washington

Industrial Users Jean Jordan-Sweet, IBM Research

Infrared Users Gwyn Williams, BNL-NSK

Nuclear Physics Steven C. Whisnant, U. of So. Carolina

Time Resolved Spectroscopy G. Lawrence Carr, BNL-NS15

Topography Michael Dudley, SUNY@ Stony Brook

Students and Post Dots Patrick Dai, Tufts U.

UV Photoemission, Surface Science Boris Sinkovic, U. of Connecticut

XAFS Mark Chance, Albert Einstein COILof Med.

X-ray Scattering, Crystallography Luz J. Martinez-Miranda, U. of Maryland

General User Oversight Committee

The GUOC resolves disputes between General Users, PRTs, and NS15 staff. Members were:

Simon Bare, UPO Mark Chance, Albert Einstein COILof Med.

Dale Sayers, NCSU Joel Brock, Cornell U.

5-2
Science AdvisoryCommittee

The Science Advisory Committee (SAC)evaluates thescience programs at the NSIS and makes

recommendations to the Chairman. The SAC met in March of 1998 and its members were:

Boris Batterman, CHESS,Cornell U. Martin Blume, Brookhaven National Laboratory

Stephen Burley, RockefellerUniversity Sol Gruner, CHESS,Cornell U.

Stephen Harrison, HHMI, Harvard U. Franz Himpsel, U. of Wisconsin, Madison

Keith Hodgson, SLAC John Parise, SUNY@ Stony Brook

Jochen Schneider, HASYLAB,DESY Albert J. Sievers, Cornell U.

Paul Sigler, HHMI,Yale U. Sunil Sinha, APS,Argonne National Laboratory

General User Proposal Study Panels

The Proposal Study Panels met in November 1997, March 1998, and July 1998 to review and rate General

User research proposals for the FY 1998 cycles. PSPmembers are drawn from the scientific community

and usually serve a two year term. Members during FY 1998 were:

UV Panel

Daniel Fischer NIST

David Hanson SUNY

Laszlo Mihaly SUNY

Boris Sinkovic NYU

David Tanner U. of Florida

X-Ray Imaging/Other Panel

Harald Ade NCSU

X-Ray Spectroscopy Panel

Chuck Bouldin NET

Bruce Bunker U. of Notre Dame

Lars Furenlid NS15

Steven Heald APS

James Penner-Hahn U. of Michigan

Linda Powers Utah State U.

Dale Sayers U. of North Carolina

Malcolm Howells LBL

Chris Jacobsen SUNY

Steve Sutton U. of Chicago X-Ray Scattering/Diffraction Panel

X-Ray Biology

Aneel Aggatwal Columbia U.

Jens Birktoft Hoffmann-LaRoche

Roger Burnett Wistar Institute

Howard Einspahr Bristol-Myers Squibb

Christopher Hill U. of Utah

James Hurley NIH

John Kuriyan Rockefeller

Thomas Terwilliger LANL

Gregory Van Duyne U. of Pennsylvania

Joel Brock

Roy Clarke

Jerome Cohen

Benjamin Chu

Takeshi Egami

Doon Gibbs

Simon Moss

Sunil Sinha

Cullie Sparks

Thomas Russell

Cornell U.

U. of Michigan

NWU

SUNY

U. of Penn

BNL-Physics

U. of Houston

ANL

ORNL

IBM

Allocation Panel

The Allocation Panel met in November 1997, March 1998, and July 1998 to allocate time on beamlines

to each General User proposal for the FY 1998 cycles. Allocation Panel members are drawn from the

scientific community and usually setve a two year term. Members during FY 1998 were:

UV Members

Harold Ade NCSU

David Heskett U. of R.1.

Jan Hrbek BNL-Chemistry

Paul Stevens Exxon

Elio Vescovo BNL-NSt5

X21-IDECS

John Tranquada BNL-Biology

Eric Jensen Brandeis U.

Eric Shirley NET

Akio Kotani U. of Tokyo

C.C.Kao BNL-NSLS

X-Ray Members

Malcolm Capel BNL-Biology

Mark Chance Albert Einstein College

Alex Darovsky SUNY-Stony Brook

Lars Furenlid BNL-NSLS

John Hill BNL-Physics

James McBreen BNL-DAS

Craig Ogata HHMI

Jean Jordan-Sweet IBM

Thomas Thurston BNL-Physics

Gavin Watson U. of Maryland

6-3
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Dong, Dowd, [Gmiir],

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POSLDOCS, .%UDENTS,

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MECHANICALMontanez

ELECTRONICPiemski

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HSAD kkOWSky

Graves, Solomon,

TECHNICIANS

Aspenleiter, Lehecka

ACCELERATORTESTFACILIm

Ben-Zvi

Babzien, Malone,

Po orekky, X. Wang,

Y~menko

SNDENT%

Doyuran, He

VISITORA. Tsunemi

TECH. Surrorm

SUPERVISORCahill

Monremagno, Harringron

* Temporary

** Reports to Denis McWhan,

BNL Assoc. Dir. for Basic Energy Sciences

[1 NSLS Personnel with Multiple Functions

() PRT personnel or member of non-NSLS division

6-4
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ADMINISTRATION

DEPUTYCHASrw,w KrMq Terrano I

Proposal Study Panels

Allocation Panel

General User Oversight Commirree (GUOC)

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H- McBrien

Bowden, Ciufo,

Loverro, Marshall,

Messana, Thompson,

ENGINEERSNC

Beauman, Chou, Lynch,

Mortazavi (Deputy), E skarkka

INJECITONRING: Bhrm

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OPrzruTSoNS J. Rothman

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Hicks COMPUTER SYSTEMS

HEAO:Smith

Dabrowski, Feng-Berman

Langenbach, M1chta,

Pearson, Ramamoorthy,

Tang, Teng

MECH.LEAOSSLPjerov

CHEC- Palo

Mm Gross,GugUelmino

Kim,Y“tascu, Stelmach,

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BUSLOINGMANAGWU

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ASST.BUILOSNGMANAGER

[van Derlaske]

USERSHOR vanDerlaske t

MECHANICAL

(Pa o, A/C), Bambina,

Hu Ybard, Newburgh,

Pop, Radulescu,

.%ntangelo, Sch- t

CARPENTERS

(Gilderdeeve)

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RF:Ramirez,

Rodriques, Vaughn

CoNTRoss & DIAGNOSTIC-S

Borrelli, Frisbie,

Nielson, Tallenc

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(S. Bennett), (Mkrgino),

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SPECIALPROJESXX

Romano, Singh I (signed) Michael Hart, Chairman

October 1, 1998

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6-5
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,\

Beam Research Energy Affiliation LocalContact Spokesperson

line Program (eV)

UIA

U1B

U2A

U2B

U3A

U3B

U3C

U4A

U4B

6-6

SEXAFS,ARUPS,XPS

(Conceptual)

IR

IR Microscopy,

Spectroscopy

Detector and system

calibration; mess. of

material optical const.;

spectrometeric properties

(Conceptual)

100-1000 Exxon

Exxon

6 meV-3 eV Carnegie Inst. Wash

6 meV-O.6 eV Albert Einstein

70-2100 Smiths Astro Obs

Bechtel Nevada

Los Alamos Natl Lab

Pacific NW Natl Lab

Photoelectron spect.; 40-1600

exp. system and detector

calibrations

Photoemission 15-200

spectroscopy to study

electronic structure in

solids, surfaces

Soft x-ray and/VUV 20-1200

photoemission

spectroscopy and photo

absorption

Los Alamos Natl Lab

Sandia Natl Lab

SFA,Inc

Boston U

No Carolina St U

BNL-NSLS

Rutgers U

Naval Res Lab

BNL-NS15

SRRC

M Sansone

516-344-3265

516-344-5759

M Sansone

516-344-3265

516-344-5759

R h

516-344-5502

202-686-2410

L Miller

516-344-5609

516-344-2091

A Burek

516-344-5521

516-344-5503

M Sagurton

516-344-5708

516-344-5504

J Park

516-344-7290

516-344-4744

P Stevens

908-730-2584

P Stevens

908-730-2584

R Hemley

516-344-5917

202-686-241 OX2465

M Chance

516-344-5787

718-430-4136/2894

R Blake

516-344-5708

505-466-0566

R Bartlett

516-344-5708

505-667-5923

K Smith

516-344-5504

617-353-6117

Y Idzerda

202-767-4481
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (eV)

