NATL INST. OF STAND i TECH

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PUBLiCATlONS

NISTSP 993

NCNR 2002

NIST Center for Neutron Research

Accomplishments and Opportunities

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^ ^ Smithsonian Center ^4iJ^ for Materials Research and Education CNBT

consortium

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National Institute of

Standards and Technology

Technology Administration

U.S. Department of Commerce

December 2002
Dr. Michael Marron

Director Biomedical Technology NCRR-National Institutes of Health

Dr. Rita Colwell

Director U.S. National Science Foundation

Dr. Patricia Dehmer

Associate Director

Office of Basic Energy Sciences

U.S. Department of Energy

Dr Roger Cohen, Manager

Strategic Planning Programs

ExxonMobil

Dr Arden Bement

Director National Institute of Standards and Technology

Rep. Constance A. Morella

8th Congressional District Maryland

Dr. Samuel Bodman

Deputy Secretary

U.S. Department

of Commerce

Phillip Bond

Under Secretary of Commerce

for Technology/Chief of Staff U.S. Department of Commerce

Dr John Marburger

Director White House Office of Science and Technology Policy

Above: Speakers at the event "Celebrating Partnerships to Promote

Stewardship of Research Resources" held at the NCNR on August 5, 2002.

On the cover: Partners with the NCNR are exemplified by their logos adjacent

to related facilities or projects.
NCNR 2002

NIST Center for

Neutron Research

Accomplishments

and Opportunities

NIST Special Publication 993

J. Michael Rowe, Director

Ronald L. Cappelletti, Editor

December 2002

U.S. DEPARTMENT OF COMMERCE

Phillip J. Bond, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Donald L. Evans, Secretary

Technology Administration

Arden L. Bement, Jr., Director
DISCLAIMER

Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept

adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily

the best available for the purpose.

National Institute of Standards and Technology Special Publication 993

Natl. Inst. Stand, Technol. Spec. Publ. 993, 72 pages (December 2002) CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE - WASHINGTON: 2002

For sale by the Superintendent of Documents, U.S. Government Printing Office

Internet; bookstore.gpo.gov — Phone: (202) 512-1800 — Fax: (202) 512-2250

Mail: Stop SSOR Washington, DC 20402-0001
Contents

Foreword iv The NIST Center for Neutron Research 1 NIST Center for Neutron Research Layout 2 Cold Source Replacement 4 Research Highlights Instrumentation Development and Applications The Advanced Liquid Hydrogen Cold Neutron Source 6 Neutron Spin Filters Based on Polarized ^He 8 Development of an Ion-Implanted Phosphorus in Silicon SRM forthe Semiconductor Industry 10

New/ Thermal Neutron Prompt Gamma-Ray Activation Analysis Facility 12 Performance Enhancements of the CHRNS 30-m SANS Instrument 14 Chemical Physics and Biology

Probing Nanoscale Disorder with Neutron Tunneling Spectroscopy 16 The "Bucket Brigade" Mechanism of Proton Diffusion in Superprotonic Conductors 18

Motion in Intermediates Along the Protein-Folding Pathway: cytochrome c 20

Neutron Reflectivity from Biomimetic Membranes: Improving Reliability Through Wavelet Analysis 22

Protein Adsorption to Metal-Chelating Lipid Monolayers 24

Hydration State of Single cytochrome c Monolayers on Soft Interfaces via Neutron Reflectivity 26

Soft Condensed Matter

Direct Measurement of the Reaction Front in Chemically Amplified Photoresists 28

Scaling of Membrane Phase Dynamics 30

Observation of Liquid-Glass-Liquid and Glass-Glass Transitions in the L64/D2O Copolymer Micellar System 32

Early-Stage Compositional Segregation in Polymer Blend Films 34 Condensed Matter and Applied Physics

Magnetic Cluster Sizes in Magnetic Recording Disks 36

Dynamical Effects of Polar Nanoregions in Relaxor Ferroelectrics 38 Emergent Excitations in a Geometrically Frustrated Magnet 40

Polaron Dynamics and the Glass Transition in Colossal Magnetoresistance Materials 42 Quantum Impurities in the Two-Dimensional Spin One-Half Heisenberg Antiferromagnet 44

Automobile Sheet-Metal "Springback": Residual Stress Measurements and Modeling 46

Serving the Science and Technology Community 48 NCNR Partnership Celebration 48 The NCNR User Program 48 The Centerfor High Resolution Neutron Scattering 49

Collaborations 49

Cold Neutrons for Biology and Technology 49

Independent Programs 49

Eighth Annual Summer School 52 Operations 53

Facility Developments 54 DAVE and Other Software Developments 54 New Monochromator Drum Shields 54 Sample Environment Equipment 55

Facility Improvements 55

Publications 56

Instruments and Contacts 68

Contacts Inside Back Cover
Foreword

Once again, it is a great pleasure to report on a year of accomplishments in all areas of the Center. Although the shutdown was prolonged by unforeseen problems

in an auxiliary system, the results when we re- started were everything that we had hoped for. The new cooling tower is functioning well, reducing the

visible plume during cold weather dramatically. This

system is now well prepared for another twenty-plus

years of operation. The work on relicensing is also on

track — the new analyses are almost complete, and

confirm the existing Safety Analysis Report. A new liquid

hydrogen cold source of improved design was installed during the same shutdown. It is working well, producing

nearly twice as many cold neutrons as its predecessor,

exactly in agreement with the detailed MCNP predictions.

In every respect, the future for neutron production at the NIST source looks excellent. As always, we continue to improve existing instru- ments and work on new ideas. An optical filter was

installed in the NG-3 30 m SANS instrument (a key part of

the NIST/NSF Center for High Resolution Neutron

Scattering), providing further gains of up to a factor of

three at long wavelength. A modification to the guide that runs through the choppers of the Disk Chopper time-offlight Spectrometer has given intensity increases of 2 to 3 over the whole wavelength range. So these two instru- ments have increased in performance by factors of

between 3 and 5 over the past year, a direct result of our

continuing investment in instrumentation. A consortium of

researchers from five universities has been awarded a grant from the National Institutes of Health to begin

development of a new Research Resource called Cold

Neutrons for Biology and Technology, which includes

construction of a new diffractometer/reflectometer for membrane and related structures. The National Science

Foundation has increased its partnership with the NCNR,

and now helps to support the high-resolution inelastic scattering instruments in the guide hall. These and other

partnerships, such as the ones with Johns Hopkins University, the University of Maryland, and Brookhaven National

Laboratory, are a key part of our plans to move forward,

and have been an essential part of our past success. And again, as always, the science being produced

fully justifies the dedication and work of the people who

provide the neutrons and instruments. While walking

through the facility during operating cycles, I am always

amazed at the breadth and depth of research now being

done with neutrons, and delighted by the energy and

intensity of the young people doing it. I derive great

pleasure helping to choose scientific highlights, and then

from reading the results of those choices. They form the

greatest portion of this report, and I hope that you enjoy

them as much as I do.

iv
TheNIST Center for

Neutron Research (NCNR)

Neutrons are powerful probes of the structure and dynamics of materials ranging from molecules inserted

into membranes mimicking cell walls to protons migrating

through fuel cells. The unique properties of neutrons (see

inset) can be exploited by a variety of measurement tech- niques to provide information not available by

other means. They are particularly well suited

to investigate all forms of magnetic materials

such as those used in computer memory stor- age and retrieval. Atomic motion, especially

that of hydrogen, can be measured and monitored, like that of water during the setting of

cement. Residual sfresses such as those in- side stamped steel automobile parts can be

mapped. Neutron-based research covers a broad spectrum of disciplines, including en- gineering, biology, materials science, poly- mers, chemistry, and physics.

The NCNR's neutron source provides

the intense beams of neutrons required for these types of measurements. In addition to the thermal energy neutron beams from the heavy water or graphite moderators, the

NCNR has a large area liquid hydrogen moderator, or cold source, that provides intense neutron beams for the only cold neutron facility presently operating in the United States. There are currently 28 experiment stations: six pro- vide high neutron flux positions for irradiation, and 22 are beam facilities most of which are used for neutron scattering

Instruments in the cold neutron guide hall.

research. The following pages show a schematic layout of

the beam facilities. More complete descriptions of instru- ments can be found at www.ncnr.nist.gov.

The NCNR supports important NIST research needs,

but is also operated as a major national user facility with

Why Neutrons?

Neutrons at the NCNR reveal properties not available to other probes. They can behave like micro- scopic magnets, can diffract like waves, or set particles into motion as they recoil from them.

Wavelengths - range from 0. 1 A to 1 00 A, allowing them to form observable ripple patterns from

structures as small as atoms to as large as proteins.

Energies - of millielectronvolts, the same as that of motions of atoms in solids or liquids, waves in magnetic materials, or vibrations in molecules. Exchanges of energy between neutrons and matter as

small as nanoelectronvolts and as large as tenths of electronvolts can be detected.

Selectivity - in scattering power varies from nucleus to nucleus almost randomly. Specific isotopes can stand out from other isotopes, even of the same kind of atom. Specific light atoms, difficult to observe

with x-rays, are revealed by neutrons. Hydrogen, especially, can be distinguished from chemically

equivalent deuterium.

Magnetism - makes the neutron sensitive to the magnetic spins of both nuclei and electrons, allowing

the behavior of ordinary and exotic magnets to be detailed precisely.

Neutrality - of the uncharged neutrons allows them to penetrate deeply without destroying samples, and

pass through walls controlling a sample's environment allowing measurements under extreme conditions.

Properties ranging from the residual stresses in steel girders to the unfolding motions of proteins are amenable to measurement by neutrons.

Capture -characteristic radiation emanating from specific nuclei capturing incident neutrons can be used

to identify and quantify minute amounts of material in pollutants or ancient pottery shards.

merit-based access made available to the entire U.S. technological community. Each year, over 1700 research participants from all areas of the country, from industry, academia,

and government use the facility for measurements. Beam

time for research to be published in the open literature is without cost to the user, but frail operating costs are recovered for proprietary research. Access is gained mainly through

a peer-reviewed, web-based proposal system with beam time

allocated by a Program Advisory Committee twice a year. For details see www.ncnr.nist.gov/beamtime.html. The National Science Foundation and NIST co-fund the Center for High Resolution Neutron Scattering (CHRNS) that operates

six of the world's most advanced instruments. Time on CHRNS instruments is made available through the proposal

system. Some access to beam time for collaborative measurements with the NIST science staff can also be arranged on other instruments.

1
A Cold Neutron Depth 3

Profiling instrument (not shown) for quantitative profiling

of subsurface impurities currently at this site will be ^ moved to another position. Shown is MACS, a triple axis cold neutron crystal spectrometer under construction with double focusing monochromator ^ and multiple crystal analyzer/ detectors that can be flexibly configured for several energies

simultaneously or for high throughput at one energy. 6 BT-7 Triple Axis Spectrometer with fixed incident energy for measurements of excitations and

structure.

BT-8 Residual Stress

Diffractometer optimized for depth profiling of residual stress

in large components.

BT-9 Triple Axis Crystal

Spectrometer for measurements of excitations and

structure.

Thermal Column a very well- thermalized beam of neutrons used for radiography, tomography, dosimetry and other experiments.

BT-1 Powder Diffractometer

with 32 detectors; incident wavelengths of 0.208 nm, 0.154 nm, and 0.159 nm, with highest

resolution of 8d/d = 8x10-4.

7 BT-2 Triple Axis Crystal

Spectrometer with polarized beam capability for measure- ment of magnetic dynamics and

stmcture.

8 BT-4 Filter Analyzer Neutron Spectrometer with cooled

Be/Graphite filter analyzer for chemical spectroscopy.

9 BT-5 Perfect Crystal Diffractometer SANS small angle neutron scattering instrument for microstructure on

the W nm length scale, sponsored by the National Science Foundation and NISI,

part of the Center for High

Resolution Neutron Scattering (CHRNS).

10 NG-7 Horizontal Sample

Reflectometer allows

reflectivity measurements of free surfaces, liquid vapor interfaces, as well as polymer coatings.

11 Neutron Interferometry and

Optics Station with perfect

silicon interferometer; vibration

isolation system provides

exceptional phase stability and

fringe visibility.

12 Spin Polarized Triple Axis Spectrometer (SPINS) using

cold neutrons with position sensitive detector capability for high resolution studies — part of CHRNS.

2
NIST Center for Neutron Research Layout

16

15

13 Spin Echo Spectrometer

offering neV energy resolution, based upon Julicli design, sponsored by NIST, Julich and

ExxonMobil — part of CHRNS.

14 Prompt Gamma Activation Analysis cold neutron fluxes allow detection limit for H of

1 |ig to 10 ng. Focused beams

are available for profiling.

15 NG-7 30 m SANS for microstojcture measurements

sponsored by NIST, ExxonMobil, and the University of Minnesota.

16 Neutron Physics Station

offering three cold neutron beams

having wavelengths of 0.5 nm,

0.9 nm, and "white" that are

available for fundamental neutron

physics experiments.

17 Fermi Chopper hybrid timeof-flight (TOF) Spectrometer

for inelastic scattering with

incident wavelengths between

0.23 nm and 0.61 nm chosen

by focusing pyrolytic graphite

crystals. A simple Fenni chopper pulses the beam.

18 Disk Chopper TOF Spectrometer a versatile time-offlight spectrometer, with beam

pulsing and monochromatization

effected by 7 disk choppers. Used for studies of dynamics in condensed matter, including macromolecular systems — part of CHRNS.

19 NG-3 30 m SANS for microstructure measurements

sponsored by the National Science Foundation and NIST - part of CHRNS.

20 Bacl(scattering

Spectrometer high intensity

inelastic scattering instrument

with energy resolution < 1 i^eV,

for studies of motion in molecular and biological systems — part of CHRNS.

21 NG-1 8 m SANS for polymer

characterization being modified

to 10 m and to be made

available for CHRNS use along

with its current use by the NIST

Polymers Division.

22 Vertical Sample

Reflectometer instrument with

polarization analysis capability

for measuring reflectivities down

to 10-8 to determine subsurface

structure.

23 Cold Neutrons for Biology

and Technology vertical sample reflectometer, to be built with polarization analysis

capability for measuring

reflectivities down to 10-^. It

will have a position- sensitive detector for measuring off- specular

reflections.
Removal of Unit 1

The bear trap is placed on special

The "bear trap" transport device is moved into place

to remove Unit 1.

Installation of Unit 2

4
i Cold Source Replacement
The Advanced Liquid

Hydrogen Cold Neutron Source

The 14 cold neutron instruments at the NCNR received a substantial

increase in performance when the liquid

hydrogen cold source, successfully operated

since 1995 (hereafter called "Unit 1"), was replaced

with an improved design (called "Unit 2") during last year's maintenance outage. The NCNR cold source is designed to maximize the useftil intensity of neutrons in the wavelength band between 0.2 nm and 2.0 nm by

providing a low temperature medium that further slows

down the neutrons exiting the heavy water moderator/

reflector of the NIST 20 MW reactor. The basic operating

principles for the cold source are the same in both designs

[1]. Using the large diameter cryogenic beam port at the NCNR reactor, a cryostat containing a thin, annular shell of

liquid hydrogen is placed in a high intensity region of the

reactor's reflector. Interaction with the slow moving

hydrogen molecules modifies the neutron energy spectrum.

A neutron guide tube system beginning close to the exit of

the cryostat transports the intense cold neutron beams to the neutron scattering instruments. The radiation heat

deposited in the moderator is removed by boiling of the

liquid hydrogen. Stable operation of the cold source is maintained by a thermosiphon; cold liquid hydrogen flows

by gravity into the cryostat from a helium cooled con- denser and the hydrogen vapor from boiling returns to the condenser in a closed, convective circulation loop. The

cryostat also includes a heavy water cooling jacket,

insulating vacuum regions and helium containment vessel

that surrounds all portions of the system containing

hydrogen.

Following the commissioning of Unit 1, detailed

simulations of the NCNR reactor and moderators became

sufficiently accurate that it was possible to explore further optimization of the cold source geometry for improved

performance using a sophisticated MCNP model of the NCNR source [2]. The Unit 2 design differs from Unit 1 in many key respects, as can be seen in Fig. 1 . Most of

the volume of the Unit 1 cryostat assembly was empty

space, leaving a large void in the reactor reflector and

lowering the neufron flux near the cryostat. The heavy

water cooling jacket of Unit 2 was expanded to fill nearly

half of the insulating vacuum void of Unit 1. This change

reduced the void in the reflector and increased the neutron

flux near the cryostat by about 40 % thus providing a cold neutron gain of the same magnitude. Because of these changes and to fully illuminate the rectangular aspect ratio of the NCNR guide system, the Unit 2 moderator chamber

is smaller than the original and is an ellipsoidal annulus,

rather than a spherical one. With a smaller vessel size, the thickness of the liquid hydrogen shell could be increased

from 20 mm to between 25 mm and 30 mm without

increasing the overall hydrogen inventory. Finally, the inner ellipsoid of the newer design is evacuated through a small vacuum port, removing most of the hydrogen vapor.

In Unit 2, the cold neutron beam passes through only

20 mm of vapor, rather than through the 300 mm path

Liquid Hydrogen

Fig. 1. Comparison between tlie original (top) and the advanced liquid hydrogen cold sources for the NIST research reactor The heavy water volume is indicated in blue, liquid hydrogen in orange, and hydrogen

vapor in yellow.

6
Instrumentation Development and Applications

length in Unit 1 . This resuhs in less neutron adsorption by

hydrogen. Collectively, these changes in the moderator

chamber add another 15 % to 20 % to the predicted gain.

The complex geometry of Unit 2 posed many

challenges for the design and fabrication of the cryostat.

Complicated elliptical vessels were designed with the aid of

finite element analysis to model their mechanical strength.

Extensive pressure testing supported this detailed modeling.

Because of the non-standard shapes, components were

precisely cut from solid blocks of Aluminum-6061 using a high-speed mill at the NIST instrumentation shop. The

geometry also placed high demands on the welding of the various components into a leak-tight cryostat satisfying

stringent quality control tests. The entire cryostat system was completely fabricated, assembled, and tested at NIST.

The replacement of Unit 1 with the new design was also a

significant technical challenge. Detailed work planning was required to ensure that the highly radioactive Unit 1 could be safely removed with the least amount of disruption to the sensitive alignment of the neutron guide net- work. Radiation damaged neutron guides near the source were also systematically replaced during the installation. The installation was completed on schedule with a minimal

dose exposure to the installation team. When the reactor resumed normal operation on March 6, 2002, the thermal and neutronic performance of

the new cold source was tested. Startup tests measured

the helium refiigerator heat load as reactor power was

increased. At 20 MW, the heat deposited in the source was measured at 1300 watts in excellent agreement with

calculations. The cold neutron flux was monitored to ensure that the thermosiphon functioned smoothly and that the moderator volume remained full of liquid hydrogen as the evaporation rate increased to over 3 g/s at full power.

Further tests established the normal operating parameters

for the cryostat and verified the protection systems under

various abnormal conditions.

The performance of the new source was

benchmarked against Unit 1 by duplicating flux measure- ments of the intensity as a function of neutron wavelength

at several Guide Hall instruments. Figure 2 is a plot of the cold source gain, defined as the ratio of intensities between

Unit 2 and Unit 1 , as a function of neutron wavelength.

The figure includes both the gain factors measured at three spectrometers and as obtained from the MCNP Monte

Carlo simulafions [2]. While the agreement is excellent, the measured gains were actually somewhat greater than

predicted, especially at long wavelengths. This additional

gain is likely due to the new guide sections replaced during

2.3

2.1

1.9

1.7

.-S 1.5

-E 1.3

CD CD

1.1

0.9

0.7 -

•

'

»

" J *

4

• MCNP

A NG-7 SANS

c NG-4 DCS

NG-1 SANS

J L J L J L

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Wavelength (nm)

Fig. 2. Gains in cold neutron flux measured at the NG-7 and NG-1 small angle neutron scattering (SANS) instruments, and at the disk chopper

spectrometer (DCS) on NG-4, compared to the predicted gains, based on Monte Carlo simulations using MCNP.

the cold source installation, an effect that is not included in the MCNP models. The new cryostat design also substantially reduces the number of fast neutrons from the cold source resulting in improved instrument signal-to-noise

levels.The advanced liquid hydrogen cold source has

successfiilly met all of its design goals. Its success demonstrates how the effective use of detailed computer

models to optimize a design can lead to substantial perfor- mance improvements. However, it also demonstrates that the complex geometry that results from such an optimization requires more complex stress modeling, new fabrication technologies and even more stringent quality assurance

testing. Most importantly, the success of the Unit 2 cold source design significantly enhances the measurement

capability of the cold neufron scattering instrumentation at NIST with intensity gains of nearly a factor of two in the important long wavelength region of the spectrum.

References

[ 1 ] R. E. Williams and J. M. Rowe, Physica B 311, 117 (2002).

[2] J. F. Briesmeister (Ed.), MCNP - A General Monte Carlo N-Particle Transport Code, Version 4B, Los Alamos National Laboratory,

LA-12625-M, Los Alamos, New Mexico (1997).

The Staff NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8560

7
Neutron Spin Filters

Based on Polarized ^He

SI1

' pin-polarized neutrons are useful 'probes of magnetic matter since

both the magnetic scattering of neutrons by

unpaired electrons and the scattering of neutrons by nuclei of non-zero spin can be strong functions

of the neutron spin state [1]. Unfortunately, the

limitations of current polarizing and analyzing devices

have substantially restricted the application of this powerful technique. ^He spin-filters have the potential to yield broadband neutron polarizers and analyzers that can be used for cold, thermal, and epithermal neutrons. Such

spin filters could make new classes of neutron scattering

experiments possible.

For certain applications there are presently no suitable devices. For example, polarization analysis of scattered beams having wide angular divergence is impractical with

reflection-based devices such as supermirrors because of

their inadequate angular acceptance and small-angle

scattering. At present, we are developing ^He-based

polarization analyzers for diffuse reflectometry and smallangle scattering (SANS) with neutrons, both of which

require analysis of a large divergence beam. ^He-based

neutron spin filters would also be advantageous on crystal

spectrometers since any monochromator or analyzer

crystal can be used, rather than just Heusler alloy, greatly

increasing the range and flexibility of the instrumentation.

Furthermore, polarizing or analyzing thermal and hot neutrons at spallation sources, where the time-of-flight

method is employed, often requires the broadband capability of ^He spin filters. In addition to their utility for neutron

scattering, polarized ^He spin filters are also of interest for nuclear and particle physics studies with neutrons, such as determination of weak coupling constants and tests of the Standard Model via accurate measurements of decay

correlation coefficients in polarized neutron beta-decay [2]. Neutron spin filters based on polarized ^He rely on

the strong spin-dependence of the neutron capture cross

section for ^He. For a sufficient thickness of 100 %

polarized ^He gas, essentially all of the neutrons with

antiparallel spin would be absorbed, while nearly all of the neutrons with parallel spin would be transmitted, resulting

in 100 % neutron polarization and 50 % transmission. In

Fig. 1 we show calculated values of the neutron polarization and neutron transmission for ^He polarization

Pjjg = 60 %, an experimentally achievable value. Since

there is a tradeoff between neutron polarization and

transmission, we also show P^^T^^, which is a useful figure-of-merit for many experiments. A transmission

analyzer can be characterized either by the transmission

asymmetry A or the flipping ratio F. For T+ and T_ defined

to be the transmissions for neutrons with polarization

parallel and antiparallel to the ^He polarization, respectively, the asymmetry is given by ^ = {T+ - T_)I{T+ + T_) and the

flipping ratio by F= TJT_ = (1 + A)l{\ - A). The flipping

ratio F is also shown in Fig. 1 . The asymmetry for a spin

filter used as an analyzer is the same as the neutron

polarization produced when it is used as a polarizer. For

the specific case of cold neutrons (A = 0.5 nm), a spin

filter used as a polarizer with P^e ^ 60 % and a pressure- length product of 7 kPa-m would yield = 90 % and = 20 %, or, when used as an analyzer, would give

A = 90 % and F= 19. We produce polarized ^He gas by two optical pumping methods: spin-exchange, which is performed directly

at high pressure (0.1 MPa to 0.3 MPa), and metastabilityo

50

40

30

20

10

0 0 1 2 3 4 5 pressure * cell length * wavelength [kPa-m-nm]

Fig. 1. Neutron polarization P„ (solid thick line), transmission 7„ (solid thin line), a figure of merit given by P^l^ (dashed line), and the flipping

ratio F (dotted line) as a function of the product of ^He pressure in Pa

(assuming a room temperature cell), cell length in m and wavelength in nm. The calculations are shovi/n for ^He polarization Pne" "Z"- "^^^ scale on the right hand y-axis is used for the flipping ratio.

8
Instrumentation Development and Applications

exchange, in which the gas is polarized at low pressure

(s; 100 Pa) and then compressed [3]. The spin-exchange

method is convenient and well matched to continuous

operation on a beamline. whereas the metastabilityexchange method has a higher polarizing rate. At present,

it has been more com enient (for either method) to polarize gas off-line and transport it to the beam line. Maintaining

the polarization in the absence of optical pumping requires

a homogeneous magnetic field and specially prepared glass

cells with slow wall relaxation. We have produced cells with relaxation times as long as one month, dominated by

the intrinsic dipole-dipole relaxation in the ^He gas itself

[4]. In the future, continuously operating spin filters can

be installed directh on the neutron instrument.

Polarization analysis allows for separation of magnetic from nuclear scattering, and also separation of

coherent from spin-incoherent scattering. In our first demonstration experiment for SANS, we used a ^He spin

filter to extract a small component of spin-incoherent

scattering in the presence of strong coherent scattering

[5]. We ha^ e continued with tests of separating magnetic

from nuclear scattering.

Recently we carried out successful tests of a polarized ^He spin filter on the NCNR NG- 1 reflectometer. The

first test experiment on a specular reflection was a careful comparison of results obtained with a ^He analyzer to those

obtained with the current technique that employs a supermirror anah zer. The test sample was an epitaxial

Muq 52Pdo.48/Fe (001) bilayer, for which chemical ordering

and magnetic exchange-bias have recently been reported

[6]. By var\'ing the magnetic field on this sample, it was

possible to test the ^He analyzer imder conditions of both

significant and negligible spin-flip scattering. We employed

a compact, magnetically shielded solenoid that was

interchanged with the analyzing supermirror on the NGl

mstrument. The solenoid adequately shielded the stray

fields from the 0.6 T magnet and guide field magnets. The

results obtained with the ^He analyzer were identical to those obtained with the supermirror analyzer. For efficient studies of diffuse scattering on a

reflectometer, the ^He analyzer will be combined with a

position sensitive detector (PSD). Two issues not tested

in the specular experiment are relevant in this case:

(1) possible depolarization of neutrons that follow trajectories off the axis of the ^He analyzer, and (2) possible

background from the ^He cell. We have established that most of the area of apertures in the magnetic shield is usable, with depolarization only occurring for a small range

of extreme trajectories. We have also determined that small

angle scattering from the cell is negligible and therefore should not pose an issue for the low neutron fluxes expected in diffuse scattering experiments. This series of

tests established the suitability of polarized ^He spin filters for diffuse reflectometry experiments, which we will pursue in the near future. We are making continual improvements in the polarization and relaxation time of our ^He cells. In the recent reflectometry experiments, the initial -''He polarization was 57 %, resulting in a neutron flipping ratio of 3

and a transmission for the desired spin state of 24 %. The

relaxation time of the polarized gas was 1 5 days on the beam line, which was somewhat reduced from the intrinsic value of 24 days for the cell due to a small fractional gradient of 3 x lO-'^ cm"i in the magnetic field of the shielded solenoid. Our aim is to increase the ^He polarization to 70 % and obtain relaxation times at the dipole-dipole

limit.

References

[1] R. M. Moon, T. Riste, and W. C. Koehler, Phys. Rev. A 181, 920- 931 (1969).

[2] Fundamental Physics with Pulsed Neutron Beams, Research

Triangle Park, North Carolina, June 1-3, 2000, edited by C. R. Gould, G. L. Greene, F. Plasil, and W. M. Snow (World Scientific, Singapore, 2001).

[3] T. R. Gentile et al, J. Res. Natl. Inst. Stand. Technol. 106, 709-729

(2001).

[4] D. R. Rich et al, Appl. Phys. Lett. 80, 2210 (2002).

[5] T. R. Gentile et al, J. Appl. Crystallog. 33, 771-774 (2000).

[6] R. F. C. Farrow et al, Appl. Phys. Lett. 80, 808 (2002).

T. R. Gentile and A. K. Thompson

National I nstitute of Standards and Technology NISTCenterfor Neutron Research 100 Bureau Drive, MS 8461

Gaithersburg, MD 20899-8461

J. A. Borchers, J. W. Lynn, K. V. O'Donovan, and C. F. Majkrzak

National Institute of Standards and Technology NISTCenterfor Neutron Research

100 Bureau Drive, MS 8562

Gaithersburg, MD 20899-8562

W. M. Snow and W. C. Chen

Indiana University Department of Physics

Bloomington, IN 47405

G. L. Jones

Physics Department

Hamilton College 198 College Hill Road

Clinton, New York 13323

9
Development of an Ion-Implanted

Phosphorus in Silicon SRM

for the Semiconductor Industry

' ilicon is the foundation material

of the electronic age, lying at the base of the 200 billion dollar world-wide

semiconductor industry. Silicon's properties are manipulated by precise implantation and distribution of other atoms (dopants), which makes the accurate measurement of impurity distributions imperative.

SEMATECH (a consortium of semiconductor manufacturers) recently listed Standard Reference Material (SRM)

implant of phosphorus in silicon as a high priority industrial need.

The U.S. semiconductor industry relies heavily on

secondary ion mass spectrometry (SIMS) for characterization of the depth distribution of dopants in silicon. To

achieve high accuracy in the concentration determination

by SIMS, standards of known dopant concentration,

conveniently provided by ion implants of certified dose, are required. Standard Reference Materials of boron and

arsenic implants in silicon (SRMs 2137 and 2134 [1]) have

already been developed by NIST as SIMS calibration

standards.

The SIMS community in the United States undertook

a round-robin study to calibrate the implanted dose of

phosphorus in silicon by consensus. Dose determinations

among laboratories varied by nearly a factor of 2, reflect- ing primarily the errors of the respective in-house stan12

11

^-^ 10 Eo

c; 9

COO

61-

5

r I 1 1 1 I I I

1 r

Mean = 8.40 X 10 •IT

1 1 I I I I i_

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Lab Number

Fig. 1. Round-robin measurements of phosphorus in silicon by

secondary ion mass spectrometry in 16 U.S. industrial laboratories, demonstrating the need for a common phosphorus reference material to improve inter-laboratory reproducibility.

dards (Fig. 1 ). These results demonstrate the need for a common phosphorus reference material to improve inter- laboratory reproducibility. In pursuit of a phosphorus in silicon SRM, a radiochemical neutron activation analysis (RNAA) procedure

has been developed, critically evaluated, and shown to have

the necessary sensitivity, chemical specificity, matrix

independence, and precision to certify phosphorus at ion

implantation levels in silicon [2, 3]. During sample irradiation, 3ip undergoes neutron capture to form ^^P, which is then separated from the matrix and measured by beta

counting. The procedure is used here to assign a value to the quantity of phosphorus in SRM 2133 (phosphorus

implanted silicon).

SRM 2133 was prepared by phosphorus implantation

of a 200 cm diameter silicon wafer. The wafer was cut

into 1 cm- pieces by means of a wafer saw, and twelve

pieces were chosen for analysis. The area of each piece was determined by measuring its dimensions using a digital

micrometer. During irradiation, ^^p may be produced via neutron capture by the implanted phosphorus, by bulk

phosphorus impurity in the wafer, and by silicon. The

latter two sources lead to measurement error, which must

be corrected. These corrections were made by measuring

silicon blanks, which were prepared by cutting a nonimplanted silicon wafer into ~ 1 cm^ pieces. Standards were prepared by deposition of standardized solutions of

phosphorus on aluminum foils. Samples, standards, and blanks were irradiated for 3 hours in irradiation tube RTl of the NIST neutron source

at a neutron fluence rate of 1.05 x 10'^ cm-^-s"'. Targets were then processed using the method developed previously [2, 3]. Silicon samples and blanks were mixed with

a few milligrams of non-radioactive phosphorus (carrier)

and dissolved in a mixture of nitric and hydrofluoric acids. Phosphorus was separated from the matrix first by

precipitation as ammonium phosphomolybdate, then as magnesium ammonium phosphate. The latter was col- lected by filtration, washed with dilute ammonium hydroxide and ethanol, air dried, weighed, and packaged for beta-ray counting. The yield, (fraction of recovered

phosphorus carrier), was determined gravimetrically,

assuming a composition of MgNH4P04-6H20. Standards were processed using a similar procedure.

10
Instrumentation Development and Applications

1

Counting of ^-P (ti/2 = 14.28 d) was performed using

a beta proportional counter. Purity of the ^-F from other

radionuclides was ascertained by gamma-ray spectros- copy, and by monitoring beta count rates over a period of

four half lives. No discernible contamination from other

radionuclides was noted. ^-P count rates were adjusted for decay time, blank correction, and for differences in beta

self-absorption.

