NATL INST. OF STAND & TECH RXC

A111QS 6=11773-

WIST

PUBLICATIONS

m
ON THE COVER

Part of the 913-detector array of the new Disk Chopper Spectrometer

(DCS) that will be available to users in 2000. To view the detectors as found in the instrument, the picture should be rotated 90°. Information about the DCS and other instruments at NCNR is available at http://www.ncnr.nist.gov/.

Photo: Mark Heifer
NCNR 1999

NIST

CENTER FOR

NEUTRON

RESEARCH

ACCOMPLISHMENTS

AND OPPORTUNITIES

NIST Special Publication 944

J. Michael Rowe, Director

Ronald L. Cappelletti, Editor Linda K. Clutter, Assistant Editor

January 2000

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

Technology Administration

Dr. Cheryl L. Shavers, Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Raymond G. Kammer, Director
DISCLAIMER

Certain commercial equipment, instruments, or materials are identified in this report to foster understanding. Such identification does not imply recommendation or endorsement by the National Institute of Standards and

Technology, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose.

National Institute of Standards and Technology Special Publication 944

Natl. Inst. Stand. Technol. Spec. Publ. 944, 80 pages (January 2000) CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE - WASHINGTON: 2000

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

Washington, DC 20402-9325
CONTENTS

Foreword iv Introduction to the NIST Center for Neutron Research (NCNR) 1 NCNR Layout 2 NCNR Images 1999 4

Research Highlights

Superlattice Magnons 6

Antiferromagnetic Spin Reorientation in Exchange-Biased Fe3 04/NiO Superlattices 8

Spin Density Wave Order in the Superconducting State of La2Cu04+y 10

Local Spin Resonance and Spin-Peierls-Like Phase Transition in ZnCr2 04 12 Compound Refractive Optics Improve Resolution of 30 m SANS Instrument 14

Polymer Brush Response to Solvent Flow 16

Macromolecular Conformation in Ultrathin Polymer Films 18

Probing the Location of the Terminal Groups of a Dendrimer 20

Self-Assemblies of Membrane Active Peptides 22

Shear Orientation of Viscoelastic Polymer-Clay Solutions 24

Unique Determination of Biomimetic Membrane Profiles by Neutron Reflectivity 26

Multi-Technique Studies of Ultrathin Si02 Films 28

Certification of an Ion-Implanted Arsenic in Silicon Standard Reference Material 30

The Rotational Dynamics of H2 in Porous Vycor Glass 32

First-Principles Computational and Neutron Scattering Study of Protonic Conductors 34

Magnetic Trapping of Ultracold Neutrons 36

Charge Disproportionation and Magnetic Ordering in CaFe03 38

Bond Valence Analysis of Ruthenates 40

Residual Stresses in Cold-Coiled Helical Automotive Springs 42

The NCNR Neutron Spin Echo Spectrometer 44

Serving the Scientific and Technological Communities 46

Reactor Operations and Engineering 50

Instrumentation Developments 51 Research Titles 56

Materials Science/Crystallography 56

Polymers 57

Complex Fluids 58

Condensed Matter Physics 59

Biomolecular Science 61 Chemical Physics of Materials 62

Instrumentation 63

Neutron Physics 63

Materials Analysis 64

Affiliations 65

Publications 66

Instruments and Contacts 76

Contacts Inside Back Cover

NIST CENTER FOR NEUTRON RESEARCH iii
FOREWORD

Once again, it is a pleasure to be able to reflect on the accomplishments of the NIST Center for Neutron Research over

the past year. In the reactor operations area, 1999 was another

outstanding year. In spite of an unsheduled maintenance shutdown,

the reactor operated 250 days, with a reliability factor of better than 90 %. The cold source availability for the period was 98 %; i.e., the

cold source held the reactor from operation 4 days during the year. The remaining spent fuel in the storage pool was shipped, providing

space for at least five years of operation. Also, an order has been

placed for a new cooling tower which will not only provide needed

capability for the next 25 years, but will also reduce the plume

visible during cold weather. Last, steady progress has been made in

preparing for a license renewal application to the Nuclear Regulatory

Commission, in order to extend the period of operation beyond 2004. We have also made great progress in instrumentation, with

the back scattering spectrometer operational; with the spin echo

spectrometer now being used for real measurements; and with the

disk chopper spectrometer being commissioned. All three of these

instruments will be available to "friendly" users in the next proposal

cycle. Other work is also advancing well-the perfect crystal small

angle scattering spectrometer (part of the NSF/NIST CHRNS) is

being installed at the reactor; the first phase of the high intensity

filter analyzer spectrometer is ready to begin installation; and the

design and manufacture of new thermal neutron spectrometers is underway. This simultaneous development program has put severe

strains on our resources, but we can now look forward to many years of benefit from the results.

Finally, as always, the results are seen in the output of the

researchers who use the facility. As was done last year, we are

presenting highlights of this work in the following chapters of this

report. I think all can agree that the results truly speak for themselves.

0¥
INTRODUCTION TO

THE NIST CENTER FOR

NEUTRON RESEARCH (NCNR)

Modern technological society is dependent upon increasingly

sophisticated use of materials, many of whose attributes are

dictated by their sub-microscopic structural and dynamical properties. Our knowledge of these properties is provided by a wide range

of scientific techniques of which the many types of scattering (for example. X-rays, light, electrons, neutrons) are arguably the most

important. Of these probes, neutrons are perhaps least familiar, but

they provide important advantages for many types of measurements.

Neutrons, as prepared for use at modern sources, are moving

at speeds comparable to those of atoms moving at room temperature,

thus providing the ability to probe dynamical behavior. At the same

time, neutrons are well matched to measurements at length scales ranging from the distances between atoms to the size of biological

or polymer macromolecules. Neutrons are sensitive to the magnetic

properties of atoms and molecules, allowing study of the underlying

magnetic properties of materials. They also scatter quite differently

from normal hydrogen atoms than they do from heavy hydrogen

(deuterium), allowing selective study of individual regions of molecular systems. Finally, neutrons interact only weakly with materials,

providing the opportunity to study samples in different environments more easily (at high pressures, in shear, in reaction vessels, etc.), and

making them a non-destructive probe. These favorable properties are

offset by the relative weakness of the best neutron sources compared

to X-ray or electron sources, and by the relatively large facilities

required to produce neutrons. As a result, major neutron sources

are operated as national user facilities to which researchers come

from all over the United States (and abroad) to perform small scale

science using the special measurement capabilities provided.

In addition to scattering measurements, neutrons can be used

to probe the atomic composition of materials by means of capture

and resultant radioactive decay. The characteristics of the decay act

as "fingerprints" for particular atomic nuclei, allowing studies of environmental samples for pollutants (e.g., heavy metals), characterization of Standard Reference Materials, and many other essential measurements. While the scattering and capture users of neutrons

are little concerned with understanding the inherent properties of the

neutron, there are important areas in physics that can be explored

by carefully measuring fundamental neutron behavior. Examples

include the lifetime of the free neutron, an important quantity in the

theory of astrophysics; the beta decay process of the neutron, the

details of which are stringent tests of nuclear theory; and the effects

of various external influences such as gravity or magnetic fields on

neutrons. The NCNR utilizes neutrons produced by the 20 MW NIST

Research Reactor to provide facilities, including the nation's only

internationally competitive cold neutron facility, for all of the above

types of measurements to a national user community. There are approximately 35 stations in the reactor and its associated beams that can provide neutrons for experiments. At the present time 26 of these

are in active use, of which 6 provide high neutron flux positions in

the reactor for irradiation, and 20 are beam facilities. A schematic

layout of the beam facilities and brief descriptions of available

instrumentation are given below. More complete descriptions can be found at http://www.ncnr.nist.gov/.

These facilities are operated both to serve NIST mission needs and as a national facility, with many different modes of access. Some

instrumentation was built years ago, and is not suited to general

user access; however, time is available for collaborative research. NIST has recently built new instrumentation, and reserves 33 % of

available time for mission needs with the balance available to general

users. In other cases, instrumentation was built and is operated

by Participating Research Teams (PRT). PRT members have access

to 75 % of available time, with the balance available to general

users. In a special case, NIST and the National Science Foundation

established the Center for High Resolution Neutron Scattering at the NCNR, with a 30 m Small Angle Scattering (SANS) instrument, a

cold neutron triple axis spectrometer, and a perfect crystal SANS

under construction. For these facilities, most time is available for

general users. While most access is for research, whose results are

freely available to the general public, proprietary research can be performed under full cost recovery. Each year, approximately 1600

researchers (persons who participated in experiments at the facility,

but did not necessarily come here) from all areas of the country, from

industry, academe, and government use the facility for measurements

not otherwise possible. The research covers a broad spectrum of

disciplines, including chemistry, physics, biology, materials science,

and engineering.

NIST CENTER FOR NEUTRON RESEARCH 1
NIST CENTER FOR

NEUTRON RESEARCH

LAYOUT

1 Horizontal Sample

Reflectometer

Horizontal surface of sample

allows reflectivity measure- ments of free surfaces, liquid vapor interfaces, as well as polymer coatings.

2 Neutron Interferometry and

Optics Station Includes perfect silicon inter- ferometer; vibration isolation system provides exceptional

phase stability and fringe

visibility.

3 Prompt Gamma Activation Analysis

Cold neutron fluxes allow

detection limit for H of 1 i^g to 10 (jug. Focused beams are

available for profiling.

4 NG-7 30 m SANS

Small Angle Neutron Scattering instrument for microstructure measurement sponsored by

NIST, the ExxonMobil Research and Engineering Co., the

University of Minnesota, and

Texaco R&D.

5 Neutron Physics Station A cold neutron beam

150 mm x 60 mm, available

for fundamental neutron physics experiments.

6 Fermi Chopper TOF

Spectrometer A hybrid time-of-flight spec- trometer for inelastic scattering, with wavelengths between

0.23 nm and 0.61 nm. The

wavelength is chosen by a focusing pyrolytic graphite

crystal, while the beam is pulsed by a simple Fermi

chopper.

7 Spin Echo Spectrometer A neutron spin echo spec- trometer offering neV energy

resolution, based upon Julich design, sponsored by NIST,

Jiilich and ExxonMobil.
11 10

10 NG-3 30 m SANS

Instrument for microstructure measurement sponsored by the National Science Foundation and NIST; part of CHRNS.

11 Backscattering Spectrometer

High intensity, very high

resolution backscattering spectrometer, with many

innovative features, and energy

resolution of approximately

1 |xeV.

12 8 m SANS

Instrument for polymer

characterization, sponsored by

Polymers Division.

13 Vertical Sample Reflectometer

Instrument for measuring

subsurface structure with

polarization analysis capability.

Reflectivities down to 10"8 can

be measured.

14 BT-8 Residual Stress Diffractometer

Diffractometer optimized for depth profiling of residual stress in large components.

15 BT-9 Triple Axis Spectrometer

Triple axis crystal spectrometer

for measurements of excita- tions and structure.

16 BT-1 Powder Diffractometer Powder diffractometer with 32

detectors; incident wavelengths

of 0.208 nm, 0.154 nm, and

0.159 nm, with highest resolution of 5d/d = 8x1

4

.

17 BT-2 Triple Axis Spectrometer

Triple axis crystal spectrometer

with polarized beam capability for measurement of magnetic

dynamics and structure.

18 BT-4 Filter Spectrometer A triple axis crystal spectrometer with a Be or Be/Graphite filter analyzer

option for chemical

spectroscopy.

19 Cold Neutron Depth Profiling A station for quantitative

profiling of subsurface

impurities and coatings, based

on neutron capture and

emission of a charged particle.

20 Thermal Column

A very well-thermalized beam

of neutrons used for radiography, tomography, dosimetry, and other experiments.

NIST CENTER FOR NEUTRON RESEARCH 3
NCNR IMAGES 1999

!

1. An incoming SANS image excites the interest of Martin Vigild (center) as Frank Bates (standing), Newell Washburn (right) and Ken Hanley,

all of the University of Minnesota,

look on.

2. NCNR's Peter Gehring describes the

analyzer of the spin polarized triple axis spectrometer (SPINS) to NCNR

Summer School participants.

3. The Spin Echo Spectrometer (NSE)

at NCNR, commissioned this year, is described in a Research Highlight in this issue.

4. Stephen FitzGerald (Oberlin College) loads a sample at the HFBS.

5. Gudrun Schmidt (NIST, Polymers

Division) awaits the display of an updated SANS image.
6. NCNR Summer School participants

interacting at the recently commissioned high-flux backscattering spectrometer (HFBS).

7. Silke Rathgeber and So Hyun Park

(both at NCNR), ready to load a sample at the NSE.

10. Dave Clem and Mike Rinehart

(both of NCNR) installing biological shielding at the DCS.

9 10 NIST CENTER FOR NEUTRON RESEARCH
SUPERLATTICE

MAGNONS

A

powerful technique for optimizing material properties is to

deposit alternating layers of different materials to form a thin

film superlattice. In particular, magnetic and non-magnetic materials grown as a superlattice exhibit a variety of tunable couplings

between the magnetic layers. Control of these couplings by varying

the layer materials and thicknesses has lead to dramatic increases in performance in certain device applications. A prime example is the

recent use of layered magneto-resistive films in high-performance

magnetic recording heads and sensors. The inter-layer magnetic

coupling can survive across as many as 30 non-magnetic atomic

planes due to its one-dimensional nature, but the coupling strength

is always much weaker than bulk material magnetic interactions. The behavior of the magnetic fluctuations (magnons) in these weakly coupled layer systems is of interest because it provides a

direct measure of the magnetic interactions responsible for the magnetic structure, and leads to a better understanding

of the unique layer to layer couplings.

Until now, the only measurements that have probed these fluctuations have

used Brillouin light scattering [1], or

ferromagnetic-resonance techniques [2], both of which measure only the longest

wavelength dynamics. These measure- ments have found interesting resonances

associated with the superlattice

structure.

It is important to directly measure

the magnons at shorter wavelengths in

order to determine the dispersion, which

directly relates to the magnetic interactions, both within and between layers,

and whether or not the magnetic fluctuation waves propagate between layers.

1

0

1.70

Only inelastic magnetic scattering techniques can provide this information, but with current neutron scattering sources the intensities from such measurements can be prohibitively low, because the amount of magnetic material in the films is so small.

In order to overcome this difficulty we have made neutron

inelastic scattering measurements on a very large superlattice of

alternating layers of dysprosium and yttrium. Dysprosium is the magnetic constituent, and it has the strongest neutron magneticscattering of all the elements. In order to maximize the amount

of Dy, 350 bilayers composed of 43 A of Dy and 28 A of Y

(designated [Dy

43/Y,g

] 350

) were grown by MBE techniques on a 2.5 cm x 1.3 cm substrate resulting in 3 mg of Dy in the sample.

The magnetic structure of this superlattice has previously

been determined to be the basal-plane helical structure of bulk

DyY Superlattice Magnon Dispersion

1.75 1.80

Q(A"

1

)

1.85 1.9

FIGURE 1. Inelastic magnetic scattering from a [Dy

43/Y28 ] 350 superlattice, obtained by subtracting 10 K data from 75 K data, shown as an intensity map

in Q-energy space. The highest intensity is 300 counts/ 30 min and decreases

by 30 counts for each level. A magnetic Bragg peak is just off the graph at Q = 1.97 A

1

.

RESEARCH HIGHLIGHTS
A. Schreyer r. w. Erwin and C. F. Majkrzak J. Kwo

Institut fur Experimentalphysik " NIST Center for Neutron Research Lucent Technologies

Festkorperphysik National Institute of Standards and Technology Bell Laboratories

Ruhr-Universitat Bochum Gaithersburg, MD 20899-8562 Murray Hill, NJ 07974

D-44780 Bochum. Germany

Dy with a coherence length greater than 4 bilayers. The helix progresses remarkably undisturbed through the conduction electrons of the non-magnetic yttrium, but with a turn-angle that is different than in the dysprosium. The coupling strength across the yttrium has been measured by applying a uniform external magnetic field. The coupling breaks down when the external field provides 0.2 meV

per Dy atom in the basal-plane, while the equivalent zone-boundary

magnetic fluctuation in bulk Dy is greater than 5 meV per Dy atom. The inelastic neutron scattering measurements were per- formed at the NIST Center for Neutron Research on the cold- neutron spectrometer SPINS. A multi-component crystal was used

to analyze the energy of the scattered neutrons in order to enhance

the measured intensity while sacrificing wave-vector (Q) resolution. Measurements were performed at 75 K as a compromise between

the size of the ordered magnetic moment and the thermal population

of magnons. The magnons of interest are those propagating along

the superlattice growth direction or the c-axis of the hep rare-earth

structure. Lower magnon energies produce higher thermal populations, but become contaminated with elastic background scattering,

so it is necessary to subtract scans taken at low temperatures where

the magnons have become depopulated in order to remove this

background. The resulting magnetic signal is shown in Fig. 1 as

a color-coded intensity map in Q-energy space. There is a clear

ridge of intensity which moves to higher energies as Q moves away

from the magnetic Bragg peak at 1.97 A"1. We have concentrated on the magnon branches that extend towards smaller Q since they move away from the intense magnetic and nuclear Bragg peaks

that produce a large elastic background. This measured dispersion is compared with bulk Dy in Fig. 2, which also shows the diffraction

pattern along the growth direction (c-axis) of the superlattice. The

bulk Dy dispersion is shown as lines originating from the magnetic

Bragg peaks at Q = 1.97 A1 and Q = 2.06 A

1

. The measured

magnons are shown as bars centered on the measured peak positions and with lengths representing the full-width-at-half-maximumintensity. The agreement with the bulk dispersion is quite good.

There is no evidence in these data of the influence of the yttrium

layers other than possibly the splitting of the dispersion into two

branches because of the superlattice structure as shown by separate

bars at both Q = 1.8 A1 and at Q = 1.75 A"1

. The observed modes

are not over-damped, but we cannot measure the damping under

the current experimental conditions. Also, these data would have

to be extended to smaller Q, in order to approach the interface

thickness. We are currently designing additional focusing configurations so that the instrumental resolution will be better optimized for measurements of this dispersion surface.

REFERENCES

[1] B. Hillebrands and G. Gtintherodt in Ultrathin Magnetic Structures I + //. edited by B. Heinrich and J. A. C. Bland (Springer \ferlag, 1994).

[2] C. F. Majkrzak et al., Adv. in Phys. 40, 99 (1991).

FIGURE 2. The dispersion along the growth direction (c-axis) measured for the [Dy^YJ^ superlattice is plotted against the energy scale on the left side.

It is compared to the measured dispersion in bulk dysprosium (solid lines) expected to originate from each of the superlattice magnetic Bragg peaks.

(Only the negative Q branches from the two low Q Bragg peaks are shown). On the right side the diffraction scan for this sample showing the superlattice peaks is displayed. This film is so large that the sample diffraction peaks are as strong as the substrate peak shown in blue on the right.