U41R

U5

U5UA

Grazing incid. 2.5 meVReflecWity in UHV 0.5 eV

transmissionEtnormal

incidencereflectivity

Diagnostic instrument

monitors beam parameters

during operations and

machine studies

Spin polarized angle- 10-200

resolved ultraviolet

photoemission

U6 (Available)

BNL-NSLS G VWliams

516-344-3634

516-344-7529

BNL-NSLS R Nawrocky

516-344-5505

516-344-4449

BNL-NSLS EVescovo

BNL-Physics 516-344-5505

ANL 516-344-7399

U of Texas

U7A XPS and XAS on surface 150-1200 BNL-Physics

and in bulk, under BNL-Chemistry

vacuum and atm.P Dow Chem

NET

U of Michigan

Rutgers U

Texas A&M U

U7B Photoemission;

SEXAFS

U8A ARUPS

NEXAFS

U8B ARUPS

NEXAFS

15-300 BNL-NSLS

10-130 UCA@Riverside

10-1000 IBM

U8C Zone plate monochr. 200-600 IBM

evaluation; reflectivity

measurements of thin

films and multilayers

U8D (Conceptual)

Scanning soft x-ray

microscopy

IBM

G Williams

516-344-3634

516-344-7529

R Nawrocky

516-344-5505

516-344-4449

EVescovo

516-344-5505

516-344-7399

Q Dong D Fischer

516-344-5507 516-344-5177

516-344-5358

Q Dong S Hulbert

516-344-5507

516-344-5358 516-344-7570

J Yarmoff J Yarmoff

516-344-5508 909-787-5336/3537

909-787-5336/3537

K Zhang R McFeely

516-344-5508 914-945-2068

R McFeely R McFeely

516-344-5508 914-945-2068

914-945-2068 ‘

R McFeely R McFeely

516-344-5508 914-945-2068

914-945-2068

6-7
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (eV)

U9A

U9B

U1OA

U1OB

Ull

(Planned)

PSD measurements of

UHV materials at room

temperature

White BNL-NSE

Beam

Absorption.;CD;MCD;

flores/phosphorescence

spectrocpy (incl. timesres. fl.)

3-12 BNL-BioIogy

(Commissioning GU

{1998} High Brightnes IR

measurements on ‘bad

metals”

IR microspectroscopy

Gas phase photoionization and

spectroscopy

6 meV-3 eV BNL-NSLS

BNL-Physics

SUNY @ Stony Brook

50 meV- BNL-NSLS

0.6 eV Northrop Grumman

5-30 BNL-DAS

BNL-Biology

BNL-NSLS

C Lanni

516-344-7766

516-344-4100

J Sutherland

516-344-5509

516-344-3406

G Carr

516-344-6220

516-344-2237

G Carr

516-344-5510

516-344-2237

J Sutherland

516-344-5509

516-344-3406

C Foerster

516-344-4754

J Sutherland

516-344-5509

516-344-3406

G Homes

516-344-5510

516-344-7579

G WNiams

516-344-7529

B Klemm

516-344-5511

516-342-4001

U12A Soft x-ray photoemission 100-800 Oak Ridge Natl Lab S Hulbert D Mullins

(SXPS);XAS; NEXAFS BNL-NS15 516-344-5913 516-344-5512

516-344-7570 423-574-2796

U121R IR and far-lR measure- 0.3 meVment time-resolved 1 eV

(pump/probe

IR & far-IR spectroscopy

U of Florida

BNL-NSL5

U13UA High res VUV/soft x-ray White BNL-NS15

abs and electron spectr. Beam

(incl. spin-polarized

photoemission)

U13UB UV/VUV spectroscopy 5-30 BNL-NStS

hi resol. Angle resolved BNL-Physics

photoemission of solid Boston U

suti.;pump-probe GU-’98 Brandeis U

U13UC Interferometry White Lucent Tech

Beam

G Carr

516-344-6220

516-344-2237

S Hulbert

516-344-5913

516-344-7570

S Hulbert

516-344-5513

516-344-7570

S Spector

516-344-5513

D Tanner

352-392-4718

S Hulbert

516-344-5913

516-344-7570

EJensen

617-736-2865

0 Wood

908-582-4457

6-8
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (eV)

U14A VUV/soft x-ray spectroscopy Auger PhotoElectron Coincidence

Spectroscopy (APECS)

U14B Diagnostic Instrument

VUV Ring beam position

monitoring

U15 Soft x-ray spectroscopy

(solids and gases)

U16A (Available)

15-300 BNL-NSLS

Rutgers U

BNL-NSM

S Hulbert

516-344-5514

516-344-5930

J Hastings

516-344-5514

516-344-3930

300-800 BNL-NSE A Wen

SUNY@Buff 516-344-5515

SUNY@SB 516-632-7918

U16B Core level Photo- 5-1000 BNL-NSLS

emission; soft X-ray

photoabsorption

spectroscopy; Auger

photoelectron coincidence

spectroscopy (APECS)

S Hulbert

516-344-5514

516-344-7570

R Bartynski

908-445-4839

J Hastings

516-344-5514

516-344-3930

D Hanson

516-632-7917

S Hulbert S Hulbert

516-344-5516 516-344-5516

516-344-7570 516-344-7570

6-9
,., , .. . ,

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X=--WY“kELkiiIN:EGUIDE

Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

xl A Soft x-ray imaging 0.25-1.0 SUNY@SB S Wirick J Kirz

No Carolina St U 516-344-5601 516-632-8106

BNL-NSLS 516-632-8095 C Jacobsen

LBNL 516-632-8093

ANL 516-344-4723

Xl B Soft x-ray spectroscopy 0.2-0.9 BNL-Physics PJohnson PJohnson

KFA - Juelich 516-344-5701 516-344-5701

Fritz-Haber-Inst 516-344-3705 516-344-3705

Boston U

X2A (Available)

X2B

X3A1

X3A2

X3B1

X-ray microtomography

Short wavelength

crystallography,

diffraction and scattering

Diffractometry; x-ray

spectroscopy; scattering

crystallography; small

angle scattering

X-ray spectroscopy;

powder diffraction

6.5-30, WB Exxon S Bennett J Dunsmuir

516-344-5610 908-730-2548

516-344-4719

18.2-29.7 SUNY@Buff

SUNY@SB

Amoco Corp

Alfred U

L Ribaud P Coppens

516-344-5603 716-645-6800,x2217

716-645-6800x2218

G M/u

516-344-5603

4.34 SUNY@SB

SUNY@Buff

Amoco Corp

Alfred U

L Ribaud P Coppens

516-344-5603 716-645-6800,x2217

716-645-6800x2218

G WU

516-344-5603

4-40 SUNY(QSB

SUNY@Buff

Amoco Corp

Alfred U

L Ribaud P Coppens

516-344-5603 716-645-6800,x2217

716-645-6800x2218

6-10
I

i,

,

Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

X3B2

X4A

X4B

X4C

X5A

Surfacescience 4-20

Multiwavelength 4-30

anomalous diffraction

analysis of crystalline

biological macromolecules

(Conceptual)

Diffractionmess. 4-15

from biological

macromolecules

Laser Electron Gamma 140-470

Source (LEGS); medium

energy nuciear physics

X5B Diagnostic

X6A (Avaiiabie)

X6B (Avaiiabie)