NIST currently certifies elemental concentrations in SRMs using one of three modes: (1) a primary method at NIST with confirmation by other method(s); (2) two

independent critically evaluated methods at NIST, and

(3) one method at NIST and different methods by outside

collaborating laboratories. Certification using a primary

method is only possible when all potentially significant sources of uncertainty have been evaluated explicitly for the application of the method and the matrix under investi- gation. Therefore, in order to certify the phosphorus

concenfration in SRM 2133 using RNAA as a primary

method it was necessary to evaluate all significant sources of uncertainty explicitly. For this set of measurements, we

considered sources of relative uncertainty greater than

0.01 % to be significant. The results of a complete

evaluation of all sources of uncertainty are hsted in Table 1

This evaluation yielded an expanded relative uncertainty of

1.27 % (as defined by ISO and NIST), and gives an approximate level of confidence of 95 %. The measured

phosphorus concentration is (9.55 ± 0.12) x lO'^ atoms- cm-.

In conclusion, we have successfully applied RNAA

as a primary method for the certification of this new SRM.

The observed relative expanded uncertainty of 1 .27 % is smaller than the 3 % value needed by the semiconductor

industry. This new SRM should greatly enhance the U.S. semiconductor industry's ability to achieve accurate and

reproducible analytical results for this key dopant in silicon.

Table 1. Individual Uncertainty Components for Determination

of Phosphorus in SRM 2133.

Source of Uncertainty Uncertainty

(la) %

Measurement Replication (a/Vn) 0.31 Measurement Replication (Standards) (a/Vn) 0.47 Measurement of Sample Area 0.012

Blank Correction 0.022

Blank Correction (Standards) 0.019

Volumetric Calibrations (Standards) 0.12

Concentration of Standard Solution 0.15 Mass Standard Solution on Foil 0.037

Radiochemical Impurity 0.13

Beta Self-Absorption 0.07

Beta Self-Absorption (Standards) 0.08

Carrier Yield Determination 0.10

Self-Shielding 0.024

Irradiation Geometry 0.09 Combined Uncertainty 0.63 Coverage Factor 2.0 Expanded Uncertainty 1.27

References

[

1 ] R. R. Greenberg, R. M. Lindstrom, and D. S. Simons, J. Radioanal. Nucl. Chem, 245, 57 (2000).

[2] R. L. Paul and D. S. Simons, Characterization and Metrologyfor VLSI Technology, ed. D. G. Seller, A. C. Diebold, T. J. Shaffner, R. McDonald, W. M. Bullis, R J. Smith, and E. M. Secula, American

Institute of Physics, AIP Conference Proceedings 550, Melville, NY, 2001, pp. 677-681.

[3] R. L. Paul and D. S. Simons, Silicon Front-End Junction Formation

Technologies, MRS Symposium Proceedings 717, ed. D. F. Downey, M. E. Law, A. Claverie, M. J. Rendon, Materials Research Society, Warrendale, PA, 2002, pp. 291-296.

R. L Paul and D. S. Simons

Chemical Science and Technology Laboratory

National Institute of Standards and Technology

Gaithersburg.MD 20899-8395
|(^ New Thermal Neutron Prompt

Gamma-Ray Activation Analysis Facility

' cientists from the Analytical

'Chemistry Division and the US Food

and Drug Administration have maintained a thermal neutron prompt gamma-ray activation

analysis (PGAA) facility at the NCNR for the past

25 years. The facility is used routinely for analysis of

major and minor element compositions of a variety of

biological, environmental and industrial materials. Recent

applications include determination of: several elements in Standard Reference Material (SRM) 1575a Pine Needles;

cadmium in SRM 2702 Inorganic Sediment; nitrogen and

phosphorus in cattail samples in collaboration with Florida

A&M University; boron in sapphire in collaboration with

Southern University; and nitrogen, sodium, phosphorus,

sulftir, chlorine, potassium, calcium, and cadmium in food,

dietary supplements, and other food-related matrices.

A new thermal neutron PGAA instrument became

operational in 2001, replacing the original thermal neutron PGAA instrument that was built in the late 1970s. The new

instrument was designed and built to improve analytical

sensitivities and limits of detection, and decrease the levels of radiation associated with use of the instalment. This was achieved by filtering the neutron beam to decrease the

fast neutron and low energy gamma-ray components of

the beam, designing the new facility components and

support structure to minimize neutron capture gammarays, and installing an improved detection system. The new thermal neutron PGAA facility is shown in Fig. 1. A cylindrical

sapphire beam filter 5.3 cm long and

4.3 cm in diameter was incorporated into the shutter assembly.

This modification

reduced the number

of fast neutrons by a

factor of 5, decreased

the thermal neutron

flux by approximately

Fig 1. Newtherr^al neutron PGAA y j facility at VT-5.

reduced low-energy gamma-ray background. With the reduction in fast neutrons, the amount of hydrogenous

shielding required to slow and capture the fast neutrons was reduced as compared with that needed in the old

facility. As a result, the background count-rate for the 2223.3 keV capture gamma-ray of hydrogen has been

reduced from about 1 count per second (cps) or the equivalent of about 0.5 mg, of hydrogen, to 0.05 cps or

the equivalent of 25 \ig of hydrogen.

A summary of the design changes for each component of the facility and their effects is shown in Table 1

.

The original beam tube and sample chamber were fabri- cated from concentric Plexiglas tubes, filled with a mixture

of paraffin and boron carbide. The new sample chamber

and beam tube were fabricated from aluminum and lined

with a 2 mm thick flexible lithiated polymer (lithoflex).

The beam tube is kept under vacuum to reduce background gamma-rays arising from neutrons scattered by air and captured in the surrounding materials. The new

sample chamber can be evacuated to fiarther reduce

background associated with neutron scatter and capture in

air. As a result of these design changes, the background

count-rates from hydrogen, nitrogen, and boron have been

reduced by a factor of 1 0 or more and carbon has been

eliminated from the background. The count rate for aluminum is about the same in the new system, despite the

large amounts of aluminum in the beam tube, beam stop,

sample chamber and support structure. The beam stop of the old facility was a separate unit.

It consisted of a steel box containing a lithiated polycarbonate cube (30 cm on a side) surrounded by lead bricks. This unit was lifted into place on top of the beam tube each

time the system was assembled. The new beam stop

consists of an aluminum box welded onto the aluminum

support structure, and is filled with a cube of borated

polyethylene (20 cm on a side) surrounded by lead. The

elimination of steel from the beam stop has greatly reduced

the background count-rate from iron. A new germanium detector with improved resolution

and peak-to-Compton ratio was installed. This detector has

a relative efficiency of 40 % (relative to a 7.6 cm cube

of sodium iodide) and 2.0 keV (peak fiill-width-half- maximum) resolution for the 1332.5 keV gamma-ray line

12
Instrumentation Development and Applications

Table 1 . Comparison of original and new thermal neutron PGAA systems

Facility Component

Old PGAA System New System Effect

Beam Stop Steel cube (61 cm on a side) Li2C03 plug, cube of Li2C03 in resin surrounded by lead bricksAluminum cube (43 cm on a side) ^LiF polymer plug, berated

polyethylene surrounded by lead bricks

Eliminate Fe

background y-rays from beam stop Beam tube Plexiglas concentric tubes with a mixture of boron

carbide in paraffin, and Li2C03 in paraffin between

them; Teflon film end windows; airfilled beam tube

Al tubing lined with ^LiF polymer capped at each end with Al and center windows of a Mg alloy Upper and lower sections evacuated, lithiated polyethylene shielding on outer two sides

Reduce H and

eliminate N

background y-rays Sample Chamber

Walls fabricated from B4C in resin with Teflon windows

covered with fused enriched Li2C03 plugs in front of and across from the detector window

Welde(;| Al plate covered with ^LiF polymer shielding; Mg

alloy thin windows in front of and across from the detector covered with the same Li2C03 plugs; chamber may be

evacuated

Reduce B and

eliminate N

background y-rays

Detection systemGe detector (27 % relative efficiency) in a Nal Compton suppressor Ge detector (40 % relative efficiency) in a BGO Compton

suppressor

Eliminate Na

background y-rays

Support

Structure

Al tripod frame with a cage to hold the beam stop Al tripod frame. The beam tube and beam stop are attached

to the frame and the detection system placed on rails

Improve structure

stability Component

Set-Up

Four separate pieces (beam tube, Al tripod, beam

stop, detection system) that are assembled individually

Assembled as one unit with a removable Ge detector Improve safety and

ease of system set-up

10^

10^

tn 10^

Coi 10^

10^

10^

10°

Background Spectrum, Original PGAA System

T

4 6 Energy (MeV)

Background Spectrum, New PGAA System

T

Energy (MeV)

Fig. 2. Comparison of tfie background spectra collected with the old PGAA system (top) and the new system (bottom).

from 6OC0. The original sodium iodide Compton suppression system was replaced with a bismuth germanate

suppressor. This modification eliminated sodium gammaray background.

The goal of reducing background radiation and

improving analytical sensitivity and detection limits has

been achieved. A comparison of spectra from background

counts from the old and the new PGAA systems is shown

in Fig. 2. The reduction in the background count-rates in the low energy region is evident. This reduction will greatly improve the detection limits for elements with

neutron capture gamma-rays in the low energy region.

With the sample chamber evacuated, nitrogen capture

gamma-rays have been eliminated from the background.

Elimination of the sodium background has improved the

detection limit for this element. Improvements in shield- ing have resulted in a decrease in the background countrates of hydrogen, boron, carbon, iron, and germanium,

improving detection limits for those elements as well.

E. A. IVIackey and R. IVI. Lindstrom

Analytical Chemistry Division National Institute of Standards and Technology

GaithersburgMD, 20899-8395

D. L. Anderson

Elemental Research Branch Food and Drug Administration College Park, MD 20740-3835 P J. Liposky NIST Center for Neutron Research

National Institute of Standards and Technology

GaithersburgMD, 20899-8561
IT Performance Enhancements of

the CHRNS 30-m SANS Instrument

Tt

'wo changes made to the optics of

the CHRNS 30-m SANS instrument

during the installation of the NCNR's new cold source have increased the flux at the sample and

the \ow-Q resolution of the instrument.

The increase in flux, over and above that provided by the new cold source, comes from replacing the instrument's cooled bismuth-beryllium filter with an "optical filter" of the type shown schematically in

Fig. 1. The optical filter replaces 10 m of straight neutron

guide and its 40 cm long Bi-Be filter with an inclined guide

section with a high critical angle supermirror reflective coating. The optical filter channels cold neutrons, with

wavelengths as short as 3 A, out of the line-of-sight of fast neutrons and gamma rays fi"om the source. The cold neutrons delivered to the SANS instrument undergo an even number of reflections in the optical filter to emerge in the horizontal direction, but displaced 14 cm vertically. To

accommodate the beam displacement, the entire SANS

instrument had to be raised; a non-trivial task that required

detailed engineering analysis, careful planning and skilled execution.

The design of the optical filter was refined with the

aid of detailed Monte Carlo calculations of the angular and

spectral distribution of neutrons transmitted by the optical

200.0

100.0

0.0

^ -100.0

-200.0

Cold source

Optical filter

NG-3 guide 15 cm high x 6 cm wide.

Removable guide sections

"Source

aperture /

Sample '^4-3 <^'^

0 10000 20000 30000 40000 50000

Axial distance from cold source center plane (mm)

Fig. 1 . Schematic elevation of the NG-3 optical filter (note vertical scale

is exaggerated for clarity). The inclined section shown in red is coated

with supermirror with critical angle approximately 3.2 times that of natural nickel. The removable guide sections are in the pre-sample flight path of the NG-3 SANS instrument.

filter. Figure 2 shows the calculated and measured gain in flux at the sample, due to the optical filter alone, for the supermirror reflectivity model shown in the inset. These

results demonstrate that the optical filter transmission is about the same as the previous crystal filter for wavelengths around 5 A, but becomes substantially better at longer wavelengths where absorption in the crystal filter becomes significant.

The optics for the CHRNS SANS instrument were

further improved by installing a system of retracting lenses and prisms near the sample position to focus 17 A neutrons onto the detector at its maximum distance, 13 m,

from the sample. A similar lens system, consisting of 28

biconcave single crystals of MgF2 for focusing 8 A

neutrons, has been in use on the NCNR's other 30-m

SANS instrument on guide NG-7 for nearly two years [1]. The refracting power of the lenses increases with the wavelength squared, but so does the distance the neutron

falls between the sample and detector due to gravity. The

vertical spreading of the focus for a beam with a waveSupermirror reflectivity models

1r

0.0

I with 0 removable guides in beam

I witti 8 removable guides in beam

Retrofitted simulation July 2002 (8 guides)

Original simulation Mar 1999 (8 guides)

4 5 6 7 8 9 10 11 12 13 14 15 16 17 A (A)

Fig. 2. Transmission gains of the NG-3 optical filter. The black circles are measured with no removable guides in the beam. The red squares

are measured with 8 removable guides in the beam. The violet circles are the original Monte Carlo simulated gain predictions (March 1999) using the supermirror reflectivity model shown in the inset. The blue

circles are simulated gains (July 2002) using the refined reflectivity model shown in the inset. These "hindsight" simulations predict the measured gains well for /W = 3.2 supermirror with R(Q = 0) = 0.930 and RMS surface roughness equal to 10 A with R(Q = 0.069 A-^) = 0.55.

14
ft I I X I ^ Instrumentation Development and Applications

length spread typical of a SANS instrument, about 1 0 % to

1 5 % FWHM, restricts the utility of the lenses alone to wavelengths less than 10 A. The new development

implemented on the CHRNS SANS instrument is to follow

the lenses with prisms that refract in the vertical direction

to counteract the effect of gravity.

Figure 3 depicts the arrangement of lenses and

prisms now installed on the CHRNS SANS instrument.

Seven MgFT biconcave lenses focus 1 7 A neutrons at the

detector, 13 m from the sample. For this distance a single

prism with an apex angle of 161° would cancel the beam

spreading due to gravity for all wavelengths [2]. Such a prism, however, would have to be 250 mm long at its base

to intercept the full beam height transmitted by the lenses 2 cm). A more practical scheme, as shown in Fig. 3, is

to stack two sets of prisms, with each prism 30 mm long

and 5 mm high with an apex angle of 143", to give the same anti-gravity effect. In this scheme, the bottoms of

each prism are coated with Gd203 to eliminate surface

reflections. The effectiveness of the lens/prism combination can

be seen in Fig. 4 that compares circularly averaged SANS

data from voids in an irradiated crystal of aluminum

obtained with pinhole collimation and with the focusing

optics. The data for the lens/prism system extend to a minimum scattering vector Q = 0.00045 A-', nearly a

factor of two lower than the pinhole collimation. Further- more, the scattered intensity is 3 times higher with the lens/prism system because a larger area of the sample can

be illuminated without degrading the ^-resolution. With

pinhole collimation, intensity at the detector is roughly

o

o

E

100

i2 10 oo

7 Lens/ 2 Prism

Ai=1.43 cm

A2=1.59 cm

Q,r„n = 0. 00048

7 8 9

Pinhole

Ai=1.43 cm

A2=0.63 cm

Qmin=0.0009 A

10"

Fig. 4. SANS from voids in an aluminum crystal measured with and

without the new focusing and gravity cancellation optics installed on the CHRNS SANS instrument. The optics halve the minimum accessible Q-value while increasing the scattered intensity roughly threefold.

proportional to Q^mm^ hence the lens/prism system represents an overall intensity gain of 48 compared with simply

reducing pinhole aperture size to achieve the same minimum Q.

The new cold source and improvements in optics are enabling microstructural studies that link nanoscale with

microscale features in, for example, polymer-clay

nanocomposites, gels, and fluxoid lattices in superconductors.

References

Correction of Gravity Effect with Prisms

Source Lens Prism Sample Detector

Fig. 3. Schematic diagram of the configuration of lenses and prisms used on the 30-m CHRNS SANS instrument. The seven biconcave

lenses focus 17 A neutrons at the detector, 13 m from the sample, and

the double stack of prisms refracts the beam vertically to cancel the

effect of gravity.

[1] S.-M. Choi, J. G Barker, C. J. Glinka, Y. T. Cheng, P. L. Gammel,

J. Appl. Cryst 33, 793 (2000).

[2] E. M. Forgan, R. Cubitt, Neutron News 9(4), 25 (1998).

J. Cook, I. G. Schroder, S. R. Kline, B. Hammouda, and C. J. Glinka NISI Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8562

S.-M. Choi NIST Center for Neutron Research

Present affiliation: Korea Advanced Institute of Science and Technology

373-1 , Guseong-dong, Yuseong-gu, Daejon,

Republic of Korea 305-701
Probing Nanoscale Disorder

with Neutron Tunneling Spectroscopy

he presence of structural disorder can have a dramatic effect on

macroscopic materials properties. At the atomic scale, structural disorder is typically

described in terms of distributions of geometrical

quantities such as bond lengths and bond angles that are determined from diffraction measurements. Alternatively, disorder can be quantified by determining the

distribution of potential energies experienced by the atomic

scale constituents of the system. The distribution is sharp

for a highly ordered (crystalline) system, while it is broad

for a disordered system. Rotational tunneling spectroscopy is a useful tool for characterizing the local molecular

environment due to its exquisite sensitivity to the local potential [1]. This approach has been used to determine

the distribution of rotational potentials felt by methyl iodide

molecules adsorbed in a series of mesoporous silica glasses. The degree of confinement-induced disorder in the methyl iodide can then be directly related to the pore

sizes in the glass.

The rotational potential felt by the methyl (CH3)

groups in methyl iodide (CH3I) arises solely from interac- tions with the local environment including the neighboring

molecules. The energies of the transitions between rotational states can be found by solving the Schrodinger

equation for the model potential by V3(l-cos(39))/2 in the angular coordinate about the C-I axis, 9. In the limit of an

infinitely high barrier, V3, the motion of the CH3 group is that of a torsional oscillator. However, if the barrier is not

too large, the wavefunctions will have significant overlap

and quantum mechanical tunneling between the potential

minima can occur. This results in a splitting of the

rotational ground state. The energy of this splitting, which

can be directly measured using cold neutron spectroscopy,

has a nearly exponential dependence upon the barrier height. This strong dependence on V3 is the reason why

turmeling spectroscopy is so sensitive to the local molecular environment and, in particular, the quenched disorder of

adsorbed molecular solids. The porous hosts used in this investigation have a range of pore size distributions with differing nominal pore

diameters and widths. Nominal pore diameters, <d>,

determined via nitrogen adsorption/desorption isotherms

range from 2.5 nm to 14.4 nm. In all cases but one

(xerogel with <d> = 10.0 nm) the porous glasses are disks. The xerogel is a fine powder with a nominal particle size of

1 1 \xm. Liquid methyl iodide (CH3I) was condensed into the porous hosts until 95 % of the open pore volume was

filled and then cooled to 5 K. Spectra were collected using

the NIST High-Flux Backscattering Spectrometer with an

energy resolution of 0.79 fj.eV. The neutron scattering spectra display broad asymmetric lines indicative of a distribution of potential barrier heights. These distributions can be extracted firom the neutron scattering data using a simple model in which a sum of Gaussian distributions of potential barriers (which

yield an asymmetric tunneling line-shape) is used to fit the spectra [2]. A sum of two potential distributions is found

to be sufficient to describe the data. One of these distribu- tions is quite broad, indicating substantial disorder of the methyl iodide solid, while the other is much narrower

suggesting a relatively high degree of order. The relative weights of the two components show a pronounced dependence on <d>. Figure 1 shows that the

fi-action of the total integrated intensity that appears in the highly disordered component of the tunneling spectrum

decreases monotonically as <d> increases. This behavior can be described with a simple model in which the rela- tively well-ordered component of the scattering is attrib- uted to CH3I molecules near the center of the pore while

10 15

<cl> (nm)

Fig. 1. Fraction of the total integrated intensity that appears in the disordered component of the tunneling spectrum as a function of the mean pore diameter. The solid line is a fit to the model discussed in the

text. The dashed line is drawn at twice the disordered layer thickness.

Inset shows the geometrical picture used in the model.

16
D KIC Chemical Physics and Biology

the highly disordered component is associated with a ring

of thickness t of disordered molecules near the pore walls. Treating the pores as circular cy linders, the fraction of

disordered molecules is just the ratio of the ring to circular

areas: /^ordered = '^t(<^ - t)/<ci>^.

The solid line in Fig. 1 compares this model to the data for t = 1.41(4) nm, which corresponds to about three molecular la\ ers. It is clear that this model provides an

excellent fit to the data. While the relative weights of the two components

depend on the pore size, the mean values, <V3>, and

widths. of the two distributions of barrier heights are found to be roughly the same for each of the hosts. This

indicates that the structure of the confined methyl iodide

both near the surface and in the center of the pores does

not depend strongly on either <d> or the width of the pore

size distribution. CH3I molecules possess a relatively large electric dipole moment. This results in the molecules being anti- aligned in the bulk cry stal structure [3]. Silica surfaces

often \ia\e h\ drox\ 1 (OH) groups which would be ex- pected to interact rather strongK with the dipole moment

of the molecules and lead to a substantial surface-molecular interaction. The surface-molecule and moleculemolecule interactions can be of similar strength leading to structural frustration in the confined solid. Thus, one would expect that the disordered fraction and even the structure of the tvvo components to be strongly influenced

b> changing the relative strengths of these interactions. In order to test this hypothesis, the surface of one set of

porous disks (<d> = 5,8 nm) was chemically treated such

that hydrophobic OCH3 groups replaced the OH groups. This change significantly reduces the surface-guest

interaction, and should therefore lead to a reduction of the disorder in the confined solid. The measured tunneling

spectra for methyl iodide adsorbed in both the treated and

untreated hosts (<d> = 5.8 nm) are shown in Fig. 2. As

seen by the prominence of the narrower peaks, the more

ordered component of the tunneling spectrum increases

substantially for the methyl iodide confined in the glass

with the hydrophobic surface as compared to the host with

the hydrophilic OH groups. In fact, the disordered fraction

decreases by about 25 %, which indicates that the thick- ness of the highly disordered layer is roughly two-thirds

that of the untreated glass. Moreover the width of the tunneling line in the highly disordered component has also decreased substantially indicating that the structure of the methyl iodide near the hydrophobic surface is more bulklike than it is near the hydrophilic surface.

"T-i— '—

treated surface as-received

-10 0 E(^eV)

10

Fig. 2. Tunneling spectrum of confined CH3I in 5.8 nm pores with and

without surface treatment to make the surface hydrophobic. The

hydrophobic surface results in a diminished disordered component.

In summary, the sensitivity of tunneling spectroscopy

to small changes in the rotational potential has allowed us

to probe the importance of surface-guest interactions in determining the disorder imposed by the confinement of

methyl iodide within mesoporous glasses. It has been

shown that the adsorbed species in the hydrophilic pores form a highly disordered layer with a thickness of approximately three molecular layers and that a more ordered

region exists in the pore center Interestingly, the molecular structures of these two regions do not depend strongly on either the average pore size or on details of the pore size

distribution. When the surface chemistry is altered so as

to reduce the importance of surface-guest interactions,

both the thickness and molecular scale disorder of the region near the wall are greatly reduced.

[2]

1 ] W. Press, in Single-Particle Rotations in Molecular Crystals,

( Springer-Verlag, Berlin, 1981).

R. M Dimeo and D. A. Neumann, Phys. Rev. B 63, 014301 (2001).

R. M Dimeo and D. A. Neumann, App. Phys. ATS (in press). R M. Dimeo, D. A. Neumann, Y Glanville, and D. B Minor, Phys.

Rev. B 66, 104201 (2002).

[3] M. Prager, J. Stanislawski, and W. Hausler, J. Chem. Phys. 86, 2563

(1987).

R. M. Dimeo and D. A. Neumann

NIST Centerfor Neutron Research

National Institute of Standards and Technology, Gaithersburg, MD 20899-8562

Y. Glanville The Pennsylvania State University University Park, PA 16802-6300

D. B. Minor

Ceramics Division National Institute of Standards and Technology

Gaithersburg, MD 20899-8520

17
The '^Bucket Brigade"

Mechanism of Proton Diffusion

in Superprotonic Conductors

|roton diffusion plays a central role

in many processes ranging from the regulation of biological functions to the production of electricity in fuel cells. The renewed

emphasis on developing the next generation of

portable sources of power requires the development

of lightweight protonic conducting materials for use as

electrolytic membranes [1]. Furthermore, understanding

the atomic-scale mechanism of protonic diffusion in candidate materials is necessary to optimize their perfor- mance. Since neutrons are particularly sensitive to hydrogen, neutron scattering is an extremely valuable

probe of proton dynamics (including diffusion). Moreover,

because the wavelength of neutrons is comparable to inter- atomic distances, neutron scattering is capable of revealing

the atomic-scale geometry of protonic motions in a way

that is unmatched by other spectroscopic probes. Computational techniques also provide detailed atomistic information about proton incorporation and dynamics. Because of

the simplicity of the scattering mechanism, computational

results can be directly compared to neutron scattering data. Thus neutron scattering and computational methods are a powerful combination for understanding the performance

of protonic conducting materials [2]. Here we briefly

describe neutron vibrational spectroscopy (NVS) and

quasielastic neutron scattering (QNS) measurements on

superprotonic conductors of the general formula MHXO4

(M = Rb, Cs, X = S, Se, etc.) that reveal detailed information on the proton-conduction mechanism.

The crystal structure of alkali-metal hydrogen

sulfates and selenates consists of chains of XO4 tetrahedra

94 M>i

(Fig. 1), which are linked by hydrogen bonds, 0-H-O.

Due to the proximity of the proton site to the midpoint of

the 0-0 separation, it is believed that the proton is dynamically disordered, yielding symmetric hydrogen bonds.

However, at a sufficiently low temperature, one expects

that the protons may order, giving rise to observable

changes in the vibrational spectrum. Above room temperature, there is an orientational order-disorder transition to a phase in which the tetrahedra are dynamically disordered

and which displays a very large protonic conductivity that should be observable by QNS.

Figure 2 summarizes NVS resuhs on RbHS04

measured using the Filter Analyzer Neutron Spectrometer.

At low temperatures, the NVS spectrum shows sharp

peaks at 83.3 meV and 99.7 meV The temperature

dependence of these peaks is quite unusual. The intensities decrease very rapidly with increasing temperature and

almost disappear at temperatures as low as 200 K. In addition, while the high-energy mode softens, as expected,

the low-energy mode hardens by about 2 meV as the temperature is increased. Near 200 K, these two modes

collapse to form a broad feature around 95 meV. This

suggests that there is significant proton motion even at this low temperature. We believe that this unusual behavior is related to dynamically disordered hydrogen bonds arising

fi-om breaking and reforming 0-H bonds. Careful neutron

diffraction studies in deuterated materials are underway to

110-

>100-

CD UJ 90

80-

-.4.

•

50 100 150 200 25 Temperature (K)3

Fig. 1. Projection of tiie MHXO4 structure, showing the zigzag pattern

of the hydrogen bonds between XO4 tetrahedra. Yellow dashed lines indicate the hydrogen bonds.

Fig. 2. Temperature-dependent NVS measurements of RbHS04, As

discussed above, these results suggest very large amplitude proton motions are present at temperatures as low as % 100 K. The right panel

illustrates the dynamically disordered hydrogen bonding, which is most

likely responsible for this unusual temperature dependence.

18
Chemical Physics and Biology

look for significant changes in the apparent locations or thermal factors of the protons at these temperatures. It should be noted that since this type of dynamical disorder

is localized to two neighboring oxygen ions, it cannot be

responsible for long-range protonic conduction.

To probe protonic diffusion directly, the temperature

dependence of the QNS was measured for CsH(S04)i.^. (Se04),- (x =s 0.24) above room temperature

using the Fermi-Chopper time-of-flight Spectrometer. The

data were fit as a function of the scattering vector Q

(assuming both elastic and quasielastic components) in order to extract the Elastic Incoherent Structure Factor

(EISF), which is defined as the fraction of the total scattering that is elastic. Figure 3 shows the EISF as a function of Q for several different temperatures. The fact that a non-zero EISF is observed even at 475 K indicates

that, within the time window of the measurement

(< 20 ps), the hydrogen motion is localized rather than

diffusive. Moreover, the

fact that the EISF changes

with temperature indicates the existence of

non-energetically equivalent

proton-sites.

The best fit to the EISF

(shown by the

solid lines in

Fig. 3) was

obtained assuming two types of hopping motions for the protons between pairs of inequivalent sites. The agreement

between the data and the model is excellent. The two jump

distances, 1.4 A and 4.5 A, are essentially independent of

temperature (see Fig. 4). Looking at the structure, these can easily be identified as the reorientation of the SO4-H

group around the quasi-threefold (1.4 A) and the quasitwofold (4.5 A) axes (Fig. 4). The ratio of the times that the proton spends in each of the two sites depends exponentially on temperature as expected (solid lines in the upper left panel of Fig. 4). For the short-distance reorientation, the time ratio goes rapidly to unity around 405 K,

just before the super-protonic phase transition, indicating

that the two sites are equally populated. For the longdistance reorientation, the ratio approaches 0.2 at the highest temperature.

1.0 1.5

Fig. 3. EISF (dots) and fits (solid lines) at different temperatures for CsH(S04)i.^(Se04)^ (x 0.24).

O

C

3

'

- . • • ••••

300 350 400 450 500 Temperature (K)

Fig. 4. Top: Temperature dependence of the ratios of the residence times to Tj for the pair of twosite hopping motions identified by QNS.

Bottom: The two jump distances obtained from QNS as a function of temperature. These distances correspond to the two reorientational motions shown on the right. The red circles correspond to the motion depicted on top while the blue squares correspond to the motion shown on the bottom.

These findings

are consistent

with a previ- ous neutron- powderdiffraction study on the high-tempera-

,ture phase of

CSHSO4,

which revealed

four different orientations of

each tetrahe- dron [3]. Most probably

the four

orientations mimic the dynamical

orientational disorder of the tetrahedra that we observe by

QNS. We also note that the two types of dynamic

orientational disorder shown in Fig. 4 do not result in longrange protonic conduction since the motions are localized on a single tetrahedron. However, when one combines

these two motions with the dynamically disordered

hydrogen bond implied by NVS, the mechanism of protonic conduction can be understood. Namely, the protons move between two neighboring tetrahedra via dynamically

disordered hydrogen bonds. The tetrahedra then reorient,

allowing the protons to move to a third tetrahedron, again

via the dynamically disordered hydrogen bonds. Thus the tetrahedra play the role of a "bucket brigade" by accepting a proton from an adjacent tefrahedron then turning and handing

it the tetrahedron on the other side. On the atomic scale, superprotonic conductivity occurs in the MHXO4 family of

compounds due to this efficient mechanism of transporting

protons through the lattice. References

[ 1 ] National Hydrogen Energy Roadmap, DOE, Germantown, MD,

2002.

[2] T. Yildirim, B. Reisner, T. J. Udovic, and D. A. Neumann, Sol. State Ionics 145, 429 (2001).

[3] A. V. Belushkin, C. J. Carlile, W. I. F. David, 1. R. Ibberson, L. A.

Shuvalov, W. Zajac, Physica B174, 268 (1991).

I Yildirim, D. A. Neumann, and T. J. Udovic

NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8562

19
Motion in Intermediates Along the

Protein-Folding Pathway: cytochrome c

P

roteins are long macromolecular

chains consisting of amino acid

repeat units that, in the native state, adopt a well defined and intricately folded three-dimensional conformation. The ability to predict a priori

the native three-dimensional structure of a given

amino acid sequence, the so called "protein folding

problem," is essential for the full promise of genetic

therapies to come to fruition [1]. In fact, many apparently

unrelated diseases (e.g., Alzheimer's, Mad Cow, cystic

fibrosis, and even many cancers) result from protein

folding gone wrong.

In order to obtain detailed knowledge of the protein

folding mechanism, extensive characterization of the relevant interactions, structure and dynamics is required at each step of the protein-folding pathway. To this end,

researchers have been investigating the properties of

proteins in the native, partially unfolded and the completely

unfolded states to obtain "snapshots" of the relevant behavior of intermediates along the folding pathway,

yielding information intended to facilitate rationalization of

folding mechanisms.

To deepen our understanding of the molecular

motions involved in protein folding and, hence, the role of

dynamic behavior on the overall folding mechanism, we

employed quasielastic neutron scattering (QENS) as a dynamical probe of several folded states of the electron

transfer protein cytochrome c (see Fig. 1). QENS provides

Fig. 1. The native state of cytochrome c.

-0.5 0.0 0,5

tio) (meV)

Fig. 2. Illustration of the general quasielastic neutron scattering profile of a protein in solution indicating the narrow scattering from the global

diffusion and the broad scattering due to the internal side chains of the amino acid residues.

a method for directly probing the internal dynamics of

biomolecules on the picosecond time scale and Angstrom

length scale. In this technique neutrons exchange energy

and momentum with the nuclei of the sample, allowing the forms, geometry, amplitudes and time-dependence of the motions involved to be determined. By making use of the

large incoherent cross section of hydrogen nuclei and the

capabilities of the Disk-Chopper Spectrometer at « 32 |aeV

resolution it was possible to collect data on five different cytochrome c folded states (in order of increasing unfolding): native (N), salt induced molten globule (MG), alkaline

denamred (D^u^), acid denatured (D^^^^ and guanidine

hydrochloride unfolded (U).