NIST CENTER FOR NEUTRON RESEARCH 7
ANTIFERROMAGNETIC SPIN

REORIENTATION IN EXCHANGE-BIASED

Fe304 /NiO SUPERLATTICES

The magnetic hysteresis loop of a ferromagnetic material can be

displaced along the field axis as a result of magnetic exchange

coupling to an antiferromagnet. This "exchange-biasing" phenomenon was discovered over 40 years ago in oxidized Co particles [1] and has been observed in a variety of thin films and multilayers.

Artificial spin-valve structures with exchange-biased layers show

great promise for applications as magnetoresistive sensors in read

heads. Recent theories [2-4] make specific predictions about the origin of exchange biasing and the response of the antiferromagnetic

layer. High-angle neutron diffraction is an ideal probe as the antiferromagnet gives rise to distinct reflections of magnetic origin.

We have performed neutron diffraction studies of exchange-biased

[001] Fe,0/NiO superlattices on the SPINS and BT-9 triple-axis

spectrometers. These measurements confirm that the NiO layers

retain their bulk antiferromagnetic structure in which ferromagnetic

{111} planes alternate direction along each <111> axis. Our data show that exchange biasing is associated with domain walls that form and "freeze" within the antiferromagnetic NiO layer. Upon

field cooling into the exchange-biased state, magnetic domains lock

within the NiO layers and do not change with subsequent application of magnetic fields. In contrast, the antiferromagnetic domain

sizes in unbiased samples prepared by cooling in zero field depend

sensitively on the strength of the applied field. We focus here on a Fe,04(6 nm)/NiO( 1 1 nm) superlattice

deposited using oxygen plasma-assisted molecular beam epitaxy. Measurements of the magnetic hysteresis loop show little evidence

of exchange biasing after cooling in zero field. Strong exchange

biasing is induced upon field cooling the superlattices from high

temperatures. For our superlattice, the biasing field at 30 K is 0.043 T after field cooling from 550 K. For the diffraction experiments the sample was oriented as shown in the inset of Fig. 1. Vertical magnetic fields, H, were

applied in the sample plane. In this configuration, the (1 1 1) and

(111) NiO antiferromagnetic reflections lie in the scattering plane.

Using a horizontal-field magnet, the (1 1 1) and (1 1 1) reflections

could be accessed by rotating the sample 90° about the growth

axis. Figure 1 shows a typical growth-axis (00/) scan through the

(111) reflection for the superlattice. Structural stacking faults [5] at

the NiO/Fe,0, interfaces limit the coherence of the Fe,0, structural

3 4 3 4 and magnetic order to a single Fe,0

4 layer. As a result, we can

easily separate the broad Fe

3 04 and narrow NiO contributions to the

reflection and track the latter as a function of field. The neutron scattering data reveal that the magnetic domain

sizes in the antiferromagnetic NiO depend on the presence or absence of exchange biasing. Figure 2 shows the full-width-at-half- maximum (FWHM) for the ( 1 1 1 ) NiO peak scanned along the (00/) and (//0) directions after cooling in a 6 T field (i.e., exchange-biased

state) and cooling in zero field (i.e., unbiased state). After field

cooling, the FWHM of the NiO reflection scanned along the (00/) growth direction shows no dependence on field.

0.68 0.72 0.76 0.80 0.84 QZ (A" 1 )

FIGURE 1 . Zero-field growth-axis (00/) scan through the (111) reflection for the Fe304(6 nm)/Ni0(11 nm) superlattice after cooling to 78 K in a 6 T field parallel

to [110]. The broad Fe3 04 peak is shown in red, and the remaining scattering

is from the NiO. The green arrow marks the FWHM of the NiO peak. The inset shows the scattering diagram.

8 RESEARCH HIGHLIGHTS
J. A. Borchers and R. W. Erwin

NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD 20899-8562

Y. Ijiri Department of Physics, Oberlin College

Oberlin, OH 44074

S.-H. Lee

NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD 20899-8562

and

University of Maryland

College Park, MD 20742

D. M. Lind and P. G. Ivanov

Department of Physics, Florida State University Tallahassee, FL 32306 Aron Qasba

Department of Physics Massachusetts Institute of Technology

Cambridge, MA 02139

The antiferromagnetic domain size along the growth direction, determined from the inverse of the FWHM, remains constant near 750 A after field cooling. This contrasts with the pronounced

field-dependence of the FWHM observed after cooling in zero field

(Fig. 2). In this state, the FWHM is smallest near zero field, but approaches the constant field-cooled value when the magnitude of

the field is greater than 2 T The corresponding domain size varies from approximately 1200 A in zero field to 800 A in high fields. Growth-plane (7/0) scans through the NiO reflection show a similar

difference between the field dependence of the FWHM after cooling

in zero field and cooling in a 6 T field (Fig. 2). Upon field cooling, domain walls both parallel and perpendicular to the growth direction lock into the antiferromagnetic layer, presumably due to the exchange coupling between the NiO antifer- romagnetic moments and the Fe,04 moments that are aligned parallel to the cooling field. After cooling in zero field, the domains are

X

5

o

<3

o

CD

0.015

0.014

0.013

0.012

0.011

0.024

0.022

0.020

0.018

Field Cooled (Exchange Biased)

(00/) Scan

(110) Scan

-60 -40 -20 0 20 40 60

Field (kG)

Zero Field Cooled

(Unbiased)

(00/) Scan

(110) Scan

•60-40 -20 0 20 40 60

Field (kG)

FIGURE 2. Fu II- width-at-half -maximum (FWHM) of the (111) NiO reflection as a

function of field at 78 K after cooling in a 6 T field and after cooling in zero

field. The top plots show the FWHM of the peak along the (00/) direction. The

bottom plots show the FWHM from (110) scans. The black, blue and red data

are from each field cycle.

larger, but reversibly decrease in size in high fields (Fig. 2) as the magnetic frustration increases. Consistent with several theoretical

predictions [2,3] we believe that exchange biasing may originate

from magnetic frustration that leads to "frozen" domain walls in the

field-cooled state. We also observe that the magnitude of the ordered NiO

moments in all four of the {111} domains in the Fe

3 04/NiO superlattices depends upon applied field. After cooling in a large vertical

field, the intensity of the antiferromagnetic (111) NiO reflection

reversibly decreases as the field is increased. (The behavior is

qualitatively similar after cooling in zero field.) Analogous fieldcooled measurements of the (111) NiO peak were performed in

a horizontal field and surprisingly show a comparable intensity

decrease. Some of the NiO moments thus seem to disappear out

of all four {111 } domains. We speculate that these NiO spins

may become disordered as a result of the high internal fields.

Simultaneously, some of the NiO moments reorient perpendicular

to the Fe,04 magnetization direction in high fields [6]. While this

"spin-flop" response is favored by some theoretical models [4], it

does not appear to be directly responsible for the exchange biasing

for these samples.

Future studies will focus on the characteristics and origin

of the "spin-flop" response of the NiO spin structure to large magnetic fields. In addition, we will further explore the differences between the antiferromagnetic domains for the exchange-biased and

unbiased conditions.

REFERENCES:

[1] W. H. Meiklejohn and C. P. Bean, Phys. Rev. 102, 1413 (1956); 105, 904

(1957).

[2] A. P. Malozemoff, J. Appl. Phys. 63, 3874 (1988).

[3] T. C. Schulthess and W. H. Butler. Phys. Rev. Lett. 81, 4516 (1998).

[4] N. C. Koon, Phys. Rev. Lett. 78, 4865 (1997).

[5] J. A. Borchers, R. W. Erwin, S. D. Berry, D. M. Lind. J. F. Ankner, E. Lochner, K. A. Shaw and D. Hilton, Phys. Rev. B 51, 8276 (1995).

[6] J. A. Borchers, Y. Ijiri, D. M. Lind, P. G. Ivanov, R. W. Erwin, S.-H. Lee

and C. F. Majkrzak, J. Appl. Phys. 85, 5883 (1999).

NIST CENTER FOR NEUTRON RESEARCH 9
SPIN DENSITY WAVE ORDER IN THE

SUPERCONDUCTING STATE OF La2Cu04+Y

n the high temperature (high-T ) superconductors, the multiple

oles played by the electrons continue to defy theoretical understanding. It appears that all high-T superconductors are based on

structures with Cu02 planes, in which the electrons on neighboring copper ions are strongly coupled magnetically. In systems based on La,Cu04

, antiferromagnetism is a dominant feature of the phase

diagram at low doping levels, and conventional itinerant-electron

behavior dominates in the high doping regime. Intermediate doping

levels are described by neither, but this is where the superconducting properties are optimal. In our experiments, we focus on the evolution of magnetic properties from the insulating antiferromagnet to

the superconductor.

It is becoming increasingly apparent that incommensurate

spin structures are universal to the high-T superconductors.

Especially noteworthy is the observation of static incommensurate

magnetic ordering coexisting with superconductivity in

La, , Ndn ,Sr CuO, and recently in La, Sr CuO, [1, 2]. Further

1.6-x 0.4 x 4 > 2-x x 4

L J experiments are needed to understand the coexistence of the incommensurate spin density waves (SDW) and superconductivity, the

details of the spin structure, and the influence of pinning potentials.

A crystal of La,Cu0

4+y with a superconducting transition

at = 42 K was produced by doping pure La2 Cu04 electrochemically with a large quantity of excess oxygen (y « 0.12). The

superconducting shielding signal measured after cooling in zero

field is shown in Fig. la. The transition is very sharp with an onset T = 42 K. Our initial characterization suggests that the crystal is

a bulk superconductor with a hole concentration similar in density

and homogeneity to that of La2 SrCu04 crystals with x 0.15. At temperatures below the superconducting T , we observe

elastic magnetic scattering at a quartet of incommensurate positions

centered around (100), which is the Bragg position for the antifer- romagnetism in the undoped insulator. Surprisingly, we find that the incommensurate wavevectors are not precisely along the Cu-O-Cu

bond direction, but are rotated by about 3°.

In Fig. 2a we show elastic scans along the in-plane h

direction through an incommensurate position for various temperatures using 5 meV neutrons. Below 42 K, the observed peaks

are extremely sharp and are resolution-limited, while above 42 K

(a) superconducting

diamagnetism H = 5G

J

h- (BCS order param.

• E, = 13.7 meV

• Ef = 5.0 meV

0

-0

\ -o

0

0

-0

0

00.-. 05 1

.10 i

15 |

20 I

.25 ^

.30

10 20 30 40

Temperature (K)

50

FIGURE 1. (a) Magnetic susceptibility measured after cooling in zero

field, (b) Peak intensity of the incommensurate elastic scattering as a

function of temperature. The measurement was performed with two different neutron energies of 13.7 meV and 5 meV. The solid line denotes the BCS

superconducting order parameter squared, with a T of 41 K.

the peaks disappear. The solid lines in the figure are Gaussians

convolved with the instrumental resolution which indicate that the

in-plane static magnetic order is correlated over distances larger

than 400 A. From this, we conclude that static long-range magnetic

order exists in the superconducting state of La,Cu04+y. Also, the SDW order is not specific to a tetragonal crystal structure as previously believed since this crystal is orthorhombic; it is a more

general phenomenon.

We then investigated how the static spin arrangement is

correlated between CuO, planes. The /-dependence of the incommensurate scattering is shown in Fig. 2b. The intensity modulation

of both the (10/)- and (01/)-centered scattering is reminiscent of the

spin structure of the undoped parent compound La,Cu04

. The solid

lines in both panels represent fits to Gaussian lineshapes convolved

with the instrumental resolution, assuming a model for the stacking

arrangement and spin direction identical to that of pure La,Cu04

.

10 RESEARCH HIGHLIGHTS
Y. S. Lee, Ft. J. Birgeneau, and M. A. Kastner

Department of Physics Massachusetts Institute of Technology

Cambridge. MA 02139

Y. Endoh, S. Wakimoto, and K. Yamada

Department of Physics Tohoku University Aramaki Aoba

Sendai 980-77, Japan

R. W. Erwin and S.-H. Lee

NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD 20899-8562

G. Shirane

Department of Physics Brookhaven National Laboratory

Upton, NY 11973

800 i i i i i i i

700 - (a)

0

min) 600 • 45K

A 30 K m (O=0

iunts/1 500

1.3 K

o

>, 400

300 ••gf»l

200

100

1.08 1.10 1.12

{h, 0.128, 0)

1.14

400

(10/)centered

- 400

200

— 0 &

(01/)centered

0 2 4

/(r.l.u.)

Here, the only free parameters are the width and a single overall

intensity scale factor. The agreement is clearly satisfactory, with the

fit indicating that the spins are correlated across » 3 CuO, planes.

We conclude that the stacking arrangement of the magnetically

ordered planes in our La,Cu0

4+y sample follows that of undoped

insulating La,Cu04

, even though the magnetic order in the CuO,

planes is incommensurate. This is the first direct evidence that the magnetism of the doped superconductor mimics the magnetism in

the undoped insulator in such a specific way. We show in Fig. lb the peak intensity of the elastic signal

as a function of temperature measured using both 13.7 meV and

5 meV neutrons. The fact that one obtains identical results for the

temperature dependences of the intensities with these two different

neutron energies and, concomitantly, energy resolutions indicates

that the scattering is truly elastic. The intensity of the elastic scattering turns on at approximately the same transition temperature as

superconductivity. Noting that the intensity of the magnetic scattering is proportional to the square of the magnetic order parameter, we plot the square of the BCS order parameter curve over the data

using a T of 41 K. The agreement indicates that the magnetism

exhibits mean field behavior just like conventional superconductivity. This is very surprising given the two dimensionality of the

ordered magnetism. The size of the ordered moment is 0.15 [x B

, which is 25 % of the ordered moment in pure La,Cu04

. Our

results argue against an itinerant electron description of the incommensurate magnetism since it is difficult to see how a delocalized model can support interplanar spin correlations and choose the same preferred spin direction as in insulating La2 Cu04

. It appears

that the spins are localized and ordered in this high temperature

superconductor.

REFERENCES

[1] J. M. Tranquada et al.. Phys. Rev. Lett. 78, 338 (1997).

[2] H. Kimura et al., Phys. Rev. B59, 6517 (1999).

FIGURE 2. (a) Scans along the in-plane H direction over one of the incom- mensurate SDW peaks for various temperatures, (b) The top panel shows the /-dependence of the SDW scattering centered about the (10/) position. The

bottom panel shows scattering centered about the (01/) position.

NIST CENTER FOR NEUTRON RESEARCH
LOCAL SPIN RESONANCE AND

SPIN-PEIERLS-LIKE PHASE

TRANSITION IN ZnCr O

I ost magnets order when the thermal energy drops below

I a microscopic energy scale for magnetic interactions. The

topology of certain lattices can, however, reduce the energy gain

associated with long range ordering thus favoring more entropic

phases. Figure 1 shows one such lattice, the tetravalent site in

the pyrochlore structure, that forms a network of corner-sharing

tetrahedra. As shown in the figure, antiferromagnetically (AFM)

interacting spins on the lattice cannot satisfy all their exchange

interactions simultaneously. This phenomenon, called geometrical

frustration, can lead to macroscopic classical ground state degeneracy and offers the possibility of qualitatively new states of matter.

Theoretical studies have in fact shown that spins with nearest neigh- bor antiferromagnetic Heisenberg interactions on the pyrochlore lattice do not have a long range ordered phase at all.

Pyrochlore magnets studied experimentally so far exhibit a coninuous phase transition at a finite temperature, Tf

, into a glassy

phase with static short range correlations [1]. Spinel antiferromagnets, AB,04

, in which the octahedral B site forms the same magnetic lattice as in the pyrochlore structure, however behave quite

differently. For instance, ZnCr,04 exhibits a first order phase transition to a long-range ordered Neel phase at T = 12.5 K , much less

than the Curie-Weiss temperature 10 I = 393 K. We have explored

this ordered phase and the corresponding phase transition through

inelastic neutron scattering [2], Figure 2 provides an overview of our neutron scattering

results as a color image of / (Q, w) at three temperatures. For T > T , Figures 2a and 2b show a constant-Q ridge centered at Q * 1.5 A

1 and extending beyond 10 meV. The ridge indicates quantum critical fluctuations of small AFM clusters, most likely

antiferromagnetically correlated tetrahedra, and closely resembles

those obtained in similar experiments on other frustrated AFM.

For T < T , however, the low energy spectral weight concentrates

into a sharp constant-energy mode centered at fid) = 4.5 meV = IJI » k

BT.. The wave vector dependence of this resonance

intensity reveals that it is an excitation among antiferromagnetically

correlated nearest neighbor spins. Though they can not be seen

in Fig. 2c, there are in fact magnetic Bragg peaks in the elastic

scattering channel (see Fig. 3b), which provide evidence for longrange order for T < T . It is unusual that excitations of such localized character exist in a long-range ordered phase. The resonance

Frustrated

FIGURE 1 . A network of corner-sharing tetrahedra. When two spins in a

tetrahedron are aligned antiparallel to each other then the third spin can not satisfy its antiferromagnetic interaction with the other two spins

simultaneously.

indicates the presence of weakly interacting spin clusters within the

ordered phase, which is a key feature of geometrically frustrated magnets.

Theoretical work indicates that magnetic order cannot devel- op in an isotropic spin system with nearest neighbor antiferromagnetic Heisenberg interactions on the pyrochlore lattice. It is natural

to ask what deviation from this model causes order to develop

in ZnCr2 04 ? To answer the question we probed the temperature

dependence of static and dynamic features of this system in the

vicinity of the phase transition. Figure 3 shows that long range

antiferromagnetic order (blue squares in frame (b)) and the local

spin resonance (frame (a)) appear simultaneously in a spectacular

first order transition. It also shows that magnetic ordering is accompanied by a cubic to tetragonal lattice distortion (red circles in frame (b)). The lattice distortion plays a crucial role in relieving

frustration and allowing long-range order to develop. It is well known that exchange interaction between Cr3+ ions whose oxygen

coordination octahedra share an edge are strongly dependent on the oxygen bond angles and hence the metal ion spacing. As a conse- quence the tetragonal strain e

a > 0 and ec < 0 yields weaker AFM

interactions between spins occupying the same basal plane and

stronger AFM interactions between all other spin pairs. This reduces

1 2
S.-H. Lee C. Broholm, NCNR and NIST Center for Neutron Research Department of Physics and Astronomy

National Institute of Standards and Technology The Johns Hopkins University Gaithersburg, MD 20899-8562 Baltimore, MD 21218

and

University of Maryland

College Park, MD 20742

T.H. Kim

Francis Bitter Magnet Laboratory Massachusetts Institute of Technology Cambridge, MA 02139

the energy of a particular long range ordered spin configuration with

respect to the low energy degenerate manifold thus allowing the system to achieve long range order. The overall picture that emerges

is that of two distinct phases in competition: a cubic cooperative

paramagnet and a tetragonal long-range ordered antiferromagnet.

Though the spin Hamiltonian has a lower expectation value in the

latter phase, the lattice energy is greater and the entropy is lower

in the tetragonal phase. The phase transition occurs when the free energy of the tetragonal low entropy phase drops below that of the

disordered cubic paramagnet.