SUNY@Buff

SUNY@SB

Amoco Corp

Aifred U

Howard Hughes

Howard Hughes

BNL-Physics

Norfoik St U

Ohio U

U of So Caroiina

SUNY@SB

Syracuse U

U of Virginia

VA Poiytech a St U

U of Paris

KFA-Jueiich

Frascati Natl Lab

U of Rome II

Osaka U

L Ribaud P Coppens

516-344-5603 716-645-6800,x2217

716-645-6800x2218

C Ogata W Hendrickson

516-344-5604 212-305-3456

516-344-7435

COgata W Hendrickson

516-344-5604 212-305-3456

516-344-7435

C Thorn A Sandorfi

516-344-5605 516-344-7951

516-344-7798

6-11 [

~
Beam Research Energy Affiliation “LocalContact Spokesperson

line Program (keV)

516-344-5930 516-344-2738

X7A High resolution 5-45 Air Products & Chem D COX D COX

structural studies BNL-Physics 516-344-5607 516-344-5607

through powder Mobil 516-344-3818 516-344-3818

diffratilon Carnegie Inst of Was

UOP

U of Pennsylvania

SUNY@SB

Chevron

UCA@Santa Barbara

NIST

X7B Crystallography; 5-21

wide angle scattering

Swedish Nat Res Coun J Hanson T Koetzle

BNL-ChemistIy 516-344-5707 516-344-4384

516-344-4378

X8A

X8C

X9A

X9B

X1OA

XIOB

6-12

Calibration of mirrors& 0.26-5.9

dector systems; material

optical constants;

spectrometric propetiles

Diffraction from 5-20

biological macromolecules

and detector calibrations

AXAF

Time-resolved x-ray White

footprinting; Beam

Small angle scattering 2.1-18.8

EXAFS;multiple anomalous

diffraction (MAD);

protein x-ray diffraction

Diffraction; small 6-15.2

angle scattering

crystallography;

scattering SAXA; WAXS

Scattering; 8 and 12

crystallography

PXD, Reflectivity

Los Alamos Natl Lab M Sagurton

Smiths Astro Obs 516-344-5708

Bechtel Nevada

Sandia Nat] Lab

Pacific NW Natl Lab

Los Alamos Natl Lab M Sagurton

Natl Res Coun/Canada 516-344-5708

R Blake

505-466-0566

516-344-5521

J Berendzen

505-665-2552

UCA@LA

Hoffman-La Roche

BNL-Biology

Albert Einstein

Rockefeller U

Sloan-Kettering lnst

Albert Einstein

NIH

Exxon

Exxon

M Sullivan

516-344-5609

516-344-3800

M Sullivan

516-344-5787

516-344-3800

S Bennett

516-344-5610

516-344-4719

S Bennett

516-344-5610

516-344-4719

M Chance

718-430-4136

718-430-2894

M Chance

718-430-4136

718-430-2894

R Kolb

908-730-2970

R Kolb

908-730-2970
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

Xloc EXAFS 4.0-24.0 Exxon M Sansone P Stevens

516-344-3265 908-730-2584

516-344-5759

XIIA EXAFS

XIIB EXAFS

X12A Instrument development

and x-ray physics

4.5-35 Naval Res Lab K Pandya D Sayers

Mobil 516-344-5611 919-515-4453

U of Connecticut 516-344-7734

No Carolina St U

Paul Scherrer Inst

BNL-DAS

The DuPont Co

U of Washington

Rice U

111Inst Tech (IIT)

Naval Surf War Cntr

Georgia Inst Tech

U of Notre Dame

Advanced Fuel

NJ Inst of Tech

1.7-8 Naval Res Lab

NJ U of Tech

Mobil

No Carolina St U

The DuPont Co

BNL-DAS

U of Connecticut

Paul Scherrer Inst

Naval Surf War Cntr

Ill Inst Tech (IIT)

U of Washington

Rice U

BNL-NSIS

X12B Time-resolved and static 7.6-13.06 BNL-Biology

x-ray diffr. of macromol.

crystallography

X12C Macromolecular 8-13 BNL-Biology

crystallography; multiwavelength anomalous

dispersion (MAD)

K Pandya D Sayers

516-344-5611 919-515-4453

516-344-7734

J Ablett

516-344-2738

516-344-5627

M Capel

516-344-5712

516-344-5234

R Sweet

516-344-5642

516-344-3401

P Siddons

516-344-2738

M Cape]

516-344-5712

516-344-5234

R Sweet

516-344-5642

516-344-3401

6-13
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

X13A,

X13B

X14A

X14B

X15A

X15B

X16A

X16B

X16C

X17B1

X17B2

R&D optics development

soft x-ray utilization

BNL-NSLS EJohnson

516-344-5913

516-344-4603

EJohnson

516-344-5913

516-344-4603

Scattering crystallogr. 2.5-40

spectroscopy phase ID and

resid. strain mess. high

temp x-ray diffraction

Oak Ridge Natl Lab

Univ of Ill Urb Chain

U of Tennessee

U of Houston

Sandia Natl Lab

J Bai

516-344-5614

516-344-2583

G Ice

423-574-2744

(Planned) Manuf. res. White

for hard x-ray Iithogrphy

exposures for precision

microfabrication

BNL-NSLS EJohnson

516-344-5913

516-344-4603

EJohnson

516-344-5913

516-344-4603

X-ray standing waves 3-20, WB ANL

BNL-NSIS

Northwestern U

No Carolina St U

Ill Inst Tech (IIT)

Z Zhong

516-344-5617

M Bedzyk

847-252-7763

516-344-7395

X-ray absorption 1.8-10

spectroscopy of complex,

reactive, very dilute

systems

Lucent Tech

Surface diffraction 4-12 Lucent Tech

U of Illinois

rapid access for sample 7.85

characterization; powder

characterization;thin

film characterization

Lucent Tech

Novel spectroscopy; 3-16

diffraction

X-ray scattering at high 20-100, WB

pressure and temperature

Medical research: 27-35

radiotherapy

Lucent Tech

U of Illinois

BNL-NSL5

SUNY@SB

BNL-NSLS

BNL-Medical

Stanford U

111Inst Tech (IIT)

Stanford U

P Northrup

516-344-3565

P Citrin

908-582-5275

W Lehnert

516-344-5715

516-344-3635

W Lehnert

516-344-5715

516-344-3635

W Lehnert

516-344-5715

516-344-3635

Z Zhong

516-344-5717

516-344-5617

N Gmi.ir

516-344-5617

516-344-2490

K Evans-Lutterodt

908-582-2154

516-344-2125

K Evans-Lutterodt

908-582-2154

516-344-2125

K Evans-Lutterodt

908-582-2154

516-344-2125

J Hastings

516-344-3930

516-344-5514

W Thomlinson

516-344-3937

6-14
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

X17C

X18A

X18B

X19A

X19C

X20A

HiP research; energy 10-100, WB

dispersive diffraction

from microscopic sample

volumes

Diffuse and surface 4-20

scattering

X-ray spectroscopy 7-40

X-ray absorption 2-8

spectroscopy: EXAFS

and XANES

Topography; liquid 4-25, WB

surface scattering

X-ray Scattering and 6.3-12

diffraction

Naval Res Lab J thl H Mao

LLNL 516-344-5917 202-686-4454

Carnegie Inst of Was 202-686-2410 ESkelton

U of Chicago 202-767-3014

U of Missouri

U. of Maryland

BNL-DAS

U of Illinois

Purdue U

Penn St U

UOP

Chevron

AlliedSignal

BNL-NSIS

Dow Chem

PPGIndustries

General Electric

BNL-DAS

Rutgers U

BNL-NSLS

U of Kentucky

UCA@Davis

S Ehrlich

516-344-5618

516-344-7862

G Lied]

317-494-4100

S Khalid P Siddons

516-344-5718 516-344-2738

516-344-7496 S Khalid

516-344-7496

S Khalid S Khalid

516-344-5718 516-344-5718

516-344-7496 ~ 516-344-7496

Johns Hopkins U Z Huang

Army Research Lab 516-344-5719

SUNY@SB 312-702-7229

NASA

U of Wisconsin

Northrop Grumman

Dartmouth Coil

U of Chicago

U of Illinois

MIT

IBM

X20B Scattering at fixed 17.4 (fixed) IBM

energy MIT

M Dudley

516-632-8500

J Jordan-Sweet R Birgeneau

516-344-5720 617-253-4937

914-945-3322

J Jordan-Sweet J Jordan-Sweet

516-344-5720 516-344-5720

914-945-3322 914-945-3322

6-15
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

X20C

X21

X22A

X22B

X22C

X23A2

X23A3

X-ray scattering and

diffraction with high

flux by multilayer

monochromator

Inelastic x-ray

scattering

X-ray scattering of thin

films, multilayers, catalytic materials, electrochemical interfaces

X-ray scattering and

surfaces; magnetic stud.