In a typical QENS experiment of this sort, a monochromatic beam of neutrons is scattered by a buffered

solution containing the protein, the contribution of the

scattering from the buffer is removed, and the resulting

profile is considered to be that resulting from just the protein [2, 3]. Figure 2 depicts the general neutron

scattering profile from a protein in solution, illustrating the

distinct scattering from global (bulk translational and

rotational diffusion) and internal (protein side-chain)

dynamics. A profile of this sort is analyzed with a two

Lorentzian fit model — a narrow Lorentzian to fit the global motion and a broad Lorentzian to fit the internal

20
4R:NS.^ > Chemical Physics and Biology

motions. The two Lorentzian fit model permits the average

ensemble time scale of global and internal side-chain

motions to be ascertained separately.

The half width at half maximum of both Lorentzian

fit functions, corresponding to the global and internal motions as a function of scattering vector squared {q-) are given in Fig. 3. An effective diffusion coefficient (Deff) is determined from the slope of -Tgiobai a function of q-. As evident from the tabulated results, D^^ generally decreases as the protein unfolds reflecting the correspondingly higher specific molecular volume of non-native

folding states. The exception lies with the acid denatured

state that, due to the sfrong electrostatic interactions present in the system, shows a near native D^^.

0.04 I

' I I I

I

I I I I

I

I I I I

I

I I

State D„ff/(10-^cm2/s)

A decrease in the relative time scale of the internal motions is observed as a function of protein unfolding. It

is believed that the rather close-packed native structure provides more sharply defined, short-range interactions between the proximate side chains of the amino acid

residues. Upon unfolding of the protein, these interactions

are diminished by the increased separation between side chains and small, weakly interacting buffer molecules

between them.

The results of this study demonstrate the type of

dynamic information that can be determined from QENS

experiments performed on a protein in several different

structural states. As the nature of the unfolding medium

displays a critical role in the internal dynamics of the unfolded states of cytochrome c, any attempts to correlate features between different folding states should take this

into account. In combination with other characterization

techniques, information of this sort will prove beneficial to the understanding and development of accurate protein

folding mechanisms.

[1] A. R. Dinner, M. Karplus, Angew. Chem. Int. Ed. 40, 4615 (2001).

[2] Z. Bu, D. A. Neumann, S-H. Lee, C. M. Brown, D. M. Engelman,

C. C. Han, J. Mol. Biol. 301, 525 (2000).

[3] J. Perez, J.-M. Zanotti, D. Durand, Biophys. J. 77, 454 (1999).

0 0.5 1 1.5

(/2/(A-2)

0.40

Native 0.30 h MG

>

E

0.20

0.10

I I I I

I I I I I I

I I r I II I I I

I

I I I I I

I I I

State

D,

D.

|- U,

'alk

acid • • •

_ • ^

Q I I I I I I I I I I I r I I I I I I I I I I I I I I r I ] I 0 0.5 1 1.5 2 2.5 3

q2/(A-2)

Fig. 3. Plot of the half width at half maximum of the global (top, native

only) and internal (bottom) Lorentzian as a function of scattering vector squared. The tabulated effective diffusion coefficients are given for each

folded state of cytc.

A. Pivovar and D. A. Neumann

NIST Centerfor Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD 29899-8562

21
Neutron Reflectivity from

Biomimetic Membranes: improving

Reliability through Wavelet Analysis

Pj H

nderstanding such key biological processes as molecular recognition,

protein insertion, and molecular self-assembly

in Irving biological membranes remams a challenge. Membrane materials mimicking biological ones (biomimetic membranes) provide model systems

to address this issue, and, because of its special

sensitivity to hydrogen, neutron reflectivity (NR) offers a unique way to reveal thin film structures in biomimetic

membranes.

The feasibilits' of using phase-inversion techniques in NR to reveal such structural details has been demonstrated

[1]. It is possible to directly measure the real part, ri(0),

of the complex reflection coefficient r(Q) as a function of

wavevector Q and to mathematically invert it to obtain the

0 40 80 120

x//o

Fig. 1. Diagram of model (top) for which the computed scattering length

density p (x) is the thick grey curve. Trends converge: p.^(x), pjx), . . .,^p(x).

scattering length density (SLD) depth profile p(x) of the

film. There remains much to do, however, in defining the

reliability of the results, especially in accessing the un- avoidable reduction of spatial resolution induced by data

truncated at a maximum wavevector, Q^^x- Wavelet

analysis provides a systematic and useful approach to the problem [2]. In using Wavelet MultiResolution Analysis (WMRA),

SLD profiles are characterized by a fmest length scale 4 ~ 1 A and coarser scales, ^ = 2-j£q, with j negative. p{x)

is viewed as a coarse "trend" pj{x) at resolution level J, with added "detail" Ajp(x) giving the trend at the next finer

scale, Pj+i(x) = Pj(x)+Ajp(x). Relative to a base scale of

resolution ^j, the SLD profile thus can be represented by

the trend plus all remaining detail, p(x) =p^(xj+Xz\ p(x).

The experimental p(x)^ associated with a given ^max

determined by the instrument, is a blurred representation of

the veridical SLD. It can be thought of as a coarse image

bracketed by neighboring trends for this 2maxWMRA provides spatially localized orthonormal bases

for this description. A family of wavelets called Daubechies-8 seems well suited to NR analysis. For

illustration, we use a realistic SLD profile obtained by

molecular modeling to represent a hybrid lipid membrane

on a thin gold film (diagram on top of Fig. 1), a biomimetic

system typical of those being studied in many laboratories. The model p(x), seen in the back panes of Figs. 1 and 2, consists of the gold layer, a hydrogenated alkanethiol layer,

and a deuterated lipid monolayer.

Figures I and 2 depict the convergence of the WMRA descriptions of p(x) as trend and detail. The

"overall" shape of p(x) effectively is determined by the trend p.4ix) and detail A_^p{x), i.e., by trend p.^(x).

However, emergence of the prominent double peaked

structure of the lipid head group near x/1q =100 needs detail A_^p(x). Subsequent detail mainly acts to sharpen the edges

between the film's components.

Figure 3 shows the effective contributions of the trend and the successive spatial detail to the reflection coefficient r(Q), each calculated exactly. The edgesharpening detail seen in Fig. 3 is not revealed in the

reflection spectrum below Q^q~ 0.6. Figure 4 shows the "smeared" p(x) obtained by direct inversion of the reflec22
40 120

Fig. 2. Trend plus detail converges: Pi(x)+A iP(x)+A 3p(x), . . .,- p{x).

0.2 0.4 0.6 0.8

Fig. 3. Effective contributions to Q^r^(Q) generated by the trend p4(x)

(in red) and the details A^p (x) for / = -4, -3, -2, -1 shown in Fig. 2. The

Q^r^(Q) contributions are labeled by the SLD's that produced them.

tion from p(x) using data truncated at Q^zx- 0-2 A-^. This

is seen to fall "between" the trends p.4ix) and p.^ix),

stemming from low-pass filters with roU-offs at Q w 0.2 and Q « 0.4 A-', respectively. This is expected

from the fact that the Fourier transforms of trends and

detail overlap to a degree. Thus, a "pure" trend cannot be

observed in the truncated data.

r inverted from

truncated r^{Q)

40 80 120

X/lr

Fig. 4. Inverted r^(Q) (black) using only data truncated at Q/o = 0.2. Trends p^{x) (red) and p.-^i^) (blue) of the actual p(x).

Wavelet analysis thus provides a systematic method

for assessing the correctness of density profiles measured

by NR. It promises to add reliability in unraveling struc- tures of importance in biomimetic membranes.

References:

[1] C. F. Majkrzak, N. F. Berk, S. Krueger, J. Dura, M. Tarek, D. Tobias,

V. Silin, C. W. Meuse, J. Woodward, and A. L. Plant, Biophysical J., 79, 3330 (2000).

[2] Wavelets were first applied to x-ray reflectivity with different focus and using different techniques by I. R. Prudnikov, R. D. Deslattes, and R. D. Matyi, J. Appl. Phys., 90, 3338 (2001).

N. F. Berk and C. R Majkrzak NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8562

23
Protein Adsorption to

IMetal-Cheiating Lipid Monolayers

he adsorption of proteins to surfaces, especially lipid layers,

plays a critical role in biochemical processes

within living systems. These include membrane

signaling and recognition, toxin detection, and

mitigating the effects of toxin/biowarfare agents.

Specific issues to be addressed are: protein orientation

and surface density, monolayer versus multilayer adsorption, specific versus non-specific interactions, and lateral order and conformational changes upon adsorption

including denaturization of protein [1]. In this work neutron reflection is combined with

grazing incidence x-ray diffraction (GIXD) to study the

interactions of the protein myoglobin with Langmuir

monolayers of synthetic lipids. Neutron reflection is used

to determine the adsorbed amount and to obtain information regarding the orientation and conformation of the adsorbed myoglobin [2]. GIXD is used to study the response of the lipid layer that occurs upon protein

binding.

For lipid layers we have used the synthetic lipid

distearyl imino-diacetate (DSIDA) that contains receptors

for the metal ion Cu2+. The use of metal ion coordination

to target the adsorption of proteins to lipid membranes has

been studied extensively. This method uses specific

coordination interactions between Cu2+ and naturally

occurring histidine units in myoglobin.

A Langmuir monolayer of 100 % DSIDA was spread

onto the surface of buffered D2O or H2O (Fig. 1 ) and then

compressed to a surface pressure of » 40 mN/m where it forms a solid condensed phase layer (see GIXD data

below). A dilute solution of CuCh was injected under the condensed DSIDA monolayer. The Cu2+ ions chelate at the imino-diacetate site as indicated in Fig. 1

.

Neutron reflectivity data for the condensed lipid layer

with added Cu2+ ions are shown in Fig. 2 for both the HjO

and D2O buffered subphases. Myoglobin was then

injected into the subphase and neutron reflectivity data were taken repeatedly to monitor the time dependence of

protein adsorption. The adsorbed protein layers reached

quasi-equilibrium at « 14 h after adding myoglobin into the

solution. Only final sets of reflectivity data with adsorbed

protein (for both H2O and DjO subphases) are shown in Fig. 2. The very large change in the reflectivity after

Lipid Tails

Air

OH OH OH OH OH OH OH OH OH OH OH OH

Head

Groups

Myoglobin

Buffered Subphase

Fig. 1. Schematic of histidine groups on myoglobin adsorbing to

distearyl imino-diacetate (DSIDA) molecules at chelated Cu^^ ion sites.

protein injection indicates a significant adsorption of

protein under the lipid layer.

Solid lines in Fig. 2 are fits to the reflectivity data

from which the segment concentration profile of protein can be obtained. Simultaneous fits to both sets of data

show that the dimension of the quasi-equilibrium adsorbed

myoglobin layer is 36 A +/- 2 A, and that the segment

volume fraction of protein is ~ 50 %. Unit cell dimensions

of myoglobin from its crystal structure are (a, b, c) =

lipid + Cu^'

after 14.9 h with myoglobin

lipid + Cu^'

after 13.7 h

with myoglobin

0.00 0.05 0.10 0.15 0.20

Fig. 2. Neutron reflectivity for 100 % DSIDA on buffered DjO and HjO

subphases with and without myoglobin in the subphase. Solid lines are

fits to the data as described in the text.

24
Chemical Physics and Biology

5 10^

410^ o

5: 3105 a1 210^

1 10^

DSIDA

1 1

(a)

-

j

DSIDA+Cu^-^

1

1

510^

1 1 (b)- DSIDA + Cu2-^+MY0 410^ (peak returns) 1

310^

210^

1 105 ^/dSIDA + Cu^-'+MYO

— —1

(no peak)

1

1 0.5 1,5 2.5 0.5 1.5 2.5

Fig. 3. Surface diffraction peal< at a constant surface pressure of 40 mN/m: (a) 1 00 % DSIDA and also with Cu2^ (b) 1.9 h (no peai<) and 4.4 h (peak returns) after myoglobin injection.

(64.84, 30.98, 34.92) A. Thus, the protein in all likelihood

is bound to the lipid layer in its native state, i.e., not

denatured.

If no CUCI2 is added to the subphase, then no change

in the neutron reflectivity signal is observed upon injection

of myoglobin. Alternatively, if we inject a strong Cu

scavenging agent (EDTA) in the subphase after the protein

adsorption, the reflectivity reverts back to that of the pure

condensed lipid layer. This clearly shows that we are observing very specific binding of the protein to the chelated Cu2+ sites on DSIDA.

Important insight has been revealed in complementary GIXD data from the DSIDA system. Figure 3a shows

the surface diffraction peak from the tails of a condensed

DSIDA monolayer at an in-plane wavevector Q^y= 1.50 A-'. This corresponds to a hexagonal packed lipid layer with a nearest neighbor spacing of 4.21 A. Insertion of Cu^+ions

into the layer does not seem to affect the 2-D crystalline

order of the lipid layer except for a slight change in lattice spacing.

When myoglobin is added to the subphase at a

constant surface pressure of 40 mN/m, the diffraction peak arising from the hexagonal packing of the DSIDA

tails (at Q^^= 1.50 A-i) is drastically reduced at short times

(Fig. 3b). This indicates a large perturbation in the 2-D

crystallinity of the lipid layer upon insertion of protein. The

surface diffraction peak, however, reappears after a few

hours (Fig. 3b). The peak is slightly shifted to a higher

value of Q^y, and the distribution of intensity normal to the surface (not shown) indicates a substantially increased tilt of the lipid tails. By contrast, no change in the diffraction peak is observed after addition of myoglobin when the surface layer is maintained at a constant area (after initial compression to 40 mN/m).

We hypothesize that the

protein is able to insert into the

lipid monolayer when it is maintained at a constant

pressure of 40 mN/m, but does

not insert when at constant area

(surface pressure in this case

rises from 40 mN/m to 43 mN/m). Thus far, all the neutron reflection data have

been obtained at constant

surface area. In future work we will examine adsorption to

lipid monolayers composed of

100 % DSIDA at constant surface pressure. We expect to see very different arrangement of the protein adsorbed

layers for conditions at which the protein inserts into the

lipid monolayer versus when it does not. In summary, a combination of neutron reflectivity

and GIXD has proven to be a very powerful way to study

both the protein adsorption to lipid monolayers as well as

structural changes that the lipid layer itself undergoes as the protein is adsorbed. Because of different contrast conditions for neutrons and x-rays, neutron reflectivity

profiles are very sensitive to the adsorption of the protein,

while GIXD is ideally suited for examining in detail any

changes in the 2-D ordered structure of the lipid layer itself This successful study opens up a rather large field to examine other important lipid-protein interactions such as insertion of biological toxins into a lipid layer. Preliminary

studies of neutron reflectivity and GIXD to examine the adsorption of cholera toxin to monolayers of glycolipids (a

class of lipids containing sugar molecules which are found on

cell surfaces) show extraordinary promise in this regard.

References!

[1] K. M. Maloney, D. R. Shnek, D. Y. Sasaki, and F. H. Arnold, Chemistry & Biology, 3, 185, (1996).

[2] M. S. Kent, H. Yim, D. Y. Sasaki, J. Majewski, G. S. Smith, K. Shin,

S. K. Satija, and B. M. Ocko, Langmuir 18, 3754,(2002).

M. Kent and H. Yim

Sandia National Laboratory Albuquerque, NM 871 85

S. K. Satija NIST Centerfor Neutron Research

National Institute of Standards and Technology

Gaithersburg,MD 20899-8562

J. Majewski

Los Alamos National Laboratory Los Alamos, NM 87545

25
Hydration State of Single

cytochrome c Monolayers on Soft

Interfaces via Neutron Reflectivity

pter is critical, not only for the correct folding of proteins but

also for the maintenance of this folded structure. The internal molecular motions m proteins,

which are necessary for biological activity, are very dependent on the degree of flexibility which is determined by the level of hydration. The nmnber of

water molecules hydrating a functioning protein is thus an issue of great interest. Given an appropriate model

system, neutron scattering, particularly sensitive to hydrogen, provides a way to measure this water content. Previous optical spectroscopy studies have shown

that yeast cytochrome c (YCC) covalently bound to a soft interface (Fig. 1) and partially hydrated by a moist helium

atmosphere can be fully fimctional with respect to the oxidation-reduction chemistry of its iron porphyrin prosthetic group [1, 2, 5, 6]. This system thus provides an

opportunity to examine the water distribution required to maintain the structvire and function of the protein YCC.

Unlike x-rays, neutrons scatter very differently from

hydrogen and deuterium. This fact allows the water

distribution in the monolayer profile structure of YCC to be

obtained by comparison. The neutron scattering length

density profile derived from neutron reflectivity for a YCC

monolayer hydrated by D^O is compared to the profile for

identical hydration with HjO.

The silicon surface layer of an iron-silicon (Fe/Si) or

iron-gold-silicon (Fe/Au/Si) multilayer solid substrate can

bind a self-assembled monolayer (SAM) to form the soft

surface used to tether the YCC monolayer (See diagrams

at the top of Fig. 3.) Such a multilayer substrate has two

key advantages in a neutron (or x-ray) reflectivity experi- ment: a multilayer substrate dramatically enhances this scattering for momentum transfer normal to the substrate

surface, and a multilayer substrate also provides an

important reference profile structure for the unique

interferometric phasing of the reflectivity data. Neutron reflectivities (Fig. 2) were collected on the NG-1 reflectometer for both H2O and D2O hydration cases

for two such SAMA^CC samples. One SAM formed a nonpolar surface (-CH3/-SH = 6:1 mixed endgroups), and

150

-150

-300

1 1 1 1 1

bare Fe/Si

YCC/H2O

YCC/D2O

1 0.02 0.04 0.06

50

0

^ -50

-100

-150

1 '

r

'

1

bare Fe/Au/Si

YCC/H2O

YCC/D2O

0.02 0.04 0.06

Fig. 1 . Molecular dynamics "snapshot" of YCC tethered to the soft surface of an uncharged-polar self-assembled monolayer (SAM).

Fig. 2. Top: normalized reflectivity data with incident neutron spins

parallel to the iron magnetization for the bare multilayer substrate, substrate plus nonpolar SAM plus YCC/DjO, and substrate plus

nonpolar SAM plus YCC/HjO. Bottom: data for similar arrangements

with the uncharged polar SAM on a Fe/Au/Si substrate. In the top plot the H2O data are offset by 150 units and the DjO data by 300 units on the

ordinate, and in the bottom plot the HjO data are offset by 75 units and

the D2O data by 150 units on the ordinate. (Note: IstnOIX.)

26
Chemical Physics and Biology

the other SAM formed an uncharged polar surface

(-0H/-SH = 6:1 mixed

endgroups). These data were analyzed using a new

interferometric phasing

method that makes use of

two features: the neutron

scattering contrast between the Si and Fe layers

in a single reference

multilayer structure, and a constrained refinement

approach using the finite extent of the gradient of

the profile structures for the systems [3]. The

water distribution profiles

for the two SAIVLTCC

monolayers provided by

this analysis are shown in Figs. 3a and 3b. For hydration with

D2O, these profiles show

that the protein monolayer

is 3 A to 4 A closer to the

substrate surface for the uncharged-polar SAM compared

to the nonpolar SAM. This finding is in excellent agree- ment with simulations of these systems [3, 4], and arises because residues on the protein's surface interact strongly

with the polar SAM's hydroxyl endgroups via hydrogenbonding, thus drawing the YCC closer to the SAM surface. Given these water distribution profiles, the number of

water molecules hydrating the YCC monolayer at each

SAM can be calculated. Allowing for proton exchange in the cytochrome c molecule itself ( * 1 7 polypeptide backbone hydrogens and « 104 side chain hydrogens), we

obtained values of* 167 water moleculesAfCC at the uncharged polar SAM (exposed to He at 81 % relative humidity) and « 297 water moleculesA'CC at the nonpolar

SAM (exposed to He at 88 % relative humidity) with

relative errors of order 20 % to 25 %. These findings

allow quantitative comparison to molecular models,

opening an important window to understanding the role of

water in protein functioning.

Fig. 3. The absolute neutron scattering length density profiles for partial hydration with DjO and H^O and their difference profile for both the nonpolar SAM (a) and the uncharged polar SAM (b) cases. The boundaries for the cytochrome c protein region of the profiles used for calculation of the amount of water hydrating the protein are

z = 1 0 A and z = 60 A. Schematics of the composite structures are shown above their respective scattering

length density profiles approximately to scale.

^^^^ff Hi ^ffia

[1] J. A. Chupa, J. P. McAuley, R. M. Strongin, A. B. Smith, J. K.

Blasie, L. J. Peticolas, and J. C. Bean, Biophys. J. 67, 336 (1994).

[2] A. M. Edwards, J. K. Blasie, and J. C. Bean, Biophys. J. 67,1346

(1998).

[3] L. R. Kneller, A. M. Edwards, C. E. Nordgren, J. K. Blasie, N. F. Berk, S. Krueger, and C. F. Majkrzak. Biophys. J. 80, 2248 (2001).

[4] C. E. Nordgren, D. J. Tobias, M. L. Klein, and J. K. Blasie. Biophys.

J., in press.

[5] J. M. Pachence, S. M. Amador, G Maniara, J. Vanderkooi, P L. Dutton, and J.K. Blasie. Biophys. J. 58, 379 (1990).

[6] J. M. Pachence, and J. K. Blasie. Biophys. J. 59, 894 (1991).

L. R. Kneller, N. F. Berk, S. Krueger, and C. F. Majkrzak NISI Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg,MD 20899-8562

J. K. Blasie, A. M. Edwards, and C. E. Nordgren

Department of Chemistry

University of Pennsylvania

Philadelphia, PA 191 04

27
Direct Measurement

of the Reaction Front in

Chemically Amplified Photoresists

If

he semiconductor industry is rapidly

approaching the need to fabricate sub- 100 nm structures to continue perfor- mance increases in integrated circuits. Photolithography remains the enabling technology for the

fabrication of integrated circuit patterns. Although

industry is able to commercially produce 130 nm

features, lithographic materials and processes are not

ftiUy available for the production of sub- 100 nm structures. New materials must be able to produce structures with dimensional tolerances of 2 nm to 5 nm, dimensions

near the size of the polymer chain molecules in the imaging

layer. Current imaging layers, chemically amplified photoresists, are multi-component materials consisting of a polymer resin initially insoluble in an aqueous base developer solution, a photoacid generator (PAG), and other

additives. A schematic diagram of the fabrication process and an example structure are shown in Figs. 1 and 2. The

patterns are generated in the resist by exposure to UV

radiation through a mask. In the exposed areas, the PAG

decomposes, forming an acid species. Upon baking, the acid diffuses and catalyzes a deprotection reaction rendering the insoluble resist soluble in a developer. The soluble

regions are then removed with the aqueous base developer.

Control over this process is dominated by the events in the

transitional region between exposed and unexposed areas of the photoresist.

The initial development of chemically amplified

photoresists was a key technological breakthrough further- ing the continued use of optical photolithography for the

Fig. 1 . At left, SEM image of a litliograpliically fabricated structure with

a nominal critical dimension of 150 nm and 300 nm pitch. At right, schematic illustration of patterning through a mask to create the

structure.

UV radiation, X< 248 nm

1^ p n pif^jplr UUi Ui UUUii i

photoacid generated

base soluble

Reaction-diffusion front

profile determines both

the final front structure and where dissolution is allowed

§100%

Q.

CD Q 0%

Photoresist film

Silicon

lithographic interface

Solubility limit

Fig. 2. Schematic diagram of the reaction-diffusion process in chemically amplified photoresists. The transitional region between exposed and unexposed regions is particularly important for critical dimension and roughness control.

fabrication of sub micrometer features. The importance of

chemically amplified photoresist concepts is illustrated by

the industry-wide use of these materials in the fabrication

of state-of-the-art devices today and into the foreseeable

future. With the imminent need for sub- 100 nm feature

+ C02 + CD2 =C-CD3

CD,

OH

PHOSt

0

dPBOCSt

Fig. 3. General deprotection reaction in a chemically amplified

photoresist. Deuterated molecular parts with strong contrast to neutrons are shown in red.

28
Soft Condensed Matter

NEUTRON

A\

4- 1 0.20

rrr^ 400 .1200 1600

z(A) X-RAY

-2-

V777A Silicxin substrate r—| d-PBOCSt

I 1 PHOSt/PFOS

I 1 PHOSt/Acid

Deprotected polymer

-10-

-12-

0.00

r T

I

I I 1 !

I

1 1 I T

I'

1 T t -I'

0.05 0.10 0.15

T

0.20

o

(e)

o

o . =< :

- o -

o -

400 800 1200 1600

z(A)

Fig. 4. (a) schematic diagram of the processing steps including the application of each

film layer, exposure to UV radiation, a post-exposure bake (PEB) and development,

(b) and (d) show the NR data and compositional depth profile and (c) and (e) show the XR data and density depth profiles from each step.

sizes, nanometer level control over the spatial evolution of

the deprotection reaction front and the subsequent development steps is needed. The current level of understanding

of the acid-catalyzed reaction-diffusion process is not

sufficiently detailed to achieve this goal.

To meet the need for spatially detailed data, we have

developed, in collaboration with the IBM T. J. Watson

Research Center and the University of Texas at Austin, an

experimental methodology to directly measure the spatial

evolution of the deprotection reaction front through each

processing step. By using model photoresist polymers

with a deuterated protection group, neutron and x-ray

reflectivity (NR, XR) measurements are able to follow the compositional and density profiles of the reaction-diffusion process in an idealized transitional region in a bilayer film

stack. Neutron contrast with the reaction is possible

because the reaction products involving the deuterated

protection group are volatile, as illustrated in Fig. 3. The NR and XR resuhs from a series of bilayer

samples are shown in Fig. 4. NR and XR measurements were taken after each processing step from the spincoating of each film layer through exposure and bake to the dissolution of the upper layer and any deprotected

polymer. The data show that the deprotection reaction

front broadens with time within the photoresist. The initial

interfacial width was approximately 4 nm wide

whereas the reaction front was nearly 20 nm

wide. Upon development, the data show that the developed film remained sharply defined

with a surface roughness of approximately 4

nm as well. Although the reaction front was much wider than the final interfacial width, the

selectivity of the dissolution process allows for the fabrication of well-defined nanostructures with diffusive fransport mechanisms.

The spatial detail afforded by the developed methodology can play an important role

in not only the qualitative description of the reaction-diffusion process, but also with the

quantitative determination of physical parameters and changes in any physical or chemical

properties over the nanometer length scales required for control over the fabrication of

sub- 100 nm structiires. In addition, the

strategy developed here is general and can be

adapted for the study of candidate photoresist

materials being developed for future applications. "[This work [1]] opens a window of

opportunity to construct structure-property relationships

between chemical transport mechanisms and ultimate resist

resolution. It may also lead to insights into the ultimate,

intrinsic resolution limits and critical dimension control of

polymer-based imaging materials." [2]

References:

[

1 ] E. K. Lin, C. L. Soles, D. L. Goldfarb, B. C. Trinque, S. D. Bums,

R. L. Jones, J. L. Lenhart, M. Angelopoulos, C. G. Willson,

S. K. Satija, and W. L. Wu, Science, 297, 372 (2002).

[2] E. Reichmanis and O. Nalamasu, Science, 297, 349 (2002).

E. K. Lin, C. L. Soles, R. L. Jones, J. L. Lenhart, and Wen-li Wu

Polymers Division National Institute of Standards and Technology

Gaithersburg,MD 20899-8541

S. K. Satija NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg,MD 20899-8562

D. L. Goldfarb and M. Angelopoulos IBM

TJ. Watson Researcli Center Yorktown Heights, NY 10598

B. C. Trinque, S. D. Burns, and C. Grant Willson

University of Texas at Austin

Austin, TX 7871
Scaling of Membrane Phase Dynamics

Membrane phases are one example

of the variety of complex fluid structures formed by surfactant molecules in

solution. They are most commonly encountered

in biological systems, but are also used extensively

in a variety of commercial applications from personal

care products to foods to paints. The diagram in Fig. 1 shows the regularly stacked lamellae of the L„ phase and

the convoluted meandering channels of the "sponge" or L3

phase. The topological distinctions between these two

phases result in very different macroscopic properties.

The anisotropic lamellar phases are birefringent and

viscous, with complicated flow responses, while the

isotropic sponge phases are clear and generally flow freely

with constant viscosity. However, these very distinct phases are adjacent in the phase diagrams of many sys- tems, and very dilute sponge phases exhibit a transient birefringence when shaken, which suggests a shear- induced transition to a lamellar state. Due to the experimental challenges of studying both the structure and

rheology of such dilute phases, the exact nature of the

transient birefringence has remained somewhat controversial. Both sponge and lamellar structures have scaling

properties: their characteristic lengths (see Fig. 1), the channel width, ^, and the smectic periodicity, d, scale with

the ratio of the membrane thickness, 5, to the membrane

volume fraction, (j). The dynamics of these phases are dominated by thermodynamic fluctuations of the membranes, which also scale with these parameters. Gates and

Milner predict the scaling relationship and shear response

to be expected for an isotropic diblock copolymer phase

[1 ]. They note that this phase is topologically similar to sponge phases, and therefore expect the relationship to extend to such systems as well. Their analysis indicates

that flow should dampen fluctuations normal to both the flow velocity ( V) and the velocity gradient ( W), eliminating channels in those directions. This would result in a

quasi-first order phase transition to a lamellar state with its membranes parallel to the {V, W) plane, i.e., perpendicular

to Z, (conventionally the "a" orientation) occurring at a

critical shear rate: ~ k^T/t]^^ ~ k^T(^/S//rj^^ where

is the Boltzmann constant, T is the temperature, and tj^

is the solvent viscosity.

From the equation, it is clear that fransient birefrin- gence, occurring at low shear rates, requires very dilute samples, i.e., having small ^. Furthermore, the ^^/tj^

dependence suggests that increasing solvent viscosity to slow membrane fluctuations would relax this requirement.

Taking our lead from previous microemulsion work [2], we found that dextrose could be dissolved at volume

fractions up to 40 % in the heavy brine solvent (0.2 mol of

NaCl in D2O to make a 1 L solution) of cetylpyridinium

chloride/hexanol membrane systems without altering their phase diagrams. The maximum dextrose addition changes

^5 from 1.1 mPa-s to 13.6 mPa-s. Then for a series of

sponge samples having membrane volume fractions from

Fig. 1. Representations of two types of membrane morphologies: the sponge (L3) and lamellar (LJ phases with their corresponding

characteristic lengths.

3 % to 10 %, the factor (/>^/% can be varied by more than

two orders of magnitude. Plots of the reduced viscosity

and shear stress (Fig. 2b) versus the rescaled shear rate parameter, yrjj^^, display master curve behavior, clearly

showing that these macroscopic responses measuring the dynamics of this system scale as predicted. The corre- sponding scaled micro-structural response parameters,

explored by Couette SANS (Fig. 2c, d) likewise exhibit excellent scaling behavior. Moreover, the strong correlation

between these macroscopic and microscopic responses

leads to a detailed picture of the mechanisms involved.

The response exhibits three distinct regions [3]. (See

Figs. 2 and 3.) At low shear rates (Region I), the sponges

show their familiar constant viscosity Newtonian behavior

and isotropic scattering. No structural changes occur

since the applied shear rate is much less than the dynamic

response rate of the channels. In region II, when the shear

rate approaches this rate, the density of connections in the gradient direction ( W) decreases, leading to a gradual

30
Soft Condensed Matter

60

40- \ °

3020P^ ^^^I^t^

DCccooccooaxxxx)coRheology

10^ 10^ 10^ 10"

(nm-') Open

symbols

1.8

1.6

10'

'I

(d) o ! m

"

•

I

1

Scattering

Filled symbols

0.8

0.6

0.4

0.2

10= /03(Pa)

10' 0 V 10-^ lO'^

Fig. 2. (a) Rheological data for a range of membrane volume fractions ((zij and dextrose concentrations (t//

(b) The same plotted to show master curve behavior, indicative of scaling, (c) The corresponding master

curve variation of the scattering anisotropy, A^f^f^ = (Iz -I rv)/(/z + ' rv). and (d) the rescaled correlation peak position and intensity. Regions I, II and III are discussed in the text.

development of smectic order in that direction, and thus

causing the observed decrease in viscosity. At shear rates high enough to totally eliminate the channels along FFthe

intensity I^- saturates, indicating the appearance of a lamellar phase with the membranes fully-aligned parallel to Z In view of the theory, this is an unexpected result: the order develops in the so-called "c"

orientation, indicating that it is fluctuations

in the gradient direction ( W) that are being suppressed rather than in the

vorticity (Z) direction of the predicted "a"

orientation. Also the complete lack of a rheological stress plateau (Fig. 2a) and the gradual change of the peak position

(Fig. 2d) both preclude the possibility of

the transition being first order. The

aligned lamellar phase remains stable

over only a narrow range of

shear rates in region II before

collapsing at the onset of

region III to a structure with

correlations on length scales » which is only observed

for samples with sufficiently

high solvent viscosities and low

membrane concentrations.