There are strong analogies between the phase transition in ZnCr,04 and the spin-Peierls (SP) transition. In both cases the high T phase is nearly quantum critical and can lower its energy

through a lattice distortion. In both cases the transition occurs from

I (Q, hw) (1/meV/Cr)

0 0.1 0.2

12

4

-

0

12

4

-

012

S. W. Cheong

Department of Physics and Astronomy

Rutgers University Piscataway, NJ 08854

and

Bell Laboratories, Lucent Technologies Murray Hill, NJ 07974

W. Ratcliff II Department of Physics and Astronomy

Rutgers University Piscataway, NJ 08854

(Q = 1.5A- 1 ,u)) (1/meV/Cr)

0.5

3 2

1 - o

II3

(b)

(3/2,3/2,0)

(1/2,1/2,2)

' (1,2,1/2)

0 10 20 30 T(K)

FIGURE 3. (a) Image of inelastic neutron scattering for Q = 1.5 A

1

, (b)

T- dependence of magnetic Bragg scattering from a powder, <rm (blue squares), and of lattice strains measured n a single crystal (red circles).

a strongly correlated paramagnet: T « 0CW, and in both cases low

energy spectral weight is moved into a finite energy peak.

There are also important differences between the two transitions. The low T phases are qualitatively different, the transition in ZnCr,04 is a first order one, while the SP transition is second order, and the change in entropy at T plays an important role in ZnCr2 04

, but not in a SP transition. The central idea that finite lattice rigidity

can preclude a spin liquid at T = 0 however does carry over and

should be relevant for any frustrated magnet when other symmetry

breaking interactions are sufficiently weak.

REFERENCES

[1] J. S. Gardner, B. Gaulin, S.-H. Lee, C. Broholm, N. P. Raju, J. E. Greedan,

Phys. Rev. Lett. 83, 211 (1999).

[2] S.-H. Lee, C. Broholm, T. H. Kim, W. Ratcliff II and S. W. Cheong, Phys. Rev. Lett., in press.

FIGURE 2. Contour maps of the magnetic neutron scattering intensity at temperatures spanning the phase transition at T= 12.5(5) K. The data were

taken by utilizing a flat analyzer and two-dimensional position-sensitive detector at the SPINS spectrometer.

NIST CENTER FOR NEUTRON RESEARCH 13
COMPOUND REFRACTIVE OPTICS IMPROVE

RESOLUTION OF 30 m SANS INSTRUMENT

n the most favorable cases, cold neutrons can be deflected I through an angle of a degree or two by grazing incidence reflection, but by only an arc second or two by refraction. Hence grazing

incidence reflection optics has long been considered the most promising means for focusing neutrons for applications such as smallangle neutron scattering (SANS). Numerous attempts over more

than 30 years to produce highly reflective surfaces for neutrons have been vitiated, however, by SANS from the mirror surfaces

themselves, which blurs the focus. The best mirrors produced thus

far are only marginally better for SANS than pinhole collimation,

i.e., circular apertures separated by long distances.

Scientists at Bell Laboratories recently took a fresh look at

this problem and proposed that multiple refraction from relatively

high index, low absorbing material could be superior to reflection

optics or conventional pinhole collimation for SANS. Initial measurements [1] at Ris0 National Laboratory, Denmark, demonstrated

the proposed focusing effect, but did not make quantitative comparisons with reflection optics or pinhole collimation for application

in SANS instruments. Measurements made recently at the NCNR

in collaboration with the Bell Labs scientists [2] have addressed

these issues and have demonstrated and quantified the significant

FIGURE 1 . Now installed in the pre-sample flight path of the NG-7 30 m

SANS instrument are two sets of MgF2 biconcave lenses that can be inserted

into the beam under computer control. The 28-lens array in the foreground focuses 8.44 A neutrons at a distance of 15 m from the lenses, and the

6-lens set focuses 18 A neutrons at the same distance. Each lens is 25 mm

in diameter, has a radius of curvature of 25 mm, and is 1 mm thick in the

center.

14

Source Sample

aperture aperture Detector

FIGURE 2. Upper panel, conventional SANS pinhole collimation. The source and sample apertures, A

1p and A2p , respectively, determine the shape and extent

of the beam profile, l(x), at the detector plane. Lower panel, focusing lens geometry. Ideally, the source aperture, Au

, alone determines the beam profile.

improvement in resolution that can be achieved with compound

refractive optics.

Our tests were made with the same set of cylindrical biconcave MgF, (magnesium fluoride) lenses used in the Ris0 study. Up

to 30 lenses were placed end-to-end near the sample position of the 30 m SANS instrument to focus neutrons, emanating from a circular

source aperture 15 m upstream, onto the plane of instrument's twodimensional detector. Figure 1 shows an array of 28 lenses for

focusing 8.44 A neutrons at a distance of 15 m from the sample,

next to a set of 6 lenses for focusing 18 A neutrons at the same

distance. For this geometry, as depicted in Fig. 2, the lenses ideally

produce a 1:1 image of the source aperture at the detector inde- pendent of the size of the sample. Since the scattering signal is

proportional to sample size, the lens system can, in principle, be

used to improve resolution more efficiently, by reducing the size of

the source aperture, than is possible with pinhole collimation where

both the source aperture and sample size must be reduced proportionally to improve angular resolution. Aberrations and small-angle

scattering by the lenses could, however, blur the image to such RESEARCH HIGHLIGHTS
S.-M. Choi, J. G. Barker and C. J. Glinka Y. T. Cheng p. |_. Gammel

NIST Center for Neutron Research NeuTek Bell Laboratories, Lucent Technologies

National Institute of Standards and Technology Darnestown, MD 20878 Murray Hill NJ 07974

Gaithersburg. MD 20899-8562

-30 -20 -10 0 Y(mm)

10

FIGURE 3. Red dots are measured points along the vertical profile of the image

formed by the 28 lens array shown in Fig. 1 of a 9.5 mm diameter source of neutrons 15 m upstream from the lenses. The blue dots are a Monte Carlo

calculation of the profile that includes the effects of spherical and chromatic

aberrations as well as the broadening caused by gravity. The shoulder in the measured profile at Y = 0 is due to a residual fast neutron component in the beam.

a degree that any advantage over pinhole collimation, which does produce a sharply defined beam spot at the detector, would

be lost.To accurately measure the intensity profile produced by the

lenses, a dysprosium foil was positioned at the focal plane and

exposed to the focused beam for approximately 2 h. The activated

foil was then placed in contact with a high resolution image plate

which stored the image produced by the emitted gamma rays with a

spatial resolution of better than 0. 1 mm. A typical profile obtained from reading out the image plate is shown in Fig. 3. Also plotted in

the figure is a Monte Carlo calculation of the profile that includes

the effects of spherical and chromatic aberrations as well as the broadening caused by gravity. The measured profile agrees with the

simulation down to intensity levels of 10'3 of the peak intensity and

has an overall signal-to-background ratio in the wings approaching

105

, which is highly satisfactory for most SANS measurements. The practical benefit provided by the lenses is demonstrated

by the SANS data from voids in a single crystal (2.5 cm in diameter and 1 cm thick) of fast-neutron-irradiated aluminum shown in

0.0001 0.001 Q (A

1

)

0.01

FIGURE 4. Small-angle scattering from voids in a single crystal (2.5 cm in diameter and 1 cm thick) of fast-neutron-irradiated aluminum. The measure- ments were made under equivalent resolution conditions (i.e. nearly identical beam spot size at the detector) using both simple pinhole collimation and the 28 biconcave lens array shown in Fig. 1. The integrated gain in intensity due

to the lenses is approximately 26.

Fig. 4. The measurements were made under equivalent resolution

conditions (i.e., nearly identical beam spot size at the detector)

using both simple pinhole collimation and the 28 biconcave lens

array shown in Fig. 1. The first data point unaffected by the beam

stop in both data sets occurs at Q «= 0.001 A"1

, but the scattered

intensity at the detector (counts/cm2/s) is more than 10 times higher

by using the lenses to illuminate a much larger area of the sample.

The focusing lenses shown in Fig. 1 are now installed for

routine use in the NCNR's 30 m SANS instrument on guide NG-7.

Further testing is planned to understand, and hopefully eliminate,

the sources of parasitic scattering that contribute to the tails of the beam profile seen in Fig. 3, prior to installing a lens system in the NIST/NSF 30 m SANS instrument on guide NG-3.

REFERENCES

[1] M. R. Eskildsen, P. L. Gammel, E. D. Isaacs, C. Detlefs, K. Mortensen. D.

J. Bishop, Nature 391, 563-566 (1998).

[2] S. -M. Choi, J. G. Baker, C. J. Glinka, P. L. Gammel, Proceedings of the Xlth International Conference on Small-Angle Scattering, 1999, J. Appl.

Cryst. (in press)

NIST CENTER FOR NEUTRON RESEARCH 15
POLYMER BRUSH

RESPONSE TO SOLVENT FLOW

The presence of polymer chains grafted or adsorbed onto a

surface can dramatically alter the forces that affect interactions between surfaces. The equilibrium properties of such polymer brush systems have been studied for the past two decades, yielding general agreement between theory and experiment. Conversely, the nonequilibrium properties of polymer brushes are still under intense

theoretical and experimental investigation. Of particular interest

is the response of a brush to the frictional forces imposed by

solvent flow. The behavior of polymer brushes subjected to flow

has important technological implications for the rheology of colloidal dispersions stabilized by polymer layers, for the lubrication

properties of polymer coated interfaces, for biocompatibility of medical implant devices, and for permeation flow through polymercontaining porous media [1]. The height of a polymer brush is determined by the equilibrium conformation of the tethered chains, which depends on

both the grafting density and quality of solvent. The basic physics

governing the static behavior of a polymer brush result from a

competition between two opposing tendencies: 1) elastic contraction, as the chains attempts to maximize their entropy by adopting

random walk configurations, and 2) monomer-monomer interactions, such as polymer-polymer repulsions, and polymer-solvent

wetting [2, 3]. Polymer chain stretching in densely grafted brushes has been

studied by many different techniques including surface forces apparatus [4], neutron reflectivity [5], and small angle neutron scattering

(SANS) [6]. In general, there is good agreement with results from

experiment, simulations and analytical calculations [3].

Oscillatory shear measurements performed with a surface

forces apparatus suggest that the normal forces between a pair of brush surfaces are altered when sheared. However, these measure- ments do not give the actual brush profile either with or without

shear. Effective hydrodynamic thickness measurements of polymer

brushes under shear indicate a thickening of the brush; whereas neutron reflectivity experiments on adsorbed PS-PEO block copolymer

brushes on a silica surface show no effect of shear on the brush

density profile in good solvent, and a slight increase in poor solvent. These earlier reflectivity measurements were limited to shear rates

of 10,000 s"

1 [7] since the adsorbed PS-PEO block copolymer

FIGURE 1. Schematic illustrating the effect of shear on grafted brushes

predicted by Miao et al. [8] Such an effect would be consistent with the

present data. 1

pump and head it"Si crystal

solvent reservoir SS shear base

FIGURE 2. Shear cell. Arrows denote solvent flow direction. The polystyrene brush is grafted onto the Si crystal.

brushes have a tendency to come off the surface at higher shear

rates.

Predictions from theoretical calculations of brush profiles

under shear span the gamut of possibilities, ranging from brush

thickening to brush compression, including no effect of shear flow on the density profile [3]. Miao et al. [8] predict that the response of

a brush to the solvent shear flow is displayed as chain tilting toward

and chain stretching along the direction of flow. However, the

overall conformational properties such as brush thickness remain

essentially unaffected (Fig. 1 ). We have performed neutron reflectivity measurements on a

chemically grafted polymer in both good and poor solvents at shear

rates over an order of magnitude greater than previously reported.

Our neutron reflectivity experiments measure the segment density

profile of the polymer brushes under shear in an experimental

cell similar to the one used by Baker et al. [9], (Fig. 2). We

use deuterated polystyrene (d-PS), 83 kg/mol, with a trichlorosilane end group to bind the d-PS brush chemically onto a single

crystal Si surface [5]. We used a good solvent, toluene, and a poor

1 © RESEARCH HIGHLIGHTS
Robert Ivkov, Paul Butler, and Sushil K. Satija L.J. Fetters NIST Center for Neutron Research Exxon

National Institute of Standards and Technology Annandale, NJ 08801

Gaithersburg, MD 20899-8562

-6 I i 0.01 0.02 0.03 0.04 0.05 0.06 Q (A"

1

)

FIGURE 3. Representative shear data for deuterated polystyrene brush under shear in cyclohexane (a), and toluene (b). In both cases, black

circles represent shear of 0 s\ whereas red squares represent data taken

at 30,000 s

1

.

solvent, cyclohexane, as the solvent media. The dry brush height was measured by X-ray reflectivity to be 17.5 nm. Without shear

the brush extends to 31 nm in cyclohexane and 75 nm in toluene. We measured the brush profile at several shear rates, up to 130,000

s

1

, yet we see no effect of shear on the brush density profiles in

either solvent (Fig. 3). No desorption of the polymer brush was

ever observed. In fact, the neutron reflectivity profiles at 0 s

1 and

130,000 s"

1 look identical, indicating less than a 2 % to 3 % change

in the brush density profile. We have also been able to establish that the slight shear induced swelling reported by Baker et al. [7] for a poor solvent

(cyclohexane), was probably due to frictional heating of the solvent.

In high shear fields, heat generated from friction between the

solvent and interior surfaces of the apparatus does not readily

dissipate, causing a = 2 °C to 3 °C rise in the temperature of

the shear cell. We were able to demonstrate that the brush height

in cyclohexane is unaffected by shear when the cell temperature

is carefully controlled. An elevated cyclohexane temperature swells

the brush as the solvent quality improves. Naturally, these effects were not observed in toluene. Thus, our neutron reflectivity data represent the first comprehensive measurements of shear effects on the density profile of a

grafted polymer brush into regimes that are predicted by some to

0.01 0.02 0.03 0.04 0.05 Q(A"1

)

display an effect. We cannot at this time determine if the brush

responds as predicted by Miao et al. [8], or if there is insufficient

solvent penetration into the brush to exert enough force on the

chains to induce conformational changes. Future measurements will

distinguish between these cases.

REFERENCES

[1] J. L. Harden and M. E. Cates, J. Phys. II France 5, 1093 (1995).

[2] P.-G. de Gennes, Macromolecules 13, 1069 (1980).

[3] S. Grest, Adv. Polym. Sci., in press.

[4] G. Hadziannou, S. Patel, S. Granick, and M. Tirrell, J. Am. Chem. Soc.

108, 2869 (1986).

[5] A. Karim, S. K. Satija, J. F. Douglas, J. F. Ankner, and L. J. Fetters, Phys. Rev. Lett. 73, 3407 (1994).

[6] P. Auroy, Y. Mir, and L. Auvray, Phys. Rev. Lett. 69, 93 (1992).

[7] S. M. Baker, A. Callahan, G. Smith, C. Toprakcioglu, and A. Vradis, Physica B 241-243, 1041 (1997).

[8] M. L. Miao, H. Guo, M. J. Zuckermann, Macromolecules 29, 2289 (1996).

[9] S. M. Baker, G. S. Smith, R. Pynn, P. Butler, J. Hayter, W Hamilton, and L. Magid, Rev. Sci. Instrum. 65, 412 (1994).

NIST CENTER FOR NEUTRON RESEARCH 17
MACROMOLECULAR CONFORMATION

IN ULTRATHIN POLYMER FILMS

Since thin polymeric films are ubiquitous in technological applications such as paints, lubricants, and adhesives, a critical

characterization of their thermophysical properties is essential. A

central premise in the development of theories for predicting the

properties of polymer melts in confined geometries is that chains

maintain their unperturbed Gaussian conformation, which they

adopt in the bulk, in the direction parallel to the surfaces under all

conditions [1,2]. These assumptions, which form the foundations of

the important field of polymer thin films, have been questioned on

the basis of indirect experimental findings [3,4]. We have utilized

the power of small angle neutron scattering, especially the high

neutron flux at NCNR, to unequivocally characterize the chain

structure and conformation in ultrathin polymer films, and thus have

resolved this important fundamental question.

The experimental measurements of chain conformations and

system thermodynamics in thin films have remained elusive due

to the small amounts of sample material involved. To illustrate

this point, a thin film of 10 nm incurs a decrease in signal by

lxl04 from a typical bulk polymer sample. In this case, the noise

is comparable to the signal, complicating the experiments. Prior to upgrades of the cold neutron source at the NCNR, data collection

times were prohibitive. Improvements in sample preparation, which

are discussed in detail elsewhere [5,6], have allowed us to measure

molecular size and conformation of an isotopically labeled blend

of polystyrene (25 wt% d-PS/75 wt% h-PS) in films as thin as

12 nm. Two blends of nominally matched molecular weight, Mn,

of 270,000 and 650,000, respectively, were utilized. These were

labeled 270k and 650k, respectively. Solutions of the blends were

spin cast on silicon substrates (Semiconductor Processing) and

annealed at 120 °C (T « 105 °C).

The scattered intensity for a 15 nm thick film of the 270k

blend is compared to an analogous bulk sample in Fig. 1. It is clear from the figure that, on a unit volume basis, the thin film scattering

is higher than that of the bulk. We postulated that this difference is

attributable to the scattering from the imperfections at both the air and the substrate interfaces, which is driven by the relatively high

neutron contrast at these boundaries. To evaluate this component,

films of pure d-PS were spin cast under identical conditions and

their scattering measured. The pure d-PS film data were fit with a simple Debye-Bueche

form factor to obtain parameters for a roughness term. The blend

film data were then fit by scaling this roughness term and adding a component obtained from the Random Phase Approximation (RPA)

model. In the fitting, two RPA model parameters were also varied:

the blend chain radius of gyration (R

g

) and the Flory interaction

parameter. The combined model is illustrated as the solid line in

Fig. 1 along with the roughness term (long dashed line) and RPA

term (short dashed line). The fact that the RPA term is very close

to the data for the bulk blend illustrates that the film and bulk

400.0 |

, , ,

1

300.0 -

0.0 1 ' =

' 1 1 0.000 0.010 0.020 0.030 0.040 Q(A-1 )

FIGURE 1 . Plots of l(Q) as a function of 0 for dPS/hPS blends of Mn =

270k. Filled symbols, bulk sample; open symbols, data for a film of thickness D = 18 nm. The fit to these data (solid line) was obtained by utilizing both

a roughness term (long dashed line) as well as the standard RPA form (short dashed line).

18 RESEARCH HIGHLIGHTS
R.L.Jones, S.K.Kumar D.L.Ho, R.M. Briber T.P. Russell

Department of Materials Science and Engineering Department of Materials and Nuclear Engineering Polymer Science Department

Pennsylvania State University University of Maryland University of Massachusetts

University Park, PA 16802 College Park, MD 20742 Amherst, MA 01003

samples have nearly the same Rc

. Using this combined model, R

g was determined for films ranging in thickness over two decades

(0.5 Ro < D < 50 RJ. The molecular size was found to be independent of film thickness (Fig. 2). Since the scattering vector is primarily in the surface plane, this conclusion is consistent with theoretical assumptions and suggests that chain conformation in the direction

parallel to the surfaces are unaffected by confinement.