under magnetic fields

X-ray Scattering studies

of magnetism; structure

and phase behavior of

metal surfaces

EXAFS

Topography; smallangle scattering

4-11

5-1o

10 NOM.

5-1o

3-12

4.7-30

5-30, WB

IBM

MIT

BNL-NS15

BNL-Physics

BNL-DAS

U of Maryland

BNL-Physics

ANL

BNL-Physics

ANL

U of Maryland

NIST

NIST

J Jordan-Sweet

516-344-5720

914-945-3322

J Jordan-Sweet

516-344-5720

914-945-3322

C Kao

516-344-5721

516-344-4494

J Hill

516-344-3736

516-344-5622

E DiMasi

516-344-5622

516-344-2211

J Hill

516-344-5622

516-344-3736

J Woicik

516-344-5823

516-344-5236

C Kao

516-344-5721

516-344-4494

D Gibbs

516-344-4608

516-344-5622

D Gibbs

516-344-4608

D Gibbs

516-344-4608

J Woicik

516-344-5823

D Fischer G Long

516-344-5507 301-975-5975

516-344-5177 516-344-5623

X23B EXAFS; scattering 3-10.5 Naval Res Lab J Kirkland T Elam

crystallography 516-344-5723 202-767-3015

516-344-2258

6-16

— _——
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

X24A Atomic, molecular, and 1-5 NET B Karlin T Jach

optical physics with BNL-NSIS 516-344-7863 301-975-2362

x-rays Northwestern U 516-344-5624

U of Rhode Island

U of Tennessee

Brooklyn Coil - CUNY

U of Maryland

X24C Photoemission and 6-1800 eV Naval Res Lab

reflectance spectroscopy

X25 High intensity, high 3-30 BNL-NS15

brightness photon beam;

high Q-resolution elastic

scattering

J Rife M Kabler

516-344-5724 202-767-2223

202-767-4654

L Berman L Berman

516-344-5625 516-344-5625

516-344-5333 516-344-5333

X26A X-ray Microscopy; 4-20, WB

structural biology;

atomic and molecular

physics

X26C Dev. and applic. of x-ray 4-30, WB

microscopy techniques;

Laue diffraction protein

crystallography

X27A NSLSR&D only; instrument

development and x-ray

physics

X27B NSLSR&D only; Develop

exposure techniques;

matls. char.; and tool

development for microfab.

U of Chicago/CARS

BNL-DAS

BNL-Biology

U of Georgia/SREL

Cold Spring Harb Lab

SUNY@SB

BNL-Biology

BNL-DAS

U of Chicago/CARS

U of Georgia/SREL

Cold Spring Harb Lab

SUNY@SB

BNL-NSIS

BNL-NSLS

G Shea-McCarthy

516-344-5626

516-344-2229

SSutton

630-252-0426

G Shea-McCarthy

516-344-5726

516-344-2229

R M.I

516-367-8872

B Dowd

516-344-5738

516-344-7092

EJohnson

516-344-5627

516-344-4603

P Siddons

516-344-2738

EJohnson

516-344-5627

516-344-4603
Beam Research Energy Affiliation LocalContact Spokesperson

line Program (keV)

X27C Simultaneous small ~ AlliedSignal FYeh B Hsiao

wide angle x-ray BNL-Physics 516-344-5627 516-632-7793

scattering (SWAX)in real General Electric 516-632-7892

time USAF

Montell Polyolefins

NET

SUNY@SB

NIH

X28A Instrument development

and detector development

for the X-ray Ring

X28B Photon-based diagnostics

and detector development

for the X-ray Ring

X28C Photon-based diagnostics

and detector development

for the X-ray Ring

X29A (Available)

X29B (Available)

X30 Diagnostic Instrument

6-18

BNL-NSLS EJohnson EJohnson

516-344-5913 516-344-4603

516-344-4603

BNL-NSLS

BNL-NSLS

BNL-NSIS

EJohnson EJohnson

516-344-4603 516-344-4603

516-344-5913

P Stefan PStefan

516-344-2117 516-344-2117

516-344-5728

. .—. .— —4—— —-—. . . . . .

f

!


BeamlineUIA

D.G. Castner, “Surface Characterization of Oriented

Afterglow Fluorocarbon Films”, Plasma Processing of

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Dordrecht, pps. 221-230, (1997).

D,G. Castner, P. Favia, and B.D. Ratner, “Deposition

of Fluorocarbon Films by Remote RF Glow Discharge”, Surface Modification of Polvmeric

Biomateriak, editors B.D. Ratner and D.G. Castner,

Plenum Press, New York, pps. 45-52, (1997).

J,G. Chen, J. Eng, Jr., and S.P. Kelty, “NEXAFS

Determination of Electronic and Catalytic Properties

of Transition Metal Carbides and Nitrides: From

Single Crystal Surfaces to Powder Catalysts”, Catalysis

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J.G. Chen, “NEXAFS Investigations of Transition

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J. G. Chen, B. Friihberger, J. EngJr., and B.E. Bent,

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B, Dhandapani, S. Rarnanathan, C.C. Yu, S.T.

Oyama, and J.G. Chen, “Synthesis, Characterization

and Reactivity Studks of Supported MOZC with

Phosphorous Additive”, j of Catal, 176,61-67,

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J. Eng, Jr., B.E. Bent, B. Fruhbe~ger andJ.G. Chen,

“Reaction Mechanisms of Cyclohexene and 1,3-

Cyclohexadiene: Decomposition on Clean Mo(l 10)

and Dehydrogenation on Carbide-Modified Mo(l 10)”,

Langmuir, 14, 1301-1311, (1998).

D. Fischer, W.R. Caseri, and G. Hdmer, “Orientation

and Electronic Structure of Ion Exchanged Dye

Molecules on Mic* An X-Ray Absorption Study”,

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A.B. Gurevich, A.V. Teplyakov, M.X. Yang, B.E. Bent,

M.T. Holbrook, and S.R. Bare, “Synthesis, Bonding,

and Reactions of p-Bonded Allyl Groups on CU(1OO):

Allyl Radical Ejection”, Ltmgzwir, 14, 1419-1427,

(1998).

M.J. Kong, A.V. Teplyakov, J.G. Lubovits~, and S.F.

Bent, “NEXAFS Studies of Adsorption of Benzene on

Si(100)-2xl”, Su& Sci., 411,286, (1998).

Y. Luo, D. Slater, M. Han, J. Moryl, R.M. Osgood, Jr.,

and J.G. Chen, “In Situ Investigation of the Surface

Chemistry ofAtomic Layer Epitaxial Growth of II-VI

Semiconductor Thin Films”, Langmuir, 14, 1493-

1499, (1998).

V.S. Lusvardi, M.A. Barreau, J.G. Chen, J. Eng Jr., B.

Friihberger, and A.V. Teplyakov, “A NEXAFS Investigation of the Reduction and Reoxidation of

Ti02(OOl)”, Su~ Sci., 397,237-250, (1998).

A.V. Teplyakov, B.E. Bent, and J.G. Chen, “Reaction

Mechanisms of Dehydrocyclization of l-hexene to

Benzene on Cu~Pt(l 11): A NEXAFS and IL41RS

Investigation”, Langmuir, 14, 1337-1344, (1998).

A.V. Teplyakov, A.B. Gurevich, M.X. Yang, B.E. Bent,

and J.G. Chen, “NEXAFS and TPD Studies of MoIecuka.rAdsorption of Hydrocarbons on CU(1OO):

Segmental Correlation with the Heats of Adsorption”,

Su$ Sci., 396,340-348, (1998).