While more work remains to determine the nature of this

final structure, we note that it has been predicted that sup- pression of fluctuations by

shear should eventually destabilize a bulk lamellar system [4 ]. While the magnitude of

the critical shear rates are consistent with theory and we

have now confirmed the scaling behavior of the shear

response, the nature of the

transition and the orientation of the shear-induced smectic

state are not as predicted. The theory does not, in fact, extend straightforwardly to the topologically similar sponge

phases as expected, and a more sophisticated model is needed to fully explain the details of shear response in this class of systems.

(c)

,l ' 1

1

1 1

i

' A* 1

jo:* f

I L n 1 m

1 0|0 1 ^A

, I**

10" 10^

r77,/03 (Pa)

10^ 10^

RADIAL

TANGENTIAL

Fig. 3. (a) Schematic of the beam incidence on the Couette SANS cell in radial and tangential

geometries, (b) Scattering patterns in radial and tangential geometries for a = 0.05, ii/ = 0.4 sponge sample at a range of shear rates over the three rheological regions.

References:

[1] M. E. Gates and S. T. Milner, Phys. Rev. Lett. 62, 1856 (1989).

[2] Chen V., PhD Thesis, University of Minnesota (1988).

[3] L. Porcar et ai, Phys. Rev. Lett., in press.

[4] S. Ramaswamy, Phys. Rev. Lett. 69, 112 (1992), and R. Bruinsma

and Y. Rabin, Phys. Rev. A 45, 994 (1992).

L. Porcar Oak Ridge National Laboratory Oak Ridge, IN 37831-6393

Present address:

University of Maryland, College Park, MD 20742

W. A. Hamilton and P. D. Butler Oak Ridge National Laboratory Oak Ridge, IN 37831-6393

G. G. Warr

The University of Sydney

Sydney, NSW 2006, Australia

31
Observation of Liquid-Glass-Liquid

and Glass-Glass Transitions in the

L64/D2O Copolymer Micellar System

'he glassy state of matter is ubiquitous, ranging from ordinary

window glass to polymers to proteins. Yet, the nature of the transition between liquid (L) and

glassy (G) states remains one of the unsolved

problems in the physics of condensed matter. Modecoupling theory (MCT), originally developed for supercooled simple liquids, makes predictions of liquidglass (L-G) and glass-glass (G-G) transitions in a colloidal

suspension. Here we present small-angle neutron scattering

(SANS) and photon correlation spectroscopy (PCS)

measurements confirming these predictions.

In a recent series of papers [1,2] MCT predicts that

in colloidal systems with a sufficiently short-range effective inter-particle attractive interaction one can observe two

types of kinetic glass transitions (KGT). The KGT can be

the result of a "cage effect," originating trom the excluded

volume effect of the particles at high volume fractions and

at high temperatures, or the result of a particle bonding to

its nearest neighbors at low k^T and at all volume fractions. One particularly interesting feature in this novel state of matter is the occurrence of two distinct amorphous

glassy states called respectively the "repulsive glass" (Gj^)

and the "attractive glass" (G^), as the result of the two

0.46 0.47 0.48 0.49 0.50 0.51 0.52 0.53 0.54 0.55

volume fraction 0

Fig. 1. The lines represent phase boundaries (in T*- plane) determined by mode-coupling theory for a colloidal system with a short- range attraction (s = 0.03). The phase points shown are for the L64/D2O

micellar solution. (Liquid state: orange, glassy states: blue, red, and

green.) The results confirm the existence of the attractive branch in the

predicted glass-transition boundary, and the G^-Gr transition.

distinct mechanisms for the structural arrest mentioned

earlier. With PCS and SANS measurements, we succeeded

in detecting both these transitions in L64/D2O micellar

system at high volume fractions [3]. L64 is a symmetric tri-block copolymer of composition (PEO)]3(PPO)3o(PEO)i3. Above 20 °C, the copoly- mers self-assemble into spherical micelles each with PPO

segments packed into a compact core and PEO segments

forming a corona around it. The short-range attraction

arises from the overlap of PEO chains in the corona

regions when two micelles approach one another. The

depth of the attractive well increases with temperature

1.0

0.8

s 51 .0 % mass fraction (0 =0.536) L -G^ -L

Fig. 2. The ISF as measured by photon correlation spectroscopy at three different volume fractions, cp, at different temperatures. (Data

follow the same color scheme as in Fig. 1 .) The top panel shows the re- entrant L-G^-L transition. The line highlights a region of logarithmic time dependence preceding the plateau in the liquid state just before the

transition [4]. Evidence of the G^-Gp transition can be seen in the middle

panel. By comparing the long-time limit of the ISF's with the predictions

of mode-coupling theory (MCT), the two different types of the glasses can be identified by their respective Debye-Waller factors. The bottom

panel is for a volume fraction of 0.544, which is the end point

predicted by MCT. f,^ and become identical, confirming the

prediction.

32
J.G-fejLg^^ > Soft Condensed Matter

because water becomes an increasingly poor solvent as temperature rises.

If the interaction is modeled by a square-well potential, the crucial control parameters of the phase behavior

are: the volume fraction, cp = 7ipd'^/6, the effective temperature, = k^T/u, and the fractional well-width

parameter, e - A/d. p is the number density of the spheres,

d its hard core diameter, A its attractive well-width, and -u

its well-depth.

The calculated glass-fransition lines, for the case of

£ = 0.03 [2], are shown in Fig.l in the {T*,(p) plane. On

V

120

40

120

80

40

120

80

120

40

-35.0% mass fraction ((/) =0,460) L

^J JI^

- 39'o °c

41.0 °c

45.0 °C

-52.0% (0=0.535) L-G^-L;%

..--^^^

• 15.0 °C

17.5 X

0 21.0 X

• 23.0 X

35.0 X

• 49.0 X

• 51.0 X

k ' 55.0 X

iftr-,._ . . . Resolution Function

54.2% (0=0.542) Gr -G^,a

rl

: J ^

-^aM.^* .•

• 15.0 X

22.5 X

• 27.5 X

• 36.0 X

• 37.5 X

• 43.5 X

• 45.0 X

, • 50.0 X

IW. . . Resolution Function

-54.4% (0=0.544) y\,

^ J)

• 15.0 X

22.5 X

• 27.5 X

• 32.5 X

» 34.0 X

• 37.5 X

• 43.5 X

• 50.0 X

imj. Resolution Function

K/K„

Fig. 3. SANS scaled intensity distributions vs. reduced scattering vector

for the micellar solutions at four values of (p, at different temperatures.

(Data follow/ the same color scheme as in Fig. 1 .) The top panel is for (p= 0.460. All the scaled intensities are characterized by a unique length scale and collapse into a single master curve for all temperatures. The

second panel is for ^=0.535: the system is clearly characterized by two

length scales. While the narrower peak is resolution limited, the broader peak is similar to the one observed in the first panel. If we identify the broader peak to represent the liquid state, then the narrower peak should

represent the glassy state. The system thus shows a re-entrant L-G-L

transition. The third panel is for (p= 0.542. Again, two length scales

characterize the system. The narrower peak is resolution-limited and the

slightly broader peak is also nearly so. The results can be interpreted as showing a transition between two amorphous solid states, i.e., a G-G

transition. The last panel is for ^3= 0.544, which is predicted as the A3

point, at temperatures ranging from 15 °C to 50 °C. The two different types of glasses indeed become identical at this volume fraction.

going from higher to lower T*, at volume fractions less than 0.5365 L-G^ transitions occur, and at volume frac- tions greater than this value, one has a possibility of

observing Gr-G^ transitions. Figure 2 shows normalized photon correlation

functions (coherent intermediate scattering frinctions, ISF)

measured at q » 0.001 A-' and at three different volume

fractions, as a function of temperature [3]. For the (p where the L-G^ transition is possible, one can see that in the L state, the long-time limit of the ISF,^, is zero, while

in the G^ state, /^'^ » 0.4 to 0.5, which is the value of the Debye-Waller factor of the glassy state. The KGT is thus

characterized by a discontinuous change off^. At

<p = 0.542, we observe the G^ (f^'' » 0.4) to G^ transition

(/^^ « .7). At (p= 0.544, which is called the singularity

end point, our measured ISF's show identical values of

Z^*^" « 0.4 in the two glassy states, confirming the theory.

Figure 3 shows scaling plots of SANS intensity disfributions at four volume fractions, and at different temperatures, spanning the regions of the phase diagram

where the L, L-G-L, G-G, and two identical glasses

{A2 point) are located. The scale is set by a unique length

parameter, the average inter-particle distance. Verification of mode-coupling theory predictions

through photon-correlation spectroscopy and small-angle neutron scattering measurements on a micellar system

provides a basis for improved understanding of the glass

transition in general.

References:

[1] L. Fahbian. W. Gotze, F. Sciortino, P. Tartaglia, and F. Thiery, Phys.

Rev. E 59, R1347 (1999).

[2] K. Dawson, G. Foffi, M. Fuchs, W. Gotze, F. Sciortino, M. Sped,

P. Tartaglia, Th. Voigtmann, and E. Zaccarelli, Phys. Rev. E 63, 011401 (2001).

[3] W. R. Chen, S. H. Chen, and F. Mallamace, Phys. Rev. E 66, 021403 (2002).

[4] F. Mallamace, P. Gambadauro, N. Micali, P. Tartaglia, C. Liao, and

S. H. Chen, Phys. Rev. Lett. 84, 5431 (2000).

S.-H. Chen and W.-R. Chen

Massachusetts of Institute of Technology

Cambridge, MA 021 39

F. Mallamace

Massachusetts of Institute of Technology

Cambridge, MA 021 39

and

University of Messina

Messina, Italy
Early-Stage Compositional

Segregation in Polymer Blend Films

etting plays an important role in diverse applications ranging from

insecticide sprays to detergency. This interest,

in part, has motivated a great deal of fundamental

research involving the spreading (wetting) of a

liquid on a solid surface. Polymer blends are of great

commercial importance and therefore their thermodynamic and phase separation behaviors have been widely

studied. The structure and properties of thin blend films are governed by the interplay between phase separation and

surface segregation driven by polymer-surface interactions. The nature of the segregation depends on whether

the mixture forms a stable one-phase fluid or phaseseparates [1, 2]. In the former case, the surface-enrichment-layer (SEL) grows and stabilizes to an equilibrium

value. In the latter case the initially formed SEL breaks into droplets for partial wetting and grows unsteadily for complete wetting [1]. The late stage evolution of the surface enrichment layers thus exhibits "non-universal"

growth laws, depending on the phase stability, wetting

characteristics of the blend, confinement, as well as on the

details of the polymer-surface interaction potential [2]. The

universality of surface segregation at the early-stage,

however, has not been explored, partly because the compositional changes are normally rapid [3, 4]. We

therefore designed a measurement that can access the

short time and small length-scale surface-enrichment

regime.

A critical blend film near the glass transition of the polymers is utilized so that the chain dynamics are greatly

slowed down even under thermodynamically strong

segregation conditions. The polymers are deuterated

poly(methyl methacrylate) (dPMMA) and poly(styrenera^-acrylonitrile) (SAN). This polymer blend has a lower

critical solution temperature (LCST) below as revealed

by small-angle neutron scattering measurements. A 445 A

film of dPMMA/SAN (50/50 by mass) was obtained by

spin-casting fi"om a common solution. After drying at a temperature slightly below T^, the films were annealed in a vacuum oven at (130 ± 0.1) °C for various times ranging

from 1 min to 36 h. After drying and after each step of

annealing, the film was measured using neutron reflectivity

(NR). An atomic force microscopy study indicated that the film roughness was below 6 A throughout the measurement.

Figure 1 shows NR spectra after several annealing

intervals. The spectra were analyzed using a model-fitting

scheme. The best fits are shown as the solid curves, and

their corresponding compositional profiles are shown in

Fig. 2. The inset of Fig. 2 shows the evolution of the dPMMA volume fraction in the depletion zone (^^j) and at the surface {(f>^. The former decreases monotonically,

suggesting that equilibrium has not been achieved, while

the non-monotonic variation of the latter is due to the surface relaxation at the initial time.

The surface excess, z* = J[<z^(x) - ^d\dx, is shown

in Fig. 3, and can be fit to a power law f0.4i±o.oi for early

times (solid line), and a stretched exponential form for the

entire time (dashed curve). The latter gives z*(oo) = 72 A

at the saturation, z* starts to deviate from the power-law

behavior at about 9 h (indicated by the arrow in Fig. 3)

corresponding to z* = 40 A and 4 = 57 A, where 4 is the surface correlation length characterizing the decay of the surface enrichment composition. These crossover scales

in the kinetics are comparable to the bulk correlation length

length 4, ~ 60 A, suggesting a transient saturation. After

that, the SEL will grow unsteadily, entering the later stage

of the wetting layer growth [4]. The inset of Fig. 3 shows that ^ nearly follows a power law of /0 25±o.oi^ except for initial times. Note that

0.00 0.02 0.04 0.06

-1i

0.08

/c(A-')

Fig. 1. Selected neutron reflectivity spectra after various times at 130 "C.

34
Soft Condensed Matter

0.2 -I • ' • ' • ' ' ^

0 100 200 300 400

Depth (A)

Fig. 2. (z^tjPMMA profiles that give the best fit. The inset shows the

evolution of surface composition, (circles) and depletion layer composition, (p^ (triangles).

2.0

0.5

f 0.41 9^

2.0

1,5

' 0.5 1,1.

•

•

2 3 4 5 1,1, log(f)(s)

2 3 4 5 6 log(f)(s)

Fig. 3. z* with a power-law fit (solid line), f ''^, and a stretched exponential function (dashed curve). The arrow denotes a z* ^ 40 A and

the transition to slower growth. The inset shows the surface correlation

length.

right after drying, z*(0) = 4 A, indicating a segmental scale of saturation from processing the film (spin-casting and

drying). Thus, the initial "anomaly" of (j)^ and may

reflect the relaxation of the highly non-equilibrium compositional profiles. While most of the previous work focused on the kinetics after the formation of the initial layer on the order of the correlation length, the transient early-stage of

the SEL has received little attention. The interpretation of

the apparent power law growth will thus require further

investigation.

In summary, during the early stage of surface

segregation, enrichment at a monomer length-scale occurs

first, followed by a segregation layer that grows to the order of the bulk correlation length, 4^ which coincides

with the radius of gyration of polymers deep in the twophase regime. Thus, the two observed distinct surface

saturation states correspond to the characteristic scales of

macromolecules. However, at near criticality, previous

studies suggest a large discrepancy between 4 and

pointing to the need to consider three length scales: that of

the monomer, the molecular size, and the size of compositional fluctuations. The extent of universality in the early

stage growth kinetics therefore needs further investigation.

The present study is the first to quantitatively examine this important phenomenon.

References:

[1] S. Dietrich, in Phase Transitions and Critical Phenomena, ed. by

C. Domb and J. L. Lebowitz, Academic Press, London (1988)

Vol. 12.

[2] IC. Binder, J. Non-Equilib. Thermodyn. 23, 1 (1998), and references

therein.

[3] S. Puri and K. Binder, J. Stat. Phys., 77, 145 (1994); S. Pun and

K. Binder, Phys. Rev. E, 49, 5359 (1994).

[4] H. Wang, and R. J. Composto, Phys. Rev. E, 61, 1659 (2000).

H. Wang, J. F. Douglas and C. C. Han

Polymers Division

National Institute of Standards and Technology

Gaithersburg, Maryland 20899-8542

S. K. Satija NISI Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg, Maryland 20899-8562
Magnetic Cluster Sizes

in iVIagnetic Recording Disks

he equivalent of Moore's law for magnetic recording is that the areal density of magnetically written bits increases at 60 % to 100 % per year, and, of equal interest to the consumer, the cost per megabyte decreases at 40 % to 50 % per year. To achieve this, the noise in the magnetic media must be continuously reduced,

which is accomplished by decreasing the size of the magnetic clusters — regions of the media that are magnetically coupled. The cluster size must decrease, since the media noise primarily results from the finite cluster size; the bit transitions are narrower when the clusters are

smaller. Presently, cluster sizes are believed to be about

10 nm to 15 nm, but accurate knowledge of the size distribution and even the average size is lacking. A com- mon assumption is that the cluster size is identical to the

10"

5

1

1

'

(a) So

\ — 8:^0 A 6 = 0.6 T

lO'*

lO'^

m io2

10^

10^

lO'^

TO i-i

10^

10"

0.002 0.005

Fig, 1. SANS intensity for magnetic disl^s So and Cy, averaged around tlie incident beam direction whiichi was perpendicular to surface of the disks. In (a) and (b) the blue lines show data for no applied field (high noise state), while red lines show data for a 0.6 T field. Two sample-to-detector distances were used, with Q ranges of 0.0025 A-i to 0.025 A-^ and 0.025 A-^ to 0.3 A-^ . In (c) and (d) the blue squares are the magnetic

SANS, the difference of the zero and 0.6 T scattering intensities in (a) and (b). The red line shows the best

fit to a model described in the text. The arrows mark the approximate Q where the slope of the data changes.

crystalline grain size of the media [1], but this has not been

demonstrated.

We have conducted Small Angle Neutron Scattering

(SANS) measurements of the magnetic cluster size in actual recording disks and quantified the size distribution. The measurements were performed at NG-7 30 m SANS

instrument with unpolarized neutrons with wavelength of

7 A and a relative wavelength spread of 1 1 %. Since SANS

is caused by both physical and magnetic inhomogeneities,

it is necessary to separate these contributions and to isolate the magnetic cluster SANS. This was done with two

separate measurements. Data were first taken for disks in an initial, high noise state where there are a maximum

number of interfaces between magnetic clusters. This is accomplished by first fully magnetizing the disks in a circumferential direction. Then, the disks were scanned

with a recording head field in the opposite direction and with

a strength approximately equal

to the remnant coercivity of

the media. This causes ap- proximately half of the magnetic clusters to reverse

direction, leaving a maximally

noisy state. In this state, the SANS contains contributions

from the physical film struc- ture (grains) and the magnetic

film structure (magnetic

clusters). Data were then

obtained with a magnetic field of 0.6 T applied parallel to the disk surface. This field orients the magnetic moments in the

clusters predominantly along

the field and, by examining the ^-dependence of the SANS, we can determine the SANS

from the physical film structure. Subtracting the zero field and 0.6 T spectra leaves the desired magnetic SANS [2, 3].

0.01 0.02 0.05

36
?1 V i^vS^isnsr ^ Condensed Matter and Applied Physics

The disks, denoted So, To and Cy, are those used in three product generations. The magnetic media in each

two-sided disk was a Co-Pt-Cr alloy (25 nm to 40 nm

thick) sandwiched between a carbon layer and one or more

nonmagnetic underlayers. The disks were sliced into eight

pieces and stacked to create 1 6 magnetic layers for the SANS measurements. The relative signal-to-noise ratio (Sq/NJ varied from 0 db (So) to 3 db (To) to 6.5 db (Cy).

SANS data for both magnetic fields are shown in

Fig. la and lb. Subtracting these two spectra leaves the desired magnetic SANS, which are shown in Fig. Ic and

Id. It is apparent that for increasing Sq/N^^ (So to Cy)

there is an increase in the Q where the slope changes,

which establishes that the disks with higher Sq/N^ have

smaller average cluster size. In addition, there is a distribu- tion of cluster sizes, since there are no oscillations in the data and the change in slope is gradual.

To determine the cluster size distribution, we have

modeled the cluster shapes as cylinders, since TEM shows

the physical grains adopt a columnar morphology. The

magnetic SANS data are well fitted using a log-normal

distribution of cluster sizes. These distributions are shown

in Fig. 2, while the fits to the data are shown in Fig. 1. Such magnetic cluster size distributions have not been

reported before for recording media, and allow us to draw

several important conclusions.

First, these results show that the media Sq/N^ is inversely correlated with the magnetic cluster size. This is apparent from Fig. 2 when one recalls that So/N,„ increases

from So-To-Cy. This provides firm experimental

verification of the models that have proposed smaller

clusters give larger Sg/N^ [!]• A second conclusion

follows from a comparison of the magnetic cluster size to the physical grain size, shown in the inset to Fig. 2. The

average cluster size is slightly larger than the average grain

size, and, for the most advanced media (Cy), this differ- ence is < 10 %. This shows that the intergranular magnetic

interactions are not very strong, especially for the ad- vanced media; hence, the size of the media noise sources

scales with crystalline grain size. This result validates

previous (implicit or explicit) assumptions [1,4].

The cluster size distribution is quite broad with a lognormal r of about 0.5. Recent models of the magnetic

recording properties of media have begun to include

microstructural disorder [1], and have shown that the magnetic cluster size distribution has significant effects on

these properties. Thus, the exact cluster size distribution is important for these models. Our results provide empirical

100 200 300 400 500 600 700

cluster diameter [A]

Fig. 2. Green, red and blue curves show the best-fit distributions for disks Cy, To and So, respectively. The triangles mark the average cluster

size. The log-normal rare 0.56, 0.52 and 0.46 for Cy, To and So,

respectively. The inset shovi/s the average magnetic cluster diameter versus the average physical grain diameter, obtained from x-ray

diffraction and TEM.

data on this distribution, which, when incorporated into the models, will improve their reliability.

Our results have implications for magnetic recording

technologies. While the lack of coupling is desirable from

an Sy/N^, perspective, the broad distribufion is not, since

large clusters will contribute to noise and the small clusters will be thermally unstable. Reducing this distribution will be

a major challenge for media designers. Finally, the methodology we have developed will be applicable to future media

where the average cluster sizes are < 10 nm. References:

[1] Y. Zhang and H. N. Bertram, IEEE Trans. Magn. 35, 4326 (1999).

[2] J. Suzuki, K. Takei, Y. Maeda, Y. Morii, J. Magn. Magn. Mater. 184,

116, (1998).

[3] J. F. Loftier, H.-B. Braun, W. Wagner, Pliys. Rev. Lett., 85, 1990

(2000).

[4] M. F. Doemer, K. Tang, T. Amoldussen, H. Zeng, M. F. Toney,

D. Weller, IEEE Trans. Magn. 36, 43 (2000).

M. F. Toney and K. Rubin IBM Almaden Research Center San Jose, CA 95120

S.-M. Choi NISI Centerfor Neutron Research

Present affiliation: Korea Advanced Institute of Science and Technology

Yuseong-gu, Daejon, Republic of Korea 305-701

C.J. Glinka NISI Centerfor Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8562

37
Dynamical Effects of Polar

Nanoregions in Relaxor Ferroelectrics

I elaxor ferroelectrics exhibit

^exceptional piezoelectric properties.

Single crystals of some of these materials can

achieve ultrahigh strains under applied electric

fields that are fially one order of magnitude larger

than those attainable in conventional lead-zirconatetitanate (PZT) ceramics, which are widely used in

solid-state actuators that convert electrical energy into mechanical energy. The additional properties of large

electromechanical coupling and low dielectric loss suggest

that industrial use of relaxors may revolutionize the areas of medical imaging, naval sonar, and other acoustic

applications. Relaxors are further characterized by a markedly fi-equency-dependent dielectric susceptibility that

is very broad in temperature. The recent neutron scatter- ing studies briefly described here provide new insight on

the behavior of these systems.

PZN

>

3

0.2 0.3

(2, k, 0)

Fig. 1. Contour plot of the neutron inelastic scattering intensity measured in PZN in its cubic phase in the (200) Brillouin zone. The

color scale varies logarithmically with intensity, and is limited in range

to make the weaker features more visible.

A key feature that appears to be common to all of the relaxor compounds, and which is believed to play a fundamental role in producing the enhanced piezoelectricity, is the formation at high temperature of tiny regions of local and randomly-oriented electric polarization just several unit

cells in size, also known as polar nanoregions (PNR). The

existence of these PNR was inferred from the observation

that the optical index of refraction in a variety of disordered

ferroelectric systems deviates from a linear temperature

dependence at a temperature far above [2]. Pb(Zn,/3Nb2/3)03 (PZN) and Pb(Mgi/3Nb2/3)03

(PMN) are two of the most studied compounds as their piezoelectric responses rank among the highest [1]. These

compounds crystallize in the complex perovskite structure Pb(B'B")03, where the B' and B" atoms are generally

heterovalent. Thus the relaxor compounds possess not only chemical disorder, but usually a mixed-valence

character as well. Our studies of PZN and PMN have focused on

understanding the mechanism underlying the formation of

the PNR, as well as their effect on the lattice dynamics.

The latter are clearly manifest in neutron scattering

measurements. The long-wavelength transverse optic

(TO) phonons are heavily damped in energy below in PZN, which gives rise to the anomalous "waterfall" feature shown in Fig. 1 [3]. This damping is strongly wavevector

dependent, and becomes significant when the wavelength

of the lattice vibration becomes comparable to the average

size of the PNR, which is estimated to be of the order of

30 A to 40 A. Subsequent experiments were performed above = 620 K in PMN to look for a soft mode, given the obvious similarities to the classic soft-mode ferroelectric PbTi03. Surprisingly, the phonon damping persists well

above T^, as shown in Fig. 2 [4]. This implies that the PNR exist as dynamic entities above T^, but are still effective at inhibiting the propagation of long wavelength

phonon modes. Even more interesting is how the zonecenter TO mode softens and broadens in energy as the temperature approaches from above, and that only the zone-center TO mode becomes overdamped (no peak at non-zero energy) at T^. Modes at higher wavevector q

become overdamped too, but only below T^. This behav38
Condensed Matter and Applied Physics

ior suggests that the zone-center TO mode condenses at

r^j, thereby giving rise to the PNR. Consistent with this picture is the observation that the square of the zone-center TO mode energy varies Hnearly with temperature, as happens in normal soft-mode ferroelectrics. This is shown

in Fig. 3, which summarizes the soft TO mode dynamics

in PMN between 1 0 K and 1 1 00 K [5]

An anomalous broadening of the acoustic modes,

shown in the upper panel of Fig. 3, also occurs at T^, as does the onset of diffuse scattering associated with the PNR. The difftise scattering structure factors can be

reconciled with those of the TO phonons in different Brillouin zones by postulating a uniform shift of the PNR

along their polarization direction [6]. Furthermore, a model

that couples the TA and TO modes is able to describe all of

the observed phonon lineshapes extremely well [7]. This

then suggests a novel idea in which PMN exhibits the condensation of a coupled soft TO mode at T^. Such a coupled-mode would carry an acoustic component, and

thus provide a natural explanation of the uniform shift of

the PNR. If true, this would complete an elegant description for the dynamical formation of the PNR in PMN, and

most likely other relaxors as well.

References:

[1]

[2]

[3]

[4]

[5]

[6]

[7]

S.-E. Park and T. R. Shrout, J. Appl. Phys. 82, 1804 (1997).

G. Bums and F. H. Dacol, Solid State Comm. 48, 853 (1983). P M. Gehring, S.-E. Park, and G. Shirane, Phys. Rev. B63, 224109

(2000).

P. M. Gehring, S. Wakimoto, Z.-G. Ye, and G. Shirane, Phys. Rev.

Lett. 87, 277601 (2001).

S. Wakimoto, C. Stock, R. J. Birgeneau, Z.-G. Ye, W. Chen, W. J. L. Buyers, P M. Gehring, and G Shirane, Phys. Rev. B65, 172105

(2002).

K. Hirota, Z.-G Ye, S. Wakimoto, P. M. Gehring, and G. Shirane, Phys. Rev. B65, 104105 (2002).

S. Wakimoto, C. Stock, Z.-G. Ye, W. Chen, P M. Gehring, and

G. Shirane, submitted to Phys. Rev. B.

P. M. Gehring

NIST Centerfor Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD 20899-8562

S. Wakimoto and C. Stock

University of Toronto

Toronto, Ontario Canada M5S 1A7

Z.-G. Ye and W. Chen

Simon Fraser University Burnaby, British Columbia Canada V5A1S6

G. Shirane

Brookhaven National Laboratory Upton, NY 11973

39
Emergent Excitations in a

Geometrically Frustrated Magnet

A

"Chinese" checkerboard having an

equal number of black and white

marbles cannot have every neighbor being the opposite kind, whereas a square checkerboard

can. The triangular array on a Chinese checkerboard offers an example of "geometrical finstration". Frustration (i.e., a condition in which some relation among the components cannot be satisfied simultaneously) is an important concept in understanding disor- dered states of matter. Systems in which a large diversity

of states are involved are common in biology, chemistry

and physics [1,2]. Notable examples are glasses, liquids

and proteins. Magnetic systems offer extreme examples of

frustration in the form of spin lattices, where all interac- tions between spins cannot be simultaneously satisfied. Such geometrical frustration can lead to the emergence of

qualitatively new states of matter, having "composite"

degrees of freedom.

To explore this possibility, we examined magnetic

fluctuations in ZnCr204 [3]. The B-site of this spinel lattice occupied by spin-3/2 Cr^+ leads to a magnet with dominant

nearest neighbor interactions on the lattice of comersharing tetrahedra [4] shown in Fig. 1 . Because the spin

interaction energy is minimized when the four spins on

each tetrahedron add to zero, interactions do not call for long-range order, but simply define a restricted phase

space for fluctuations. Just as composite fermions can emerge from degenerate Landau levels in a two-dimensional electron gas, the near-degenerate manifold of states in a frustrated magnet is fertile ground for emergent

behavior [5]. Neufron scattering provides the most effective tool to study possible composite spin degrees of freedom by

directly probing the form factor of such entities. Fig. 2 (a,b)

show the wave vector dependence of the low energy

inelastic neutron scattering cross section in the spin-liquid

phase of ZnCr204. The data exhibit broad maxima at the Brillouin zone boundaries, signaling the emergence of

confined nano-scale spin clusters. Rather than Fourierinverting the data, we consider potential spin clusters and

test the corresponding prediction for the form factor against

the data. Individual tetrahedra would be prime candidates for such clusters, as they constitute the basic motif of the

pyrochlore lattice. However, a tetrahedron is too small to account for the observed features. The next largest

symmetric structural unit is the hexagonal loop formed by

a cluster of six tetrahedra (Fig. 3). Two spins of each

tetrahedron occupy the vertices of a hexagon while the other two spins belong to different hexagons. It is possible

to assign all spins on the spinel lattice to hexagons simultaneously, thus producing N/6 weakly interacting degrees of

freedom (Fig. 1 ). An outstanding fit is achieved for the antiferromagnetic hexagonal spin loops, as displayed in Fig. 2 (c, d). Thus, rather than scattering from individual

spins, neutrons scatter from antiferromagnetic hexagonal

spin clusters. In effect, ZnCr204 at low temperatures is not

a system of strongly interacting spins, but a protectorate of

weakly interacting spin-loop directors. Since the six hexagon spins are anti-parallel with each other, the staggered magnetization vector for a single hexagon, which

shall be called the spin loop director, is decoupled from the 12 outer spins, and hence its reorientation embodies the

Fig. 1 . The lattice of corner-sharing tetrahedra formed by the

octahedrally coordinated B sites in a spinel structure with chemical

formula AB2O4. A periodic assignment of all spins in the pyrochlore

lattice is made to four different types of non-overlapping hexagons,

represented by the colors blue, green, red, and gold. Every spin belongs

to just one hexagon and each such hexagon carries a six-spin director. The resulting tetragonal structure of these hexagons has a unit cell of 2a X 2a ^ 3c and can be described by a stacking of two different types of three-layer slabs along the c-axis. The hexagon coverage on consecutive

slabs is in fact uncorrelated, so that a macroscopic number of random

slab-sequences can be generated.

40
\jnTy:r4S^^ > Condensed Matter and Applied Physics

long-sought local zero-energy mode for the pyrochlore

lattice.Composite degrees of freedom are common in strongly interacting many body systems. Quarks form

hadrons; hadrons form nuclei; nuclei plus electrons form

atoms; atoms form molecules that in turn are the basis for complex biological functionality. Planets, stars, galaxies

and galactic clusters are examples of clustering on grander

length scales. However, to our knowledge, the emergence

of a confined spin cluster degree of freedom has not

previously been documented in a uniform gapless magnet.

The discovery is important because magnets offer an

opportunity not afforded by the aforementioned systems,

namely, to monitor emergent structure in complex interact- ing systems with microscopic probes such as neufron

scattering and NMR. The collapse of a geometrically

frustrated magnet into a director protectorate could for example be a useful template for exploring aspects of

protein folding [2J.

References:

[1] p. G. Debenedetti et al.. Nature 410, 259 (2001).

[2] P. G. Wolynes and W. A. Eaton, Physics World 12, 39 (1999).

'[3] S.-H. Lee, C. Broholm, W. Ratcliif, G. Gasparovic, Q. Huang, T. H. Kim, and S.-W. Cheong, Nature, in press (2002).

[4] S.-H. Lee et al., Phys. Rev. Lett. 84, 3718 (2000).

[5] R. B. Laughlin and D. Pines, Proc. Natl. Acad. Sci. U.S.A. 97, 28

(2000).

o

o'

o

Intensity {Q,ficj) (counts/min)

20 40 60

Fig. 2. (a), (b): Color images of inelastic neutron scattering intensities from single crystals of ZnCr204 in the (hkO) and (hkk) symmetry planes

obtained at 7 = 15 Kforfify =1 meV. The data are a measure of the dynamic form factor for self-organized nano-scale spin clusters in the

material, (c), (d): Color images of the square of the form factor calculated for antiferromagnetic hexagon spin loops averaged over the

four hexagon orientations in the spinel lattice. The excellent agreement

between model and data identifies the spin clusters as hexagonal spin

loops.