2.00

1.00

0.00

2.00

§ 1.00

0.00

G.Bulk

FIGURE 2. Plots of ratios of R and 1(0), derived from the RPA component

(short dashed line in Fig. 1) of the fits to the blend thin film data, to their corresponding bulk values. The ratios are plotted versus the ratio of the film thickness to the bulk R

g

. Data are displayed for blends with Mn = 270k (filled

circles) and Mn = 650k (open circles).

Our results clearly show that, in the thinnest films, the volume pervaded by a coil is decreased as compared to the bulk.

This is because the R

g in the direction parallel to the surfaces is

unaffected, while the corresponding quantity in the third direction is

strongly reduced. In conjunction with other studies, which indicate

a thickness-independent density in ultrathin polymer films, these

conclusions indicate decreased intermolecular entanglement in thin polymer films. Since entanglement density directly affects the dynamic properties of polymeric systems, we contend that unusual

thin film properties, such as the anomalous thickness dependence of

diffusion coefficients and glass transition temperatures, are caused

by this reduced entanglement density near a surface. With thin films as a model system, and continuing increases in cold neutron flux, SANS at the NCNR is now an appropriate

tool to study a host of problems involving interfacial structure,

finite size phase behavior, and nano-patterning in systems as far

ranging as engineering thermoplastics to biological systems. These,

and related problems, are the focus of investigation in our research

groups.

REFERENCES

[1] D. N. Theodorou, Macromolecules 21, 1400 (1988).

[2] S. K. Kumar, M. Vacatello, D. Y. Yoon, J. Chem. Phys. 89, 5206 (1988).

[3] P. M. Calvert, Nature 384, 311(1996).

[4] C. W. Frank et al., Science 273, 912 (1996).

[5] D. L. Ho et al., Macromolecules 31, 9247 (1998).

[6] R. L. Jones et al., Nature 400, 146 (1999).

NIST CENTER FOR NEUTRON RESEARCH 19
PROBING THE LOCATION OF THE

TERMINAL GROUPS OF A DENDRIMER

Dendrimers represent a new class of macromolecules developed

in recent years. Typically, a dendrimer structure has a tri- or

tetrafunctional core, which is surrounded by several "generations"

of stepwise added trifunctional monomers, leaving the last generation with a large number of terminal units as shown in Fig. 1

.

The molecular weight doubles with each generation, leading to

high molecular weights, and causing the dendrimer to become very compact and crowded.

Many of the potential technological applications of dendrimers depend on their segment density distribution. Previous scattering studies have shown that dendrimers have uniform interiors and are quite spherelike in their shape [1]. The location of the

terminal groups is also of importance, since they are usually different chemically from the rest of the dendrimer. This invites a number

of applications such as the support of catalysts or drugs or their

use as hyperfunctional crosslink sites. The accessibility of these

terminal groups depends on their location compared to the other dendrimer units.

FIGURE 1 . Dendrimer structure with labeled terminal units.

The location of the terminal units can be determined by labeling the last generation of the dendrimer with deuterium and using

contrast matching techniques. Figure 1 shows the labeled groups in

red and the rest of the dendrimer in blue. By choosing the proper mix of h- and d- solvents, the interior of the dendrimer will be

matched, making only the labeled end groups visible in small angle

neutron scattering (SANS).

A sixth generation polyamidoamine (PAMAM) dendrimer was reacted with acrylonitrile (vinyl-d3) to give the deuterium

labeling for the SANS. Ethylene diamine was reacted with the dendrimer to give a labeled seventh generation dendrimer. A similar

reaction was used to make a seventh and eighth generation den- drimer without labeling. Solutions of unlabeled eighth generation

dendrimer were made in mixtures of CH? OH and CD^OH for determination of the match point. Three samples were analyzed, an

unlabeled dendrimer in CD,OH (high contrast), an unlabeled den- drimer in the match mixture (dendrimer matched), and the labeled dendrimer in the match mixture (interior matched).

0 0.05 0.1 0.15 0.2 Q(A"1

)

FIGURE 2. SANS from G8 dendrimer in CD,0H/CH30H mixtures.

20 RESEARCH HIGHLIGHTS
Andreas Topp, Barry J. Bauer, and

Eric. J. Amis

Polymers Division

National Institute of Standards and Technology

Gaithersburg, MD 20899-8542

June W. Klimash, Ralph Spindler, and

Donald A. Tomalia

Michigan Molecular Institute 1910 West Saint Andrews Road

Midland, Ml 48640

SANS was performed at the 30 m facilities at NIST. The

spectrometers were operated at a wavelength of X - 6 A, and a wavelength spread of AA./A. = 0.15.

Figure 2 is a plot of SANS of dendrimer solutions with different CD,OH contents. The intensity is the strongest in pure CD,OH,

weakens as CH,OH is added and increases again when pure CH,OH

is used. The coherent scattering intensity varies as I « (b

s

- bD)

2

where b

D

is the contrast of the dendrimer and b

s is the average

contrast of the solvent mixture.

Figure 3 is a plot of the square root of the scattered intensity

versus solvent composition with the values to the right made negative so that a straight line can be put through all of the data points.

The zero intersection is at a mass fraction of 60.5 CH,OH which was the composition used in the matching experiments.

Figure 4 is a plot of the SANS of the three G7 samples.

The circles give the scattering from the high contrast sample, showing strong scattering typical of large spherical dendrimers. The

diamonds show the SANS of the same dendrimer, but under match

conditions. This sample has no measurable coherent scattering signal, demonstrating that the match conditions have been achieved. The labeled dendrimer SANS is given by the squares. The scattering

is weak because only the labeled terminal groups scatter. A Guinier analysis of the scattering of the high contrast sample gives the radius of gyration (R

g

) of the whole dendrimer, and

the labeled - contrast match sample gives the Ro of only the terminal

groups. The Ro of the whole dendrimer is (34.2 ± 0.2) A, while the R

g of the terminal groups is (39.3 ± 1.0) A. The terminal groups of a seventh generation PAMAM dendrimer are 15 % larger than the average of all of the units.

Therefore, the terminal units of a dendrimer are concentrated in the

outer shell of a dendrimer.

REFERENCES

[1] T. J. Prosa, B. J. Bauer, E. J. Amis, D. A. Tomalia, R. Scherrenberg, J. Polym. Sci.: Polym. Phys. 35, 2213, (1997).

0.35

"

0.30 -

0.25 -

E

0.20 - oa 0.15 -

0.10 -

0.05 -

0 -

-0.05 0.02

o G7 [H] in CD3 OH

G7 [D] in contrast match solvent o contrast match solvent

0.04 0.06 0.08 Q(A"1

)

0.10 0.12

FIGURE 3. Location of the match point. FIGURE 4. SANS of labeled and unlabeled G7 dendrimer in match and

high contrast solvents.

NIST CENTER FOR NEUTRON RESEARCH 21
SELF-ASSEMBLIES OF

MEMBRANE ACTIVE PEPTIDES

I n recent years we have made progress by neutron diffraction

in a major structural challenge, namely in detecting and analyzing the structures of peptide assemblies in fluid membranes [1,2]. These experiments were performed with membranes in the form

of oriented multilayers. Originally the samples were investigated in

full hydration so that the physical properties of the lipid bilayers were close to those at physiological conditions. However, it was

soon realized that new phenomena involving peptide-lipid interactions occur when the sample hydration is varied. In general,

in full hydration, the peptide organization in each membrane

is uncorrected to the neighboring membranes. As the hydration

level decreases, the peptides become correlated between bilayers, even though the membranes are still fluid. In many cases, further

dehydration strengthens the correlation such that the peptide organization in the multilayers crystallizes [2]. The crystallization

provides the possibility for high-resolution diffractional studies.

Investigations along this line might also lead to useful information

for crystallization of membrane proteins.

Antimicrobial peptides are inducible innate host defense molecules found in all multicellular organisms, including humans and

plants. These peptides have a folded size comparable to the membrane thickness. All evidence indicates that antimicrobial peptides

act by permeabilizing the cell membranes of microorganisms. But

the molecular mechanisms of their actions are still not clear. We

have found that all peptides, when they are bound to lipid bilayers,

exhibit two distinct oriented circular dichroism spectra, one at low

peptide-to-lipid ratios (P/L) and another at high P/L. This indicates

that each peptide has two different physical states of binding to a membrane.

The transition from the low to the high P/L spectrum occurs

over a narrow range of P/L as if there is a threshold concentration,

called P/L*. At concentrations below P/L*, the peptides are embedded in the headgroup region, as suggested by the peptide orientation and the membrane thinning effect. At concentrations above P/L*,

neutron in-plane scattering showed that the peptides form pores

in the membranes, while no pores were detected below P/L*. The

detection was achieved by exploiting the sensitivity of neutrons

to D,0, which had replaced the water in the membrane pores. As an example, Fig. 1 shows neutron in-plane scattering taken at

1

0.8

0.6

N 0.4 § 0.2

0

-0.2

± *

+ *

+ _

+

o

+

" ° ° +

% +

+ 4

0 0.1 0.2 0.3 Q(A-1)0.4 0.5

1.5 -

~ 1 E

0.5 -

(b)

0.2 0.3 Q(A"1)

FIGURE 1. In-piane SANS from alamethicin in DLPC lipid bilayers at a high

peptide-to-lipid ratio where the peptides self-assemble to form channels

through the lipid bilayer as depicted in Fig. 2. In the upper panel, the channels were filled with either D2 0 (+), giving strong scattering contrast, or H2 0 (o). In the lower panel the lipid was deuterated, providing stronger scattering contrast with H20 in the channels (+) compared with D20 (o). These data were taken atANL.

Argonne National Laboratory (ANL) of alamethicin in protonated

lipid bilayers (Fig. la) and in deuterated lipid bilayers (Fig. lb),

with D,0 or H,0 filling the pore channels. The peak in these data

is due to the fairly regular pore spacing and is most pronounced

when there is a strong contrast, either between D20 and protonated

lipid, or between H,0 and deuterated lipid. All four sets of data are

consistent with the model shown in Fig. 2 once the differences in

contrast are taken into account (solid curves). Thus we concluded

1-2 RESEARCH HIGHLIGHTS
Huey W. Huang

Rice University Department of Physics Houston, TX 77005-1892

FIGURE 2. Model for the channels formed by octamers of alamethicin in DLPC

bi layers that is consistent with the in-plane SANS data shown in Fig. 1.

C

") '5

a *

I » ( ) > i

FIGURE 3. Examples of SANS patterns from channel-forming peptides in lipid bilayers at various temperatures and stages of dehydration. The upper left panel is for magainin pores in fully hydrated fluid bilayers. As this and other

peptide/lipid systems studied are dehydrated, the pores in adjacent bilayers become correlated and eventually crystallize.

that alamethicin in DLPC bilayers forms octameric pores in the

barrel-stave fashion.

Interestingly, the barrel-stave model is not the only possible pore formation. We have detected another type, called toroidal

pores, in which the lipid monolayer bends continuously from one

leaflet to another like the inside of a torus [1]. However, while

the evidence for the pores is clear by the detection of the water (D,0) channels through the lipid bilayers, the evidence for the pore

structures is indirect. Thus the discovery of the crystalline phases

is an important new development for the field of antimicrobial

peptides.

We developed a method of off-plane scattering [2] to record

the diffraction pattern on a SANS instrument that includes both the

in-plane and out-of-plane momentum components. Figure 3 exhibits some typical diffraction patterns as recorded on the NG-3 30 m

SANS instrument's detector by this method. The top left panel

shows the diffraction pattern of magainin pores in fully hydrated

fluid bilayers. When the sample was slightly dehydrated, the pattern changed to the top middle panel. Our analysis [2] showed that the

positions of the magainin pores in each bilayer become correlated with the pores in adjacent bilayers, even though the bilayers are still

in the fluid phase. The cause of this correlation was hypothesized to

be due to the hydration force. Upon further dehydration or cooling,

the pore arrangement crystallized into a lattice (the left panel of

the middle row) having ABCABC stacking of hexagonally ordered

planes.

The other crstalline patterns shown in Fig. 3 were from

magainin and other peptides in various lipids at different hydration

levels and temperatures. These crystalline phases offer a new way

of studying peptide-lipid interactions that will help us to understand

the molecular mechanisms of membrane active peptides in cell

biology.

REFERENCES

[1] K. He, S. J. Ludtke, D. L. Worcester, and H. W. Huang. Biochemistry

34, 16764 (1995); Biophys. J. 70, 2659 (1996); S. J. Ludtke, K. He, W.

T. Heller, T. A. Harroun, L. Yang, and H. W. Huang. Biochemistry 35, 13723 (1996).

[2] L. Yang, T. M. Weiss, T. A. Harroun, W. T. Heller, and H. W Huang.

Biophys. J. 75, 641 (1998); 77, 2648 (1999).

NIST CENTER FOR NEUTRON RESEARCH 23
SHEAR ORIENTATION OF

VISCOELASTIC POLYMER-CLAY SOLUTIONS

Shear-induced structural changes in complex fluids of anisotropic species are very general phenomena, occurring in polymer

solutions, liquid crystalline materials and block copolymer melts. The purpose of our work is to investigate the influence of shear on the structure of a highly viscoelastic, aqueous clay-polymer solution. Many structural models have been proposed for such solutions

[1-3], but little is definitively known about mesoscopic properties or

shear behavior. This information is important in the production of nanocomposite materials [4].

In our work, we use small-angle neutron scattering (SANS) to

study a solution of the synthetic hectorite type clay, Laponite LRD

(Laporte Industries Ltd.), and poly(efhylene-oxide) (PEO) (Mw = 106

g/mol). The results reported here are for a highly viscoelastic solution containing a mass fraction of 3 % LRD and 2 % PEO at room

temperature. The clay particles produce transparent dispersions of

disk shaped particles ca. 300 A in diameter and ca. 10 A thick [5,6]. The pH and ionic strength of the solutions were controlled by the

addition of NaOH and NaCl, respectively.

Figure 1 shows the shear rate dependence of the birefringence

of the clay-polymer solution. A distinct minimum in the birefrin- gence is observed at a critical shear rate of approximately 40 s

1

. The source of the shear dependence of the birefringence is due to

the alignment of the clay particles and the PEO. Previous work

demonstrated that the sign of the birefringence of the clay particles

oriented along a flow field is negative, therefore at low shear rates,

the orientation of the clay dominates the birefringence. Above the

critical shear rate, the birefringence due to the orientation of the polymer chains dominates.

A double logarithmic plot of viscosity, v\, versus shear rate shows that the solution is shear-thinning over the entire range

according to a power law with exponent m = -0.65. No signature of

the critical shear rate is observed in the viscosity behavior. The SANS shear cell utilized has been described previously [2]. It consists of a cylinder that rotates within an outer

cylinder with the sample in the gap between them. The instrument was configured in both "radial" (incident beam parallel to the

shear gradient along the cylinder diameter) and "tangential" (inciT

dent beam passing between the cylinders, parallel to the flow direction) geometries. Using 9 A wavelength neutrons gives a Q range between 0.0027 A" 1 and 0.0199 A

1 . The primary contrast in the

-100

-50 0 50 100 150 200 250 300 350 400 450

dydt (s"

1

)

FIGURE 1 . Optical birefringence as a function of shear rate. The arrow

indicates the shear rate where the minimum in the birefringence occurs.

SANS experiment used to detect the orientation of the clay platelets and polymer chains under shear is between D2 0 and the other

solution components.

The results obtained from the polymer-clay solutions in the

"radial" and "tangential" beam configurations are summarized in

Fig. 2. At low shear rates, a diffuse isotropic ring of SANS intensity

is observed (Fig. 2a). The diffuse ring corresponds to an average

spacing between platelets of 800 A to 1100 A. With increasing shear

rate, the ring becomes more diffuse (Fig. 2b) and an anisotropic

streak develops parallel to the vorticity axis of the flow field (the

cylinder axis). If we neglect the main reflected beam which appears

as a background streak in the gradient direction for tangential beam

measurements (Fig. 2d), the anisotropic streak becomes the dominant feature in both scattering geometries with increasing shear rate

After cessation of shear, the streaks relaxed to an isotropic state in

| less than 2 min. To account for the SANS and birefringence results, our cur

rent understanding is that the polymer chains are in a dynamic

adsorption/desorption equilibrium with the clay particles to form

a network. The peak position in the quiescent scattering pattern

in Fig. 2a is an indication of the mesh size of this network

(<=» 1000 A). A 2 % solution of only PEO, at the same pH, polymer

and salt concentration showed no anisotropic SANS scattering at

.24 Hi SE IS E GHLIGHTS
Gudrun Schmidt, Alan I. Nakatani, Alamgir Karim, Paul D. Butler and Charles C. Han NIST Center for Neutron Research Polymers Division National Institute of Standards and Technology

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

Gaithersburg. MD 20899-8544

shear rates up to 100 s

1

. Similarly a 3 % aqueous clay solution shows no evidence of an anisotropic SANS pattern. Therefore, we

can conclude that the anisotropic SANS pattern observed in the clay-polymer solutions is due to this coupling between clay platelets and polymer, allowing a higher orientation than either single component in solution can produce. From the birefringence data, the

clay particles orient at low shear rates, while strong orientation of

the PEO does not occur until the critical shear rate is exceeded.

Since the clay platelets and the PEO chains are of comparable size

(both about 300 A), the lack of internal flexibility of the rigid clay

particles makes them much easier to align than the flexible polymer

chains.According to SANS patterns from both beam configurations

(Fig. 2) the shear flow results in an alignment of clay platelets

orienting with their surface normals in the vorticity direction. One

would expect the surface normals to orient along the gradient direca) radial beam b) radial beam

Low High

FIGURE 2. SANS patterns of the clay-polymer solutions as a function of shear

rate in the radial geometry (a-c) and tangential geometry (d) at shear rates of

a) 0.5 s"

1

, b) 20 s

1

, c) 90 s

1

, d) 90 s

1

.

tion of the flow field, however, the type of orientation observed

in these clay-polymer solutions is also observed in some liquid

crystalline lamellar phases, block copolymer solutions, and melts. The critical shear rate is the shear rate at which the rate of chain

desorption is slower than the terminal relaxation time of the chain,

hence chain extension is observed in the birefringence.

On cessation of shear, the stress on the network decays

almost immediately, and the recovery of the isotropic structure is

controlled by the relaxation of the stretched chains. As the chains

retract, the coupling of the chains to the clay allows the platelets

to randomize in orientation in the local viscous environment. The

recovery from anisotropy is much faster than expected from simple

Brownian motion of only the clay particles in a medium of the same viscosity as the clay-polymer solution exhibited macroscopically, and is indicative of the dynamic coupling of the polymer

chains to the clay. Future work will compare the relative rates of

the relaxation in the PEO and clay with the cooperative adsorption/

desorption kinetics which occur during deformation.

REFERENCES

[1] A. Mourchild, A. Delville, J. Lambard, E. Lecolier, R Levitz, Langmuir

11, 1942(1995).

[2] H. J. M. Hanley, G. C. Straty, Langmuir 10, 3362 (1994).

[3] F. Pignon, A. Magnin, J. M. Piau, J. Rheol. 42, 1349 (1998).

[4] S. Rossi, P. F. Luckham, S. Zhu, Rev. I Fr. Petrol 52, 199 (1997).