A.V. Teplyakov, M.J. Kong, and S.F. Bent, “DielsAlder Reactions of Butadienes with the Si(100)-2xl

Surface as a Dieneophile: Vibrational Spectroscopy,

Thermal Resorption and Near Edge X-ray Fine

Structure Studies”, J Cbem. Phys., 108,4599, (1998).

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BeamlineU3C

T. Takaoka, T. Takagaki, Y. Igari, and I. Kusunoki,

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S.S. Dhesi, C.B. Stagarescu, K.E. Smith, D.

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Diebold, “Novel Electronic and Magnetic Properties

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Pt(l 1 l)”, J. Vat. Sci. Tecbnol., A16, 990-995, (1998).

J.A. Rodriquez, S. Chaturvedi, M. Kuhn, J. van Ek, U.

Diebold, P.S. Robbert, H. Geisler, and C.A. Ventrice,

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C. Waldfried, D.N. McIlroy, T. McAvoy, D.

Welipitiya, P.A. Dowben, and E. Vescovo, “Strain

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C. Waldfried, D. Welipitiya, T. McAvoy, P.A.

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BeamlineU7A

D.G. Castner, P. Favia, and B.D. Ratner, “Deposition

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10860-10869, (1997).

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J.A. Rodriguez, S. Chaturvedi, M. Kuhn, and J. Hrbek,

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Reactivity”, J Phys. Chem. B, 102,5511-5519, (1998).

J.A. Rodriguez, T. Jirsak, S. Chaturvedi, andJ. Hrbek,

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A. Kazimirov, G. Scherb, J. Zegenhagen, T.-L. Lee,

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D.J. Chadl, P.H. Citrin, C.H. Park, D.L. Adler, M.A.

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C. Kim, D.A. Walko, and I.K. Robinson, “Refined

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Y.S. Chu, I.K. Robinson and A.A. Gewirth, “Properties

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A-20
A.I. Frenkel, D.M. Fanning, I.K. Robinson, D.L.

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M.L. Rivers, “Melting and Crystal Structure of Iron

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A-21
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J. Akella, S. Weir, J.M. Wills, and P. Soderlind,

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“X-Ray Diffraction with a Double Hot-Plate LaserHeated Diamond Cell, Properties of the Earth and

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H.K. Mao, R.J. Hemley, and A.L. Mao, “DiamondCell Research with Synchrotrons Radiation”, Advances

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A-22

S.M. Peiris and D.L. Heinz, “Compression of Seven

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J. Shu, H.K. Mao, J. Hu, Y. Fei, and R.J. Hemley,

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D.W. Brown, P.E. Sokol, and S.N. Ehdich, “New

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A-23
L.X. Chen, T. Rajh, Z. Wang, and M.C. Thurnauer,

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S.R. Bare, “Surface Structure of Highly Dispersed

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A-24
H,S, Lee, X.Q. Yang, C.L. Xiang, and J. McBreen,

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H. Chung, D.T.J. Hurle, and D.F. Bliss, “The Influence of Polari~ on Twinning in Zincblende Structure

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A, Vairavamurthy, “Characterization of Sulfur-Containing Functional Groups in Sedimentary Humic

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A-25
M. Dudley, B. Raghothamachar, Y. Guo, X.R. Huang,

H. Chung, D.L. Larson, Jr., D.T.J. Hurle, D.F. Bliss,

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Polarity Effects from a Study of Magnetic Liquid

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P.G. Neudeck, W. Huang, and M. Dudley, “Breakdown Degradation Associated with Elementary Screw

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B. Raghothamachar, H. Chung, M. Dudley, and D.J.

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A-26
BeamlineX20A

H.D. Abrufia, J.M. Feliu, J.D. Brock, L.J. Buller, E.

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BeamlineX20B

W.J. Nuttall, S.C. Perry, D.R. Bowyer, W.G. Stirling,

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BeamlineX20C

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A-27
L.D. Madsen, “Device Contacts and Interconnects”,

Activitv Re~orc Tanuarv 1997 -December 1997

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BeamlineX21

F. Bartolome, J.M. Tonnerre, L. Seve, D. Raoux,

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BeamlineX22A

R.R Atilc, and J.X. Wang, “02 Adsorption and

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A-28

N.M. Jisrawi, M.W. Ruckman, T.R. Thurston, G.

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C.-H. Lee, H.-Y. Lee, K.S. Liang, and T.-B. Wu,

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Pt(l 11): Structures and Determination of Oz Adsorption on Pt(l 1 l)”, Proceedimzs of the SYm~osium on

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M. Deutsch, and B.M. Ocko, “X-ray and Neutron

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A-29
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A-30

BeamlineX23A2

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736-739, (1998), BNL 64220.

L. Berman “Biological Macromolecular Crystallography at the NSLS’, Synch. Rad NWS, 814, 11-15,

(1995), BNL 65011.

L.E. Berman, Z.J. Yin, S.B. Dierker, E. Dufresne,

S.G.J. Mochrie, O.K.C. Tsui, S.K. Burley, F. Shu,

X.L. Xie, M.S. Capel, and RM. Sweet, “Performance

of the Double Mukilayer Monochromator on the

NSLS Wiggler Beam Line X25”, Svnchrotron Radiation Instrumentation: Tenth US National Conference,

AIP Conference Proceedings. 417, pp. 71-79, (1997),

BNL 64792.

S.V. Bukmov, G.I. Dudnikova, N.M. Naumova, F.

Pegorao, I.V. Pogorelsky, and V.A. Vshivkov,

“Charged Particle Acceleration in Nonuniform Plasmas”, AIP Conference Proceedings, 398,422, (1997),

BNL 63685.

W.A. Ca.Eebe, C.C. Kao, L.E. Berman, J.B. Hastings,

M.H. Krisch, F. Sette, and K. H%-rdiinen, “Spin

Resolved Resonant Raman Scattering”, J Appl. I%ys.,

79/8, 1-3, (1996), BNL 65066.

W.A. Caliebe, C.C. Kao, M. Krkch, T. Oversluizen,

P. Montanez, and J. B. Hastings, “Optical Design

and Performance of the Phase II Inelastic Scattering

Beamline at the National Synchrotrons Light Source”,

Svnchrotron Radiation Instrumentation, edited by

E. Fontes, AIP Conference Proceedimzs, 417,6,

(1997), BNL 64808.

B-1
-. —.

G. L. Carr, P. Dumas, C. J. Hirschmugl, and G. P.

WUiams, “Infrared Synchrotrons Radiation Programs

at the National Light Source”, iVuovo Cimento, 20D,

375, (1998), BNL 64713.

G. L. Carr, R. P.S. M. Lobo, C. J. Hirschmugl, J.

LaVeigne, D. H. Reime, and D. B. Tanner, “Time

Resolved Spectroscopy Using Synchrotrons Infrared

Pukes”, Accelerator Based Sources of Infrared and

Abdications, SPI~ 3153,80, (1997), BNL 64879.

G.L. Carr and G.P. Williams, “Infrared

Microspectroscopy with Synchrotrons Radiation”,

SPIE Proceedings, 3153,51, (1997), BNL 64881.

D. Chapman, E. Pisano, W. Thomlinson, Z. Zhong,

R.E. Johnston, D. Washburn, D. Sayers, and K.

Malinowska, “Medical Applications of Diffraction

Enhanced Imaging”, Breast Disease, 10, 197-208,

(1998), BNL 65490.

D. Chapman, W. Thornlinson, Z. Zhong, R.E.

Johnston, E. Pisano, D. Washburn, D. Sayers, and

C. Segre, “Diffraction Enchanced Imaging Applied to

Materials Science and Medicine”, Synch. I/ad News,

11,2, (1998), BNL 65439.

C.L. Foerster, “Synchrotrons Light Source Measurements of Photon Stimulated Resorption from Vacuum

Chamber Materials”, Synch. &d. News, 11,5, (1998),

BNL 65863.

C.L. Foerster, C. Lanni, R. Lee, G. Mitchell, and

W. Quade, “Te.srs of an Environmentally Safe UHV

Cleaning Process for BNL Accelerators and Storage

Rings”, J Vat. Sci. Tech., A15/3, 731, (1997), BNL

63582.