Fig. 3. Spin cluster surrounding a hexagon (shown in gold) in the pyrochlore lattice of Fig. 1.

S.-H. Lee, Q. Huang

NISI Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8562

C. Broholm, G. Gasparovic

Department of Physics and Astronomy The Johns Hopkins University

Baltimore, MD 21 21

W. Ratcliff, S.-W. Cheong

Department of Physics and Astronomy

Rutgers University Piscataway, NJ 08854 I H. Kim

Francis Bitter Magnet Laboratory Massachusetts Institute of Technology

Cambridge, MA 021 39

41
Polaron Dynamics

and the Glass Transition in

Colossal Magnetoresistance Materials

The recent discovery of colossal magnetoresistance (CMR) effects in the manganese oxide class of materials (such

as Laj.^A^MnOj (A = Sr, Ca, Ba)) has rekindled

intense interest in these systems, both because of

their fundamental properties as well as their technological potential for read/write heads in magnetic

recording media, sensors, and spin-polarized electronics. The role of local charge correlations and their competition

with magnetic and electronic ground states is one of the most striking new features of the transition metal oxides

such as cuprate superconductors and nickelates, but is most elegantly highlighted for these CMR manganites. Our

neutron scattering results near optimal doping show that the short-range polaron correlations are completely

dynamic at high T, but then freeze upon cooling to a temperature T„. This glass transition suggests that the paramagnetic/insulating state arises from an inherent orbital frustration that inhibits the formation of a long range

orbital- and charge-ordered state. Upon further cooling

into the ferromagnetic-metallic state, where the polarons

melt, the diffuse scattering quickly develops into a propagating, transverse optic phonon.

In the ground state these CMR materials are ideal isotropic ferromagnets. As the system is warmed through

the Curie temperature of this half-metallic system the disorder in the spins begins to inhibit the hopping of the (magnetic) conduction electrons, and this in turn provides

enough time for the lattice to distort and form polarons that trap the electrons. The ferromagnetic-paramagnetic

transition is thus accompanied by a metal-insulator transition; cooling into the ferromagnetic state, or alternatively

inducing a magnetization by application of a field, converts

the insulator back into a metal, producing the CMR effect. To investigate the dynamics of these polarons, we

have carried out inelastic neutron scattering measurements

on a single crystal of optimally-doped LagjCaojMnOj

{Tq = 252 K) [1]. Fig. 1 shows the energy dependence of

the polaron scattering at the peak of the polaron correla- tions [2]. The data reveal that there is a purely elastic component, indicating that the system still possesses order,

and since spatially this order is short range in nature we

interpret this as a polaron glass.

The data in Fig. 1 also exhibit dynamics, in the form

of quasielastic scattering (peaking at zero energy). Figure

2 shows the temperature evolution of both the dynamic

and purely elastic components, obtained on the optimallydoped CMR bilayer manganite Laj 24Sri 76Mn207 [3]. On

decreasing the temperature from 460 K we see that the

quasielastic scattering narrows in energy, with a width that decreases approximately linearly until T « 7^ « 3 1 0 K

while the integrated intensity of the scattering is approxiLaQ7CaQ3Mn03 Polaron Dynamics

600 Q = (2.25, 1.75,0) 500

1

7'=260K -

^ 400 E1 300 OO"55 ^ 200 i

100 1

0

2 0 2 4 6 8 10 12 14

Energy (meV)

Fig. 1. Polaron dynamics at the peal( in tlie correlation function at 260 K, just above = 252 K, in LagjCag 3Mn03. The data reveal a pure elastic signal (indicating an ordered state) and dynamic quasielastic scattering.

mately temperature independent. Below « 3 10 K the behavior of the quasielastic width and intensity abruptly

changes, and a new, purely elastic component, develops in the spectrum. The elastic scattering develops rapidly

below Jg, and appears to track the resistivity of the

material. This increase in the elastic intensity is accompanied by a concomitant decrease of the quasielastic intensity, while the energy width exhibits a change in slope,

becoming approximately constant for Tq< T < T^. To further probe the origin of this quasielastic

scattering we compiled the map of the dynamical scatter- ing above 7* shown in Fig. 3. The inelastic response

shows that the dynamical scattering still has siarprisingly

42
Condensed Matter and Applied Physics

well-defined correlations at these elevated temperatures,

demonstrating that the polarons are not isolated Jahn-Teller

Mn^' deformations, but are dynamically correlated. The

dynamical correlation length obtained from these data is

5: 12 A, comparable in size to the static correlation length

found at lower T. These dynamic correlations are still present up to 460 K, the highest T explored so far. From our measurements we can identify three regimes. For 7" > 7* the observ ed scattering is dominated

by correlations that are completely dynamic. The

0 100 200 300 400 500

]-(K)

Fig. 2. Temperature dependence of the elastic (a) and quasielastic

intensity (b) of the CMR bilayer manganite (Tc = 114 K). (c) Quasielastic width of the Lorentzian response. Dashed lines are guides to the eye. Error bars correspond to standard deviations obtained from the least squares analysis.

quasielastic energy width from these correlations varies

linearly with T, which is qualitatively what is expected for a continuous phase transition. The second regime occurs

for < r < 7*, and is dominated by frozen static polaronic correlations as revealed by the rapid development

of the elastic component below 7^. The development of

the elastic component is accompanied by a decrease of the

quasielastic intensity, while the spatial correlations remain

short range in nature. This behavior is clear evidence for a freezing transition, analogous to the freezing transition found in structural glasses or geometrically frustrated spinglasses. Our data strongly suggest that T* represents a phase fransition from a polaronic liquid to a polaronic

glass. This polaron glass then melts at Tq as the ferromagnetic metallic state sets in.

4.0 n

0.15 0.20 0.25 0.30 0.35

(2+q, 2-q, 0)

Fig. 3. Dynamic polaron correlations above the glass transition.

References:

[ 1 ] J. W. Lynn, F. M. Woodward, D. N. Argyriou, Y. Ren, Y. M.

Mukovskii, A. A. Arsenov (preprint).

[2] C. P. Adams, J. W. Lynn, Y. M. Mukovskii, A. A. Arsenov, and D. A. Shulyatev, Phys. Rev. Lett. 85, 3954 (2000); J. Appl. Phys. 89. 6846 (2001).

[3] D. N. Argyriou, J. W. Lynn, R. Osbom, B. Campbell J. F. Mitchell, U. Ruett, H. N. Bordallo, A. Wildes, and C. D. Ling, Phys. Rev.

Lett. 89, 036401 (2002).

J. W. Lynn and F. M. Woodward

NIST Centerfor Neutron Research

National Institute of Standards and Technology, Gaithersburg,MD 20899

D. N. Argyriou, R. Osborn, and J. F Mitchell Argonne National Laboratory Argonne.lL 60439
Quantum Impurities

in tiie Two-Dimensional Spin

One-Half Heisenberg Antiferromagnet

A

phase transition is the transformation of a system from one state to another, e.g. from an ordered phase to a disordered phase. In magnetic iron for example,

the ordered ferromagnetic phase gives way to the disordered paramagnetic phase when fluctuations

overwhelm the forces tending to order the system. In thermal phase transitions the amplitudes of these fluctuations increase with temperature, and the transition occurs

at a "critical" temperature Tq. By contrast, quantum phase

transitions occur only at T = 0 K [1]. The relevant

fluctuations are thus quantum mechanical in nature and can overwhelm the tendency to order when some other

parameter of the system is varied. A conceptual example

would be a ferromagnetic system at T = 0 that is continuously diluted with some non-magnetic material until it undergoes a transition to the paramagnetic state. The hope for insight into the physics of high temperature superconductors has generated enormous interest

in the case of the two-dimensional (2D) spin-Vz squarelattice Heisenberg antiferromagnet (5" = Vi SLHAF) because

it models La2Cu04, the parent compound of the first hightemperature superconductor. It has been theorized that a quantum phase transition might occur in La2Cu04 by

doping with static, non-magnetic, atoms [2]. We have

investigated the properties of the 2D 5" = Yi SLHAF using

complementary neutron scattering and numerical simulations. Our results demonstrate that the spin-diluted

Heisenberg antiferromagnet La2Cuj.-(Zn,Mg)-04 is a prototype system for square-lattice site percolation in the extreme quantum limit of 5" = Vi [3]. In the pure system (z = 0), magnetic Cu2+ ions form a 2D square lattice dominated by an antiferromagnetic nearest-neighbor exchange

mediated by intervening oxygen ions, which leads to longrange antiferromagnetic order at low temperature. Replacement of the Cu spins with non-magnetic Zn2+ and

Mg2+ ions randomly dilutes the antiferromagnetic sheets,

weakening the antiferromagnetic order. With sufficient site dilution the system undergoes a geometric transition from

having one infinite connected cluster of Cu spins below the percolation threshold to only finite disconnected clusters above the percolation threshold (around 41 %), as shown

in Fig. 1 . Our results demonstrate that random disorder

and quantum fluctuations both play a strong role in determining the properties of this system near the percolation threshold. Previous experiments [4] suggested that La2CU].-(Zn,Mg),04 might become disordered at zero temperature well below the classical percolation threshold

because of quantum fluctuations. This question remained

unresolved because of a lack of suitable samples, but highquality single crystals of La2Cuj.^(Zn,Mg)^04 grown at the

T. H. Geballe Laboratory for Advanced Materials at Stanford University allowed us to solve this quantum

percolation problem. Figure 2 shows the dilution dependence of the antiferromagnetic ordering (Neel) temperature

T^. Although a purely 2D system cannot have long-range

order at nonzero temperature, small interlayer couplings

allow long-range 3D order to occur when the 2D correla- tions become large enough. Monte Carlo calculations (also

shown in Fig. 2) indicate that this occurs at correlation

lengths of around 100 lattice constants for both the pure

and diluted systems. Our results for T-^{z) agree with

previous measurements at lower concentrations [4], but we find that at higher concentrations falls off more

slowly and does not reach zero until the percolation

threshold.

Fig. 1 . A schematic of finite sections of the infinite lattice at dilution levels well below (31 %), just below (40.7 %), and above (45 %) the

percolation threshold. Sites on the infinite cluster are shown in red, sites on finite disconnected clusters are blue, and diluents are in white. The inset is a close-up view for z = 40.7 %, showing the role that magnetic Cu and non-magnetic Zn/Mg ions play in the experimental

system.

44
Condensed Matter and Applied Physics

15 30

Dilution z (%)

Fig. 2. Neel temperature phase diagram of La2Cu^.2(Zn,IVIg);04. Single

crystal results are from neutron diffraction, powder results are from SQUID Magnetometry. Lines are Monte Carlo results for the temperature

at which spin-spin correlations reach the specified length.

To study the 2D static properties of

La^Cui.. (Zn,Mg).04, we measured the 2D instantaneous

spin-spin correlation length ^ using a 2-axis energyintegrating technique in the paramagnetic phase above T-^. The results are shown in Fig. 3 (colored symbols) for a number of different concentrations and across a broad

range of temperatures. Quantum Monte Carlo results for the nearest-neighbor Heisenberg model are shown as black

symbols. There are no adjustable parameters in this comparison, and the experimental and Monte Carlo results match exceptionally well up to the percolation threshold. We can see that dilution not only weakens the correlations

at a given temperature, but that it also slows down the rate

at which they grow as the system is cooled. At low

concentrations, ^ scales exponentially in inverse temperature. Near the percolation threshold, however, <^ exhibits

power law behavior in inverse temperature, and above the percolation threshold it saturates at a finite length at low

temperature.

We have shown that La2Cui.,(Zn,Mg),04 is an

excellent model system for studying percolation in a 2D

S = Vi Heisenberg antiferromagnet. A long-range-ordered

ground state persists up to the percolation threshold even

though quantum fluctuations increase as dilution is in- creased. Further studies of the dynamics will provide more insight into the role of disorder in this quantum

many-body system.

200

100 -

50

,20

10

z

= 0%

• z = 8(1)%

AZ = 19(1.5)% V2 = 31(1.5)% OZ- 35(1.5)% <Z = 40(2) %

z

= 43(2) %

10° 10^

Fig. 3. Spin-spin correlation length (in units of the lattice constant) vs. inverse temperature (scaled by the nearest neighbor exchange energy J

of the pure system) for different concentrations of non-magnetic ions. Colored symbols are experimental results, obtained from measurements

ofthe static structure factor. Black filled symbols are quantum Monte

Carlo results for z = (8, 20, 31, 35, 41, and 46) % dilution. Results for z = 0 % are from [5, 6]. No adjustable parameters are used in the comparison.

References:

[ 1 ] S. Sachdev, Quantum Phase Transitions, Cambridge University Press (Cambridge, 1999).

[2] Y.-C. Chen et a!., Phys. Rev. B 61, R3772 (2000).

[3] O. P Vajk et al. Science 295, 1691 (2002).

[4] M. Hucker et al, Phys. Rev. B 59, R725 (1999).

[5] R. J. Birgeneau et al, Phys. Rev. B 59, 13788 (1999).

[6] B, B. Beard et al, Phys. Rev. Lett. 80, 1742 (1998).

0. P. Vajk, P. K. Mang, and M. Greven

Stanford University Stanford, OA 94305 R M. Gehring and J. W. Lynn

NIST Center for Neutron Researcii

National institute of Standards and Teclinology

Gaithersburg.iVID 20899-8562
Automobile Sheet-Metal

^^Springback": Residual Stress

Measurements and Modeling

Aserious impediment to the use of

lighter-weight, higher-strength

materials in automobile manufacturing is the

relative lack of understanding about how these

materials respond to the complex forming operations that go into shaping a blank of metal into automobile body parts. One of the most vexing and

costly problems is "springback" — the tendency of sheet metal to lose some of its shape when it is removed from

the die. Springback is very pronounced with two of the

likeliest candidates for weight reduction: high-strength steel and aluminum alloys, than it is with standard steel. Unless

it is well managed and taken into account when the dies are designed, it leads to parts that are ill-fitting and deviate

excessively from design intent. American auto manufacturers, through the Springback Project of the USCAR consortium', are engaged in a major effort to predict springback by means

of sophisticated finite element modeling ("FEM"). However, the accuracy of predictions of large strain plasticity

under complex load histories, such as those applied during

stamping processes, is uncertain because of incomplete

validation of the FEM programs. Surprisingly, calculated

residual stress, one of the key mechanical properties

predicted by the state-of-the-art FEM codes, had not been

compared with experimental measurements. The present

work is the first comprehensive effort to determine the

residual sfresses of interest. Diffraction provides a powerflil means of very

accurately measuring microstructure, strains (from which

stresses are determined) and mechanical behavior in a way

not possible with other techniques. More importantly,

diffraction facilities available to the NCNR include neufron

diffraction, laboratory x-ray diffraction and synchrotron

x-ray diffraction (at Argonne's Advanced Photon Source).

These constitute the full spectrum of diffraction probes of

residual stress and microstructure for surface, sub-surface

and bulk specimens. The test specimens employed for this study were two deep-drawn "Demeri" cups: one, thin-

' USCAR is the umbrella organization of DaimlerChrysler, Ford and

General Motors, which was formed in 1992 to further strengthen the technology base of the domestic auto industry through cooperative,

pre-competitive research.

110 mm j

Fig. 1. The deep-drawn steel cup. The aluminum cup was similar, except for wall thickness.

walled (a 1 mm) 6022-T4 aluminum; the second, thicker- walled (3.2 mm) steel. The latter is shown in Fig. 1. The objective of this project was to determine the

residual stresses in the "simple" model specimens formed

similarly to stamped auto parts. Modelers in the USCAR

consortium would use FEM to predict the stress distribu- tions to validate their codes. At this time, the modeling part

of the project is still in progress. Two distinct experimental studies were performed.

The first utilized synchrotron x-rays to determine the

stress distribution in a ring and pieces (Fig. 2) cut from the

Fig. 2. Pieces cut from the aluminum cup and examined by synchrotron

x-rays.

46
Condensed Matter and Applied Physics

synchrotron results

CO CL

g

'(/J

•o- - axial middle

-<> -axial-5 mm

Hi—hoop-middle -—hoop-5 mm

neutron results

0.4 0.6 depth (mm)

Fig. 3. Axial and hoop stresses for the 0.9 mm thici< aluminum cup as determined by synchrotron x-rays.

1 1.5 2 2.5

depth from surface (mm)

Fig. 4. Hoop stresses as a function of depth in the 3.2 mm thicl< steel cup, as determined by neutron diffraction.

aluminum cup (which except for wall thickness, was

initially like the steel cup shown in Fig. 1). The critical point of this study is to determine the stress distribution in the ring and, ultimately, whether the FEM could predict it. Directly related to this was how the measured stress distribution compared with the simple linear depth dependence used in analytical calculations to predict the opening

of the ring when cut. The residual stresses determined from the x-ray

diffraction measurements are shown in part in Fig. 3. Representative neutron diffraction results for the steel cup

are shown in Fig. 4. The more complete results shown for the aluminum

ring, the first such measurements on deep-drawn cups,

satisfy both symmetry' and stress balance requirements.

However, the stresses vary around the circumference and

in the axial direction, and differ strongly from ideal bending

stresses. So even for the "simple" model system, the

plastic deformation process and the resultant stresses are very complex.

In summary, these results provide the first throughthickness stress distributions by which springback model

predictions of residual stress can be tested. Furthermore,

synchrotron radiation and neutrons are the only nondestructive methods that are able to provide the necessary

accuracy and spatial resolution needed to obtain these

results. Finally, successful modeling of springback requires successful prediction of these stress distributions.

References

T. Gnaeupel-Herold. H. J. Prask, R. J. Fields, T. J. Foecke, M. F. Shi, and

U. Lienert, submitted to Mater. Sci. Eng. A

T. Gnaupel-Herold and H. Prask NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg.MD 20899-8562

R. Fields

Metallurgy Division National Institute of Standards and Technology

Gaithersburg.MD 20899-8553

D. Haeffner Advanced Photon Source Argonne National Laboratory Argonne.lL 60439

E. Chu

Alcoa Technical Center Alcoa Center, PA 15069-0001

47
Serving the Science

and Teciinology Community

NCNR Partnership

Celebration

This year marks the tenth anniversary of

the start of user experiments in the NCNR guide

hall. The NCNR has maintained working partnerships with a number of government agencies, industrial laboratories, and academic institutions since it was

commissioned over 30 years ago. Several key partnerships are highlighted in this section. A special event

celebrating NCNR partnerships and a decade of success was held on August 5, 2002, with a number of distin- guished visitors in attendance. The inside cover of this report identifies persons addressing the audience at this celebration. The speakers noted the key role of partnerships in the growth and success of the NCNR and their impact on U.S. neutron science. Many of their comments

referred to a recent report from the Office of Science and

Technology Policy on the "Status and Needs of Major

Neutron Scattering Facilities and Instruments in the United

86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02

Fiscal year

Fig. 1. Numbers of NCNR Research Participants overtime.

States." This report encourages the formation of partnerships such as those at the NCNR, especially between

federal agencies, to promote effective stewardship of large federal research resources. The speeches and a guided

tour of the facility for the visitors provided a satisfying

perspective on the development of the NCNR into one of

the world's leading and most productive neutron scattering

facilities. The number of NCNR research participants has more

than doubled over the last decade (Fig. 1) and has continued to increase, despite an extended shutdown for the

installation of the advanced cold source and new cooling

towers. As detailed in the recent OSTP report, the NCNR

now accommodates more than half of all neutron users in the US.

The NCNR User Program

During the past year, we have made a significant shift toward entirely Internet-based proposal submission and

review. Users have been sending proposals to us on our Web-page form for more than six years, but now it has

become the exclusive method for standard submission of

beam time proposals. Local beam time requests from

NIST staff are managed through the same system. Peer

reviews of proposals are also communicated to us elec- tronically through a Web form, resulting in faster and more

efficient decisions on instrument time, to the benefit of

users and their research programs.

Two calls for proposals were made in the past year, and more than 390 proposals were received in response. The proposed experiments show increasing activity in research on soft condensed matter and bioscience, al- though more mature areas such as magnetism and polymer

research have held their own. Proposals are now nearly

equally divided between those for structural investigations,

mainly SANS and reflectometry, and studies of dynamics,

requesting one of the newer high-resolution specfrometers

in the guide hall. After a thorough review process by external referees and by the NCNR Program Advisory Committee (PAC),

approved proposals were allocated beam time. The PAC is a panel of accomplished scientists with expertise across a broad range of neutron methods and scientific disciplines.

It is the body primarily responsible for proposal review and

48
Serving the Science and Teciinoiogy Community

recommending user policies for the NCNR, working

closely with the Center's Director and staff. Its current membership includes Sanat Kumar (Rensselaer Polytechnic

histitute, chair), Robert M. Briber (University of Maryland), Michael K. Crawford (DuPont), Yumi Ijiri (Oberlin

College), Dieter K. Schneider (Brookhaven National

Laboratory), Kenneth Herwig (Oak Ridge National Laboratory), Michael Kent (Sandia National Laboratory), Robert

Leheny (Johns Hopkins University), John Tranquada

(Brookhaven National Laboratory), and Sossina Haile

(California Institute of Technology).

The Center for High Resolution

Neutron Scattering

One of the most important partnerships between the NCNR and another agency is with the National Science

Foundation (NSF) through its support of the Center for High Resolution Neutron Scattering (CHRNS). Five

instruments in the NCNR guide hall, and one in the thermal

instrument area, are operated by CHRNS, comprising a

crucial component of the user program. The instruments

include a 30 m SANS instrument, the SPINS triple-axis

spectrometer, the neutron spin-echo spectrometer, the high-flux backscattering spectrometer, the disk-chopper

time-of-flight spectrometer, and the ultra-small angle

scattering diffractometer. Most of the instrument time

allocated by the PAC now goes to experiments carried out on CHRNS instruments. An additional SANS

diffractometer on neutron guide NG-1, which up to now

has been used primarily for NIST programmatic research,

is being upgraded to a more powerful 10 m instrument

with a new detector, and will be made available to CHRNS

users. In aggregate, the CHRNS instruments provide

structural information on a length scale from 1 nm to ~ 1 0 fim, and dynamical information on energy scales from « 30 neV to « 100 meV. These are the widest ranges

accessible at any neutron research center in North

America.

Collaborations

Direct collaborations on specific experiments remain

a common way for users to pursue their ideas using

NCNR facilities, accounting for approximately half of the number of instrument-days. The thermal-neutron triple- axis spectrometers are mainly scheduled in this way. Most

of the time reserved for NIST on these and all other NCNR

instruments is devoted to experiments that are collaborations with non-NIST users. Collaborative research

involving external users and NIST scientists often pro- duces results that could be not obtained otherwise.

Fig. 2. Sanat Kumar, Dieter Schneider, and Rob Briber of the PAC

consider proposals for beam time.

Another mode of access to the NCNR is through more formal research consortia. Groups of researchers

from various institutions join forces to build and operate an

instrument. Typically, a substantial fraction of the time on

the instrument is then reserved for the consortium members, and the remaining time is allocated to general user

proposals. For example, a group including ExxonMobil,

the University of Minnesota, and NIST cooperates on the NG-7 30 m SANS instrument. Similar arrangements

involving other consortia apply for the horizontal-sample

reflectometer, the high-resolution powder diffractometer,

the filter-analyzer spectrometer, and the neutron spin-echo

spectrometer.

Cold Neutrons for Biology and

Technology

An important new partnership with five universities,

NIST and the National Institutes of Health is now proceeding with the design and construction of a new reflectometer dedicated to bioscience and biotechnology. The

University of California at Irvine leads the consortium

whose purpose is to provide a new national resource for investigations in structural biology. Research leaders from

Penn State, Rice, Carnegie Mellon, Duke, and the Los

Alamos National Laboratory are included in the consortium.

independent Programs

There are a number of long standing

programs located at the NCNR that involve

other parts of NIST, universities,

industrial laboratories, or other

government agencies.
The Nuclear

Methods Group

(Analytical Chemistry

Division, Chemical Science and

Technology Laboratory) has as its principal goals the development and

application of nuclear analytical techniques

for the determination of elemental compositions with greater accuracy, higher sensitivity

and better selectivity. A high level of competence

has been developed in both instrumental and radiochemical neutron activation analysis (INAA and

RNAA). In addition, the group has pioneered the use of

cold neutron beams as analytical probes with both prompt

gamma activation analysis (PGAA) and neutron depth

profiling (NDP). PGAA measures the total amount of a

particular analyte present throughout a sample by the

analysis of the prompt gamma-rays emitted upon neutron

capture. NDP, on the other hand, determines concentrations of several important elements (isotopes) as a fianction of depth within the first few micrometers of a surface by

energy analysis of the prompt charged-particles emitted

during neutron bombardment. These techniques (INAA,

RNAA, PGAA, and NDP) provide a powerful combination

of complementary tools to address a wide variety of

analytical problems of great importance in science and

technology, and are used to help certify a large number of

NIST Standard Reference Materials.

A large part of the group's efforts is directed towards

the exploitation of the analytical applications of the guided

cold-neutron beams available at the NCNR. The Group's

involvement has been to design and construct state-of-theart cold neutron instruments for both PGAA and NDP and

provide facilities and measurements for outside users, while retaining and utilizing our existing expertise in INAA

and RNAA.

The Neutron Interactions and Dosimetry Group

(Physics Laboratory) provides measurement services,

standards, and fundamental research in support of NIST's

mission as it relates to neutron technology and neutron

physics. The national and industrial interests served

include scientific instrument calibration, electric power

production, radiation protection, defense nuclear energy

systems, radiation therapy, neutron radiography, and

magnetic resonance imaging.

The Group's research may be represented as three major activities. The first is Fundamental Neutron Physics

including magnetic trapping of ultracold neutrons, operation of a neutron interferometry and optics facility, development of neutron spin filters based on laser polarization of

3He, measurement of the beta decay lifetime of the neutron, and investigations of other coupling constants and

symmetries of the weak interaction. This project involves

a large number of collaborators Irom universities and

national laboratories. The second is Standard Neutron Fields and Applications utilizing both thermal and fast neutron fields for materials dosimetry in nuclear reactor applications and for personnel dosimetry in radiation protection. These neutron

fields include thermal neutron beams, "white" and monochromatic cold neutron beams, a thermal-neutron-induced

fission neutron field, and -^-Cf fission neutron fields,

both moderated and unmoderated.

The third is Neutron Cross Section Standards

including experimental advancement of the accuracy of

neutron cross section standards, as well as evaluation,

compilation and dissemination of these standards. The Polymers Division of the Materials Science and

Engineering Laboratory has several program elements at the NCNR covering the technological areas of electronics,

multiphase polymeric, and biological materials. The

purpose of the electronics materials program is to help the U.S. microelectronics industry address their most pressing

materials measurement and standards issues. The struc- ture of nanoporous thin films, used in integrated circuits as low-dielectric-constant insulators, is characterized through

a combination of small angle neutron scattering (SANS),

x-ray reflectivity, and ion scattering measurements.

Advances such as vapor contrast matching techniques

provide unique information about critical parameters such

as the porosity, average pore size, and wall mass density. In addition, several instruments at NCNR provide unique

high-resolution measurements that guide the development

and fundamental understanding of next-generation polymeric photoresist materials for sub- 1 00 nm lithography.

Measurements include the segmental dynamics of the polymers that govern the mobility of an acid catalyst,

direct measurement of the deprotection reaction that leads

to patterned areas, and the structural characterization of

lithographically prepared structures. In the multiphase polymeric materials program, the objective is to understand underlying principles of phase

behavior, local structure, and flow that control morphology

and structure during processing of multiphase materials

such as polymer blends and nanocomposites (polymers

filled with clay platelets, carbon nanotubes, or triblock

copolymer micelles). SANS and reflectivity measurements

in equilibrium, in transient conditions, and under external

50
Serving the Science and Teciinoiogy Community

fields, provide essential information for general understanding as well as for specific application of polymer blend/

alloy systems. For example, the structure induced by

shear alignment of nanoparticle/polymer solutions has been

elucidated with SANS, small angle light scattering, and

rheological measurements. Customers include material

producers and users, ranging fi^om chemical, rubber, tire, and automotive companies, to small molding and compounding companies. The research focus on polymeric

materials includes commodity, engineering and specialty

plastic resins, elastomers, coatings, adhesives, films,

foams, and fibers. The biological materials initiative is committed to demonstrating the use of inelastic neutron scattering (INS)

as a unique measurement tool for understanding the dynamics in several important biological systems. For

example, INS has been used to elucidate changes in protein

dynamics that occur in the final stages of protein folding.

Likewise, INS and low fi-equency Raman scattering have

been developed as measurement tools to identify the dynamical aspects of a good sugar or polyalcohol for protein stabilization and cryopreservation. Effective

preservatives must suppress the high frequency motions

that are precursors to protein unfolding and denaturation.

The ExxonMobil Research and Engineering

Company is a member of the Participating Research Team

(PRT) that operates, maintains, and conducts research at the NG-7 30 m SANS instrument and the NG-5 Neutron

Spin Echo Spectrometer. Their mission is to use those

instruments, as well as other neutron scattering techniques

available to them at NCNR, in activities that complement

research at ExxonMobil's main laboratories as well as at its

affiliates' laboratories around the world. The aim of these

activities is to deepen understanding of the nature of

ExxonMobil's products and processes, so as to improve

customer service and to improve the return on shareholders' investment. Accordingly, and taking full advantage of

the unique properties of neutrons, most of the experiments

use SANS or other neutron techniques to study the

structure and dynamics of hydrocarbon materials, especially in the fields of polymers, complex fluids, and

petroleum mixtures. ExxonMobil regards its participation

in the NCNR and collaborations with NIST and other PRT

members not only as an excellent investment for the company, but also as a good way to contribute to the

scientific health of the nation. The U.S. Army Research Laboratory is the current manager of a 30-year NCNR-Army partnership sponsoring

a research team. This group performs materials research

and engineering in support of Army needs and missions

and works jointly with NIST/NCNR in developing and

improving neutron methods and instrumentation. A key

contribution of Army researchers at the NCNR is a highly

successful neutron facility to map residual stress and

texture within large components such as jet turbine blades

and structural welds. This resource is critical to development and performance of industrial and transportation

systems and military hardware.

The Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration (FDA), directs and maintains a neutron activation analysis (NAA) facility

at the NCNR. This facility provides agency-wide analytical

support for special investigations and applications research,

complementing other analytical techniques used at FDA

with instrumental, neutron-capture prompt-gamma, and

radiochemical NAA procedures, radioisotope x-ray fluores- cence spectrometry (RXRFS), and low-level gamma-ray

detection. This combination of analytical techniques

enables diverse multi-element and radiological information

to be obtained for foods and related materials. The NAA

facility supports agency quality assurance programs by

developing in-house reference materials, by characterizing

food-related reference materials with NIST and other

agencies, and by verifying analyses for FDA's Total Diet

Study Program. Other studies include the development of

RXRFS methods for screening foodware for the presence

of Pb, Cd and other potentially toxic elements, use of

instrumental NAA to investigate bromate residues in bread

products, and use of prompt-gamma NAA to investigate

boron nutrition and its relation to bone strength.

The Smithsonian Center for Materials Research

and Education Nuclear Laboratory for Archeological

Research (SCMRE) has chemically analyzed over 24 000

artifacts by INAA at the NCNR over the last 25 years. SCMRE's research programs draw extensively upon the

collections of the Smithsonian, as well as those of national

and international institutions. The chemical analyses

provide a means of linking these diverse collections

together to study continuity and change involved in the production of ceramic objects. INAA data are used to determine if groups of ceramics have been made from

the same or different raw materials. The ceramics

then can be attributed to geographic regions,

specific sources, workshops and even indi- vidual artists. The ability to combine

chemical data for semi-complete or whole vessels with that derived from

the analysis of materials recov-
ered from recent excavation programs

provides many new opportunities for study. Museum vessels

that are found to be similar and

attributable to some geographic location

provide a basis for exploring changing

aspects of style, iconography, textual history

and even ideology. In an integrative manner, the ESfAA program enhances the importance of

collection materials for the study of the past. A number of universities have also established

long-term programs at the NCNR. The University of

Maryland is heavily involved in the use of the NCNR,

and maintains several researchers at the facility. Jolins

Hopkins University participates in research programs in magnetism, soft condensed-matter physics, bioscience,

and in instrument development at the NCNR. The University of Pennsylvania is working to help develop biological

applications of neutron scattering. It is also participating in the second stage construction of the filter analyzer neutron

spectrometer, along with the University of California at Santa Barbara, DuPont, Hughes, and Allied Signal.

The University of Minnesota participates in two PRTs, the NG-7 30 m SANS and the NG-7 reflectometer. The University of Massachusetts also participates in the latter PRT.

Eighth Annual Summer School

With support from the National Science Foundation,

NCNR and CHRNS held their annual Summer School on

Neutron Scattering from June 3-7, 2002. The subject matter of the school alternates in successive years between

techniques designed to investigate structure, and those

devoted to spectroscopy and dynamics. The course this year focused on structural studies with SANS and neutron

reflectometry (NR). Forty graduate students and

postdoctoral fellows from institutions across the US

attended the Summer School this year. The format of the meeting in recent years has emphasized hands-on experi- ence with CHRNS instruments. For much of the week,

students in small subgroups circulated among various

instruments set up to perform illustrative experiments, and

analyzed data using NCNR-supplied resources. Among the experiments was a characterization by SANS of the

structure of clay platelets dispersed in water. The neutron

reflectometry experiments comprised measurements on

thin films and multilayer materials. On the final day, the subgroups made presentations on the results of their

studies. According to student evaluations, the school was

highly effective in introducing them to the principles and

practice of structural studies with neufron instruments.