[5] J. D. F. Ramsay, S. W. Swanton, J. Bunce, J. Soc. Faraday Trans. 86, 3919 (1990).

[6] F. Pignon, A. Magnin, J. M. Piau, B. Cabane, P. Lindner, O. Diat, Phys. Rev. E 56, 3281 (1997).

NIST CENTER FOR NEUTRON RESEARCH 25
UNIQUE DETERMINATION OF

BIOMIMETIC MEMBRANE PROFILES BY

NEUTRON REFLECTIVITY

ew biomimetic membrane materials, of fundamental importance in understanding such key biological processes as molecular recognition, conformational changes, and molecular selfassembly, can be characterized using neutron reflectometry. In particular, scattering length density (SLD) depth profiles along the normal to the surface of a model biological bilayer, which mimics

the structure and function of a genuine cell membrane, can be

deduced from specular neutron reflectivity data collected as a function of wavevector transfer Q. Specifically, this depth profile can be

obtained by numerically fitting a computed to a measured reflectivity. The profile generating the best fitting reflectivity curve can

then be compared to cross-sectional slices of the film's chemical

composition predicted, for example, by molecular dynamics simulations [1]. However, the uniqueness of a profile obtained by conventional analysis of the film's reflectivity alone cannot be established

definitively without additional information. In practice, significantly

different SLD profiles have been shown to yield calculated reflectivity curves with essentially equivalent goodness-of-fit to measured

data [2], as illustrated in Fig. 1.

The existence of multiple solutions, only one of which can be

physical, is especially problematic in cases where a key additional

piece of structural or compositional information is lacking as can happen in the investigation of these biological membrane systems.

Why this inherent uncertainty? The neutron specular reflection amplitude for a model SLD can be computed exactly from first

principles; the square of its modulus gives the measurable reflectivity. It is firmly established, however, that the complex amplitude

is necessary and sufficient for a unique solution of the inverse problem, that of recovering the SLD from reflection measurements. Unambiguous inversion requires both the magnitude and phase of

reflection. Once these are known, practical methods [3] exist for

extracting the desired SLD.

In fact, considerable efforts were made about a quarter century ago to solve the analogous "phase problem" in X-ray crystallography

using known constraints on the scattering electron density [4] and by

the technique of isomorphic substitution [5]. Variations of the latter approach have been applied to reflectivity, using a known reference

layer in a composite film in place of atomic substitutions. These

2-

0.1 . 0.2 Q(A"1

)

FIGURE 1 . Family of scattering length density profiles obtained by modelindependent fitting of the reflectivity data in the inset. The profile represented

by the blue dashed line is unphysical for this Ti/TiO film system yet generates

a reflectivity curve that fits the data with essentially equivalent goodness-of-fit

(all the reflectivity curves corresponding to the SLD's shown are plotted in the

inset but are practically indistinguishable from one another).

FIGURE 2. Reflectivity curves for the thin film system depicted schematically in the inset, one for a Si fronting (red triangles), the other for Al

2 03 (black circles). The curve in the lower part of the figure (blue squares) is the real part of the complex reflection amplitude for the films obtained from the reflectivity curves

by the method described in the text.

26 RESEARCH HIGHLIGHTS
C. F. Majkrzak, N. F. Berk, S. Krueger, J. A. Dura C. W. Meuse, V. Silin, J. Woodward, A. L. Plant M. Tarek

NIST Center for Neutron Research NIST Biotechnology Division Department of Chemistry

National Institute of Standards and Technology National Institute of Standards and Technology University of Pennsylvania

Gaithersburg, MD 20899-8562 Gaithersburg. MD 20899-8311 Philadelphia, PA 19103

solution methods, however, were tied to the Born approximation,

which generally is valid in crystal structure determination but which

fails catastrophic ally at low Q (low glancing angles) in reflection from slab-shaped samples such as thin films. Exact inversion

requires accurate knowledge of the reflection amplitude over the

entire Q-range, especially at low Q.

In this decade the reflection phase problem has been exactly

solved using a protocol of three reflectivity measurements on composite films consisting of the film of interest in intimate contact with each of three known reference layers [6, 7]. Subsequently, variations

using only two measurements have been shown to partially solve

the phase problem, an additional procedure being required to choose

between two solution branches, only one of which is physical [8,

9]. In the past year [10], an exact solution has been found for a two measurement strategy in which the film surround, either the

fronting (incident) or backing (transmitting) medium, is varied. This new approach is simpler to apply than reference layer methods

and is adaptable to many experiments. Surround variation neutron

FIGURE 3. SLD profile (red line) resulting from a direct inversion of the Re r of

Fig. 2 compared with that predicted by a molecular dynamics simulation (white

line) as discussed in the text. The headgroup for the Self-Assembled-Monolayer

(SAM) at the Au surface in the actual experiment was ethylene oxide and was

not included in the simulation but, rather, modelled separately as part of the

Au. Also, the Cr-Au layer used in the model happened to be 20 A thicker than

that actually measured in the experiment.

reflectometry has been successfully applied to the challenging type

of biological membrane depth profiling described earlier.

In Fig. 2 are plotted a pair of neutron reflectivity curves measured for the layered film structure schematically depicted in

the upper right inset, one with Si and the other with A1

2 03 as the

fronting medium. The lower part of Fig. 2 shows the real part of

the complex reflection amplitude for the multilayer as extracted from

the reflectivity data, according to the method described above, and

which was subsequently used to perform the inversion to obtain

the SLD shown in Fig. 3. For comparison, the SLD predicted by

a molecular dynamics simulation is also shown in Fig. 3, in a

slightly distorted version, corresponding to a truncated reflectivity

data set, which indicates the spatial resolution of an SLD obtainable

in practice. This latter SLD was obtained by inversion of the reflection amplitude computed for the exact model SLD, but using values

only up to the same maximum Q value (0.3 A

1 ) over which

the actual reflectivity data sets were collected. Overall, agreement

between the experimentally determined profile and the theoretical

prediction is remarkable, essentially limited only by the Q-range of

the measurement. Surround variation neutron reflectivity thus makes

it possible to measure complicated thin film structures without the

ambiguity associated with curve fitting. The veridical SLD profile is

obtained directly by a first principles inversion.

REFERENCES:

[1] M. Tarek, K. Tu, M.L. Klein, and D. J. Tobias, Biophys. J. 77, 964 (1999).

[2] N. F. Berk and C. F. Majkrzak, Phys. Rev. B 51, 11296 (1995).

[3] P. E. Sacks, Wave Motion 18, 21 (1993).

[4] H. A. Hauptman, Science 233, 178 (1986).

[5] J. M. Cowley, Diffraction Physics, 2nd Ed., (North Holland, Amsterdam,

1990), p. 131.

[6] C. F. Majkrzak and N. F. Berk, Phys. Rev. B 52, 10825 (1995).

[7] V.O. deHaan, A. A. van Well, S. Adenwalla, and G.P Felcher, Phys. Rev. B 52, 10830(1995).

[8] T. Aktosun and P. E. Sacks, Inverse Problems 14, 211 (1998).

[9] C. F. Majkrzak and N. F. Berk, Physica B 267-268, 168 (1999).

[10] C. F. Majkrzak and N. F. Berk, Phys. Rev. B 58, 15416 (1998).

NIST CENTER FOR NEUTRON RESEARCH 27
MULTI-TECHNIQUE STUDIES OF

ULTRATHIN SiQ2 FILMS

f I Cun"ent gate dielectrics in silicon based devices are only a few nm thick. Optical techniques such as ellipsometry are used to monitor film thicknesses and optical properties in production. However, for the current integrated circuit (IC) generation

the accuracy of ellipsometry degrades because parameters such

as thickness and index of refraction (which reflects the composition) become strongly correlated. Thus, it is difficult to unambiguously determine these parameters simultaneously, and the accuracy

of ellipsometry would benefit from an independent calibration. In

reflectometry techniques, on the other hand, these parameters are

nearly decoupled. The thickness of a layer is approximately inversely proportional to the oscillation period of the reflected intensity,

whereas the differences in scattering length density SLD (also an

indicator of composition) between the layers is related to the amplitude of the oscillations. Neutron reflectometry (NR) is better suited

than X-ray reflectometry (XR) for the study of the Si02/Si system

because there is a relatively large contrast (or difference in SLD)

between the scattering length densities of the two materials: 65 %,

vs. 7.6 % for X-rays.

Consider as an example a sample with a nominally 10 nm

thick thermal oxide film on silicon. This moderate thickness was

chosen to increase our confidence in the results of the various

characterization methods, while remaining thin enough that the

results are relevant to film of technological interest. Figure 1 shows

spectroscopic ellipsometry (SE) data and corresponding best fits for

the sample with surface contamination and after an organic cleansing. Nominally, the only change is a decrease in the thickness of the contamination layer [1].

In XR data (Fig. 2) two oscillation periods are observed

for the contaminated sample. The high frequency oscillation corre- sponds to the SiO, film, whereas the low frequency modulation is due to the thinner contamination layer (which is not present after

cleaning, indicating removal of the contamination.)

The NR measurements (Fig. 3) were done in a vacuum to reduce the air scattering background. This allowed us to achieve

a very large range in reflectivity, over 108

, which is among the

best examples in NR measurements to date. A slightly thinner contamination layer in NR is consistent with the fact that the XR

was done in air, during which the contamination was growing. This was confirmed by changes in XR scans immediately following those

in Fig. 2. The average of the 5 measurements of the SiO, film thickness was 10.27 ±0.13 nm. The excellent agreement among the results

for the three different techniques increases our confidence in the

1.00

o.5o

;

000

1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Photon Energy (eV)

0

-1

-2 _ -3

CJ> g -5

CD ^ -6 3 -7

-8

-9

-10

2.0 L-fa

: 03

CXJ 1.5 <^S

" C

E 1.0 -£

E= 0.5 . cO -O 0.0

CJ> 5 10 15

Depth (nm)

FIGURE 1. Comparison of spectroscopic ellipsometry experimental data, x \' and A, to the fits (solid line) for the clean and surface contaminated sample. The inset shows < e,> and <s2> as a function of depth determined by the fit.

FIGURE 2. X-ray reflectivity and best fits for the clean and surface contaminated sample. The inset shows the scattering length density profile determined by the fits.

28 RESEARCH HIGHLIGHTS
J. A. Dura and C. F. Majkrzak

NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD, 20899-8562

C. A. Richter, N. V. Nguyen and J. R. Ehrstein

Semiconductor Electronics Division

National Institute of Standards and Technology

Gaithersburg, MD, 20899-8122

FIGURE 3. Neutron Reflectivity data and best fit for a sample with surface

contamination. The inset is the scattering length density profile determined

by the fit.

parameters extracted via these models. Thus the XR and particularly

the NR corroborate the correct analysis required in SE (which is the

technique most practical in monitoring production). To further investigate the applicability of these techniques to

thinner SiO, layers, we simulated the SE and the XR and NR curves

for 6 nm, 4 nm, and 2 nm thick layers of SiO,. For a realistic and

consistent set of roughness parameters in the models, we used the

average values obtained from the actual measurements previously

discussed. The SE simulation, Fig. 4a, shows distinct differences

in both the magnitude and shape of A among the three thicknesses shown. In models of XR, shown in Fig. 4b, only very weak oscillations are seen for even the thickest of the SiO, layers because of

the low contrast between SiO, and Si. However, in NR, for SiO,

layers as thin as 2 nm strong oscillations are clearly seen above

the 10"8 lower limit, demonstrated in Fig. 3. Therefore both NR and

SE are well suited for the study of SiO, films as thin as 2 nm.

Encouraged by these models, we obtained NR data for a thinner,

2.4 nm, sample. While these data are not yet fit to a model curve, we note that both the reflected intensities and oscillation amplitude

are similar to those of the 2.0 nm model, indicating similar interface

widths.

160

140

120

100

80

60

7(a) , \ —~~~~~

1 •' s — / / s

I • /

1 /

A"\-*<V. \

/ ^- \\

/ ' / ~ /'/ /2.0nm —\K ^ 4.0 nm

s^v6.0 nm .... t .... i ,

40.0

30.0

20.0 5<

10.0

0.0

2.0 3.0 4.0 5.0 Photon Energy (eV)6.0

1.0

-1.0 IVMb)

-3.0 ^^enmXR

-5.0

-7.0 \ , o-/ \ / v\ 4 nm NRX^/-—

\2 nm NR

-9.0

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 Q (nm"1

)

FIGURE 4. Model calculations for thin S1O2 Alms of thickness indicated in the

figure, on Si. a) Spectroscopic ellipsometry, and b) unless otherwise noted

solid lines are neutron reflectometry models. For clarity the 6 nm (4 nm)

films are shifted up by 2(1) orders of magnitude. The data points are for a

== 2.4 nm film. We have shown that three different techniques can offer complimentary information on the structure of thin SiO, films on Si.

All offer a significant degree of sub-monolayer thickness sensitivity,

although in NR there is a much higher contrast between SiO, and

Si than in XR.

REFERENCES

[1] For details see: "Neutron Reflectivity, X-ray Reflectivity, and Spectroscopic

Ellipsometry Characterization of Thin Si02 on Si," J. A. Dura, C. A.

Richter, C. F. Majkrzak, and N. V. Nguyen" Appl. Phys. Lett. 73, 2131

(1998).

NIST CENTER FOR NEUTRON RESEARCH 29
CERTIFICATION OF AN ION-IMPLANTED

ARSENIC IN SILICON

STANDARD REFERENCE MATERIAL

The secondary-ion mass spectrometry (SIMS) community in

the United States recently undertook a round-robin study to

calibrate the implanted dose of arsenic in silicon by consensus.

"Variations in dose determination among laboratories were as high as 30 %, reflecting primarily the errors of the respective in-house standards. By contrast, in an international round-robin exercise sponsored by the International Standards Organization (ISO) the U.S.

laboratories achieved a relative standard deviation of 4 % for nine

independent determinations of the boron content in an unknown

boron-doped silicon sample. This level of agreement was only possible because all the laboratories used SRM 2137 Boron Implant in

Silicon as a common reference material. These results demonstrate

the need for a common arsenic reference material to improve interlaboratory reproducibility. Furthermore, SEMATECH (a consortium

of semiconductor manufacturers) recently listed SRM implants of phosphorus and arsenic in silicon as high priority industrial needs.

Consequently, a Standard Reference Material (SRM 2134 Ion- Implanted Arsenic in Silicon) was produced at NIST, using a wafer

from the SIMS intercomparison. The material for this SRM was

provided by a major ion implanter manufacturer who supplied three 200 mm diameter wafers that had been implanted with arsenic at

an energy of 100 keV (in the same batch). One of the wafers was

diced and distributed to 12 participating laboratories for the arsenic

round-robin study described above. Each of the remaining wafers

could provide 221 SRM units, enough for an estimated 10 year supply. One of the remaining wafers was therefore diced into 1 cm x 1 cm pieces with a wafer saw for use as SRM 2134. Because of the

specificity and matrix independence of instrumental neutron activation analysis (INAA), this technique was chosen as the primary

method for certification of the arsenic implanted dose. Ten analytical specimens of silicon were selected from

among the 22 1 pieces cut from the wafer to determine arsenic

content and test for homogeneity. Two blank chips of silicon were

analyzed in parallel. Pre-irradiation handling was done on a class 100 clean bench. In a Teflon TFE beaker, the specimens and blanks were rinsed together in ultrapure (UP) water, rinsed with 95 %

ethanol, cleaned ultrasonically for one minute in ethanol, and rinsed

twice with UP water. The samples and blanks were then agitated for one minute in UP water, blotted on Whatman 41 filter paper, and

105 559.08

560 570

Energy, keV

FIGURE 1 . Region of the gamma-ray spectrum for analysis of As in SRM 2134.

Limits of peak and baseline areas are indicated by vertical lines.

air-dried. Each was weighed and heat-sealed in a polyethylene bag

that had been cleaned in high purity nitric acid. A dilute solution standard was prepared by gravimetrically

diluting a 10 mg/g solution of As^O., in dilute ammonia to about 2 mg/kg. Another solution was prepared similarly from SRM 3103a

Arsenic Spectrometric Solution. Aliquants of both solutions were weighed from a polyethylene pipette onto 1-cm disks of acidleached Whatman 41 filter paper and dried to produce standards

with about 200 ng arsenic each. Two standards from each solution were irradiated with the samples. A blank filter paper was shown in

a separate experiment to contain no significant arsenic (« 0.01 %

of the amount in the standards). Samples, standards, and blanks were stacked in the irradiation container in the following sequence: standard, blank, five

samples, two standards, five samples, blank, and standard. The

stack was irradiated for four hours in the RT- 1 pneumatic tube of

the NIST research reactor, at a thermal fluence rate of 7.7 x 10' 3

cnr

2s'. The container was inverted halfway through the irradiation

to equalize to the first order for the axial fluence rate gradient along

the container.

After irradiation the silicon samples were cleaned ultrasonically for one minute in de-ionized water, blotted dry, and

heat-sealed in clean conventional polyethylene bags for counting.

30 RESEARCH HIGHLIGHTS
Robert R. Greenberg, Richard M. Lindstrom, and

David S. Simons

Chemical Science and Technology Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8300

Gamma-ray activity was assayed at 10 cm from a germanium detector with a 1.71 keV resolution and 40 % relative efficiency at 1333

keV. Each sample and standard was counted at least twice, after

the 2.62 h

31 Si matrix activity had substantially decayed. The 559 + 563 keV doublet of 76As in each spectrum was integrated with

the SUM computer program [1]. See Fig. 1. No evidence indicating

significant heterogeneity among samples could be seen when the observed sample-to-sample precision was compared to what was

expected from counting statistics combined with other sources of

analytical variability. 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 [2].

Table 1. Individual Uncertainty Components for Determination of Arsenic in SRM 2134.

Source of Uncertainty Individual Uncert. (1s) %

Basis Measure - Sample Area / Micrometer Accuracy 0.012

Basis Measure - Sample Area / Precision (n = 26)1 0.0089

Concentrations of Comparators (Standards) 0.106

Mass Determination - Comparators 0.041

Isotopic Variability 0

Blank and Blank Correction (n = 102

)

1 0.013

Irradiation Geometry Differences 0.039

Neutron Self - Shielding/Scattering Differences 0.024

Timing 0

Irradiation Interferences Negligible

Measurement Replication (n = 9)

1 0.081

Counting Statistics - Standards (n = 105

)

1 0.073

Counting Geometry Differences 0.009

Pulse-Pileup 0.066

Dead-Time Effects (inadequacy of LT extension) Negligible

Decay Timing Effects (Half life related) 0.053 Gamma-Ray Self Shielding 0.004 Gamma-Ray Interferences 0.00004

Peak Integration Method 0.033

Overall 0.189

' '^"indicates degrees of freedom which are listed for Type A sources of uncertainty.

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

investigation. In addition, confirmation of measurements by a pri- mary NIST method may be accomplished by one or more of the

following: determination of certified constituents in other SRM(s)

or CRM(s) of similar matrix and constituent concentration range;

a second NIST technique with appropriate controls; or results of measurements from selected outside collaborating laboratories with

appropriate experience.