P. Fenter, F. Schreiber, L.E. Berman, G. Stoles,

P. Eisenberger, and M.J. Bedzyk, “On the Structure

and Evolution of the Buried S/Au Interface in SelfAssembled Monolayers: X-ray Standing Wave Results”,

Sufi Sci., 412/413, 213-235, (1998), 65964.

J. W. Freeland, S. Doheriy, V. Chakarhn, C.-C. Kao,

J.-H. Park, J. G. Zhu, and Y.U. Idzerda, “Identifyhg

Layer Switching in Magnetic Mukilayers with X-ray

Resonant Magnetic Scattering”, Appl. Phys. Lett., 71,

276, (1997), BNL 64232.

H.P. Freund and L.H. Yu, “Electron Trajectories in a

Self-Consitent Wiggler Field Composed of a Dipole

Lattice”, Nucl Instrum. And Meths. In Phys. Res. A,

375,304-8, (1996), BNL 65341.

J. Giacomini, H. Gordon, R. O’Neil, A. VanKessel,

B. Cason, D. Chapman, W. Lavender, N. Gmur, R.

Menk, W. Thomlinson, Z. Zhong, and E. Rubenstein,

“Bronchial Imaging using Xenon K-Edge

Dichromography”, Nucl Instrurn. Meths., A406,

473-478, (1998), BNL 64693.

A.P. Graham, F. Hofmann, J. P. Toennies,

G.P. Williams, C.J. Hirschmugl, and J. Ellis, “A High

Resolution Helium Atom Scattering and Far Infrared

Study of the Dynamics and the Lateral Potential

Energy Surface of CO Molecules Chemisorbed on

CU(OO1)”, ~ of Chem. phys., 108/18,7825-7834,

(1998), BNL 65803.

W.S. Graves, I. Ben-Zvi, E.D. Johnson, S. Krinsky,

J. Skaritka, M.H. Woodle, and L.H. Yu, “Design of

the Source Development Lab Bunch Compressor”,

Proceedings of the 1997 Particle Accelerator Confer-

~, p. 1197, (1997), BNL 65005.

W.S. Graves, S.K. Feng, P.S. Pearson, and J.D. Smith,

“Innovative Aspects of the SDL Control System”,

Proceedimzs of the 1997 Particle Accelerator Confer-

- p. 2437, (1997), BNL 65004.

W. S. Graves and E. D. Johnson, “A High Resolution

Electron Beam Profile Monitor”, Proceedimw of the

1997 Particle Accelerator Conference, p. 1993, (1997),

BNL 65006.

W. S. Graves, E. D. Johnson, and T.O. Raubenheimer,

“The Source Development Lab Linac at BNL”,

Proceedirms of the 1997 Particle Accelerator Confer-

= p. 776, (1997), BNL 63812.

W. S. Graves and L. Solomon, “Harmonic Generation

FEL Magnets: Measured B-fields Compared to 3D

Simulations”, Proceedirws of the 199 5 Particle Accelerator Conference, p. 1414, (1996), BNL 63813.

N. Guilaumou, P. Dumas, G.L. Carr, and

G.P. Williams, “Synchrotrons Infrared

Microspectrometry Applied to Petrography in Micron

Scale Rangti Fluid Chemical Analysis and Mapping”,

Appl. Spectro., 52, 1029, (1998), BNL 65865.

B-2
I

M. Hart, “X-Ray Optical Beamline Design Principles”,

X-Rav and Neutron Dvnamical Diffraction: Theorv

and Atmlications, edited by A. Authier, S.

Lagomarsino, and B. K. Tanner, Nato ASI Series,

B357, 73-90, (1996), BNL 63976.

H. Hashizume, N. Ishimatsu, O. Sakata, T. Iizuka,

N. Hosoito, K. Namikawa, T. Iwazumi, L. Berman,

G. Srajer, C. T. Venkataraman, J. C. Lang,

C.S. Nelson, and L.E. Berman, “Resonant X-ray

Magnetic Scattering from the Twisted States of an

Fe/Gal Multilayer”, F’bysic4 B248, 133-139, (1998),

BNL 64718.

P.E. Haustein, L.E. Berman, G. Faigel, J.R Grover,

J,B, Hastings, and D.P. Siddons, “Nuclear Bragg

X-ray Scattering of Synchrotrons Radiation by

57FezO~:Methodology and Studks of Dynamical

Processes”, Hypetjine Interactions, 58,2445-50, (1990),

BNL 65342.

D. Heskett and L. Berman, “Applications of X-ray

Standing Waves in Studies of Surface, Films and Bulk

Materials”, Synch. Raa! News, 7/6,5,(1994),

BNL 65010.

D. Heskett, P. Xu, L. Berman, C.- C. Kao, and M.J.

Bedzyk, “The Geometric Structure of Rb/Cu(l 11)

Investigated with X-ray Standing Waves: Rb Coverage

Dependence”, Su~ Sci., 344,267-75, (1995).

J.P. Hill, C.-C. Kao, and McMarrow, “K-edge Resonant X-ray Magnetic Scattering from a Transition

Metal Oxide: NiO”, l%y~. Rev., B55, R8662, (1997),

BNL 63775.

S.L. Hulbert and G.P. Williams, “New Experimental

Facilities at the National Synchrotrons Light Source

VUV Ring”, Synch. Rad News, 10, 1, (1997),

BNL 65800.

N. Jamin, P. Dumas, J. Moncuit, W.H. Friedman,

J.-L. Teillaud, G.L. Carr, and G.P. Williams, “Chemical Imaging of Living Cells by Synchrotrons Infrared

Microspectrometry”, SPIE, 3153, 133-140, (1997),

BNL 65802.

N. Jamin, P. Dumas, J. Moncuit, W.H. Friedman,

J.-L. Teillaud, G.L. Carr, and G.P. Williams, “Chemical Imaging of Nucleic Acids, Proteins, and Lipids of a

Single Living Cell. Application of Synchrotrons Infrared

Microspectrometry in Cell Biolo@’, Cell. andMol

Bio., 44/1, 9-13, (1998), BNL 65476.

N. Jamin, P. Dumas, J. Moncuit, W.H. Friedman,

J.-L. Teillaud, G.L. Carr, and G.P. VWliams, “Highly

Resolved Chemical Imaging of Living Cells Using

Synchrotrons Infrared Microspectrometry”, Proceedir-ws

of the National Academv of Science, 95,4837, (1 998),

BNL 64796.

C. Kao, W. Caliebe, and J. Hastings, “Inelastic X-Ray

Scattering at the National Synchrotrons Light Source”,

Rev. Sci. Instwn., 6719,3363,(1996),BNL 63147.

C.C. Kao, W. Caliebe J.B. Hastings, and J.M. Gillet,

“X-ray Resonant Raman Scattering in NiO: Resonant

Enhancement of the Charge Transfer Excitations”,

Pbys. Rev., B54, 16361, (1996), BNL 63598.

W.D. Kimura, I.V. Pogorelsky, Y. LhI, K.P. Kusche,

A. van Steenbergen, J.C. Gallardo, J. Sandweiss, D.B.

Cline, D.C. Quimby, and M. Babzien, “Inverse

Cerenkov Acceleration using an IFEL Prebuncher”,

Proc. Advanced Accelerator Concerns Seventh

Workshom October 13-18, U Editors,

S. Chattopadhyay, J. McCullough and P. Dahl, MP

Press,M CP398, pp. 608-17, (1997), BNL 65237.

C.-H. Ko, J. Kirz, K. Maier, B. Winn, H. Ade,

S. Hulbert, E. Johnson, and E. Anderson,

“Chemical State Mapping on Material SurFaces with

the XIA Second Generation Scanning Photoemission

Microscope (XIA SPEM-11), SPIE, 2516, 150-59,

(1995), BNL 65122.

M. Kovar, R.V. Kasza, K. Grifi%hs, P.R. Norton,

G.P. Williams, and D. Van Campen, “Synchrotrons

Radiation FTIR Spectroscopic Studies of Water on

Ni(l 10)”, Surj Rev. andLetts., 512,589-598, (1998),

BNL 65742.