Fig. 3. Eighth Annual Summer School on Neutron Scattering participants concentrate on neutron

reflectometry results under the guiding hand of NCNR's Sushil Satija.

52
Operations

T'he NIST neutron source (NBSR) operated for 153

full power (20 MW) days or approximately 94 % of

the scheduled time for this year. A typical operating year

consists of seven cycles. A cycle has 38 days of continu- ous ftill power operation, followed by 1 1 days of shutdown

maintenance, refiieling, and startup preparations. This

year, the NBSR was in a scheduled extended shutdown for maintenance and facility improvements until March 6, 2002. Those improvements included a new cold source, new transformers and

switchgear for the

building electrical system, a new plumeabatement cooling

tower, and new shim arm seal assemblies.

The new seal assemblies have characteristics superior to the

old assemblies and

provide greater assurance of dependable shim arm

operation. The

replacement of the

electrical equipment

and the cooling tower will increase the reliability of the NBSR over the next 25 years. In pursuit of that same

goal, detailed inspections of vital systems and components

were completed using ultrasonic probes, visual examinations, and remote examinations with miniature cameras and

fiber-optic imaging equipment. The only major mainte- nance item scheduled for completion this shutdown was a

Seymour H. Weiss, Chief, Operations & Engineering

determination of the status of the Thermal Column Tank

Cooling System. After a thorough investigation, the

capability of the Thermal Column was preserved by

Reconfiguring the cooling system and replacing original

components within the biological shield. A new tank has

been ordered and will be available if it becomes necessary

to replace the tank in the future. A number of important personnel issues were

addressed in FY2002, including the effect of a surge of

impending retire- ments on the NBSR.

All licensed operators were requalified

this year. Three new senior operators were licensed by the Nuclear Regulatory

Commission, a new

deputy chief for Operations was

appointed, and

significant progress was made on

addressing recruit- ment and retention

questions.

Substantial changes to facility security were completed this year to fulfill the intent of the President's

directives on homeland security. A vehicle exclusion area was established and surveillance equipment was improved.

Other changes are on-going and Operations & Engineering

is consulting with the U.S. Nuclear Regulatory Commission on security matters on a regular basis.

Tliomas J. IVlyers, Deputy Chief, and Chief of Operations
Facility Developments

DAVE and Other Software

Developments

Scientists at the NCNR, with support

from the National Science Foundation via CHRNS,

have developed a new software tool for the reduction, visualization, and analysis of neutron inelastic scattering data. DAVE, short for the Data Analysis and

Visualization Environment, is an integrated suite of

interactive software tools with a visual interface for treating and analyzing neutron inelastic scattering data sets. Using a powerful graphical interface, users can reduce

their data from one of the inelastic spectrometers, make

cuts through the scattering ftinction, and fit them with the lineshape of their choice from a library of model ftinctions. The goal of the DAVE software package is to allow

users, whose neutron scattering experience ranges from

casual to expert, to reduce, visualize, and analyze their

inelastic neutron scattering data sets with a minimum of

effort by using a set of visually intuitive tools. The

software has been in use on many of the inelastic neutron

scattering instruments since January 2002 and was

released to the user community in July. The source code is available from the NCNR website to run on PC, Linux, and

Mac platforms. Project and download information are available at http://vvww.ncnr.nist.gov/dave.

New, easy to use software for reducing and fitting neutron reflectivity data is under active development at the NCNR. The new data reduction tools employ an intuitive

S (Q, omega) Intensity

0.2 0.4 0.6 0.8 1.0 1.2 mean 0(A-'')

Fig. 1. An example of DAVE output: Dispersion curve of a magnetic

excitation as measured using the Disl< Chopper Spectrometer.

graphical interface developed using open source software

to read and process a variety of raw data files, including

specular scans, background measurements, rocking

curves, polarized beam, and slit scans. Using these new

tools, the user can perform a variety of data correction and

manipulation tasks to produce reduced data sets of the sample reflectivity as a ftinction of wavevector. The

software supports a wide range of data formats from both

the NG-7 and NG- 1 reflectometers and single channel or multichannel, position-sensitive detectors.

Cnltii- Hap

utnilB.QTnJ'tIS

Fig. 2. Graphical interface image of neutron reflectivity data obtained

using a position sensitive detector with corresponding slices of constant

wavevector.

A new graphical interface has also been developed

for the reflectivity- fitting program 'mlayer' [1]. This

program allows users to model and fit scattering length

density profiles to measured reflectivity data. The new

interface for this program provides a wide set of graphical

tools for adjusting and refining model parameters, controlling the fit, and constraining the model profile. A similar

graphical interface has also been developed for the pro- gram that treats polarized neutron reflectivity data. Further

information on these tools is available at the website:

www.ncnr.nist.gov/programs/reflectometry/software.

New Monochromator Drum Shields

This year the NCNR ordered two new monochromator drum shields for the new BT-7 neutron triple axis

spectrometer and for the BT-4 filter analyzer instrument.

Fabrication and testing of one of these drum shields has

been completed and delivery of both is planned for Dec.

2002.

Monochromator drum shields are a key component in

crystal spectrometers, forming a thick, moving shield that surrounds the intensely illuminated monochromator and

allowing the diffracted beam to be directed at a variety of

54
Facility Developments

take-off angles towards the sample. The design of the new drum shields is based on a concept originally developed for the Advanced Neutron Source project at Oak

Ridge National Laboratory which uses pairs of counter- opening shield wedges to allow the large diameter neutron beams to enter the drum. For the NCNR drums, this design concept was adapted for the specific dimensions of

the NCNR source and to optimize the manufacturability of

the shield. This double wedge design uses a precision cam

track to position the shield wedges around the 20 cm beam

opening as the drum is rotated to various take-off angles.

The drum shield is rotated using a stepper motor driven gear system. The take-off angle range is between 0° and

120° and the drum can be built into either clockwise or counter-clockwise rotating models. The NCNR will be the

first neutron laboratory to implement this double-wedge

design for a monochromator shield. Sample Environment Equipment

The suite of available sample support equipment at the NCNR continues to be upgraded and enhanced. This

year, the superconducting magnet system with dilution

refrigeration was upgraded from the seven Tesla coils available last year to the full design field coils that provide

11.5 Tesla. This system has demonstrated a 22 mK base

temperature and full magnetic field strength.

The NCNR also received a new nine Tesla horizontal

field superconducting magnet with single crystal windows

using a design specifically optimized for small angle

scattering experiments. This system uses a split coil design and windows in either direction to allow the magnefic field to be directed parallel or perpendicular to the neutron beam axis. Extensive heat shielding extends

operation of the magnet to the higher sample temperatures

needed for biology or polymer physics experiments

without significantly altering liquid helium consumption.

Other new equipment made available this year

includes a pulse tube closed cycle refrigerator (CCR) with

an operating temperature range of 3 K to 325 K, two low

temperature CCRs (10 K to 325 K), one high temperature

CCR (15 K to 800 K), one 50 mm helium cryostat (1.5 K

to 300 K) and fifteen additional temperature controllers.

Facility Improvements

Taking advantage of the opportunity provided by an extended interruption in routine operations, the NCNR staff completed several improvements to the facility during the outage early this year. The helium gas blanketing system,

which provides a continuous flow of helium gas to the first

Fig. 3. George Baltic (center, NCNR) confirms completion of a monochromator drum with Paul Brand (left, NCNR) and Rich Porter, president of Ingersol Contract Manufacturing Company.

1.5 m of neutron guide closest to the cold source, was

replaced with a new gas control system. Sensors and

controllers on the guide vacuum systems were replaced

and upgraded during the cold source installation. A

computerized supervisory and control system for the

facility was expanded to include monitoring of the guide vacuum pumping system.

Several improvements were made in CI 00, the

location of the thermal neutron instruments. These include

the installation of wiring and breaker panels that are part of

a new power distribution system for the thermal instru- ments. The new system provides each neutron station with independent panels and outlet locations at the floor

level adjacent to the experimental work area. A new

catwalk system was also designed for accessing the face of the biological shield above the thermal instruments.

This will be a significant safety and performance improvement for maintenance activities in this area. A prototype

for a perimeter shield was also accepted this year. The

perimeter shields surround the thermal neutron spectrometers and separate the operating area of the spectrometers

from other work areas on the floor.

In the Guide Hall, the concrete floor was repainted.

The original surface was badly worn and needed replace- ment. A three-color design was adopted to help

differentiate work areas, walkways, and fire protection equipment.

References

[1] J.F. Ankner and C.F. Majkrzak, SPIE 178, 260 (1992).

55
Publications^

Abdurashitov, J. N., Gavrin, V. N., Girin, S. V., Gorbachev, V. V., Gurkina, P. P., Ibragimova, T. V., Kalikhov, A. V., Khaimasov,

N. G, Knodel, T. V., Mirmov, I. N., Shikhin, A. A., Veretenkin,

E. P., Vermul, V. M., Yants, V. E., Zatsepin, G T., Bowles, T.

J., Teasdale, W. A., Nico, J. S., Cleveland, B. T., Elliott, S. R., Wilkerson, J. R, "Measurement of the Solar Neutrino Capture

Rate by the Russian American Gallium Solar Neutrino Experiment During One-Half of the 22-Year Solar Cycle

Activity," Jour. Exp. Th. Phys., in press.

Abdurashitov, J. N., Gavrin, V. N., Kalikhov, A.V., Matushko, V. L., Shikhin, A. A., Yants, V. E., Zaborskaia, O. S., Adams, J. M.,

Nico, J. S., Thompson, A. K., "A High Resolution Low

Background Fast Neutron Spectrometer," Nucl. Instrum. Meth. A 476 (1-2), 318 (2002).

Allen, A. J., Long, G. G, Boukari, H., Ilavsky, J., Kulkami, A., Sampath, S., Herman, H., Goland, A. N., "Microstructural

Characterization Studies to Relate the Properties of Thermal

Spray Coating to Feedstock and Spray Conditions," Surf Coat. Techn. 146, 544 (2001). Amos, T. G, Huang, Q., Lynn, J. W., He, T., Cava, R. J., "Carbon

Concentration Dependence of the Superconductivity Transition Temperature and Structure of MgC^Nij," Solid State Commun. 121 (2-3), 73 (2002). Anderson, C. R., Andersen, K. H., Stirling, W. G, Sokol, R E., Dimeo, R. M., "Dynamics of Superfluid ^He Confined in Xerogel Glass," Phys. Rev. B 65, 174509-174519 (2002).

Argyriou, D. N., Lynn, J. W., Osbom, R., Campbell, B., Mitchell, J.

F. , Ruett, U., Bordallo, H. N., Wildes, A., Ling, C. D., "Glass

Transition in the Polaron Dynamics of CMR Manganites,"

Phys. Rev. Lett. 89, 036401 (2002).

Arsenov, A. A., Bebenin, N. G, Gaviko, V. S., Adams, C. P., Lynn, J. W., Mashkautsan, V. V., Mukovskii, M., Shulyatev, D. A., Ustinov, V. v., Zainullina, R. L, "Absence of Polaron Conductivity in La^gBa„,Mn03," Phys. Status Solidi A 189 (3), 673

(2002).

Bagci, V. K., Gulseren, O., Yildirim, T., Gedik, Z., Ciraci, S., "Metal Nanoring and Tube Formation on Carbon Nanotubes," Phys. Rev. B 66, 045409 (2002).

Baklanov, M. R., Kondoh, E., Lin, E. K., Gidley, D. W., Lee, H.-J., Mogilnikov, K. P., Sun, J. N., "Comparative Study of Porous SOG Films with Different Non-Destructive Instrumentation,"

in Proceedings ofthe National Interconnect Technology

Conference, in press.

Bao, W., Aeppli, G., Christianson, A. D., Fisk, Z., Hundley, M. F., Larderda, A. H., Lynn, J. W., Pagliuso, P. G., Sarrao, J. L., Thompson, J. D., "Magnetic Properties of Heavy Fermion

Superconductors CeRhln, and CeRhln^," in Proceedings of

Physical Phenomena at High Magnetic Fields-IV (World

Scientific, Singapore, 2002), p. 350.

Bao, W., Aeppli, G, Lynn, J. W., Pagliuso, R G, Sarrao, J. L., Hundley, M. F., Thompson, J. D., Fisk, Z., "Anisotropic

Three-Dimensional Magnetic Fluctuations in Heavy Fermion

CeRhln^," Phys. Rev. Lett. 65, 100505 (2002). Bao, W., Christianson, A. D., Pagliuso, P. G, Sarrao, J. L., Thompson, J. D., Lacerda, A. H., Lynn, J. W., "Effect of La-Doping

on Magnetic Structure in Heavy Fermion CeRhln^," Physica B

312, 120(2002).

Bao, W., Trevino, S. F., Lynn, J. W., Pagliuso, R G, Sarrao, J. L., Thompson, J. D., "Effect of Pressure on Magnetic Structure in Heavy Fermion CeRhIn,," Appl. Phys. A, in press.

Bauer, B. J., Byrd, H. M., Guttman, C. M., "Small Angle Neutron

Scattering Measurements of Synthetic Polymer Dispersions in Matrix-Assisted Laser Desorption/Ionization Matrixes," Rapid

Commun. Mass. Spectrom. 16 (15), 1494 (2002).

Bauer, B. J., Guttman, C. M., Liu, D. W., Blair, W. R., "Tri-alphanaphthylbenzene as a Crystalline or Glassy Matrix for Matrixassisted Laser Desorption/Ionization: a Model System for the Study of Effects of Dispersion of Polymer Samples at a Molecular Level," Rapid Commun. Mass. SP 16 (12), 1192

(2002).

Becker, D. A., Mackey, E. A., "Analytical Intercomparison on NIST

Renewal Pine Needles SRM 1575a," Trans. Am. Nucl. Soc, in press.

Becker, P. R., Mackey, E. A., Demiralp, R., Epstein, M. S., Donais,

M. K., Goessler, W. A., Porter, B. J., Wise, S. A., "Heavy

Metals and Other Trace Elements Measured in Tissues of Marine Mammals Archived by the Alaska Marine Mammal

Tissue Archival Project from the Bering Sea and Cook Inlet, Alaska," in Proceedings ofThe AMAP Heavy Metals Workshop, in press.

Bianco-Peled, H., Dori, Y, Satija, S., Schneider, J., Sung, L., Tirrell, M., "Structural Study of Langmuir Monolayers Containing

Lipidated Poly (Ethylene Glycol) and Peptides," Langmuir

17(22), 6931 (2001).

Biggs, S., Walker, L. M., Kline, S. R., "The Formation of an Irrevers- ibly Adsorbed and Organised Micelle Layer at the Solid-Liquid

Interface," Science, in press.

Bishop, R. L., Blackman, M. J., "Instrumental Neutron Activation Analysis of Archaeological Ceramics: Scale and Interpretation," Acc. Chem. Res., in press. Blackman, J. C, Raman, S., Dickens, J. K., Lindstrom, R. M., Paul, R. L., Lynn, J. E., "Thermal-Neutron Capture by Pb-208,"

Phys. Rev. C 65 (4), 045801 (2002). Blackman, M. J., Redford, S., "Northern Syrian Luster and Fruitware: Petrographic and Chemical Implications for Productions and

Distribution," Antiquity, in press.

Publications are counted over a 1-year period. This year we inaugurate a policy of counting publications up through

July 31, 2002. Hence, there is overlap with publications reported for 2001 that were counted through October 31, 2001.

56
Publications

Bliesner, R., Uma, S., Yokochi, A., Sleight, A. W., "Structure of NaBi,V,0|^ and Implications for Ionic Conductivity," Chem.

Mater. 13 (11), 3825, 2001.

Bordallo, H. N., Chapon. L. C, Cook., J. C, Copley, J. R. D., Goremychkin, E., Kern, S., Lee, S.-H., Yildirim, T., Manson,

J. L., "Spin Excitations in 3D Molecular Magnets Probed by

Neutron Scattering," Appl. Phys. A, in press.

Borgoul, P., Kidwell, C. B., Ondov, J. M., "System for Precise Control of Volumetric Flow Rate During Sampling with a Cascade Impactor. Aerosol. Sci. Technol. 36, 397 (2002).

Bossev, D. R, Kline, S. R., Israelachvili, J. N., Paulaitis, M. E., "Pressure-Induced Freezing of the Hydrophobic Core Leads to a L|^ H| Phase Transition for Cj^E^ Micelles in D,0,"

Langmuir 17 (25), 7728 (2001 ).

Bossev, D. P., Ferdinand, S., Paulaitis, M. E., "Effect of Pressure on

Microstructure in Water-in-Oil and Oil-in-Water

Microemulsions for C^^E^ n-Octane/D^O Mixtures," Langmuir,

in press.

Branford, W., Green, M. A., Neumann, D. A., "Structure and

Ferromagnetism in Mn^* Spinels: AM^^Mni ^O^ (A = Li, Cu; M = Ni, Mg)," Chem. Mater 14, 1649 (2002').

Broholm, C, Aeppli, G, Chen, Y., Dender, D. C, Enderle, M.. Hammar, P. R., Honda, Z., Katsumata, K., Landee, C. P., Oshikawa, M., Regnault, L. R, Reich, D. H., Shapiro, S. M.,

Sieling, M., Stone, M. B., Tumbull, M. M., Zaliznyak, 1., and

Zheludev, A., "Magnetized States of Quantum Spin Chains,"

in High Magnetic Fields - Applications in Condensed Matter

Physics and Spectroscopy, (edited by C. Berthier, L.P. Levy,

G Martinez, Springer Verlag 2002), p. 211. Brown, C. M., Manson, J. L., "Solid State Ligand Dynamics in Interpreting Mn[N(CN)2]2(pyrazine): A Neutron Spectros- copy Study," J. Amer. Chem. Soc. 124, 12600 (2002).

Bu, Z., Chowdhuri, Z., Callaway, D. J. E., "Coexistence of Fluctuat- ing Secondary Structure and Long-Range Tertiary Interaction in Highly Denatured Alpha-Lactalbumin - A Neutron Scattering

Study," Protein Sci., in press.

Bu, Z., Cook, J., Callaway, D. J. E., "Dynamics Regimes and

Correlated Structural Dynamics in Native and Denatured

Alpha-Lactalbumin," J. Mol. Biol. 312, 865 (2001 ).

Burghardt, W. R., Krishnan, K., Bates, F. S., Lodge, T. P, "Linear

Viscoelasticity of a Polymeric Bicontinuous Microemulsion,"

Macromol. 35, 4210 (2002).

Butler, P. D., Porcar, L., Warr, G. G, Hamilton, W. A., comment on

"Evidence of a Sponge-to-Lamellar Phase Transition Under

Shear by X-Ray Scattering Experiments in Couette Cell," Phys.

Rev. Lett. 85, 059601 (2002).

Caliskan, G, Kisliuk, A., Tsai, A. M., Soles, C. L., Sokolov, A. P., "Influence of Solvent on Dynamics and Stability of a Protein,"

J. Non-Cryst. Solids 307, 887 (2002).

Campbell, B. J., Billinge, S. J. L., Lynn, J. W., Osbom, J. W., Osbom,

R., Sinha, S. K., "The Structure of Jahn-Teller Polarons in the Colossal Magnetoresistive Manganites," in Proceedings From

Semiconductors to Proteins: Beyond the Average Structure, edited by Billinge, S. J. L., and Thorpe, M. F., (Kluwer,

Academic/Plenum, New York, 2002) p. 183.

Campbell, B. J., Osbom, R., Argyriou, D. N., Vasiliu-Doloc, L., Mitchell, J. F., Sinha, S. K., Ruett, L. U., Islam, Z., Lynn, J. W., "Structure of Nanoscale Polaron Correlations in a Colossal Magnetoresistive Manganite," Phys. Rev. B 65 (1), 014427

(2002).

Cappelletti, R. L., Clutter, L. K., edited by, "MSEL, FY2001

Programs and Accomplishments," NISTIR 6798, (2001).

Cappelletti, R. L., Clutter, L. K., edited by, "NCNR 2001 Accomplishments an Opportunities," NIST SP 977, (2002).

Carpenter, J. M., Iverson, E. B., Mildner, D. F. R., "Time Focusing

of Pulsed-Source Crystal Analyzer Spectrometers II Practical Expressions," Nucl. Instrum. & Methods 483 (3), 784 (2002). Chen, W. C, Bailey, C, Borchers, J. A., Gentile, T. R., Hussey, D.

H., Majkrzak, C. P., O'Donovan, K. V., Remmes, N., Snow, W.

M., Thompson, A. K., "Polarized ^He Analysers for Neutron

Reflectometry," Physica B, in press.

Chen, W. C, Beuser, B. J., "Small-Angle Neutron Scattering Measurements of Deuteride (Hydride) Formation and Decomposition in Single-Crystal Pd," Phys. Rev. B 65, 014102 (2001). Chen, W.-R., Chen, S.-H., Mallamace, F., "Small-Angle Neutron

Scattering Study of the Temperature-Dependent Attractive

Interaction in Dense L64 Copolymer Micellar Solutions and its Relation to Kinetic Glass Transition," Phys. Rev. E 66, 021403

(2002). Chen, Y. Y, Lodge, T. P., Bates, F. S., "Influence of Long-Chain

Branching on the Miscibility of Poly(ethylene-r-ethylethylene) Blends with Different Microstructure," J. Polym. Sci. 40, 466

(2002). Chen-Mayer, H. H., Lamaze, G. P, Coakley, K. J., Satija, S. K., "Two Aspects of Thin Film Analysis: Boron Profile and

Scattering Length Density Profile," Nuc. Inst. Meth. B.,

in press. Chen-Mayer, H. H., Lamaze, G P., Mildner, D. F. R., Zeissler, R., Gibson, W. M., "Neutron Imaging and Prompt Gamma

Activation Analysis Using a Monolithic Capillary Neutron

Lens," in Proceedings ofthe 3 International Congress on

Analytic Sciences, Analytical Science, (ICAS 2001 , Tokyo,

Japan, August 2001) p. 629. Chen-Mayer, H. H., Mildner, D. F. R., Lamaze, G. P., Lindstrom, R. M., "Imaging of Neutron Incoherent Scattering fi^om Hydrogen

in Metals," J. Appl. Phys. 91 (6), 3669 (2002).

Choi, S. M., Chen, S. H., Sottmann, T., Strey, R., "The Existence of Three Length Scales and Their Relation to the Interfacial Curvatures in Bicontinuous Microemulsions," Physica A 304, 85 (2002). Chong, K. P., Sung, L., VanLandingham, M. R., "Solid Micromechanics: Research and Challenges," in Proceedings of

the 13''' Micromechanics Europe (MME 2002) Workshop,

(Sinaia, Romania, Oct. 6-8, 2002), in press.

Ciraolo, M. F, Hanson, J. C, Toby, B. H., Grey, C. P, "Combined

X-Ray and Neutron Powder Refinement and NMR Study of

Hydrochlorofluorocarbon HCFC-124a (CF,HCF,C1) Binding

onNaX," J. Phys. Chem. B 105 (49), 12330 (2001).

Clarke, W. B., Guscott, R., Downing, R. G, Lindstrom, R. M., "Endogenous Lithium and Boron Red Cell to Plasma Ratios: Normal Subjects Versus Bipolar Patients Not on Lithium

Therapy," Bipolar Disorders, in press.

57
Clarke, W. B., Guscott, R., Lindstrom, R. M., "Binding of Lithium

and Boron to Human Plasma Proteins II: Results for a Bipolar Not on Lithium Therapy," Biol. Trace Element Res.,

in press.

Coakley, K. J., Chen-Mayer, H. H., Lamaze, G. R, Simons, D. S., Thompson, P. E., "Calibration of a Stopping Power Model for Silicon Based on Analysis of Neutron Depth Profiling and

Secondary Ion Mass Spectrometry Measurements," J. Nucl.

Instrum. & Meth. B 192 (4), 349 (2002).

Coakley, K. J., Yang, G. L., "Estimation of the Neutron Lifetime: Comparison of Methods Which Account for Background,"

Phys. Rev. C 65 (6), 064612 (2002).

Colle, R., Zimmerman, B. E., "A Dual-Compensated Cryogenic

Microcalorimeter for Radioactivity Standardizations," Appl.

Radiat. Isotopes 56 (1-2), 223 (2002).

Copley, J. R. D., "NIST Recommended Practice Guide; The

Fundamentals of Neutron Powder Diffraction," NIST SP

960-2,(2001).

Crawford, M. K., Harlow, R. L., Marshall, W., Li, Z., Cao, G,

Lindstrom, R. L., Huang, Q., Lynn, J. W., "Structure and Magnetism of Single Crystal Sr^RUjO^^: A Ferromagnetic

Triple-Layer Ruthenate," Phys. Rev. B 65, 214412 (2002).

DeWall, J., Dimeo, R. M., Sokol, R E., "Slow Difftision of Molecular Hydrogen in Zeolite 13X," J. Low Temp. Phys., in press. Deyhim, A., Zhou, J., Schwartz, F., Krueger, S., Gregurick, S., "Small Angle Neutron Scattering Studies of PNA & DNA Systems,"

Biophys. J. 82 (1), 622 (2002). Dimeo, R. M., Chowdhuri, Z., Meyer, A., Gehring, P. M., Neumann,

D. A., "The NIST High-Flux Backscattering Spectrometer,"

Appl. Phys. A, in press. Dimeo, R. M., Neumann, D. A., Glanville, Y., Minor, D. B., "Pore

Size Dependence of Rotational Tunneling in Confined Methyl

Iodide," Phys. Rev. B 66, 104201 (2002).

Douglas, J. F., Kent, M. S., Satija, S. K., Karim, A., "Polymer

Brushes: Structure and Dynamics," Encyclopedia of Materials: Science and Technology, 7218, (2001). Downing, R. G, Iyengar, G. V., "Methodological Issues in the Analytical Determination of Boron," Environ. Health

Perspect., in press.

Dubsky, J., Matejicek, J., Prask, H. J., Gnaupel-Herold, T., "Residual and Applied Stresses in Plasma Sprayed Cr.O^ Coatings,"

Mater. Sci. Forum 404, 419 (2002). Dubsky, J., Prask, H. J., Matejicek, J., Gnaupel-Herold, T, "Stresses

in Plasma Sprayed Cr^O, Coatings Measured by Neutron

Diffraction," in Proceedings ofthe International Conference on

Neutron Scattering (Munich, Germany, September 2001 ), in press. DuUo, A. R., Ruddy, F. H., Seidel, J. G, Adams, J. M., Nico, J. S., Gilliam, D. M., "The Neufron Response of Miniature Silicon Carbide Semiconductor Detectors," Nucl. Instrum. Meth. A.,

in press.

Dyar, D., Wiedenbeck, M., Robertson, D., Cross, L. R., Delaney, J.

S., Ferguson, K., Francis, C. A., Grew, E. S., Guidotti, C. V., Hervig, R. L., Hughes, J. M., Husler, J., Leeman, W., McGuire,

A. v., Rhede, D., Rothe, H., Paul, R. L., Richards, I., Yates, M.,

"Reference Minerals for Microanalysis of Light Elements," Geostandards Newsletter 25 (2-3), 441 (2001 ).

Eid, K., Portner, D., Borchers, J. A., Loloee, R., Tsoi, M., O'Donovan, K. V., Pratt, W. R, Bass, J., "Mean-Free Path

Effects in CPP Magnetoresistance of Magnetic Multilayers,"

Phys. Rev. B 65 (5), 054424 (2002).

Elliot, J., Meuse, V., Silin, V., Krueger, S., Woodward, J. T, Pefralli- Mallow, T. P., Plant, A. L., "Biomedical Membranes on Metal

Supports: Opportunities and Challenges," in Proceedings ofthe Biomolecidar Films: Design, Function, andApplication, edited by J. Rusling (New York, Marcel Dekker, Inc.), in press.

Faraone, A., Chen, S.-H., Fratini, E., Baglioni, P., Liu, L., Brown, C. M., "Rotational Dynamics of Hydration Water in Dicalcium

Silicate by Quasi-Elastic Neutron Scattering," Phys. Rev. E 65

(4), 040507 (2002).

Farrow, R. F. C, Marks, R. F., Toney, M. F., Hannibal, K., David, S., Kellock, A., Borchers, J. A., O'Donovan, K. V., Smith, D. J., "Spontaneous Chemical Ordering and Exchange Bias in Epitaxial Mn^ ^^Pd^ ^g/Fe (001) Bilayers Prepared at Room

Temperature," Appl. Phys. Lett. 80 (5), 808 (2002).

FitzGerald, S. A., Thomas, J. J., Neumann, D. A., Livingston, R. A., "A Neutron Scattering Study of the Role of Diffusion in the Hydration of Tricalcium Silicate," Cement and Concrete Res. 32 (3), 409 (2002).

Fitzsimmons, M. R., Leighton, C, Nogues, J., Hoffmann, A., Liu, K., Majkrzak, C. F., Dura, J. A., Groves, J. R., Springer, R. W.,

Arendt, P. N., Leuier, V., Lauter, H., Schuller, I. K., "Influence of In-Plane Crystalline Quality of an Antiferromagnet on

Perpendicular Exchange Coupling and Exchange Bias," Phys. Rev. B 65 (13), 8(2002).

Fratini, E., Chen, S.-H., Baglioni, P., Cook, J., Copley, J., "Dynamic

Scaling of Quasi-Elastic Neufron Scattering Specfra From

Interfacial Water," Phys. Rev. E 65 (1), 010201 (2001).

Fujita, M., Yamada, K., Hiraka, H., Gehring, P. M., Lee, S.-H., Wakimoto, S., Shirane, G, "Static Magnetic Correlations Near

the Insulating-Superconducting Phase Boundary in La,^ Sr^CuO^," Phys. Rev. B 65 (6), 064505 (2002).

Fultz, B., Witham, C. K., Udovic, T. J., "Disfributions of Hydrogen

and Strains in LaNi^ and LaNi^^^Sn^^s'" J- Alloys Compnds.

335(1-2), 165 (2002).

Garvey, C. J., Parker, I. H., Simon, G R, Whittaker, A. K., Knott, R.

B., "An Experimental Sfridy by NMR and SANS of the Ambient Hydration of Paper," in Proceedings ofthe 12'^ Fundamental Research Symposium (Pulp and Paper Fundamental Research Society, Oxford, 2001), p. 359.

Gehring, P. M., Wakimoto, S., Ye, Z.-G, Shirane, G, "Ferroelecfric Dynamics in the Perovskite Relaxor PMN," in AIP Conference

Proceedings 626, 89 (2002).

Gehring, R M., Wakimoto, S., Ye, Z.-G, Shirane, G, "Soft Mode

Dynamics Above and Below the Bums Temperature in the Relaxor Pb(Mg,,3 Nb,,,)©,," Phys. Rev. Lett., 87 (27), 277601

(2001).

Geissler, E., Hecht, A. M., "Treatment of Incoherent Signal Subfraction," in Proceedings ofthe Frontiers in SAXS and SANS,

ESRF-ILL-CEA Workshop (Grenoble, France, February 12-13, 1999), edited by Deme B., Diat O., Narayanan T., Zemb T., Report No. ILL99DE3002, (2002).

58
Publications

Geissler, E., Hecht, A. M., Rochas, C, Horkay, F., Bley. F., Livet, F., "Structure and Dynamics of Silica-Filled Polymers by SANS

and Coherent SAXS Scattering Methods and Polymers," in Proceedings ofthe 20''' Discussion Conference on Scattering

Methodsfor the Investigation ofPolymers, (July 9-12, 2001,

Prague, Czech Republic), in press.

Geissler, E., Horkay, F., Hecht, A. M.. Deschamps, P., "Neutron

Scattering From Elastomer Gels," Kautschuk, Gummi, and

Kunstoffe 54, 446 (2001).

Gentile, T. R., "Overview of Polarized Neutron Sources," in Proceedings ofthe Ninth International Workshop on Polarized Sources and Targets (Nashville, Indiana, USA, Sept. 30 - Oct.

4, 2001, edited by V.P. Derenchuk and B. von Przewoski,

j World Scientific, Singapore, 2001), p. 233.

Gentile, T. R., Rich, D. R., Thompson, A. K., Snow, W. M., Jones,

' G. L., "Compressing Polarized ^He Gas with a Modified

Diaphragm Pump," J. Res. Natl. Inst. Stand. Technol. 106,

' 709-729 (2001).

\ Gibson, W. M., Chen-Mayer, H. H., Mildner, D. F. R., Prask, H. J., Schultz, A. J., Youngman, R., Gnaupel-Herold, T., Miller, M.

E., Vitt, R., "Polycapillary Optics Based Neutron Focusing for

' Small Sample Neutron Crystallography," Advances In x-ray

I Analysis 45, in Proceedings ofthe 50"' Denver X-Ray Confer-

: ence (July 2001, Denver, CO), in press.