In order to certify the arsenic concentration in SRM 2134

using INAA as a primary method it is therefore necessary to evaluate all significant sources of uncertainty explicitly. For this set of measurements, we considered sources of uncertainty greater than

0.01 % relative to be significant. The results of a complete evaluation of all sources of uncertainty are listed in Table 1. This evaluation yielded an expanded relative uncertainty of 0.38 % (as defined by ISO and NIST) and gives an approximate level of confidence

of 95 %. The arsenic concentration observed was 91.20 ng/cnr ±

0.35 ng/cm2.

In conclusion, we have successfully applied INAA as a primary method for the certification of this new SRM. The observed

relative expanded uncertainty of 0.38 % is considerably smaller

than the 1 % value desired 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.

REFERENCES

[1] R. M. Lindstrom, Biol. Trace Elem. Res. 43-45, 438 (1994).

[2] W. May, R. Parris, C. Beck, J. Fassett, R. Greenberg, F. Guenther, G. Kramer, S. Wise, T. Gills, J. Colbert, R. Gettings, B. MacDonald, NIST

Spec. Pub. 260-136, 2000.

NIST CENTER FOR NEUTRON RESEARCH 31
THE ROTATIONAL DYNAMICS OF H2 IN

POROUS VYCOR GLASS

Porous materials play an increasingly important role in the

exploration of fundamental scientific issues related to diverse

technological applications including adhesion, lubrication, tribology

and the engineering of materials. Surface interactions and finite size

effects both play a key role in the qualitative modification of the

properties of the materials contained within the porous host. Due to

its light mass and weak electronic interactions, molecular hydrogen

is an ideal system to probe the effects of surface interactions. H2 is

well described as a quantum rigid rotor with discrete energy levels

labeled by the rotational quantum number, J, and energies given by

Ej = BJ(J + 1 ) where B is the rotational constant which is equal

to 7.35 meV for H,. These energy levels can be studied by using

neutrons to stimulate the J = 1 to J = 0 transition of the H, molecule,

a process that is normally doubly forbidden due to the quantum statistics obeyed by H,. When neutron stimulated conversion occurs,

the neutron gains an amount of energy equal to the rotational energy

of the molecule. This results in an extremely clean signal since

all other processes are frozen out at the low temperatures of these measurements.

Studies of the rotational levels of H, adsorbed in \y cor,

a commercially available porous glass, were carried out for pore

fillings ranging from 0.10 (corresponding to less than a single

monolayer on the pore surface) to 0.92 (corresponding to nearly full

pores). As can be seen in Fig. 1, at low filling fractions only a single

broad peak at 10 meV is present which can be attributed to the

scattering from an adsorbed layer of H, strongly bound to the pore

surface. The appearance of scattering at 14 meV, corresponding to

the free molecule transition, for fillings above 0.45 is associated with the appearance of "bulk"-like material in the pore center. The clear separation of the scattering from molecules adsorbed on the walls and in the pore center suggests that these are quite

distinct states which we refer to as the bound and bulk-like states,

respectively.

The shift in the energy of the rotational transition at low

fillings can be directly related to the interaction of the molecules

with the surface [2]. Figure 2 shows the shift of the J = 1 to

J = 0 transition as a function of the rotational energy barrier for

the molecule. From Fig. 2 one finds that the observed rotational energy of 10 meV corresponds to an orientational potential with

a barrier height of VB/B

H = 2.7 (V

B = 19.8 meV). The magnitude

FIGURE 1 . The top panel shows a contour plot of the inelastic scattering from H2 in Vycor at various pore fillings at 6 K. The bottom panel is a cut through the contour plot at f = 0.65 (indicated by the line).

of this potential is quite large, comparable to that seen in alpha

alumina, a catalyst used for ortho-H, enrichment [3], and on leached

glass [4]. Careful inspection of the data reveals that the peak due to

the bound state actually shifts from 9.1 meV to 10.1 meV between

filling fractions, f, of 0.20 and 0.27. Thus for f between 0.27 and

0.45, the bound state may be separated into a layer in direct contact

with the pore wall and a layer that feels a weaker orientational

potential. The scattering from these two layers can be separately

determined assuming the intensity from the first layer varies linearly

with filling. The scattering from the second surface layer can be obtained from the difference of the monolayer and bilayer spectra. The scattering from the second layer is centered at E = 11.3 meV, compared

32 RESEARCH HIGHLIGHTS
D. W. Brown

Manual Lujan Jr. Neutron Scattering Center Los Alamos National Laboratory Los Alamos, NM 87545

P. E. Sokol

Department of Physics The Pennsylvania State University

University Park, PA 16802

S. A. FitzGerald

Department of Physics

Oberlin College

Oberlin, OH 44074

1 -

H

2

Full Pore H 9 Monolayer

Full Pore V = 19.8 meV

i

E = 41.7 meV

Monolayer

25.7 meV

3V/B

FIGURE 2. Shift of the rotational energy levels of H2 as a function of

barrier height.

to the first layer which is centered at 9.1 meV, indicating that the second layer interacts less strongly with the wall. The width of the peak we associate with the bulk-like molecules is due entirely to instrumental resolution. This is consistent

with the view of these molecules as being free rotors with a

single well defined value for B. On the other hand, the width of

the peak which we attribute to the bound layer is much broader

than the instrumental resolution. A single well defined orientational

potential would yield a shift in the peak location, as observed, but no additional broadening, since the energy levels would still be well

defined. Thus, we attribute this additional width to a distribution of

orientational potentials which can also be directly extracted using

the model of White and Lassettre [2] (Fig. 2). After correcting

for instrumental effects, the strength of the scattering at a given

energy is directly proportional to the number of molecules which

feel the corresponding orientational potential. Thus, plotting the

scattering as a function of V/BH

, directly yields the distribution

of orientational potentials shown in Fig. 3. As can be seen, the

—I

First Layer Second Layer

-4 -2 4

V/B

10 12

FIGURE 3. Distribution of potential barriers felt by the molecules in the first (red) and second (blue) layers.

orientational potential for the first layer is broad, asymmetric, and

centered at VB = 3.5B

H

, whereas the potential of the second layer is

relatively narrow and centered at VB = 2.0B

H

, indicating a weaker

interaction with the surface. The data allow us to draw the following picture of the adsorption of molecular hydrogen on a porous glass surface. The first monolayer is bound tightly to the rough pore surface. The rough

surface prevents free rotation of the molecule, altering the rotational energy states. The second layer perceives the surface roughness

smoothed by the presence of the first layer, and accordingly, the

rotational transitions are affected to a lesser degree. Subsequent to

the completion of the second monolayer, the H, molecules sense no significant orientational interaction from the glass surface. This

is in agreement with the picture presented by Katsaros et al. [5],

in which surface roughness is created by dangling bonds on the

pore surface.

REFERENCES

[1] J. Dekinder, A. Bouwen and D. Schoemaker, Phys Rev B 52, 15872 (1995).

[2] D. White and E. N. Lassettre, J. of Chem. Phys. 32, 72 (1960).

[3] I. F. Silvera, Rev. of Mod. Phys. 52, 393 (1980).

[4] M. Mohnke and W Saffert, Gas Chromatography, edited by M. Swaay

(Butterworths, London, 1962), p. 216.

[5] F. Katsaros, et al., Physica B 234, 402 (1997).

NIST CENTER FOR NEUTRON RESEARCH 3 5
FIRST-PRINCIPLES COMPUTATIONAL AND

NEUTRON SCATTERING STUDY OF

PROTONIC CONDUCTORS

Fuel cells, which produce electricity via hydrogen oxidation to

water, have emerged in the last decade as one of the key

technologies for meeting the world's energy needs well into the

21 st century. Solid-oxide fuel cells (SOFCs) are the most promising

among the many different types of fuel cells being developed.

However, the required high operating temperature of an SOFC

places stringent requirements on its component materials. Potential

candidates to replace the oxygen-conducting electrolyte used in current SOFCs include the perovskite-based high-temperature protonic

conductors (HTPCs), since switching from anionic to protonic conduction can lower the practical operating temperature from 1300 K

to around 1000 K. We undertook neutron vibrational spectroscopy (NVS) measurements of various HTPCs (namely, SrCeO, and SrZr03 aliovalently doped with different rare earth cations) in order to probe the bonding potentials experienced by the residual protons incorporated

as OH" species via steaming. At high temperatures, these protons

migrate from site to site, giving rise to protonic conduction. The

NVS measurements revealed the existence of dopant-related perturbations to the bending-mode °

energies °of OH in SrCe„„sM„„M O, , 0.95 0.05 x 3-6 (M = Sc, Ho, and Nd), confirming the trapping effects of the

dopants. The bending-mode energy could be correlated with the

size of the dopant cation, generally increasing for smaller cations. NVS measurements of SrZr

095M005H 0,_5 (M = Sc, Y, and Nd)

indicated differences in the OH bending-mode energies between

the cerates and zirconates. These differences reflect changes in the

lattice potential experienced by the protons, which ultimately effects

the proton jump rates and therefore the performance of these materials for use in fuel cells. An understanding of the dynamics of the undoped

perovskites is the first step towards a comprehensive picture of

the protonated doped materials. To explore this in more detail, we

performed ab initio total-energy calculations using the CAmbridge

Serial Total Energy Package (CASTEP). We calculated the Q = 0 phonons in the primitive unit cell (i.e., Zr

4Sr4012

) of undoped

strontium zirconate and compared with the experimental density of

states (DOS) at room temperature, as shown in Fig. 1. While at low

energies, the calculated modes are almost at the same energies as observed modes, at high energies, we overestimate the energies of

the modes by about 10 %. However there is still a one-to-one cor- respondence between the main experimental and calculated spectral

CD

30 60 90 120 Neutron Energy Gain (meV)

FIGURE 1. LEFT: A view of the structure of undoped SrZr0

3 in the [001] direction. RIGHT: Vibrational spectra for SrZr0

3 measured by neutron time-of-flight spectroscopy. The space group and the lattice parameters (in A) are also shown. Numbers in parentheses are the theoretical values. The lower solid

line is the DOS of the Q = 0 phonons calculated from first principles.

34 RESEARCH HIGHLIGHTS
T. Yildirim, T. J. Udovic. C. Karmonik, and

D. A. Neumann

NIST Center for Neutron Research

National Institute of Standards and Technology

Gaithersburg, MD 20899-8562

features, allowing us to identify the modes observed by our NVS

measurements.

In order to model the dynamics of protons trapped in Sc-doped SrZrO,, we replaced one of the Zr atoms in the \flX\flX 1 supercell by (Sc + H), which yields a cell formula

Sr

sZr.ScHO,4 (See Fig. 2). We performed calculations for protons

at either the "undoped" (U) or "doped" (D) sites. Even though the MOfe octahedra are quite rigid, the distortions due to the presence of

the proton at these sites are quite large. These distortions are also reflected by the vibrational spec- trum of the proton. The two tangential OH- bending modes depend

strongly on the proton siting. At the Sc site, the lowest tangential

mode is found at 122.9 meV However at the Zr site, the mode is much softer at 88.5 meV Interestingly, we observe new features

in our NVS spectra at these energies upon proton addition. To

further investigate this effect, we performed "embedded cluster"

calculations in which the vibrational spectrum of the H-M06 cluster

is calculated while all other atoms are kept at their equilibrium

positions. The similarity between experiment and the calculated spectrum from H-Zr06 + H-Sc06 clusters suggests that the mode

observed near 120 meV is due to protons trapped at the Sc sites

: H at the undoped site

while some portion of the peak near 80 meV is due to protons at

the undoped sites. Thus NVS can be used to determine the hydrogen occupancy of the various sites. For a better understanding of the protonic conduction in

these materials, we calculated the total energy of the system as the

proton migrates from Zr to Sc sites. We found that the doped site

has a much lower energy (-1.13 eV) than the undoped site. The

two sites are separated by an energy barrier of 1.5 eV. Hence, we

expect that most of the protons are trapped at the dopant site. This

is primarily because the proton prefers to be closer to the Sc cation,

which has a charge of +3 compared to +4 for Zr. Yet, one also

has to consider steric effects; i.e., if the dopant cation has a larger

radius, then the proton may prefer to occupy the Zr site, despite

the larger Coulomb interaction. Thus these calculations indicate

that the protonic transport is sensitive to the competition between

short-range repulsive and Coulomb interactions, and suggest that

the use of a large dopant cation is one important step in developing

a HTPC with increased protonic conductivity. We are currently

testing the usefulness of the calculated proton potentials for predicting the protonic diffusional motions observed experimentally via

quasielastic scattering measurements.

3

60 85 110

Energy (meV)

FIGURE 2. LEFT: Optimized structures when the proton is trapped at the undoped

site (top) and at the doped site (bottom). MIDDLE: Comparison of the neutron

vibrational spectrum of SrCe^Sc.HOj (top) and SrZr, Sc^Oj (calculated). Dashed and dotted lines shown at the bottom are the contributions from the H-M0S clusters, where M = Zr (undoped site) and Sc (doped site), respectively. RIGHT: Potential energy of the crystal as the proton migrates from the undoped

site (U) to the doped site (D).

Distance from U-site (A)

NIST CENTER FOR NEUTRON RESEARCH 35
MAGNETIC TRAPPING OF

ULTRACOLD NEUTRONS

The demonstration of three-dimensional magnetic trapping of

neutrons was performed this past year at NIST [1]. The techniques developed should lead to improved precision in the measure- ment of the neutron beta-decay lifetime, thereby expanding our knowledge of the weak nuclear force and our understanding of the

creation of matter during the Big Bang.

Magnetic traps are formed by creating a magnetic field mini- mum in free space. The confining potential depth is determined by

the magnetic moment of the neutron and the difference between the magnitude of the field at the edge of the trap and at the minimum. A

neutron in a low-field-seeking state (one with its magnetic moment

anti-aligned with the local magnetic field vector) feels a force pushing it towards the trap minimum and will remain confined within

the trapping region.

In order to load a neutron into a static conservative trap, its

energy must be lowered while it is in the potential well. We rely on a loading technique that employs the "superthermal process" [2].

Superfluid helium fills the trapping region and serves as a neutron

scattering medium. A neutron with kinetic energy near 1 1 K (where

the free neutron and Landau-Feynman dispersion curves cross) that

passes through the helium can lose nearly all of its energy in a

single scattering event. Neutrons that scatter to energies less than

the trap depth ( 1 mK) and in the appropriate spin state are trapped. Neutrons in this energy range are called ultracold neutrons (UCN).

Isotopically pure superfluid helium is contained in a tube

located inside the superconducting magnet and centered axially

within its trapping field (see Fig. 1). The superconducting magnet,

trapping region, and other key parts of the apparatus reside within

a cryogenic dewar. The incident neutron beam is collimated, passes

through the trapping region, and is absorbed by the beam stop. As

the beam traverses the trapping region, about 1 % of the neutrons

scatter in the helium. Some of these neutrons are trapped and the remainder are absorbed by shielding materials that surround the

helium. Low-field-seeking UCN are trapped and remain in the trapping region until they decay.

Acrylic lightguide

Magnet form

Racetrack coil

Cupronickel tube

Trapping region

Collimator Neutron Shielding

FIGURE 1 . Half-section view of the neutron trapping apparatus. A beam

of cold neutrons enters from the left, is collimated, passes through the

trapping region and is absorbed at the rear. Scattered neutrons (yellow) in the low-field-seeking spin state and with energy below the trap depth are magnetically confined. Electrons from neutron beta-decay create EUV

scintillations in the superfluid helium which are wavelength shifted to the

visible and transported to the photomultiplier (to the right).

36 ;EA HIGHLIGHTS
R R. Huffman, M. S. Dewey and F. E. Wietfeldt

Ionizing Radiation Division

National Institute of Standards and Technology

Gaithersburg, MD 20899-8461

C. R. Brome, J. S. Butterworth, S. N. Dzhosyuk,

C. E. H. Mattoni, D. N. McKinsey and J. M. Doyle

Department of Physics, Harvard University Cambridge, MA 02138

R. Golub and K. Habicht

Hahn-Meitner-lnstitut

Glienicker Strasse 100 D-14109 Berlin, Germany

The trapped neutrons are detected when they decay. When a

trapped neutron decays (into an electron, proton and anti-neutrino),

the resulting high-energy electron travels through the helium leaving a trail of ionized helium atoms. These ions quickly combine

with neutral helium atoms to form metastable diatomic molecules. Most of these molecules decay within 10 ns, emitting a pulse of

light in the extreme ultraviolet (EUV), X «= 70 nm to 90 nm. This

pulse of scintillation light is the signal of a neutron decaying in

the trap.

In an experimental run, the cold neutron beam is allowed to

pass through the trapping region, after which the beam is blocked

and pulses of light are counted. A background signal, with both

constant and time-varying components, obscures the trapped neutron signal. These backgrounds are subtracted by collecting data

0.1

- 0

0.1

0

0.1

0

-0.1 1000 2000

Time (s)

3000

FIGURE 2. Counting rate as a function of time after the neutron beam is turned off (pooled background subtracted data), (a) Trapping data set I,

N. = 560 ± 160, (b) Trapping data set II, NM = 240 ± 65, (c) Combined trapping

signal, t = 750:^ s, (d) Combined 3 He data, N3He= 53 ± 63.

K. J. Coakley

Statistical Engineering Division

National Institute of Standards and Technology

Boulder, CO 80303

G. L. Greene and S. K. Lamoreaux

Los Alamos Neutron Science Center Los Alamos National Laboratory Los Alamos, NM 87545

where the magnetic field is on during the initial loading phase, so

that UCN are confined by the trap and subtracting data where the magnetic field is off initially, so that no neutrons are trapped. Equal

numbers of each data set were taken, pooled and subtracted to give

the background subtracted data. Two sets of background subtracted data were collected: set

I with a trap depth of 0.76 mK (Fig. 2a) and set II with a lower

trap depth of 0.50 mK (Fig. 2b) due to problems with the magnet. For each set, the pooled background subtracted data are modeled to

extract the amplitude and lifetime of the decaying neutron signal.

The best fit values for the initial counting rates combined with the measured detection efficiency gives N = 560 ± 160 and Nn = 240 ± 65. Calculations using the known beam flux, trap geometry and

the theory of the superthermal process predict N, = 480 ± 100 and

N = 255 ± 50, in good agreement with the measured values. The

best fit value for the trap lifetime, t = 750 loo s, is consistent with

the presently accepted value of the neutron beta-decay lifetime of

886.7 ± 1.9 s [3]. To verify that our signal is in fact due to trapped neutrons, we

doped the isotopically pure

4 He with 'He at a concentration of 2 x

10"7 3 He/4He. This amount of 'He absorbs the trapped neutrons in

less than 1 s without affecting anything else in the experiment (less

than 1 % of the cold neutron beam is absorbed by 3 He). The data

(Fig. 2d) is modeled with the lifetime fixed at = 750 s, yielding

N,„ = 53 ± 63, consistent with zero. This confirms that our signal

3He

is due to trapped neutrons. Magnetic trapping of neutrons is a new technique that should

allow a higher precision measurement of the neutron lifetime, and

offers the prospect of precision much greater than the current limit

of one part in 103

. In order to realize the potential of this technique, we are in the process of improving our apparatus in many ways,

including increasing the size and depth of the trap. We expect to make a competitive neutron lifetime measurement in the near future.