C.A. Kuntscher, G.M. Bendele, and P.W. Stephens,

“Alkali Stoichiometry and Structure of K4Cb0 and

RbACGO”,Pbys. Rev., B55, R3366-9, (1997),

BNL 63686.

B-3

I
Y. LIU, S. A. Bogacz, D. B. Cline, and X. J. Wang,

“Micro-bunching Diagnostics for Inverse Cerenkov

Acceleration by Coherent Transition Radiation”,

Nucl. Instrum. A4etb. Pbys. Res. A., 386,295-300,

(1997), BNL 63630.

Y. Llu, D.B. Cline, X.J. Wang, M. Babzien, J.M. Fang,

and V. Ytimenko, “Micro-Bunching Diagnostics for

the IFEL by Coherent Transition Radiation”, Proceedirws of the 7fi Workshoo on Advanced Accelerator

Concepts, edited by S. Chattopadhyay pp. 664-672,

(1996), BNL 63584.

Y. LIU, X. J. Wang, D. B. Cline, M. Babzien,

J. M. Fang, J. Gallardo, K. Kusche, I. Pogorels~,

J. .Warkka, and A. van Steenbergen, “Experimental

Observation of Femtosecond Electron Beam MicroBunching by Inverse Free-Electron-Laser Acceleration”,

phys. Rev. Lett, 80,4418, (1998), BNL 64647.

R.H. Menk, A.M. Charves, F. Arfelli, L. Chapman,

W. Thomlinson, and Z. Zhong, “Three Energy

Computed Tomography with Synchrotrons Radiation”,

Pkysica Medig XIII/1, 26-29, (1997), BNL 64788.

L.M. Miller, C.S. Ca.dson, G.L. Carr, G.P. Williams,

and M.R. Chance, “Synchrotron Infrared

Microspectroscopy as a Means of Studying the

Chemical Composition of Bone: Applications to

Osteoarthritis”, SPIE Proceedings, 3153, 141, (1997),

BNL 64794.

J.B. Murphy, E. Bhun, R. Heese, J. Keane, and

S. IGinsky, “Millimeter Wave Coherent Synchrotrons

Radiation in a Compact Storage Ring”, Proc. of the

1995 Particle Accelerator Conference, p. 284, (1995),

BNL 65119.

T. Oversluizen, P.M. Stefm, and M. Iarocci, “Practical

Notes on the Construction and use of a UHV DoubleCrystal Monochromator for Synchrotrons Radiation”,

Vacuum 37/3.4, 321-25, (1987), BNL 65530.

D. T. Palmer, X. J. Wag, R. H. Miller, M. Babzien,

I. Ben-Zvi, C. Pellegrini, J. Sheehan, J. Skaritka, H.

Winick, M. Woodle, and V. Y&menko, “Commissioning Results of the Next Generation Photoinjector”,

Proceeding of the 7~ WorkshoD on Advanced

Accelerator Concerns, edited by S. Chattopadhyay

pp. 695-704, (1996), BNL 63808.

D. T. Palmer, X. J. Wing, R. H. Miller, M. Babzien,

I. Ben-Zvi, C. Pellegrini, J. Sheehan, J. Skaritka,

H. Winick, M. Woodle, and V. Yakimenko, “Emittance

Studies of the BNL/UCLA 1.6 Cell Photocathode RF

Gun”, Proceedings of the 199 7 Particle Accelerator

Conference, edited by M. Comyn, M.K. Craddock,

M. Reiser, andJ. Thomson, pp. 2687-2689, (1997),

BNL 64466.

J.-H. Park, E. Vescovo, H. -J. Kim, C. Kwon,

R. Rarnesh, and T. Venkatesan, “Direct Evidence

for a Half-Metallic Ferromagnet”, Nature, 392,

794-796, (1998), BNL 65796.

B.N.J. Persson, F.M. Hoffmann, and G.P. Williams,

“Observation of a Surface State Charge Density Wave

Condensate by Infrared Spectroscopy”, Proc. of the

~@ We-Heraeus Seminar Electronic Surface and

Interface States on Metallic Swtems at Phvsikzentrum.

Bad Honnefi Germanv, October 17-20, 1994, Editors,

E. Bertel and M. Donath, World Scientific, pp. 141-

49, (1994), BNL 65124.

I.V. Pogorels~, “Emerging ps-TW COZ Laser Technology for High Energy Physics Applications”, ~

k, pp. 799-806, (1998), BNL 65238.

I.V. Pogorelsky, “Emerging Picosecond C02 Laser

Technology”, Proceedimzs of TAERI-Kansai International WorkshoD, p. 125, (1998), BNL 64790.

I.V. Pogorelsky, “Optimization of Laser Eakefield

Accelerator Parameters”, STS Press, pp. 866-874,

(1998), BNL 65239.

I.V. Pogorelsky, “Prospects for Compact HighIntensity Laser Synchrotrons X-ray and Gamma

Sources”, AIP Conference Proceedimts, 398,951,

(1997), BNL 63684 (Rev. 01/97).

I.V. Pogorelsky, “Prospects for Laser Wakefield

Accelerators and Colliders Using COZ Laser Drivers”,

Nucl Instrum. and Meths. in Phys. Res.,AIO, 524-531,

(1998), BNL 64791.

I.V. Pogorels~, “Ultra-Bright X-ray and Gamma

Sources by Compton BackScattering of COZ Laser

Beams”, Nucl Instrum. and Meths. in Phys. Res.,411,

172-187, (1998), BNL 63985.

B-4
I. V. Pogorelsky and I. Ben-Zvi, “Emerging Terawatt

Picosecond CO, Laser Technology and Possible

Applications in Accelerator Physics”, Proceedimz of the

Particle Accelerator Conference, pp. 645-666, (1997),

BNL 64473.

I.V. Pogorelsky, I. Ben-Zvi, M. Babzien, K. Kusche,

J, Skaritka, I. Meshkovs~, A. Dublov, V. Lekomtsev,

I. Pavlishin, and A. Tsunemi, “The First Picosecond

Terawatt C02 Laser at the Brookhaven Accelerator

Test Facility”, STS Press, pp. 861-867, (1998),

BNL 65240.

I.V. Pogorelsky, I. Ben-Zvi, J. Skaritka, Z. Segalov,

M. Babzien, K. Kusche, I.K. Meskovs~,

V.A. Lekomtsev, A.A. Dublov, Y. A. Boloshin, and

G,A. Baranov, “The First Terawatt Picosecond CO,

Laser for Advanced Accelerator Studies at the -

Brookhaven ATF”, AIP Conference Proceedings, 398,

937, (1997), BNL 63650.

I.V. Pogorelsky, A. van Steenbergen, R. Fernow,

W.D. Kimura, and S.V. Bukmov, “C02 Laser

Technology for Advanced Particle Accelerators”,

AIP Conference Proceedings, 398,923, (1997),

BNL 63649.

LV. Pogorelsky, A. vanSteenbergen, J.C. Gallardo,

V. Yakimenko, M. Babzien, K.P. Kusche, J. Skarkka,

W.D. Kimura, D.C. Quimby, K.E. Robinson, S.C.

Gottschalk, L.J. Pastwick, L.C. Steinhauer, D.B. Cline,

Y. LIU, P. He, F. Camino, I. Ben-Zvi, R.B. Fiorito,

D.W. Rule, R.H. Pantell, and J. Sandweiss, “Staged

Electron Laser Accelerator (STELI.A) Experiment at

Brookhaven ATF”, Proceedimxs of the First WERIKansai International Workshop, p. 25, (1998),

BNL 64789.

K.J. Randall, Z. Xu, E. Gluskin, I. McNuky,

R. Dejus, S. Krinsky, O. Singh, C.-C. Kao,

E.D. Johnson, C.T. Chen, and G. Meigs, “Characterization of a No;el Elliptically Polarized Wiggler”,

j ofElect. Spectio. And Related Phenom., 80,433-36,

(1996), BNL 65091.