'i Gibson, W. M., Schultz, A. J., Chen-Mayer, H. H., Mildner, D. F. R., Gnaupel-Herold, T., Miller, M. E., Prask, H. J., Vitt, R.,

ij Youngman, R., Carpenter, J. M., "Polycapillary Focusing

I Optic for Small Sample Neutron Crystallography," J. Appl.

\\ Cryst, in press.

I Giebultowicz, T. M., Kepa, H., Blinowski, J., Kacman, P., "Neutron

i Diffraction and Reflectivity Studies of Interlayer Correlations

I in Magnetic Semiconductor Superlattices," Physics E 10 (1-3), 411 (2001).

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' Gilliam, D. M., Thompson, A. K., Nico J. S., "A Neutron Sensor For

Detection of Nuclear Materials In Transport," in Proceedings

\ of URSSRA Workshop ( 1 5-April 1 7, 2002, Washington, DC), in press.

j Gilra, N., Cohen C, Briber, R. M., Bauer, B. J., Hedden, R.,

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i Glagolenko, I. Y, Carney, K. P., Kern, S., Goremychkin, E. A., Udovic, T. J., Copley, J. R. D., Cook, J. C, "Quantitative

Analysis of UH, in U Metal and UO, Matrices by Neutron

' Vibrational Spectroscopy," Appl. Phys. A, in press.

Gnaeupel-Herold, T. T, "Single Crystal Elastic Constants From

Powder Measurements," in Proceedings ofAccuracy in Powder

] Diffraction. Ill (NIST Special Publication), in press.

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Stresses and Elastic Constants on Thermal Deposits," in Proceedings ofRecent Advances in Experimental Mechanics,

in press.

Granado, E., Huang, Q., Lynn, J. W., Gopalakrishnan, J., Greene, R.

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! Orbital Ordering in the Double Perovskite Ca,FeReO^," Phys.

j Rev. B, in press.

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Rev. Lett. 89 (10), 107204 (2002).

Greenberg, C. C, Teale, D. M., Foster, M. D., Turner, C. M., Corona-Galvan, S., Cloutet, E., Quirk, R. P., Majkrzak, C. F., Demaree, D., "Surface Segregation in Blends of Linear and

Regularly Star Branched Polystyrene," Macromol., in press.

Greenberg, R. R., "A Practical Approach for Evaluating the Uncertainties of Instrumental Neutron Activation Analysis Measure-

' ments," Trans. Am. Nucl. Soc, in press.

Grey, I. E., Roth, R. S., Mumme, W. G, Planes, J., Bendersky, L., Li, C, Chenavas, J., "Characterization of New 5M and 7M

Polytypes of Niobia-Doped Ca,Ta,0,," J. Solid. Sate. Chem.

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Copolymer Blends Before and After UV Exposure," in Proceedings ofthe 80''' Annual Meeting Technical Program

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Gulseren, O., Cohen, R. E., "High Pressure Thermoelasticity of Body-Centered Cubic Tantalum," Phys. Rev. Lett. 65 (6), 064103 (2002).

Gulseren, O., Yildirim, T, Ciraci, S., "A Systematic ab-initio Study of

Curvature Effects in Carbon Nanotubes," Phys. Rev. 65 (15), 153405 (2002).

Gulseren, O., Yildirim, T, Ciraci, S., Kilic, C, "First-Principles Study

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Hamilton, W. A., Porcar, L., Butler, R D., Warr, G. G, "Local Membrane Ordering of Sponge Phases at a Solid-Solution

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Hanley, H. J. M., Muzny, C. D., Ho, D. L., Glinka, C. L., Manias, E., "A SANS Study of Organoclay Dispersions," Int. J. Thermophys. 22 (5), 1435, 2001. Haseyama, T, Asahi, K., Bowman, J. D., Delheij, P. P. J., Funahashi,

H., Ishimoto, S., Jones, G, Masaike, A., Masuda, Y, Matsuda,

Y, Morimoto, K., Muto, S., Penttila, S. I., Pomeroy, V. R., Sakai, K., Sharapov, E. I., Smith, D. A., Yuan, V. W, "Measure- ment of Parity-Nonconserving Rotation of Neutron Spin in the 0.734-eV p-Wave Resonance of La- 139," Phys. Lett. B 534 (1-

4), 39 (2002).

Hassan, P. A., Raghavan, S. R., Kaler, E., "Microstructural Changes

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18 (7), 2543 (2002).

59
Hauer, B., Hempelman, R., Udovic, T. J., Rush, J. J., Kocklemann,

W., Jansen, E., Scafer, W., Richter, D. "Neutron Scattering Studies on the Vibrational Excitations and the Structure of Ordered Niobium Hydrides: The P and % Phases," Phys. Rev.

B, in press.

Hayashi, M., Hashimoto, T., Weber, M., Gruell, H., Esker, A., Han,

C. C, Satija, S. K., "Transient Interface Instability in Bilayer

Polymer Films as Observed by Neutron Reflectivity Studies,"

Macromol, in press.

Hecht, A. M., Horkay, F., Geissler, E., "Structure of Polymer

Solutions Containing Fumed Silica," Phys. Rev. E. 64 (4), 402(2001). Heuser B. J., Chen, W. C, "Small-Angle Neutron Scattering Measurements of Deuteride (Hydride) Formation and Decomposition in Single-Crystal Pd," Phys. Rev. B 65 ( 1 ), 01402 (2002).

Hirota, K., Ye, Z.-G, Wakimoto, S., Gehring, R M., Shirane, G,

"Neutron Diffuse Scattering from Polar Nanoregions in the Relaxor Pb(Mg,,3Nb„3)0,," Phys. Rev. B 65 (10), 104105

(2002).

Hjorvarsson, B., Andersson, G, Dura, J. A., Udovic, T. J., Isberg, P., Majkrzak, C. F., "Temperature Dependence of the Magnetic

Interlayer Ordering in Fe,A^,_,H^ (001) Superlattices," Phys.

Rev. B, in press. Ho, D. L., Hammouda, B., Kline, S. R., "Clustering of Poly( ethylene

oxide) in Solution Revisited," Nature, in press. Ho, D. L., Tsao, C. S., Chen, C. S., Yang, W. C, Yang, G, Chen, S., Han, C. C, "Self Assembled Single Molecule Crystals,"

Science, in press. Hoffman, A., Fitzsimmons, M. R., Dura, J. A., Majkrzak, C. F., "Investigating Magnetic Proximity Effects in NiO/Pd with

Polarized Neutron Reflectometry," Phys. Rev. B 65 (2), 24428

(2002). Hoffmann, A., Yashar, P. C, Nogues, J., Liu, K., Majkrzak, C. F., Dura, J. A., Fritzsche, H., Schuller, I. K., "Influence of

Interfacial Disorder and Temperature on Magnetization

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Horkay, F., Basser, P. J., Hecht, A. M., Geissler, E., "CalciumInduced Volume Transition in Polyacrylate Hydrogels Swollen

in Physiological Salt Solutions," Macrolmol. 2, 207 (2002).

Horkay, F., Basser, R J., Hecht, A. M., Geissler, E., "SANS from

Strongly Charged Polyacrylate Hydrogels in Physiological Salt Solutions," Poly. Preprints, (223'''' ACS National Meeting,

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Networks 98, 14''' Polymer Networks, Group Conference

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Horkay, F., McKenna, G. B., Geissler, E., "Structure and Thermodynamic Behavior of Polymeric Gels," ANTEC 2001 Proceedings

(SPE/ANTEC 2001, Technomic Pub. Co., Inc., Lancaster, PA)

2, 186 (2001). Horkay, F., Uriarte, R. J., Hecht, A. M., Geissler, E., "Neutron

Scattering Investigations on Gels," Polym. Preprints (222"'' ACS National Meeting, Chicago, IL, August 26-30, 2001,

Polymer Preprints) 43, 268 (2001).

Huang, Q., He, T., Regan, K. A., Rogado, N., Hayward, M., Haas, M.

K., Inumaru, K., Cava, R. J., "Temperature Dependence of the

Structural Parameters of the Non-Oxide Perovskite Superconductor MgCNij," Physica C 363, 215 (2001). Huffman, P. R., "Ultracold Neutrons," in McGraw-Hill Yearbook of

Science and Technology, The McGraw-Hill Publishing Co., New York 394 (2002). Huffman, R R., Thompson, A. K., Wietfeldt, R E., Yang, G. L., Alvine, K. J., Brome, C. R., Dzhosyuk, S. N., Mattoni, C. E. H., Michniak, R. A., McKinsey, D. N., Yang, L., Doyle, J. M.,

Golub, R., Habicht, K., Koch, J., Lamoreaux, S. K., Coakley, K. J., Leite, M. L. G., Maia, L., Rodrigues, A. C. M., Zanotto,

E. D., "Magnetic Trapping of Ultracold Neufrons: Prospects

for an Improved Measurement of the Neufron Lifetime," in Fundamental Physics with Pulsed Neutron Beams, World

Scientific Publishing Co. Pte. Ltd. 156 (2001). Huffman, P. R., "An Experiment to Search for Parity-Conserving

Time Reversal Invariance Using Epithermal Neutrons From the Spallation Neutron Source," in Proceedings ofthe Workshop on

Astrophysics, Symmetries, andApplied Physics at Spallation Neutron Sources, in press.

Jeng, U., Lin, T. L., Liu, W. J., Tsao, C. S., Canteenwala, T, Chiang,

L. Y, Sung, L. R, Han, C. C, "SANS and SAXS Study on Aqueous Mixtures of Fullerene-Based Star lonomers and

Sodium Dodecyl Sulfate," Physica A 304 (1-2), 191 (2002). Kang, H. J., Pengcheng, D., Mandrus, D., Jin, R., Mook, H. A., Adroja, D. T., Bennington, S. M., Lee, S.-H., Lyrm, J. W., "Doping Evolution of the Phonon Density of States and

Electron-Lattice Interaction in Nd, ^Ce^CuO^^g," Phys. Rev. B

66 (6), 064506 (2002).

Karlsson, E. B., Abdul-Redah, T, Udovic, T. J., Hjorvarsson, B., Chatzidimitriou-Dreismann, C. A., "Short-Lived Proton Entanglement in Yttrium Hydrides," Appl. Phys. A, in press.

Kent, M., "A Quantitative Study of Tethered Chains in Various

Solution Conditions Using Langmuir Diblock Copolymer

Monolayers," Rapid Commun. 21, 243 (2000).

Kent, M. S., Yim, H., Sasaki, D. Y, Majewski, J., Smith, G. S., Shin,

K., Satija, S., Ocko, B. M., "Segment Concentration Profile of Myoglobin Adsorbed to Metal Ion Chelating Lipid Monolayers at the Air-Water Interface by Neutron Reflection,"

Langmuir 18 (9), 3754 (2002). Kepa, H., Kutner-Pielaszek, J., Blinowski, J., Twardowski, A., Majkrzak, C. R, Story, T, Kacman, P., Galazka, R. R., Ha, K., Swagten, H. J. M., De Jonge, W. J. M., Sipatov, A. Y,

Volobuev, v., Giebultowicz, T. M., "Antiferromagnetic

Interlayer Coupling in Ferromagnetic Semiconductor EuS/

PbS(OOl) Superlattices," Europhysics Letters 56 (I), 54

(2001). Kepa, H., Kutner-Pielaszek, J., Twardowski, A., Majkrzak, C. F., Sadowsh, J., Story, T, Giebultowicz, T. M., "Ferromagnetism

of GaMnAs Studied by Polarized Neutron Reflectometry,"

Phys. Rev. E 64 (12), 121302 (2001). Kepa, H., Kutner-Pielaszek, J., Twardowski, A., Majkrzak, C. R,

Story, T, Sadowski, J., Giebultowicz, T. M., "Polarized Neutron Reflectometry Studies of GaMnAs/GaAs

Superlattices," Applied Physics A, in press.

60
T

Publications

Kepa, H., Kutner-Pielaszek, J., Twardowski, A., Sipatov, A. Y., Majkrzak, C. F., Story, T., Galazka, R. R., Giebultowicz, T. M., "Interlayer Correlations in Ferromagnetic Semiconductor

Superlattices EuS/PbS," J. Magn. Magn. Mater. 226, 1795

(2001) .

Khalifah, R, Ho, D. M., Huang, Q., Cava, R. J., "The Structure and

Properties of Beta-La^RuO^: A New Structure Type with

Isolated RuO^ Octahedra," J. Solid State Chem. 165 (2), 359

(2002) .

Khalifah, R, Osbom, R., Huang, Q., Zandergen, H. W., Jin, R., Liu,

Y., Mandrus, D., Cava, R. J. "Orbital Ordering Transition in La,Ru,0,„," Science 297, 2237 (2002).

Khalyavin, D. D., Troyanchuk, I. O., Kasper, Huang, Q., Lynn, J. W., Szymczak, H., "Magnetic Structure of TbBaCo^O. ^ Perovskite," J. Mater. Research 17 (4), 838 (2002).'

Khaykovich, B., Lee, Y. S., Erwin, R. W., Lee, S.-H., Wakimoto, S., Thomas, K. J., Kastner, M. A., Birgeneau, R. J., "Enhancement

of Long-Range Magnetic Order by Magnetic Field in Superconducting La^CuO^^^," Phys. Rev. B 66 (1), 014528 (2002). Kim, E., Suh, H. R., Kim, H., Char, K., Hong, J., Lee, S. H., Satija, S. K., Ivkov, R., "Neutron Reflectivity From the Monolayer of SANS Random Copolymer," Mol. Cryst. Liq. Cryst. 371, 211

(2002). Kim, H., Huang, Q. Z., Lynn, J. W., Kauzlarich, S. M., "Neutron

Diffraction Study of the Ternary Metal Zintl Compound

Ca,^MnSb||,'" J. Solid. State. Chem., in press. Kim, Y. J., Wakimoto, S., Shapiro, S. M., Gehring, P. M., Ramirez, A.

P., "Neutron Scattering Study of Antiferromagnetic Order in CaCUjTip,,," Solid State Commun. 121 (11), 625 (2002).

Kline, S. R., Choi, S. M., Rosov, N., "Neutron Spin Echo Spectros- copy Studies of Polymerized Micelles," in Proceedings Abstr. Pap. Am. Chem. Soc. 222, 53-PMSE, Part 2, 2001.

Koga, T., Shin, K., Zhang, Y, Seo, Y.-S., Rafailovich, M. H., Sokolov,

J., Chu, B., Satija, S. K., "Polymer Thin Films in Supercritical

COj," in Proceedings ofthe ASR-2000, J. Phys. Soc. Japan., in press. Kondoh, E., Baklanov, M. R., Lin, E. K., Gidley, D. W., Nakashima,

A., "Comparative Study of Pore Size of Low-Dielectric- Constant Porous Spin-on-Glass Films with Different Ways of

Non-Destructive Instrumentation," Japan. J. Appl. Phys. 40, L323 (2001).

Koubi, L., Tarek, M., Bandyopadhyay, S., Klein, M. L., "Membrane

Structural Perturbations Caused by Anesthetics and NonImmobilizers: A Molecular Dynamics Investigation," Biophys.

J. 81 3339 (2001).

Koubi, L., Tarek, M., Bandyopadhyay, S., Klein, M. L., Scharf, D., "Effects of the Non-Immobilizer Hexafluroethane on the Model Membrane Dimyristoylphosphatidylcholine," Anesthesiology 96 (4), 848 (2002). Koo, T.-Y, Gehring, P. M., Shirane, G., Kiryukhin, V., Lee, S.-G, Cheong, S.-W., "Anomalous Transverse Acoustic Phonon

Broadening in the Relaxor Ferroelectric Pb(Mg„3Nb3,3)„ Ji„P3," Phys. Rev. B 65 (14), 144113

(2002).

Krishnan, K., Chapman, B., Bates, F. S., Lodge, T. R, Almdal, K., Burghardt, W. R., "Effects of Shear Flow on a Polymeric

Bicontinuous Microemulsions: Equilibrium and Steady State Behavior," J. Rheol. 46 (2), 529 (2002).

Krishnamoorti, R., Graessley, W. W, Zirkel, A., Richter, D., Hadjichristidis, N., Fetters, L. J., Lohse, D. J., "Melt-State Polymer Chain Dimensions as a Function of Temperature," J. Polymer Physics: Part B 40, 1768 (2002).

Krishnamoorti, R., Silva, A. S., Mitchell, C. A., "Effect of Silicate Layer Anisotropy on Cylindrical and Spherical Microdomain

Ordering in Block Copolymer Nanocomposites," J. Chem.

Phys. 115 (15), 7175 (2001).

Kucklick, J. R., Becker, R R., Struntz, W. D. J., Mackey, E. A.,

Porter, B. J., Schantz, M. M., Oflaz, R. D., Epstein, M. S., Wise, S. A., Rowles, T. K., McFee, W. E., Stolen, M. K., "Persistent Organchlorine Pollutants and Elements Determined

in Tissues of Rough-Toothed Dolphins (Steno Bredanensis)

Banked from a Mass Stranding Event," NISTIR 6857 (2002).

Kucklick, J. R., Christopher, S. J., Becker, P R., Pugh, R. S., Porter, B. J., Schantz, M. M., Mackey, E. A., Wise, S. A., Rowles, T. K., "Description and Results of the 2000 NIST/NOAA

Interlaboratory Comparison Exercise Program for Organic

Contaminants and Trace Elements in Marine Mammal

Tissues," NISTIR 6849 (2002). Kwan, K. S., Nakatani, A. I., Ivkov, R., Papanek, P., "Silica Surface Treatment Effects on the Dynamics of Poly(dimethyl siloxane)

by Time-Of-Flight Neutron Spectroscopy," Polymer Preprints 42 (1), 2001.

Lai, C. H., Ming, T, Erwin, R., Borchers, J. A., "Exchange Anisotropy Between Single Twin Domain NiO and NiFe," J. Appl.

Phys. 91 (10), 7751 (2002).

La-Orauttapong, D., Noheda, B., Ye, Z.-G., Gehring, P. M., Toulouse,

J., Cox, D. E., Shirane, G., "Phase Diagram of the Relaxor

Ferroelectric (l-x)Pb(Zn,,3Nb,,3)0, ^PbTiO,," Phys. Rev. B 65

(14), 144101 (2002).

Lee, H. J., Lin, E. K., Wang, H., Wu, W.-L., Chen, W., Moyer, E. S., "Structural Comparison of Hydrogen Silsesquioxane Based

Porous Low-k Thin Films Prepared with Varying Process

Conditions," Chem. Mater. 14 (4), 1845 (2002).

Lee, J. H., Balsara, N. P., Krishnamoorti, R., Jeon, H. S., Hammouda,

B., "Designing Balanced Surfactants for Mixtures of Immiscible Polymers," Macromol. 34 (19), 6557, (2001).

Lee, S.-H., Broholm, C, Ratcliff, W., Gasparovic, G, Huang, Q., Kim, T.H., Cheong, S.-W., "Emergent Excitations in a Geometrically Frustrated Magnet," Nature 418, 856 (2002).

Lee, S.-H., Ratcliff, W., Broholm, C, Kim, T. H., Huang, Q., Cheong,

S. W., "Neutron Scattering Study of Neel to Spin Freezing

Transition Versus Dilution in Geometrically Frustrated ZnCr, , Ga, O^," Phys. Rev. B, in press.

Lee, S.-H., Tranquada, J. M., Yamada, K., Buttrey, D. J., Li, Q., Cheong, S.-W., "Freezing of a Stripe Liquid," Phys. Rev. Lett. 88(12), 126401 (2002).

Lefebvre, A. A., Lee, J. H., Balsara, N. P., Hammouda, B., "Critical Length and Time Scales During the Initial Stages ofNucleation

in Polymer Blends," J. Chem. Phys. 116 (12), 4777 (2002).

Lefebvre, A. A., Lee, J. H., Balsara, N. P., Hammouda, B., "Neutron Scattering From Pressurized Polyolefm Blends Near the Limits of Mestastability," Macromol. 33 (21), 7977 (2000).

I'

f

i

61
Leighton, C, Fitzsimmons, M. R., Hoffmann, A., Dura, J. A., Majkrzak, C. R, Lund, M. S., Schuller, I. K., "Thickness Dependent Coercive Mechanisms in Exchange Biased Bilayers," Phys. Rev. B 65 (6), 061103, 2002

Lenhart, J. L., Wu, W.-L., "Deviations in the Thermal Properties of

Ultrathin Polymer Network Level," Macromol. 35 (13), 5145

(2002).

Levin, I., Amos, T. G, Nino, J. C, Vanderah, T. A., Reaney, I. M.,

Randall, C. A., Lanagan, M. T, "Crystal Structure of the Compound Bi,Zn,,3Nb^,30,," J. Mater. Res. 17 (6), 1406

(2002).

Li, J., Yokochi, A., Sleight, A. W., Amos, T.G., "Strong Negative

Thermal Expansion along the 0-Cu-O Linkage CuScO,,"

Chem. Mat. 14 (6), 2602 (2002).

Lin, E. K., Lee, H. J., Lynn, G. W., Wu, W. L., O'Neill, M L., "Structural Characterization of a Porous Low-Dielectric- Constant Thin Film with a Non-Uniform Depth Profile," Appl. Phys. Lett. 81 (4), 607 (2002).

Lin, Y., Smith, T. W., Alexandridis, P., "Adsorption of a Rake-Tyoe

Siloxane Surfactant onto Carbon Black Nanoparticles Dis- persed in Aqueous Media," Langmuir 18, 6147 (2002).

Lin, E. K., Soles, C. L., Goldfarb, D. L., Trinque, B. C, Bums, S. D., Jones, R. L., Lenhart, J. L., Angelopoulos, M., Willson, C. G.,

Satija, S. K., Wu, W.-L., "Direct Measurement of the Reaction

Front in Chemically Amplified Photoresists," Science 297, 372

(2002).

Lin, E. K., Wu, W.-L., Lin, Q. H., Angelopoulos, M., "Feature-Shape and Line-Edge Roughness Measurement of Deep Sub-Micron

Lithographic Structures Using Small-Angle Neutron Scatter- ing," in Proceedings ofthe SPIE 26''^ Annual International Conference on Microlithography 4344, 414 (2001).

Lindstrom, R. M., and Greenberg, R. R., "Accuracy and Uncertainty

in Radiochemical Measurements: Learning from Errors in Nuclear Analytical Chemistry," J. Nucl. Radiochem. Sci., 2, Rl-4 (2001).

Lipson, D. A., Roberts, D. A., Hansen-Flaschen, J., Gentile, T,

Jones, G, Thompson, A., Dimitrov, I. E., Palevsky, H. I., Leigh, J. S., Schnall, M., Rizi, R. R., "Pulmonary Ventilation and Perfusion Scaiming Using Hyperpolarized Helium-3 MRI

and Arterial Spin Tagging in Healthy Normal Subjects and in Pulmonary Embolism and Orthotopic Lung Transplant

Patients," Magn. Reson. Med. 47, 1073 (2002). Long, S. E., Kelly, W. R., "Determination of Mercury in Coal by

Isotope Dilution Cold-Vapor Generation Inductively Coupled

Plasma Mass Spectrometry," Anal. Chem. 74 (7), 1477 (2002). Lyrm, J. W., Borchers, J. A., Huang, Q., Santoro, A., Erwin, R. W., "Magnetic Structure Determinations at NBS/NIST," J. Res.

Natl. Inst. Stand. Technol. 106 (6), 953 (2001). Lynn, J. W., Dadmun, M. D., Wu, W. L., Lin, E. K., Wallace, W. E., "Neutron Reflectivity Studies of the Interface Between a Small Molecule Liquid Crystal, and a Polymer," Liq. Cryst. 29 (4), 551 (2002). Lynn, J. W., "Review of Neutron Interferometry: Lessons in Experimental Quantum Mechanics," by Rauch, H., Werner, S. A., Physics Today 55, 56 (2002). Majkrzak, C. F., Berk, N. F., "Advances in Specular Neutron

Reflectometry," J. Appl. Phys. A, in press.

Manson, J. L., Bordallo, H. N., Lynn, J. W., Huang, Q., Feyerherm,

R., Loose, A., Chapon, L., Argyriou, N., "Magnetic Ordering and Spin Excitations in Mn(dca),(pyz) [dca = N(CN)~,; pyz = pyrazine], Appl. Phys. A, in press. Mansour, F., Dimeo, R. M., Peemoeller, H., "High Resolution

Inelastic Neutron Scattering From Water in Mesoporous

Silica," Physical Review E 66, 041307 (2002). Maranzano, B. J., Wagner, N. J., "The Effects of Interparticle Interactions and Particle Size on Reversible Shear Thickening:

Hard-Sphere Colloidal Dispersions," J. Rheol. 45 (5), 1205

(2001).

Martinho, H., Granado, E., Moreno, N. O., Garcia, A., Toniani, I., Rettori, C, Neumeier, J. J., Oseroff, S. B., "Strong Charge

Carrier Effect on the Magnetic Coupling of La-Doped

CaMnOj," Physica B, in press.

Martter, T. D., Foster, M. D., Yoo, T, Xu, S., Lizzaraga, G, Quirk,

R. P., Butler, P. D., "Determination of the Thermodynamics

Interaction Parameter for Blends of Star and Linear

Polybutadience," Macromol., in press.

Matejicek, J., Brand, P. C, Drews, A. R., Krause, A., Lowe-Ma, C,

"Residual Stresses in Cold-Coiled Helical Compression Springs

for Automotive Suspensions Measured by Neutron Diffraction," Metall. Mater. Trans. A, in press. McKelvey C. A., Kaler, E. W., "Characterization of Nanostructured Hollow Polymer Spheres with Small-Angle Neutron Scattering

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Retention of 137Cs in Sediments at the Hanford Site, Washington," Environ. Sci. Technol. 35, 3433 (2001). Meyer, A., Schober, H., Dingwell, D. B., "Stmcture, Stmctural Relaxation and Ion Diffusion in Sodium Disilicate Metis,"

Europhysics Letters 59 (5), 708 (2002).

Michels, A., Weissmuller, J., Erb, U., Barker, J. G, "Measurements

of a Magnetic-Field Dependent Correlation Length in Nanocrystalline Ni Using Small-Angle Neufron Scattering,"

Phys. Stat. Solid 189 (2), 509 (2002).

Mildner, D. F. R., Carpenter, J. M., "Time Uncertainty for Guided

Long Wavelength Neutrons on a Pulsed Source," Nucl. Instmm. & Meth. 484 (1-3), 486 (2002).

Mildner, D. F. R., Chen-Mayer, H. H., Gibson, W. M., "Focusing Neutrons with Tapered Capillary Optics," J. Appl. Phys., in press.

Mildner, D. F. R., Chen-Mayer, H. H., Gibson, W. M., GnaupelHerold, T, Miller, M. E., Prask, H. J., Schultz, A. J., Vitt, R., Youngman, R., "A Monolithic Polycaplillary Focusing Optic

for Polychromatic Neutron Diffraction Applications," Rev. Sci. Instmm. 73 (5), 1985 (2002).

Mildner, D. E R., Chen-Mayer, H. H., Gibson, W. M., Schultz, A. J., "A Monolithic Polycapillary Focusing Optic for Polychromatic Neutron Diffraction Applications," in Proceedings ofthe SPIE Conference (July 2002, Seattle, WA), in press. Mook, H. A., Dai, R, Hayden, S. M., Hiess, A., Lynn, J. W., Lee, S.- H., Dogan F., "Magnetic Ordering in YBa^CUjO^^^ Superconductors," Phys. Rev. B, in press.

62
Publications

Mukherjee, S., Cohen, R. E., Gulseren, O., "Vacancy Formation

Enthalpy at High Pressure in Tantalum," Phys. Rev. B,

in press.

Nair, S., Tsapatsis, M., Toby, B. H., Kuznicki, S. M., "A Study of Heat-Treatment Induced Framework Contraction in Strontium- ETS-4 by Powder Neutron Diffraction and Vibrational Spectroscopy," J. Am. Chem. Soc. 123 (51), 12781 (2001).

Nakatani, A. L, Chen, W., Schmidt, R. G, Gordon, G V, Han, C. C,

"Chain Dimensions in Polysilicate-Filled Poly (Dimethyl

Siloxane)," Int. J. Thermophysics 23, 199 (2002).

Nakatani, A. I., Chen, W., Schmidt, R. G, Gordon, G V, Han, C. C,

"Chain Dimensions in Polysilicate-Filled Poly(dimethyl

siloxane)," hit. J. Thermophys. 23 (1), 199 (2002).

Nakatani, A. I., Ivkov, R., Papanek, P., Jackson, C. L., Yang, H., Nikiel, L., Gerspacher, M., Krishnamoorti, R., "The Signifi- cance of Percolation on the Dynamics of Polymer Chains

Bound to Carbon Black," in Proceedings ofthe Filled and

Nanocomposite Polymer Materials, edited by A. Nakatani, R.

P. Hjelm, M. Gerpacher, R. Krishnamoorti, R. P., Materials Research Society Symposium Proceedings, Pittsburgh, PA)

661, KK4.2.1 (2001).

Natali-Sora, I., Santoro, A., Huang, Q., "Oxidation States of Fe in YBa^Fe^Og from a Bond Valence Analysis of the Structure,"

J. Solid State Chem., in press.

Nico, J. S., Abdurashitov, J. N., Gavrin, V. N., Girin, S. V, Gorbachev,

V. v., Ibragimova, T. V., Kalikhov, A. V., Khaimasov, N. G,

Knodel, V. N., Mirmov, I. N., Shikhin, A., Verentenkin, E. P., Vermul, V. M., Yants, V. E., Zatsepin, G T, Bowles, T. J., Teasdale, W. A., Wark, D. L., Cherry, M. L., Cleveland, B. T,

Davis, R., Lande, K., Wildenhain, P S., Elliott, S. R., Wilkerson, J. F., "Solar Neutrino Results From SAGE," in Proceedings ofthe 1

0''' International Baksan School: Particles and Cosmology, edited by E. N. Alexeev, V. A. Matveev, K. H.

S., Nirov, V. A. Rubakov, (Institute for Nuclear Research of the Russian Academy of Sciences, Moscow) p. 63 (2000).

Nieh, M.-P., Glinka, C. J., Krueger, S., Prosser, R. S., Katsaras, J., "A

SANS Study of the Effect of Lanthanide Ions and Charged

Lipids on the Morphology of Phospholipid Mixtures,"

Biophys. J. 82 (5), 2487 (2002).

Nieh, M.-R, Kumar, S., Ho, D., Briber, R. , "Neutron Scattering of Polymer Conformations in Energetic Neutral Pores of the Vycor," Macromol. 35, 6384 (2002). Norman, B. R., Iyengar, G V, "Further Applications of PreIrradiation Combustion and Neutron Activation Analysis

Technique for the Determination of Iodine in Food and

Environmental Reference Materials: Merits and Demerits,"

Fresen. J. Anal. Chem., in press. O'Donovan, K. V, Borchers, J. A., Majkrzak, C. F., Hellwig, O., Fullerton, E. E., "Extracting Buried Twists with Polarized Neutron Reflectometry," Appl. Phys. Lett. A, in press. O'Donovan, K. V., Borchers, J. A., Majkrzak, C. F., Hellwig, O.,

Fullerton, E. E., "Pinpointing Chiral Structures Using Front/ Back Polarized Neutron Reflectivity," Phys. Rev. Lett. 88 (6), 067201 (2002).

Olson, D. H., Toby, B. H., Reisner, B. A., "Neutron Diffraction Study of Protons in Four Lanthanum Exchanged X and LSX

Zeolites," in Proceedings ofthe 1

3'^ International Zeolite Conference, Montpellier, France, edited by Galameau, A.

Elsevier), 135 (2001).

Papanek, P., Fischer, J. E., Murthy, N. S., "Low-Frequency Amide

Modes in Different Hydrogen-Bonded Forms of Nylon-6

Studied by Inelastic Neutron Scattering and Density-Functional

Calculations," Macromol. 35 (10), 4175 (2002).

Park, S., Gies, H., Toby, B. H., Parise, J. B., "Characterization of a New Microporous Lithozinocosilicate with ANA Topology,"

Chem. Mater 14 (7), 3187 (2002).

Pate, B. D., Choi, S. M., Wemer-Zwanziger, U., Baxter, D. V,

Zaleski, J. M., Chisholm, M. H., "Structure and Magnetic

Alignment of Metalloporphyrazine Columnar Aggregates in their Mesophases and Crystalline Phases," Chem. Mater. 14

(5), 1930(2002).

Paul, R. L., "Development of a Procedure for Measuring Nitrogen by

Cold Neutron Prompt Gamma-Ray Activation Analysis,"

Analyst 126, 217 (2001).

Paul, R. L., "Development of a Procedure for Measuring Nitrogen by

Cold Neutron Prompt Gamma-Ray Activation Analysis,"

Analyst 126, 217 (2001).

Paul, R. L., "Nondestructive Measurement of Hydrogen and Other Elements by Cold Neutron Capture Prompt Gamma-Ray

Activation Analysis," Geostandards Newsletter 34 (3), 15 (2002).

Payne, A. C, Sprauve, A., Olmstead, M. M., Kauzlarich, S. M., Chan, J. Y, Reisner, B. A., Lynn, J. W., "Synthesis, Magnetic, and Electronic Properties of Single Crystals of EuMn,P„" J. Solid State Chem. 163 (2), 498 (2002).