REFERENCES:

[1] P. R. Huffman et al. Nature 403, 62 (2000).

[2] R. Golub, D. Richardson, and S. K. Lamoreaux Ultra-Cold Neutrons (Adam Hilger, Bristol, UK 1991).

[3] Particle Data Group, "Review of Particle Physics," Eur. Phys. J. C 3, 1 (1998).

NIST CENTER FOR NEUTRON RESEARCH 37
I CHARGE DISPROPORTIONATION AND

MAGNETIC ORDERING IN CaFeO.

Transition metal oxides adopting the perovskite crystal structure

(or one of its relatives) have occupied a place in the scientific

limelight for nearly fifty years now. Beginning with the discovery

of ferroelectricity in BaTiOv following World War H, the dielectric

properties of perovskites have been extensively studied over this

entire period. Today perovskite dielectrics, due to their widespread

usage in telecommunication, are still extensively studied. The dis- covery of superconductivity first in doped BaBiO , and later in

the cuprates, such as YBa2 Cu3 0?

, triggered an unprecedented

avalanche of scientific activity in the late 1980's and early

1990's. More recently, phenomena such as collosal magnetoresitance (CMR), charge, orbital and spin ordering, and phase separation in the manganate perovskites, (Ln

( x Ax )Mn03 (Ln = lanthanide

ion, A = alkaline earth ion), have captured the imagination of the condensed matter scientific community.

Ultimately the electronic and magnetic properties of a material depend upon the behavior of the outermost or valence electrons.

In a first row transition metal oxide the valence electrons are shared,

though not equally, between the 3d orbitals of the transition metal

ion and the 2p orbitals of oxygen. In compounds with the perovskite

structure the oxygen atoms are arranged in an octahedral geometry

about the transitional metal ion; each oxygen is then shared by two transition metal ions to form a three dimensional network of

corner sharing M06 octahedra. The octahedral coordination removes

the energetic degeneracy of the 3d orbitals, forming the familiar

triply degenerate t

2g and doubly degenerate e

g set of orbitals. The

eo orbitals point directly at the oxygen ligands to form a strongly

antibonding a* bond. In contrast, the t

2g orbitals have a smaller

overlap with the oxygen 2p orbitals, which leads to a weakly

antibonding it* band. If this covalent bonding interaction between

the transition metal and oxygen is weak, the valence electrons

are localized and a magnetic insulator is typically observed. If we increase the strength of the interaction sufficiently, either by

increasing the electronegativity of the transition metal ion or the

spatial overlap of the metal 3d and oxygen 2p orbitals, partial

derealization of the valence electrons can occur. Frequently, this

leads to metallic conductivity. In a number of transition metal

oxides the metal-oxygen interaction strength is such that delocalized

FIGURE 1 . The low temperature structure of CaFe03. The green spheres depict the calcium ions. The other shaded objects represent iron centered octahedra, where an oxygen atom can be found at each vertex and an iron atom at the center of each octahedron. The purple and blue objects represent Fe3* centered and Fe5+ centered octahedra respectively.

electrons and metallic conductivity are seen at higher temperatures

but give way to a magnetically ordered, insulating ground state upon cooling.

LaMn03

, SrFe03 and CaFe03 are isolectronic; they each have

an electronic configuration of t2g

3 e

g

'. According to the Jahn-Teller

theorem, the presence of a single localized electron in the doubly

degenerate e

g set of orbitals is not a stable situation. LaMn03 responds to this instability by undergoing a cooperative Jahn-Teller

distortion of the Mn06 octahedra, producing two long and four short Mn-0 bonds, Thereby, removing the degeneracy of the e

g orbitals. SrFe03 takes a different approach, by delocalizing its e

g electrons

to form a a* band. The contrasting behavior of these two materials

can be understood in terms of the strength of the metal-oxygen

38 RESEARCH HIGHLIGHTS
Patrick M. Woodward David E. Cox and Evagalia Moshopoulou Arthur W. Sleight

Department of Chemistry Department of Physics Department of Chemistry

Ohio State University Brookhaven National Laboratory Oregon State University Columbus, OH 43210 Upton, NY 11973 Corvallis, OR 97331-4003

interaction. Contrasting LaMnO, to SrFeO,, the oxidation state of

the transition metal increases from +3 to +4, which leads to an

increase in the metal-oxygen interaction strength, increasing the

width of the a* band and stabilizing a metallic ground state. Since

they both contain Fe4

*, one might expect that CaFeO, and SrFeO,

would behave very much alike. However, Ca2+

is smaller than Sr2"

1",

which causes a tilting of the Fe06 octahedra to satisfy the valence

requirements of calcium. This seemingly subtle distortion has several important consequences. The Fe-O-Fe bond is distorted away

from the linear geometry observed in SrFeO, (the Fe-O-Fe angle

is 158° in CaFe03 ). This reduces the spatial overlap of the Fe e

g and 0 2p orbitals, and the width of the a* band decreases. The

reduction in bandwidth triggers an electron localization that occurs

just below room temperature (290 K). Once electron localization

occurs, a cooperative Jahn-Teller distortion to the LaMn03 crystal

structure is expected.

However, CaFeO, refuses to conform with expectations.

Instead CaFeO, undergoes a charge disproportionation (CD), IFe4*

(t

2 V) -> Fe3+

(tJee

2

) + Fe5+

(t2g

3e °). Evidence for a CD in CaFe03 was first proposed over 20 years ago, based on Mossbauer studies

[1]. However, crystallographic confirmation of this rare phenomenon has proven elusive. Through the combined use of synchrotron

x-ray (X7a-NSLS) and neutron powder diffraction (BT-1 at NCNR),

we have elucidated the crystal structure of CaFe03 in its CD state

for the first time. The resulting structure (Fig. 1) clearly shows

the presence of two chemically and crystallographically distinct Fe

sites. The average Fe-0 bond length about the "Fe5+" site is 1.872(6)

A, while the same distance about the "Fe3+" site is 1.974(6) A. The ordered arrangement of Fe3+/Fe5+

is such that each Fe3+ is surrounded by six Fe5+ ions, and vice versa (NaCl or G-type ordering),

optimizing the Coulomb stabilization of the CD state. Alternately,

the CD process can be viewed as the condensation of a breathing

phonon mode.

In addition to electronic properties, there has long been both

technological and fundamental scientific interest in the magnetic

properties and interactions in perovskites containing transition metal

ions. Goodenough's study of the various antiferromagnetic structures observed in the (La

1 x Cax )Mn03 system was vital in the devel- opment of the Goodenough-Kanamori rules of superexchange [2]. These rules correctly predict an A-type antiferromagnetic structure

for LaMnO,. Using the same rules, we would expect CaFe03 to have a simple ferromagnetic ground state. Perhaps not surprisingly,

our investigation showed that again CaFeO, defies expectations.

Low temperature neutron powder diffraction data reveals instead

an incommensurate antiferromagnetic ground state (T

N 120 K).

Analysis of the data shows the magnetic structure to be either

a screw spiral or a sinusoidal amplitude-modulated structure. In

either case, it would appear that a long range AFM interaction

(probably between next-neighbors) is present in addition to the

nearest neighbor FM superexchange interaction.

REFERENCES

[1] M. Takano, N. Nakanishi, Y. Takeda, S. Naka and T. Takada, Mater. Res.

Bull. 12, 923 (1977).

[2] J. B. Goodenough, Magnetism and the Chemical Bond, Interscience, New

York (1963).

NIST CENTER FOR NEUTRON RESEARCH 3 9
BOND VALENCE ANALYSIS

OF RUTHENATES

B

I ond valence analysis allows us to evaluate, for any compound

'whose bonding scheme is known or assumed, the bond distances that the atoms would form in an ideal structure in which

all atomic valences are exactly balanced. In a significant number

of cases this information is sufficient to make accurate predictions

about the real crystal structure of the compound.

The bond valence method is based on two concepts that can

be stated in the following way.

(i) A bond valence v = v is assigned to a bond between

atoms i and j, of valences V(i) and V(j), so that

n(i) n(j) 2 ;

.V

v -7(0 and (1)

where n(i) and n(j) are the number of atoms in the coordination

spheres of i and j, respectively. This principle of local valence

balance is a generalization of Pauling's principle of local charge

balance in ionic crystals, and is known as the valence sum rule [1].

( ii) The sum of the bond valences around any loop in the

structure, taken with alternating signs, is equal to zero

v„ =0.

loop 'J (2)

Equation (2) expresses the mathematical conditions that result

in the most regular distribution of the valences among the bonds in

a structure and is known as the equal valence rule [1]. The system

of equations (1) and (2) allows us to evaluate the valences of all the

individual bonds if we know how the atoms are bonded together in

a structure [2]. The description of atomic bonding in terms of bond

valences is useful because the length d of a bond between atoms

i and j is a function only of the bond valence v... The relationship

between these two quantities is expressed by the empirical formula

-0.37 lnv„ (3)

where the bond valence parameter R.. depends on the nature and the

oxidation states of atoms /' and j forming the bond, and expresses

the length of a bond of unit valence. Values of/? can be evaluated from the bond distances of known structures and are tabulated for most chemical species [3,4]. By means of equations (1-3) we may

evaluate the expected bond lengths for any known atomic configu-

(a)

e Ru o • 0

FIGURE 1 . Schematic representation of (a) the 4-layer structure of TRu03 [T= 0.875 Ba + 0.125 Sr); and (b) the 9-layer structure of BaRuG,. For clarity only the Ru and 0 atoms are shown in the figure. The symbols c and / indicate the layers on which the Ru06 octahedra share corners and faces, respectively.

ration. These distances satisfy exactly the valence requirements of

the atoms and, in general, differ significantly from those determined

experimentally. The discrepancies are in some cases due to the electronic behavior of particular cations, which may cause distortions

not accounted for by the bond valence model (for example, lone

pair distortions around cations such as Bi3+ and Pb2+

, or Jahn-Teller

distortions around Mn3+ and Cu2+

). In the majority of cases, however, the bond lengths calculated with equations (1-3) are incommensurate under the constraints imposed by the crystal geometry,

and have to be stretched or compressed in order to fit them into a

particular configuration. Since these changes introduce strains into

the structure, the process of adapting the theoretical model to the

requirements of a space group symmetry must be carried out in

such a way that the violations of the bond valence sum rule and

of the equal valence rule are kept as small as possible. We have

recently applied the concepts discussed above to the determination

of the crystal structures of IRu03 (T = 0.875Ba + 0.125Sr) [5] and

BaRuO, [6], using initially only the information obtained from the

indexing of the neutron diffraction patterns of these materials (i.e.,

crystal system symmetry and lattice parameters), and ignoring any

40 RESEARCH HIGHLIGHTS
A. Santoro I. Natali Sora Q. Huang

NIST Center for Neutron Research INFM and Department of Physics and Chemistry Department of Physics

National Institute of Standards and Technology University of Brescia University of Maryland

Gaithersburg, MD 20899-8562 251 23 Brescia, Italy College Park, MD 20742

other structural details obtained in the experimental work. Since T

2+

and Ba2+ have ionic radii similar to that of O

2

, we may expect that

the structures of IRuO, and BaRuO, are built with some sphere

packing mechanism. This assumption is corroborated by the fact

that in both cases the a-parameter calculated from the average r

of the ionic radii of A and O (A = T, Ba) for the composition

AO, is in good agreement with the experimental values, and by the

fact that the ionic radius of Ru4+

is quite close to the radius of

the octahedral void formed by the close packing of oxygen anions. The periodicity n of the stacking sequences of the AO, layers

in the vertical direction of the c-axis, evaluated with the formula

n = c/(2r\/2/3), shows that 7TtuO, and BaRuO, have 4- and 9-layer

structures, respectively, in which the Ru06 octahedra are related to one another as indicated in Fig. la and lb.

In order to fit this configuration, the theoretical bond lengths

calculated with equations (1-3) have to be changed, and in particular

the A-0 bonds have to be compressed, on the average, and the

Table 1. Models of the Structure of BaRu03 (R 3 m) 12 3 4

Lattice parameters (A) and atomic positions

a 5.754 5.754 5.747(1) 0.007

c 21.142 21.626 21.602(1) 0.024

X 1/6 0.1769 0.1769(1) 0.0000

z

, 1/9 0.1087 0.1082(1) 0.0005

Z

2 2/9 0.2185 0.2175(1) 0.0010

Z

3 7/18 0.3844 0.3829(1) 0.0015

Bond distances (A)

Ba(1)-0(1) 2.877 2.877 2.8733(1) 0.004

-0(2) 2.877 2.938 2.926(2) 0.012

Ba(2)-0(1) 2.877 2.988 3.002(2) -0.014

-0(2) 2.877 2.882 2.880(2) 0.002

-0(2') 2.877 2.957 2.945(3) 0.012

Ru(1)-0(1) 2.034 2.001 2.005(2) -0.004

Ru(2)-0(1) 2.034 1.995 1.974(1) 0.021

-0(2) 2.034 1.995 2.007(2) -0.012

Ru-0 bonds have to be stretched. This process of relaxation of

the initial model is carried out by modifying the structural parameters obtained from sphere packing geometry in such way that the

violations of equations (1) and (2) are contained within reasonable bounds [7]. The results of the bond valence analysis of BaRu03 are

reported in Table 1 , where they are compared with the corresponding values determined experimentally. Similar results, reported in

reference [5], were obtained for 7RuOr The agreement between

the observed and calculated structures is quite good for both compounds, and the differences between bond distances are well within

0.02 A. This result proves that, at least in favorable cases, the bond valence method may yield an accurate model of the structure

without requiring more information than that needed to index a powder pattern. More importantly, however, it shows that the need

to satisfy the valence requirements of the atoms with an acceptably

regular distribution of the bond valences is the driving force in

determining the magnitude and the direction of the atomic shifts allowed by the symmetry, and that, as a consequence, non-bonded

metal-metal and oxygen-oxygen interactions do not play an important role in the way in which the structures of these ruthenates are

built. In particular, the shifts that pull together the oxygen atoms

forming the shared faces of the Ru06 octahedra (thus providing a

shielding effect to Ru-Ru interactions) are specifically designed to improve the local valence balance of the Ru and O atoms involved

in the Ru-0 bonds. Application of the method to structural types

other than perovskites is now under consideration.

REFERENCES

[1] D. Brown, Acta Cryst. B48, 553 (1992).

[2] M. O'Keeffe, Structure and Bonding 71, 161 (1989).

[3] D. Altermatt and I. D. Brown, Acta Cryst. B41, 240 (1985); I. D. Brown

and D. Altermatt, Acta Cryst. B41, 244 (1985).

[4] N. E. Breese and M. O'Keeffe, Acta Cryst. B47, 192 (1991).

[5] A. Santoro, I. Natali Sora and Q. Huang, J. Solid State Chem. 143, 69

(1999).

[6] A. Santoro, I. Natali Sora and Q. Huang, (in preparation).

[7] I. D. Brown, Z. Kristall. 199, 255 (1992).

Note. 1, commensurate structure derived from sphere packing geometry;

2, model obtained with the relaxation process discussed in the text; 3, experimental results; 4, difference between calculated and observed values. The theoretical bond distances calculated with equations (1-3) are: 1-0 = 2.932 A, Ba-0 = 2.948 A and Ru-0 = 1.984 A. NIST CENTER FOR NEUTRON RESEARCH 41
RESIDUAL STRESSES IN COLD-COILED

HELICAL AUTOMOMOTIVE SPRINGS

Most front-wheel-drive automotive suspension systems use

helical springs. The process chosen to produce these is,

like any other engineering dilemma, determined by quality, perfor- mance, price, environmental issues, etc. Ford Motor Company has developed a potentially cost saving cold-coiling process in which .

less time is spent treating spring metal at elevated temperatures.

The pronounced residual stress pattern within the as-cold-coiled

spring is undesirable for its unpredictable effect on fatigue and

corrosion behavior, and Ford evaluates these stresses by X-ray measurements of the surface stress field along with modeling of the

internal stresses. The success of these at-home procedures requires

an independent verification of the actual residual stress field over

the cross-section of the original wire stock. The only available wellestablished method for this is neutron diffraction, and that is where

NCNR expertise comes into play.

Generally, there are two ways to coil a spring: hot coiling

and cold-coiling. Hot coiling implies that the spring is wound from

stock at or above the recrystallization temperature. The strength

and fatigue resistance are controlled afterwards by an appropriate

heat treatment. Cold-coiling means that the helical winding takes

place at a low temperature after the spring has been hardened and

tempered. Cold-coiling allows the high temperature heat treatments

to take place on the bar stock, which is easier to handle than the

coiled end-product. The resulting residual stresses can be essentially

eliminated by a relatively low temperature tempering treatment fol- lowing the cold coiling.

The idea is to measure the residual stress field in a number of specimens that represent various stages of the production process. Using neutron diffraction one can determine the effect of the prior

processing on the residual stress state of that particular stage in

the process. Of equal importance, these measurements can serve to

verify well established elasto-plastic models that are being used to

predict the formation of residual stress. Finally one can look for a way to correlate the residual stress at the surface to the stress field

as a whole. We have looked at three cold-coiled springs. The first spring

is an as-cold coiled spring. The second one is cold-coiled followed by a relatively low temper. The third one is identical to the second

one, but in addition to being tempered the spring has been compressed to the point where the length of the spring is equal to the

FIGURE 1. Experimental setup. The three arrows indicate three directions of measured lattice spacing with respect to the specimen: A = axial, R = radial, T = tangential. In the current configuration, the spacing of planes whose

normal is parallel to T is being measured. The sampling volume is defined by

the primary aperture P and secondary aperture S, respectively.

number of windings times the wire thickness. After this the spring was allowed to relax. A small part of this torsion strain is in the

plastic region, so this spring is slightly shorter than all the others. In

the automotive industry this process is known as "bulldozing".

The measurements were carried out on the Double Axis

system for Residual stress, Texture and Single crystal analysis

(DARTS) at beam tube 8 (BT-8) in the NIST Center for Neutron

Research. This instrument is specifically designed for residual stress measurements, and to that effect is equipped with very accurately

positioned apertures as is shown in Fig. 1

.