B. Ren, F. A. Dilmanian, L. D. Chapman, X. Y. Wu,

Z. Zhong, I. Ivanov, W. C. Thomlinson and

X. Huang, “Beam Smiling in Bent Laue Monochromators”, Sv~chrotron Radia~on Instrumentation, Tenth

US National Conference, AIP Conference Proceeding,

417,95-100, (1997), BNL 64695.

F. Schreiber, A. Eberhardt, T. Y. B. Leung,

P. Schwartz, S. Wetterer, D. Lavrich, L.E. Berman,

P. Fenter, P. Eisenberger, and G. Stoles, “Adsorption

Mechanisms, Structures, and Growth Regimes of an

Archetypal Self-Assembling System Decanethiol on

Au(ll l)”, Pbys. Rev. Letts., B57, 12476-12481,

(1998), BNL 64712.

A.K. See, W.-W. Siu, R.A. Bartynski, A. Nangia,

A.H. Weiss, S.L. Hulbert, X. Wu, and C.-C. Kao,

“Enchanced Sensitivity to Oxide using Auger-Photoelectron Coincidence Spectroscopy”, SZnyfSci., 383,

L735-41, (1997).

M.L. Shek, “Observations Regarding a c(4x4)

C-Si(100) Surface”, Surf Sti., 414,353, (1998),

BNL 65307.

D.P. Siddons, C. Riekel, and J.B. Hastings, “SmallAngle X-ray Scattering at High Energies”,

J Appl. Cryw., 23,401-05, (1990), BNL 65007.

0. Singh and S. K-h&y, “Orbit Compensation for the

Time-Varying Elliptically Polarized Wiggler Operating

at 100 HZ, Nucl. lnstrum. andMeths. in Pbys. Res.,

A418, 249, (1998), BNL 65008.

0. Singh and S. I@nsb, “Orbit Compensation for the

Time-Varying Elliptically Polarized Wiggler with

Switching Frequency at 100 Hz”, Proceedimzs of the

1997 Particle Accelerator Conference, p. 2161, (1998),

BNL 64471.

0. Singh, Y. Tang, and S. Krinsky, “Orbit Feedback at

the NSLS”, Nud. Am-urn. andMetbs., in Pbys. RetL,

A418, 267, (1998), BNL 65093.

0. Singh, Y. Tang, S. Rarnamoorthy, S. Krinsky, and

L.-H. Yu, “Global Orbit Feedback Utilizing Analog

and Digital Technologies”, Proceedimm of the 1997

Particle Accelerator Conference, p. 2287, (1998), BNL

64472.

B. Sinkovic, L.H. Tjeng, N.B. Brookes,

J.B. Goedkoop, R. Hesper, E. Pellegrin,

F.M.F. De Groot, S. Altiere, S.L. Hulbert, E. Shekel,

and G.A. Sawatzky, “Local Electronic and Magnetic

Structure of Ni Below and Above T: A Spin-Resolved

Circularly Polarized Resonant Photoemission Study”,

PLys Rev. Letts., 79/18, 3510-13, (1997), BNL 65423.

B-5

I
P.M. Stefan, S. Krinsky, C. C. Kao, G. Rakowsky,

O. Singh, and L. Solomon, “Insertion Device Development in the Xl 3 Straight of the NSLS X-Ray Ring”,

Proceeding of the 1997 Particle Accelerator Confer-

= p. 727, (1998), BNL 64470.

P.M. Stefm, S. Krinsky, G. Rakowsky, L. Solomon,

and D. Lynch, “Small-Gap Undulator Research at the

NSLS Concepts and Results”, iVucl. Instnwn. ana?Meth.

in l%ys. Res., A412, 161, (1998), BNL 65092.

P.M. Stefm, D.P. Siddons, and J.B. Hastings, “A New

Beam Position Monitor for X-ray Synchrotrons Radiation Facilities”, Nucl Imtrum. And Meths. in Phys. Res.

A, 255,598-602, (1987), BNL 65529.

T. Tanabe, X. Marechal, T. Tanaka, H. Kitamura,

P. Stefim, S. Krinsky, G. Rakowsky, and L. Solomon,

“Development of an In-Vacuum Minipole Undulator

Array for National Synchrotrons Light Source InVacuum Undulatory”, Rev. of Sci. Instnwn., 69/1, 18-

24, (1998), BNL 65438.

W. Thomlinson, “Current Status and Perspectives of

Synchrotrons Radiation in Medicine”, Physics Medic~

XIII/1, 19-23, (1997), BNL 63368.

W. Thomlinson, “Synchrotron Radiation Applications

in Medical Research”, Medkal Applications of Synchrotron Radiation, edited by M. Ando and C. Uyama,

Springer-VerLrg Tokyo, pp. 2-9, (1998), BNL 64697.

W. Thornlinson, D. Chapman, Z. Zhong,

R.E. Johnston, and D. Sayers, “Diffraction Enhanced

X-ray Imaging”, Medical Abdications of Svnchrotron

Radiation, edited by M. Ando and C. Uyama, SpringerVerLrg Tokyo, pp. 72-77, (1998), BNL 64787.

A.C. Thompson, H.D. Zeman, J.N. Otis,

R. Hofstadter, E. Rubenstein, D.C. Harrison,

R.S. Kernoff, J.C. Giacomini, H.J. Gordon,

G.S. Brown, and W. Thomlinson, “Transvenous

Coronary Angiography in Dogs using Synchrotrons

Radiation”, International. of Cardiac Imaging 2,53-8,

(1986), BNL 65603.

0. K. C. Tsui, S. G. J. Mochrie, and L. E. Berman,

“Statistical Analysis of X-ray Speckle at the NSLS’,

J Synch I/ad, 5,30-36,(1998),BNL 64711.

T.A. Tyson, J.F. Federici, D. Chew, A.R. Bishop,

L. Furenlid, W. Savin, and W. Wlber, “Local Structural and Electronic Changes Accompanying

Photodoping in Yb~Cu~OG+X”,Physics C, 292, 163-

170, (1997), BNL 65159.

A. van Steenbergen, J. Gallardo, J. Sandweiss,

M. Babzien, J.-M. Fang, K. Kusche, R. Malone,

I. Pogorels~, X. Qiu, T. Romano, J. Sheehan,

J. Skaritka, and X.-J. Wang, “Status of the BNL IFEL

Accelerator”, AIP Conference Proceeding, 398,591,

(1997), BNL 63635.

A. van Steenbergen, J. Gallardo, J. Sandweiss,

J.-M. Fang, M. Babzien, X. Qui, J. Skaritka, and

X.-J. Wang, “Observation of Energy Gain at the BNL

Inverse Free-Electron-Laser Accelerator”, Pbys. Rev.

Letts., 77/13, 2690-93, (1996), BNL 63335.

J.-M. Wang, “Microwave Instabili~ as Coherent Light

Source”, P4ys. Rev. E, 58,984-991, (1998), BNL

65798.

D.L. Wetzel and G.P. Williams, “Localized (5 pm)

Probing and Detailed Mapping of Hair with Synchrotrons Powered FT-IR Microspectroscopy”, AIP Conference Proceedimzs, 430, 302, (1997), BNL 65669.

G.P. WNiams, “IR Spectroscopy at Surfaces with

Synchrotrons Radiation”, Su& Sci., 368, 1-8, (1996),

BNL 65123.

C.Y. Yang, J.E. Penner-Hahn, and P.M. Stefan, “NSLS

Xl 9A Beamline Performance for X-ray Absorption

Measurements”, Nucl Instrum. AndMeths. Res. A, 291,

157-61, (1990), BNL 65531.

H.D. Zeman, J.N. Otis, R. Hofstadter, A.C. Thompson, G.S. Brown, W. Thomlinson, R. Rubenstein,

J.C. Giacomini, H.J. Gordon, and R.S. Kernoff, “The

Imaging Technology used for Angiography at the

Stanford Synchotron Radiation Laboratory”, ~

Svnchrotron Radiation ADDlications to Digital Subtraction Amziozraphv (SYRDA), Edited by E. Burattini

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