Perahia D., Traiphol, R., Bunz, U. H., "From Single Molecules to Aggregates to Gels in Dilute Solution: Self-Organization of Nanoscale Rodlike Molecules," J. Chem. Phys. 117 (4), 1827

(2002).

Perez-Salas, U., Briber, R. M., Rafailovich, M. H., Sokolov, J., "Interfacial Fracture Toughness Between Glassy Polymer

Networks," J. of Polym. Sci. Part B: Poly. Phys., in press.

Perez-Salas, U., Nasser, L., Briber, R. M., Hamilton, W. A., Rafailovich, M. H., Sokolov, J., "Polystyrene Network

Interdiffosion," Macromol, 35 (17), 6638 (2002).

Petrash, S., Cregger, T, Zhao, B., Pokidysheva, E., Foster, M. D.,

Brittain, W. J., Sevastinov, V, Majkrzak, C. F., "Changes in Protein Adsorption on Self-Assembled Monolayers with Monolayer Order: Comparison of Human Serum Albumin and Human Gamma Globulin," Langmuir 17 (24), 7645 (2001).

Pivovar, A. M., Ward, M. D., Brown, C. M., Neumann, D. A., "Probing Vibrational Dynamics of Hydrogen-Bonded Inclusion Compounds with Inelastic Neutron Scattering and ab-initio Calculation," J. Phys. Chem. 106 (19), 4916 (2002).

Pochan, D. J., Lin, E. K., Wu, W.-L., "Surface Directed Crystalliza- tion and Autophobic in Semicrystalline Polymer Thin Films,"

Phys. Rev. Lett., in press.

Pochan, D. J., Pakstis, L., Nowak, A. P., Deming, T. J., "Self- Assembled Polypeptide Hydrogels; Morphology and Cytotoxicity," Biomacromol., in press.

Pochan, D. J., Pakstis, L., Ozbas, B., Nowak, A. P., Deming, T. J., "SANS and Cryo-TEM Sttidy of Self-Assembled Diblock

Copolypeptide Hydrogels with Rich Nano-Through

Microscale Morphology," Macromol. 35 (14), 5358 (2002).

63
Popovici, M., Stoica, A., Hubbard, C, Spooner, S., Prask, H., Gnaupel-Herold, T., Gehring, P., Erwin, R., "Multi-Wafer

Focusing Neutron Monochromators and Applications," in Proceedings ofthe SPIE Optical Science and Technology (edited by Wood, J. L., Anderson, I. S.) 4509, 21 (2001).

Porcar, L., Hamilton, W. A., Butler, P D., Warr, G G, "A New

Vapor Barrier Couette Shear Cell, for Small Angle Neutron

Scattering Measurements," Rev. Sci. Instrum. 73 (6), 2345

(2002).

Porcar, L., Hamilton, W. A., Butler, R D., Warr, GG, "Scaling of

Shear-Induced Transformations in Membrane Phases," Phys. Rev. Lett., in press.

Prask, H. J., Brand, P C, Gnaupel-Herold, T., Hicho, G. E., "Determination of Residual Stresses Using Neutron Diffraction: Tank-Car Welds and Rail Slices," in Topics on Nondestructive Evaluation Series Nondestructive Testing and

Evaluation for the Railroad Industry, (edited by H. Reis and

C. Barkan, ASNT, Columbus, OH, 2002), p. 199.

Prask, H. J., Gnaupel-Herold, T, Fisher, J. W., Cheng, X., Stuart,

J. T, "Residual Stress Modification by Means of Ultrasonic Impact Treatment," in Proceedings ofthe 2001 SEMAnnual

Conference & Exposition on Experimental an Applied Mechanics, in press.

Quijada, M. A., Simpson, J. R., Drew, H. D., Lynn, J. W., Vasiliu- Doloc, L., Mukovskii, Y. M., Karabashev, S. G, "Temperature

Dependence of Low-Lying Electronic Excitations of LaMnO^,"

Phys. Rev. B 64, 224426 (2002). Raghavan, S. R., Edlund H., Kaler, E. W., "Cloud-Point Phenomena

in Wormlike Micellar Systems Containing Cationic Surfactant and Salt," Langmuir 18 (4), 1056 (2002). Raghavan, S. R., Fritz, G, Kaler, E. W., "Wormlike Micelles Formed

by Synergistic Self-Assembly in Mixtures of Anionic and

Cationic Surfactants," Langmuir 18 (10), 3797 (2002).

Ratcliff, W., Lee, S.-H., Broholm, C, Cheong, S.-W., Huang, Q., "Freezing of Spin Correlated Nanoclusters in a Geometrically

Frustrated Magnet," Phys. Rev. B 65, 220406 (2002).

Ravel, B., Raphael, M. R, Harris, V. G, Huang, Q., "EXAFS and

Neutron Diffraction Study of the Heusler Alloy Co,MnSi,"

Phys. Rev. B 65 (18), 184431 (2002). Regan, T. M., Harris, D. C, Blogett, D. W., Baldwin, K. C,

Miragliotta, J. A., Thomas, M. E., Linevsky, M. J., Giles, J. W., Kennedy, T. A., Fatemi, M., Black, D. R., Lagerlof, K. R

D. , "Neutron Irradiation of Sapphire for Compressive

Strengthening. II. Physical Properties Changes," J. Nucl. Mater. 300(1), 47(2002).

Rich, D. R., Bowman, J. D., Crawford, B. E., Delheij, P R J., Espy,

M. A., Haseyama T., Jones, G, Keith, C. D., Knudson, J., Leuschner, M. B., Masaike, A., Masuda Y., Matsuda, Y,

Penttila S. I., Pomeroy, V. R., Smith, D. A., Snow, W. M., Szymanski, J. J., Stephenson, S. L., Thompson, A. K., Yuan,

v., "A Measurement of the Absolute Neutron Beam Polarization Produced by an Optically Pumped He-3 Neutron Spin

Filter," Nucl. Instrum. Meth. A 481 (1-3), 431 (2002).

Rich, D. R., Fan, S., Gentile, T. R., Hussey, D., Jones, G. L., NeflF, B., Snow, W. M., Thompson, A. K., "Polarized 'He Neutron Spin

Filter Development and Application at Indiana University and

NIST," Physica B 305, 203 (2001).

Rich, D. R., Gentile, T. R., Smith, T. B., Thompson, A. K., Jones, G

L., "Spin-Exchange Optical Pumping at Pressures Near I Bar

for Neutron Spin Filters," Appl. Phys. Lett. 80 (12), 2210

(2002). Rogado, N., Huang, Q., Lynn, J. W., Ramirez, A. P., Huse, D., Cava,

R. J., "BaNi,V20g: A Two-Dimensional Honeycomb Antifer- romagnet," Phys. Rev. B 65 (14), 144443 (2002). Rosenkranz, S., Osbom, R., Vasiliu-Doloc, L., Lynn, J. W., Sinha, S. K., Mitchell, J. F., "Spin Correlations and Magnetoresistance

in the Bilayer Manganite La, ^Sr, gMn,0^," Physica B 312, 763

(2002).

Rush, J. J., Udovic, T. J., "Modem Neutron Methods for the Study

of Hydrogen in Materials," in Proceedings ofSymposia on Fundamentals ofAdvanced Materialsfor Energy Conservation,

TMS, edited by D. Chandra, and R. Batista (2002), p. 161.

Santoro, A., "Past and Present Crystallographic Work at the NBS/

NIST Reactor," J. Res. Natl. Inst. Stand. Technol. 106 (6), 921

(2001).

Sayer, E. V., Yener, A. K., Joel, E. C, Blackman, M. J., Ozbal, H., "Stable Lead Isotope Studies of Black Sea Anatolian Ore

Sources and Related Bronze Age and Phrygian Artifacts from Nearby Archaeological Sites Appendix: New Central Taurus Ore Data," Archaeometry, in press.

Schmidt, G, Nakatani, A. I., Butler, R D., Han, C. C, "Small Angle

Neutron Scattering from Viscoelastic Polymer-Clay Solution Under Shear," Macromol. 35 (12), 4725 (2002).

Schmidt, G., Nakatani, A. I., Han, C. C, "Rheology and FlowBirefringence From Viscoelastic Polymer-Clay Solutions," Rheol. Acta 41 (1-2), 45 (2002). Schwahn, D., Richter, D., Lin, M., Fetters, L. J., "Cocrystallization of a Poly(ethylene-butene) Random Copolymer with C-24 in n-Decane," Macromol. 35 (9), 3762 (2002). Schwahn, D., Richter, D., Wright, P J., Symon, C, Fetters, L. J., Lin, M., "Self-Assembling Behavior in Decane Solution of Potential Wax Crystal Nucleators Based on Poly(co-olefms),"

Macromol. 35 (3), 861 (2002).

Serpico, J. M., Ehrenberg, S. G., Fontanella, J. J., Jiao, X., Perahia, D., McGrady, K. A., Sanders, E. H., Kellogg, G. E., Wnek, G.

E. , "Transport and Structural Studies of Sulfonated StyreneEthylene Copolymer Membranes," Macromol. 35, 5916

(2002) .

Shah, N., Green, M. A., Neumann, D. A., "Phase Stability in the LnCa,Mn,0, (Ln = Pr, Nd, Sm and Gd) Ruddlesden - Popper

Series," J.' Phys. Chem. Solids 63, 1779 (2002).

Shapiro, S. M., Bao, W., Raymond, S., Lee, S. H., Motoya, K., "Observation of Linear Spin Wave Dispersion in Re-Entrant Spin Glass Fe^^Al^j," in Proceedings ICNS 2001, in press.

Shen, L., Stachowiak, A., Fateen, S. K., Laibinis, P. E., Hatton, T. A., "Structure of Alkanoic Acid Stabilized Magnetic Fluids. A

Small-Angle Neutron and Light Scattering Analysis," Langmuir

17,288 (2001).

Shin, K., Koga, T, Zhang, Y, Seo, Y, Occhiogrosso, R., Rafailovich, M. H., Sokolov, J. C, Chu, B., Satija, S. K., "Anomalous

Carbon Dioxide-Induced Swelling of Polymer Thin Films at Gas- Supercritical Transition," J. Am. Chem. Soc, in press.

64
Publications

Silas J. A., Kaler, E. W., " The Phase Behavior and Microstructure of

Efficient Cationic-Nonionic Microemulsions," J. Colloid and

Interface Sci. 243 (1), 248 (2001).

Silva, A. S., Mitchell, C. A., Tse, M.E, Wang, H.-C, Krishnamoorti,

R., "Templating of Cylindrical and Spherical Block Copoly- mers Microdomains by Layered Silicates," J. Chem. Phys. 115

(15), 7166 (2001). Simmons, A., Irvin, G C, Agarwal, V., Bose, A., John, V. T., McPherson, G L., Balsara, N. P., "Small Angle Neutron

Scattering Study of Microstructural Transitions in a Surfactant- Based Gel Mesophase," Langmuir 18, 624 (2002).

Sitepu, H., Prask, H. J., "Assessment of Preferred Orientation with Neutron Powder Diffraction Data," J. Appl. Crystallogr. 35, 274 (2002).

Sitepu, H., Schmahl, W. W., Stalick, J. K., "Use of Generalized Spherical-Harmonic Model for Describing Texture in NiTi

Shape Memory Alloy by Neutron Diffraction," Appl. Phys. A, in press.

Skripov, A. V., Cook, J. C, Udovic, T. J., Kozhanov, V. N., Hempelmann, R., "Quasielastic Neutron Scattering Studies of H Motion in Laves-Phase Compounds," Appl. Phys. A. in press.

Slebarski, A., Maple, M. B., Freeman, E. J., Sirvent, C, Radlowska,

M., Jezierski, A., Granado, E., Huang, Q.-Z., Lynn, J. W.,

"Strongly Correlated Electron Behavior in the Compound

CeRhSn," Philos. Mag. 82 (8), 943 (2002). Smee, S. A., Omdorff, J. D., Scharfstein, G A., Qiu, Y., Brand, P C,

Broholm, C. L., Anand, D. K., "MACS Low Background

Doubly Focusing Neutron Monochromator," Appl. Phys. A

75, 3 (2002).

Soles, C. Douglas, J. F., Dimeo, R. M., Wu, W.-L., "The Dynamics of Confined Polycarbonate Chains with Incoherent Neutron

Scattering," Polym. Mat. Sci. Eng. 85, 81 (2001).

Soles, C. L., Douglas, J. F., Wu, W.-L., Dimeo, R. M., "Incoherent Neutron Scattering and the Dynamics of Confined Polycarbonate Films," Phys. Rev. Lett. 88 (3), 037401 (2002).

Soles, C. L., Douglas, J. F., Wu, W.-L., Peng, H., Gidley, D. W., "A

Broad Perspective on the Dynamics of Highly Confined

Polymer Films," in Proceedings ofthe MRS Conference 710

(2002),

Soles, C. L., Lin, E. K., Lehart, J. L., Jones, R. L., Wu, W.-L., Goldfarb, D., Angelopoulos, M., "Thin Film Confinement

Effects on the Thermal Properties of Model Photoresist Polymers," J. Vac. Sci. Technol. B. 19 (6), 2690 (2001).

Stone, M. B., Chen, Y., Rittner, J., Yardimci, H., Reich, D. H., Broholm, C, Ferraris D. V., Lectka, T, "Frustrated Three- Dimensional Quantum Spin Liquid in CuHpCl," Phys. Rev. B

65 (6), 064423 (2002).

Stone, M. B., Rittner, J., Chen, Y, Yardimci, H., Reich, D. H., Broholm, C, Ferris, D. V., Lectka, T., "Cu^(l,4-diazacycloheptane)2Cl_,is not a Spin Ladder,"

Phys. Rev. B, in press.

Stone, M. B., Rittner, J., Chen, Y, Yardimci, H., Reich, D. H., Broholm, C, Ferraris, D. V., Lectka, T, "Frustrated 3- Dimensional Quantum Spin Liquid in CuHpCl," Phys. Rev. B

65 (6), 064423 (2002).

Stone, M. B., Zaliznyak, I. A., Reich, D. H., Broholm, C, "Frustration Induced Quantum Disordered Phase in Two Dimensional

Heisenberg Antiferromagnet Piperazinium

Hexachlordicuprate," Phys. Rev. B 64, 144405 (2001).

Stteletzky, K. A., Zvinevich, Y, Wyslouzil, B. E., Strey, R., "Controlling Nucleation and Grovi^h of Nanodroplets in Supersonic

Nozzles," J. Chem. Phys. 116 (10), 4058 (2002). Sugiyama, M., Shefelbine, T. A., Vigild, M. E., Bates, F. S., "Phase Behavior of an ABC Triblock Copolymer Blended with A and

C Homopolymers," J. Phys. Chem. B 105, 12448 (2001).

Sung, L., Karim, A., Douglas, J. F., Han, C. C, "Modification of Thin

Film Phase Separation by a Surfactant," Macromol., in press.

Tande, B. M., Wagner, N. J., Mackay, M. E., Hawker, C. J., Jeong, C.

J., "Viscosimetric, Hydrodynamic, and Conformational

Properties of Dendrimers and Dendrons," Macromol. 34, 8580

(2001).

Tarek, M., Tobais, D. J. "The Role of Protein-Water Hydrogen Bond

Dynamics in the Protein Dynamical Transition," Phys. Rev.

Lett. 88 (13), 138101 (2002).

Tarek, M., Tobias, D. J., Chen, S.-H., Klein, M. L., "Short Wavelength Collective Dynamics in Phospholipid Bilayers: A

Molecular Dynamics Sttxdy," Phys. Rev. Lett. 87 (23), 238101

(2001) .

Terry, J. S., Heller-Zeisler, S., Ondov, J. M., "Behavior of Three Atmospheric Tracer Materials in a Pilot-Scale Coal Combuster," J. Radio. Analyt. Nuc. Chem. 251 (2), 205

(2002). Thomas, K. J., Lee, Y. S., Chou, F. C, Khaykovich, B., Lee, P A., Kastner, M. A., Cava, R. J., Lynn, J. W., "Antiferromagnetism,

ferromagnetism and Magnetic Phase Separation in Bi,Sr,Co06+5," Phys. Rev. B. 66, 054415 (2002).

Toby, B. H., "Diffraction Analysis and Crystallographic Structure Determination," Handbook of Ceramic Engineering, edited by

M. N. Rahaman, in press.

Toby, B. H., "Investigations of Zeolite Materials at the NIST Center

for Neutron Research," J. Res. Natl. Inst. Stand. Technol. 106 (6), 965 (2001).

Toby, B. H., "The Classification of Powder Diffraction Data,"

International Tables for Crystallography, in press.

Toby, B. H., "Twenty-Five Years in Crystallography, One Person's View," Zeitschrift fiir Kristallographie 87, 374 (2002).

Trouw, F., Borodin, O., Cook, J. C, Smith, G. D., "A Quasilelastic Neufron Scattering Study of the Local Dynamics of

Poly( ethylene glycol) in Aqueous Solution," J. Phys. Chem., in press.

Truong, M. T, Walker, L. M., "Quantifying the Importance of

Micellar Microstructure and Electrostatic Interactions on the Shear-Induced Structural Transition of Cylindrical Micelles,"

Langmuir 18, 2024 (2002).

Udovic, T. J., Karmonik, C, Huang, Q., Rush, J. J., Vennstrom, M.,

Andersson, Y, Flanagan, T. B., "Comparison of the Dynamics

of Hydrogen and Deuterium Dissolved in Crystalline Pd^Si^ and PdjPgg," J. Alloy Compnds. 330, 458 (2002).

Vajk, O. P, Mang, P K., Greven, M., Gehring, P M., Lynn, J. W., "Quantum Impurities in the Two-Dimensional Spin

One-HalfHeisenberg Antiferromagnet," Science 295

(5560), 1691 (2002).

65
Wada, N., Kamitakahara, W. A., "Quasielastic and Inelastic Neutron

Scattering Studies on Intercalated Water Molecules in Zeolite LTA and FAU," Mol. Cryst. Liq. Cryst., in press.

Wagner, N. J., Butera, R., "Shear Distortion and Relaxation Dynamics

of Colloidal Crystals Investigated by SANS Time Slicing,"

Phys. Rev. E, in press. Wakimoto, S., Stock, C, Birgeneau, R. J., Ye, Z.-G, Chen, W., Buyers, W. J. L., Gehring, R M., Shirane, G, "Ferroelectric Ordering in the Relaxor Pb{Mgj,3Nb2,3)03 as Evidenced by

Low-Temperature Phonon Anomalies," Phys. Rev. B 65 (17), 172105 (2002). Wakimoto, S., Tranquada, J. M., Ono, T., Kojima, K. M., Uchida, S., Lee, S.-H., Gehring, P. M., Birgeneau, R. J., "Diagonal Static Spin Correlations in the Low Temperature Orthorhombic Pccn

Phase of La, ..Nd„,Sr„„.CuO„" Phys. Rev. B 64, 174505

(2001). Wang, H. Douglas, J. F., Satija, S. K., Composto, R. J., Han, C. C,

"Early-Stage Compositional Segregation in Polymer Blend

Films," Phys. Rev. Lett., in press. Wang, H., Shimizu, K., Hobble, E. K., Wang, Z. G, Meredith, G. C,

Karim, A., Amis, E. J., Hsiao, B. S., Hsieh, E. T., Han, C. C,

"Phase Diagram of a Nearly Isorefractive Polyolefm Blend,"

Macromol. 35 (3), 1072 (2002).

Welp, K. A., Co, C, Wool, R. R, "Improved Reflectivity Fitting

Using SERF: Spreadsheet Environment Reflectivity Fitting,"

J. Neutron Res., in press.

Wesley, R., Armes, S. P., Thompson, L. J., "Block Copolymer

Interactions With Surfactants," Langmuir, in press.

Wesley, R. D., Cosgrove, T., Thompson, L., Armes, S. P., Baines, F.

L., "Structure of Polymer/Surfactant Complexes Formed by

Poly(2-(dimethylamino)ethyl Methacrylate) and Sodium

Dodecyl Sulfate," Langmuir 18, 5704 (2002).

Williams, R. E., Rowe, J. M., "Developments in Neutron Beam

Devices and an Advanced Cold Source for the NIST Research

Reactor," Physica B 311 ( 1-2), 1 17 (2002).

Wiyatno, W., Pople, J. A., Cast, A. P, Waymouth, R., Fuller, G G,

"A Scattering Study of Elastomeric Polypropylene," in press. Wong-Ng, W., Huang, Q., Levin, I., Kaduk, J. A., Dillingham, J., Huagan, T., Suh, J., Cook, L. P., "Crystal Chemistry and Phase

Equilibria of Selected SrO-R,0, CuO^ and Related Systems,

R=Lanthanides and Yttrium," Int. J. Inorg. Mater. 3 (8), 1283

(2001). Wong-Ng, W., Roth, R. S., Vanderah, T. A., McMurdie, M. H., "Phase Equilibria and Crystallography of Ceramic Oxides,"

J. Res. Natl. Inst. Stand. Technol. 106 (6), 1097 (2001). Wu, S. Y, Yang, C. C, Li, W.-H., Lee, K. C, Lynn, J. W., Yang, H. D., "Mn Ordering and Induced Ce Ordering in La„,(Ceo5Ca„5)„3Mn03," J. Magn. Magn. Mater. 239 (1-3), 14(2002).

Xu, G, Broholm, C, Reich, D. H., Adams, M. A., "Triplet Waves in Quantum Spin Liquid," Phys. Rev. Lett. 84 (19), 4465 (2000). Yamaura, K., Huang, Q., Takayama-Muromachi, E., "Crystal

Structure and Magnetism of the Linear-Chain Copper Oxides

Sr^Pbj.^BiCuO;/ Phys. Rev. B 64 (18), 184428 (2001).

Yamaura, K., Huang, Q., Takayama-Muromachi, E., "Synthesis,

Crystal Structure and Magnetic Properties of the Linear-Chain

Cobalt Oxide Sr^Pb^CoO,,," J. Solid State Chem. 164 (1), 12

(2002).

Yang, C. C, Wu, S. Y, Li, W.-H., Lee, K. C, Lynn, J. W., Wu, C.-G,

"Magnetic Ordering of Fe in NCH^-Intercalculated Iron Phosphate Fe(OH)PO^," Solid State Communications, in press.

Yang, G Y, Briber, R. M., Huang, E., Rice, R M., Volksen, W.,

Miller, R. D., "Morphological Development in Nanoporous

PMSSQ Films," Chem. Mater., in press.

Yang, G Y, Briber, R. M., Huang, E., Rice, R M., Volksen, W.,

Miller, R. D., "Morphology of Nanoporous PMSSQ Films,"

Appl. Phys. Lett., in press.

Yang, S., Mirau, P., Pai, C. S., Nalamasu, O., Reichmanis, E., Lin, E. K., Lee, H. J. Gidley, D., Frieze, W., Dull, T., Sun, J., Yee, A.

F., "Design of Nanoporous Ultra Low-Dielectric Constant

Organosilicates by Self-Assembly," in Proceedings ofthe ACS

National Meeting 2001. Polymeric Materials: Science and

Engineering 84, 287 (2001).

Yang, S., Mirau, P., Pai, C. S., Nalamasu, O., Reichmanis, E., Pail, J. C, Obeng, Y. S., Seputro, J., Lin, E. K., Lee, H. J., Sun, J., Gidley, D. W., "Nanoporous Ultra Low-Dielectric Constant

Organosilicates Templated by Triblock Copolymers," Chem.

Mat. 14(1), 369 (2002).

Yang, S., Mirau, P., Pai, C. S., Nalamasu, O., Reichmanis, E., Lin, E. K., Lee, H. J. Gidley, D. W., Sun, J., "Molecular Templating of Nanoporous Ultra Low-Dielectric-Constant (-1.5) Organosilicates by Tailoring the Microphase Separations of

Triblock Copolymers," Chem. Mat. 13, 2762 (2001).

Yildirim, T., Gulseren, O., "A Simple Theory of 40K Superconductivity in MgB,; First Principles Calculations of T^, its Dependence in Boron Mass and Pressure," J. Phys. Chem. Solids,

in press.

Yildirim, T., Gulseren, O., "First-Principles Zone-Center Theory of

Superconductivity in MgB,," Physica A, in press.

Young, S. K., Trevino, S. F., Beck Tan, N. C, "Small Angle Neutron

Scattering Investigation of Structural Changes in Nafion

Membranes Induced by Swelling with Various Solvents," J. Polym. Sci. Part B: Polym. Phys. 40 (4), 387 (2002). Young, S. K., Trevino, S. F., Beck Tan, N. C, Paul, R. L., "Utilization of Prompt Gamma Neutron Activation Analysis in the Evaluation of Various Counterion Nafion Membranes," J. Polym. Sci. Part B; Polym. Phys. 220, 134 (2000).

Yurekli, K., Krishnamoorti, R., "Dynamics of Block Copolymer

Micelles," Macrmol. 35, 4075 (2002).

Zaliznyak, I. A., Tranquada, J. M., Erwin, R., Moritomo, Y, "Spinentropy-Driven Melting of the Charge Order in Lai jSr^ jCoO,," Phys. Rev. B 64 (19), 195117 (2001).

Zeitler, T. R., Toby, B. H., "Parallel Processing for Rietveld Refine- ment," J. Appl. Crystallogr. 35, 191 (2002).

Zhang, Y, Ge, S., Tang, B., Rafailovich, M. H., Sokolov, J., Peiffer, D. , Li, Z., Lin, M., Dias, J. A., McElrath, K. O., Nguyen, D.,

Satija, S., Schwarz, S. A., "Interfacial Properties of Brominated

Isobutylene-co-p-Methylstyrene and Butadiene Polymers," in Proceedings ofthe American Chemical Society 154'^ Rubber

Conference, in press.

66
Publications

Zheludev, A., Honda, Z., Chen, Y., Broholm, C. L., Katsumata, K., Shapiro, S. M., "Quasielastic Neutron Scattering in the Highfield Phase of a Haldane Antiferromagnet," Phys. Rev. Lett., 88

(7), 077206 (2002).

Zheludev, A., Kenzelmann, M., Raymond, S., Masuda, T., Uchinokura, K., Lee, S. H., "Spin Dynamics in the Quasi-OneDimensional S=l/2 Antiferromagnet BaCu^Si^O^," Phys. Rev. B 65(1), 014402 (2002).

Zheludev, A., Maslov. S., Zaliznyak, I., Regnault, L. P., Masuda, T., Uchinokura, K., Erwin, R. W., Shirane, G., "Experimental

Evidence for Shekhtman-Entin-Wohlman-Aharony (SEA)

Interactions in Ba,CuGe,0^," Phys. Rev. B, in press.

Zhou, C, Hobbie, E. K., Bauer, B. J., Han, C. C, "Equilibrium

Structure of Hydrogen-Bonded Polymer Blends," J. Polym.

Sci. Part B: Poly. Phys., in press. Zimmerman, M. V., "X-Ray Scattering Studies of Orbital and Charge

Ordering in Pr|^Ca^MnO,," Phys. Rev. B, in press.

67
Instruments and Contacts

High resolution powder diffractometer (BT-1)

B. H. Toby, (301) 975-4297, brian.toby@nist.gov

C. Jones, (301) 975-4507, camille@nist.gov

Q. Huang, (301) 975-6164, qing.huang@nist.gov

J. K. Stalick, (301) 975-6223, judy.stalick@nist.gov

DARTS, Residual stress and texture diffractometer (BT-8)

H. J. Prask, (301) 975-6226, liank@nist.gov

T. Gnaeupel-Herold, (301) 975-5380, thomas.gnaeupelherold@nist.gov

30-m SANS instrument (NG-7)

C. J. Glinka, (301) 975-6242, cglinka@nist.gov

B. S. Greenwald, (301) 975-5795, bsgreen@nist.gov

L. Porcar, (301) 975-5049, iionel.porcar@nist.gov

30-m SANS instrument (NG-3) (NIST/NSF-CHRNS)

B. Hammouda, (301) 975-3961, hamnnouda@nist.gov

S. R. Kline, (301) 975-6243, steven.kline@nist.gov

D. Ho, (301) 975-6422, derek.ho@nist.gov

T. K. Misra, (301) 975-6650, tmisra@nist.gov

8-m SANS instrument (NG-1)

D. Ho, (301) 975-6422, derek.ho@nist.gov

C. J. Glinka, (301) 975-6242, cglinka@nist.gov

J. G. Barker, (301) 975-6732, john.barker@nist.gov

USANS, Perfect crystal SANS (BT-5) (NIST/NSF-CHRNS)

J. G. Barker, (301) 975-6732, john.barker@nist.gov

IVI. H. Kim, (301) 975-6469, kimmh@nist.gov

C. J. Glinka, (301) 975-6242, cglinka@nist.gov

Cold neutron reflectometer-vertical sample-polarized beam

option (NG-1)

C. F. iVIajkrzak, (301) 975-5251, cmajkrzak@nist.gov

J. A. Dura, (301) 975-6251, jdura@nist.gov

Cold neutron reflectometer-horizontal sample (NG-7)

S. K. Satija, (301) 975-5250, satija@nist.gov

Y.-S. Seo, (301) 973-5391, young-soo.seo@nist.gov

Triple-axis polarized-beam spectrometer (BT-2)

J. W. Lynn, (301) 975-6246, jeff.lynn@nist.gov

Triple-axis fixed incident energy spectrometer (BT-7)

J. W. Lynn, (301) 975-6246, jeff.lynn@nist.gov

Triple-axis spectrometer (BT-9)

R. W. Emn, (301) 975-6245, renwin@nist.gov

P. M. Gehring, (301) 975-3946, pgehring@nist.gov

SPINS, Spin-polarized triple-axis spectrometer (NG-5)

(NIST/NSF-CHRNS)

S. Park, (301) 975-8369, sungil.park@nislgov

S.-H. Lee, (301) 975-4257, seung-hun.lee@nist.gov

P. M. Gehring, (301) 975-3946, pgehring@nist.gov

FANS, Filter-analyzer neutron spectrometer (BT-4)

T. J. Udovic, (301) 975-6241, udovic@nist.gov

C. IVI. Brown, (301) 975-5134, craig.brown@nist.gov

J. Leao, (301) 975-8867, jleao@nist.gov

D. A. Neumann, (301) 975-5252, dan@nist.gov

FCS, Fermi-chopper time-of-flight spectrometer (NG-6)

C. IVI. Brown, (301) 975-5134, craig.brown@nist.gov

T. J. Udovic, (301) 975-6241, udovic@nist.gov

DCS, Disk-chopper time-of-flight spectrometer (NG-4)

(NIST/NSF-CHRNS)

J. R. D. Copley, (301) 975-5133, jcopley@nist.gov

I. Peral, (301) 975-6235, inma@nist.gov

HFBS, High-flux backscattering spectrometer (NG-2)

(NIST/NSF-CHRNS)

R. M. Dimeo, (301) 975-8135, robert.dimeo@nisLgov

Z. Chowdhuri, (301) 975-4404, zema.chowdhuri@nist.gov

D. A. Neumann, (301) 975-5252, dan@nist.gov

NSE, Neutron spin echo spectrometer (NG-5)

(NIST/NSF-CHRNS)

N. S. Rosov, (301) 975-5254, nrosov@nist.gov

D. Bossev, (301) 975-4662, dbossev@nist.gov

Prompt-gamma neutron activation analysis (NG-7)

R. M. Lindstrom, (301) 975-6281, dick.lindstrom@nist.gov

R. L. Paul, (301) 975-6287, rpaul@nist.gov

Other activation analysis facilities R. R. Greenberg, (301) 975-6285, rgreenberg@nist.gov

Cold neutron depth profiling (NG-0)

G. Lamaze, (301) 975-6202, lamaze@nist.gov

Instrument development station (NG-0)

D. F. R. iVlildner, (301) 975-6366, mildner@nist.gov

H. H. Chen, (301) 975-3782, chenmayer@nist.gov

Neutron interferometer (NG-7)

M. Arif, (301) 975-6303, muhammad.arif@nist.gov

D. Jacobson, (301) 975-6207, jacobson@nist,gov

Fundamental neutron physics station (NG-6)

M. S. Dewey, (301) 975-4843, mdewey@nist.gov

Theory and modelling

N. F. Berk, (301) 975-6224, nfb@nist.gov

T. Yildirim, (301) 975-6228, taner@nist.gov

Sample environment

D. C. Dender, (301) 975-6225, dender@nist.gov

68
NIST Center for

Neutron Research

For copies of or information on this report, contact:

Ronald L. Cappelletti

(301) 975-6221

ron.cappelletti@nist.gov

For additional information on the facility, contact:

J. Michael Rowe

(301) 975-6210

mil<e. rowe@nist.gov

John J. Rush

(301) 975-6231

john.rush@nist.gov

To obtain guidelines for preparing proposals

to conduct research at the facility, contact:

William A. Kamitakahara

(301)975-6878

vi/illiam. kamitakahara@nist.gov

Location of all contacts:

NIST Center for Neutron Research

100 Bureau Drive, Mail Stop 8562

Gaithersburg, MD 20899-8562

Please visit our vi^ebsite for further information: wviM.ncnr.nist.gov