For these experiments the apertures were chosen to allow

a sampling volume of 2 x 2 x 2 mm3

. The residual stress in

the three springs across the cross-section of the originally 14 mm

thick wire stock was determined by detecting the diffracted monochromatic neutron intensity with a position sensitive detector. The

neutron wavelength was chosen such that the [211] Fe planes would

scatter diffracted intensity over approximately 90°. The specimen was rotated and translated in this geometry, such that the sampling

volume was scanned across this cross-section allowing the elastic

(residual) strain to be determined from the small shifts in scattering

%2 RESEARCH HIGHLIGHTS
Jiri Matejicek and Paul C. Brand A. R. Drews

NIST Center for Neutron Research Ford Research Laboratory

National Institute of Standards and Technology Dearborn Ml 48121

Gaithersburg, MD 20899-8563

-6 -4 -2 0 2 4

x (mm)

FIGURE 2. Contour map of the residual stress in the direction of the length of the coiled bar stock, plotted on the bar stock cross-section. With reference

to Fig. 1 , this is the tangential direction. This map represents the as-coldcoiled spring. The left and right side of the map represent the convex and

concave sides respectively.

angle. This was done in three mutually perpendicular directions. These strain measurements allowed us to calculate the residual

stress in three perpendicular directions from the equations published

by Allen et al. [1] in each of the three specimens. For every speci- men, the stress free lattice parameter was determined on the basis

that the net force on the cross-section under investigation had to

be zero.From these experiments a set of interesting observations can

be made. First is the notion that the residual stress pattern across the

wire stock in the as-coiled spring is very pronounced and exactly matches what one would expect when a cylindrical bar is plastically

bent into a hoop, a process much resembling helical coiling. With

reference to Fig. 2 we note essentially uniaxial residual stress in the

length direction of the original wire stock. Through the diameter of

the stock, the stress goes from highly compressive at the convex

side to highly tensile at the concave side. On its way through

the cross-section the stress level changes sign three times, while

the maximum compressive and tensile stresses are -600 MPa and

+800 MPa respectively. For the tempered and bulldozed specimens

Annealed 1.5 coil tangential stress m

1000

cO 800

4 600

400

2 200

0 0

-200

-2 -400

-4 -600

-6 i

-800

-1000

-6 -4 -2 0 2 4

x (mm)

FIGURE 3. Same as Fig. 2, these data representing the as-tempered spring. The data for the as-bulldozed spring, though not given here, look essentially the same.

the pattern is roughly the same, albeit at a much reduced level. The

stress range being from -170 to +160 MPa as depicted in Fig. 3. The uncertainties in these stress levels are around ± 30 MPa.

This means that the bulldozing process does not introduce additional residual stresses, a fact that can be well understood considering that the plastic deformation under pure torsion is essentially

uniform and thus cannot contribute to the residual stress state. These results will allow Ford to correlate their model predictions and X-ray residual stress measurements to the complete

residual stress field. This constitutes a powerful tool in optimizing

the parameters of the spring manufacturing process.

[1] A. J. Allen, M. T. Hutchings, C. G. Windsor, and C. Andreani: "Neutron

Diffraction Methods for the Study of Residual Stress Fields," Advances in Physics, 34, 445-473 (1985).

NIST CENTER FOR NEUTRON RESEARCH 43
THE NCNR NEUTRON

SPIN ECHO SPECTROMETER

The first experiments have been performed on the NCNR's

Neutron Spin Echo (NSE) Spectrometer, which is the only

spectrometer of its kind in the United States. This cold neutron

spectrometer allows studies of dynamic processes in macromolecular systems that are relevant to, among others, polymer [1] and

biomedical [2] sciences. It covers a time-scale of 0.01 ns to 100 ns and a length-scale of 2 A to 200 A with the equivalent of extremely

high energy resolution and moderate Q-resolution. Unlike the other

high-resolution inelastic instruments at the NCNR, which measure

in the energy domain, the NSE spectrometer measures, in the time

domain, the real part of the intermediate scattering function, I(Q,t).

This is done by using the neutron's spin precession in a magnetic

field as a clock to determine the energy transfer in the scattering

process.The NSE spectrometer, developed in partnership with Exxon

Research and Engineering and the Forschungszentrum Julich in Germany [3], is located at the end position of the NG-5 guide.

The guide is tapered horizontally and then deviated so that the

spectrometer is out of the direct line of sight of the reactor core,

thereby reducing the background and the radiation load on the sample region [4]. The taper is followed by a Neutron Velocity

Selector (NVS), which transmits a A\/\ = 10 % FWHM band

of neutrons to the spectrometer. The last element of the guide

is a transmission polarizer [5], which produces a polarized beam

of neutrons with spin anti-parallel to the beam direction for wavelengths greater than 5 A. The neutrons precess, from the first tt/2

flipper (1) to the sample, through a phase angle that is determined

by the time that the neutron spends in the solenoidal magnetic field

(4) and the field integral along the neutron path. Near the sample, a

it flipper (2) rotates the spin by 180° around the vertical axis. If the

solenoid on the second arm of the spectrometer provides the same

field integral for the scattered neutron and if the scattering is elastic,

the neutron will precess through the same phase angle as along the

first arm and will end up with the original spin orientation at the

final tt/2 flipper (3). This tt/2 flipper rotates the spin back into the

horizontal plane. If the neutron is scattered quasielastically, it will

precess a slightly different number of times in the second arm of the

spectrometer and end up at the second tt/2 flipper rotated by some

angle that is proportional to the wavelength shift. The analyzer (7)

projects the component of the neutron spin that is parallel to the

field direction onto the detector.

Figure 2 shows the detector count rate as a function of current

in the phase coil (5), which changes the field integral on one arm

of the spectrometer. The field integrals for the first and second arms

of the spectrometer are equal at the echo point where the amplitude

is at a maximum, since for an elastic scatterer the neutrons all

arrive at the analyzer in phase. As the phase current is changed,

the neutron spins rotate away from the polarization axis of the

analyzer (7) and the count rate is changed. The period of this oscillation is proportional to the mean wavelength. The envelope of the

+ (2I\I"IT+Cf>) 4l\llT+<p +(2l\l"Tr+cpV)4l\lTT-tp'

FIGURE 1. (Top) Schematic plan view of the NSE spectrometer. The numbers

refer to spectrometer elements as described in the text. (Bottom) Changes

of neutron spin orientation passing through the spectrometer elements for elastically (black) and inelastically (blue) scattered neutrons.

44 RESEARCH HIGHLIGHTS
Nicholas Rosov Silke Rathgeber Michael Monkenbusch

NIST Center for Neutron Research NIST Center for Neutron Research Institut fur Festkorperforschung

National Institute of Standards and Technology National Institute of Standards and Technology Forschungzentrum Julich GmbH

Gaithersburg, MD 20899-8562 Gaithersburg, MD 20899-8562 52425 Julich and Germany

University of Maryland

College Park, MD 20742

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Phase Current (A)

FIGURE 2. Phase scan of an echo for an elastic scatterer (Grafoil). A is the amplitude at the echo point; N0H and N0FF are counting rates with the it flipper on and off, respectively, and the rr/2 flippers off. —-0.0905 A

1 ,Xn = 10A

0 10 20 30 40 50 60 70 t(ns)

FIGURE 3. Normalized and resolution-corrected measurements of the

intermediate scattering function at the indicated Q-values for 10 % SDS in D2 0

at room temperature. The resolution curve is a normalized measurement of an

elastic scatterer (Grafoil) at 10 A.

NIST CENTER FOR NEUTRON RESEARCH

oscillations gives the wavelength distribution. The amplitude A is

proportional to I(Q,t), which can be normalized by measuring the

difference in intensity with the tt flipper on and off, NQN - N0FF For

the normalizing measurement, which is proportional to I(Q,t = 0),

the tt/2 flippers are off since there is no precession of the neutrons

in this configuration. Instrumental resolution effects are removed

by dividing the normalized sample signal by the normalized values from an elastic scatterer. We have also verified the operation of the correction elements

(6) which allow non-axial and divergent neutrons to satisfy the echo

condition. These are essential for operation at high fields. The value

of the resolution amplitude at 25 ns in Fig. 3 would be at least

a factor of ten smaller without the contribution of the correction

elements. As an example of the science that is available through NSE, we have reproduced the measurements of Hayter and Penfold [6] on

a micellar solution of 10 % sodium dodecylsulfate (SDS) in D,0.

Fig. 3 shows the normalized intermediate scattering function versus

time at several Q values at, well below, and well above the interaction peak in the structure factor. The effective diffusion constant Deff(Q), obtained from I(Q,t) ; exp(-D

cfl (Q)Q2 t), varies inversely

with the structure factor, reaching a minimum at the structure factor

peak, an effect analogous to DeGennes narrowing. As a result, in

a dilute solution of interacting micelles, one may unambiguously

separate the structure factor from the form factor, which may not be

done with only a SANS measurement.

REFERENCES

[11 B. Ewen and D. Richter, Adv. Polym. Sci. 134, 1 (1997).

[2] M-C. Bellissent-Funel et al., J. Am. Chem. Soc. 120, 7347 (1998).

[3] M. Monkenbusch, R. Schaztler, and D. Richter, Nucl. Instr. Meth. Phys.

Res. A 399, 301-323 (1997).

[4] J. R. D. Copley, J. Neutron Res. 2, 95 (1994).

[5] T. Krist, C. Lartigue, and F. Mezei, Physica B 180-181, 1005 (1992).

[6] J. B. Hayter and J. Penfold, J. Chem. Soc. Faraday Trans. I 77, 1851-1863

(1981).
SERVING THE SCIENTIFIC AND

TECHNOLOGICAL COMMUNITIES

Providing neutron beam methods to the U.S. research community is a central purpose of the NCNR. Intense neutron

sources are scarce, as are the advanced instruments needed to fully

exploit them. Expert scientists will always recognize opportunities

to perform research with the most powerful tools available, so

that the existence of the NCNR as the Nation's premier reactor- based neutron facility stimulates considerable demand from the community. However, in order to foster the best possible science,

many of our procedures and activities are designed to encourage

researchers to learn more about our capabilities, and eventually to

obtain instrument time through proposals and collaborations. The

first instruments became operational in the NCNR guide hall in

1991, and a formal proposal system was started to accommodate

users from universities, industry, and government laboratories.

Since then, the quantity and the diversity of research carried out

at the NCNR has grown steadily, and the number of research

participants (Fig. 1) is now several times larger than it was just a few years ago.

2000

1500

t:t 1000

In FY99 Research Participants were from: 23 NIST Divisions and Offices 34 U.S. Government Laboratories 105 U.S. Universities 55 U.S. Industrial Laboratories

500

86 87 88 89 90 91 92 93 94 95 96 97 98 99

Fiscal Year

FIGURE 1. Research participants at the NCNR.

THE USER PROGRAM

NIST has always relied on advice from accomplished scientists

to assist in formulating policy. The Program Advisory Committee

(PAC) is the body primarily responsible for proposal review and

recommending user policies for the NCNR, working closely with

the Center's Director and staff. Its current membership includes Sanat Kumar (Penn State University, chair), Robert M. Briber

(University of Maryland), Michael K. Crawford (DuPont), Dieter K. Schneider (Brookhaven National Laboratory), Thomas P. Russell

(University of Massachusetts), Sunil K. Sinha (Argonne National

Laboratory), Emile A. Schweikert (Texas A&M University), Laurence Passell (Brookhaven National Laboratory), and Gabrielle

G. Long (NIST). At their meeting in May 1999, the PAC made several recommendations for improving the current system. They felt that pro- gram proposals for longer-term projects had not had their intended

effect of reducing the burden for external reviewers, and should

be discontinued for the time being. Noting a potential for large

increases in instrument time for biology-related proposals in the

next few years, the addition of another PAC member with expertise

in that area was recommended. The PAC discussed the results of

a recent independent survey of user satisfaction, coordinated by

Anne Mayes of MIT. Ideas for obtaining more feedback from users were also considered. Incidentally, Professor Mayes, the head of the NCNR User's Group, recently won the American Physical Society's

Dillon Medal, partly for work carried out using NCNR instruments. Most of the PAC meeting was devoted to proposal review. With the help of several written reviews for each proposal from

selected experts, the PAC considered 151 proposals requesting 1138

instrument-days, and allocated 514 instrument-days to 95 proposals

for SANS, reflectometry, SPINS, and time-of-flight instruments. The PAC usually meets twice a year, but because of a planned

shutdown for cold source and reactor upgrades, only one meeting was held in 1999.

4 6
FIGURE 2. Nick Rosov explains the operation of the Neutron Spin Echo

Spectrometer to summer school participants.

SUMMER SCHOOL ON METHODS AND

APPLICATIONS OF NEUTRON SPECTROSCOPY

Each summer for the past five years, the NCNR has held a one- week school to introduce researchers to the methods of neutron

scattering. Organized by senior staff members John Copley and

Peter Gehring, the 1999 summer school was devoted to spectroscopy with neutrons, with an emphasis on the opportunities afforded by new instruments in the guide hall. Most of the 32 participants, chosen from almost 60 who applied, were graduate students and postdoctoral fellows. The curriculum consisted of lectures by NCNR

staff and experts from other institutions, tours of the facility, and

four three-hour, hands-on, sessions at instruments in the guide hall.

Informal discussions among students and the resident staff were

also an important part of the school's activities. Beginning with lectures on the fundamental concepts of

nuclear and magnetic scattering, the agenda turned to talks on applications of neutron spectroscopy to a wide range of research topics.

Subsequent presentations covered the reactor and cold source,

specific scattering techniques, computer modeling and ab initio

calculations, and the operating principles of various spectrometers

used in the experimental sessions. In the latter, students and staff

used time-of-flight, backscattering, triple-axis, and neutron spin- echo spectrometers to measure, respectively, quasielastic scattering from water, rotational tunneling in solid methyl iodide, magnetic

excitations in a geometrically frustrated antiferromagnet, and

coherent scattering from the time domain in a system of spherical

micelles. (The last example is illustrated in the article on the Neutron Spin Echo Spectrometer.) The lecture materials will be

placed on the NCNR website, in order to reach as wide an audience

as possible.

THE CENTER FOR HIGH-RESOLUTION NEUTRON

SCATTERING (CHRNS)

Supported by the National Science Foundation (NSF), CHRNS is a very important component of the user program. It operates a suite of

three instruments, including a 30 m SANS machine, the SPINS triple-axis spectrometer, and a double-crystal, high-resolution SANS.

The last of these is under construction. Approximately 40 % of the

instrument time allocated by the PAC goes to experiments carried

out on CHRNS instruments. The NSF is currently reviewing the CHRNS renewal proposal, which requests support for upgrading

existing instruments and including an improved 9 m SANS instru- ment within CHRNS. Approval would mean an increase of more

than 50 % in CHRNS' capacity to serve users.

COLLABORATIONS

Direct collaborations on specific experiments remain a common

way for users to pursue their ideas using NCNR facilities, accounting for approximately 60 % 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 also devoted to experiments that are

collaborations with non-NIST users. Another mode of access to the NCNR is through Participating

Research Teams (PRTs). In this case, groups of researchers from

various institutions join forces to build and operate an instrument.

Typically, 50 % to 75 % of the time on the instrument is then

reserved for the PRT, and the remaining time is allocated to general

user proposals. For example, a PRT involving ExxonMobil, the

University of Minnesota, Texaco R&D and NIST cooperates on

the NG-7 30 m SANS instrument. Similar arrangements involving

other PRTs apply to the horizontal-sample refiectometer, the highresolution powder diffractometer, and the neutron spin-echo spectrometer.

NIST CENTER FOR NEUTRON RESEARCH *7
INDEPENDENT PROGRAMS

There are a number of programs of long standing located at the NCNR which involve other parts of NIST, universities, industrial

laboratories, or other government agencies.

The Polymers Division of the Materials Science and

Engineering Laboratory has two major program elements at the NCNR. In the first, the purpose is to help the U.S. microelectronics

industry in addressing their most pressing materials measurement

and standards issues. In today's ICs and packages, the feature size on a chip is ever shrinking, approaching 250 nm, while the size

of a polymer molecule is typically 5 nm to 10 nm. As feature size

shrinks, the structure and properties of interfaces play an increasingly important role in controlling the properties of the polymer

layers used in interconnects and packages. NIST scientists use both

neutron reflectivity and other neutron scattering methods to characterize polymer/metal interfaces with regard to local chain mobility,

moisture absorption, glass transition temperature, and crystalline

structure. In the second program element, the objective is to understand underlying principles of phase behavior and phase separation

kinetics of polymer blends, both in the bulk and on surfaces, in

order to help control morphology and structure during processing.

SANS and reflectivity measurements in equilibrium, in transient

conditions, and under external fields provide essential information

for general understanding as well as for specific application of polymer blend/alloy systems. Customers include material producers

and users, ranging from chemical, rubber, the, and automotive companies, to small molding and compounding companies. The focus

of research on polymeric materials includes commodity, engineering

and specialty plastic resins, elastomers, coatings, adhesives, films,

foams, and fibers. 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 instru- ment and the recently commissioned NG-5 Neutron Spin Echo

Spectrometer. The mission is to use those instruments, as well as

other neutron scattering techniques, 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 experi- ments 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 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 during neutron

capture. NDP on the other hand, determines concentrations of

several important elements (isotopes) as a function 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. During the past several years, a large

48 SERVING THE SCIENTIFIC AND TECHNOLOGICAL COMMUNITIES
part of the Group's efforts has been directed towards the exploitation

of the analytical applications of the guided cold-neutron beams

available at the NIST Center for Neutron Research. The Group's

involvement has been to design and construct state-of-the-art 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 Center for Food Safety and Applied Nutrition of the

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 (INAA), neutron-capture

prompt-gamma (PGAA), and Radiochemical Neutron Activation

Analysis (RNAA) procedures, radioisotope X-ray fluorescence 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 foodrelated reference materials with NIST and other agencies, and by

verifying analyses for FDA's Total Diet Study Program annually.

Other studies include the development of RXRFS methods for

screening foodware for the presence of Pb, Cd, and other potentially

toxic elements, use of INAA to investigate bromate residues in

bread products, and use of PGAA to investigate boron nutrition and its relation to bone strength. The FDA's NAA laboratory personnel frequently provide intra-agency technical assistance, the most

recent example being participation in the production of the docu- ment "Accidental Radioactive Contamination of Human Food and

Animal Feeds: Recommendations for State and Local Agencies" by

the Center for Devices and Radiological Health. 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 reso- nance imaging. The Group's activities may be represented as three major activities. The first is Fundamental Neutron Physics - including operation of a neutron interferometry and optics facility, devel- opment of neutron spin filters based on laser polarization of -He, 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 from 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 235U fission neutron

field, and 252Cf 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.

Several 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. Johns Hopkins University participates in research programs in solid state physics 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 construction of a new 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 refiectometer. The University of Massachusetts also participates in the latter PRT

NIST CENTER FOR NEUTRON RESEARCH
REACTOR OPERATIONS

AND ENGINEERING

! he reactor operated for 250 full power (20 MW) days during the

past year, or 68 % of real time. This meets our goal, and was

achieved in spite of a shutdown for maintenance early in the fiscal

year. The reactor operated with better than 90 % predictability—i.e.

,

days operated on the day originally scheduled. This is substantially

better operation than is specified in national goal of 85 % reliability

for user facilities. Just after the end of the fiscal year, another fuel shipment was made, thus clearing additional space in the spent fuel

storage pool. This completes our current round of scheduled spent

fuel shipments. There is now ample storage space for at least 5 years

of continuous 20 MW operation.

TRTR Chairman-Elect, Pedro Perez, presents NIST Director, Raymond G. Kammer,

with a plaque stating:

"The National Organization of Test, Research and Training Reactors recognizes

the National Institute of Standards and Technology on the occasion of its centennial as the foremost measurements and standards laboratory in the

world, and honors NIST for 100 years of distinguished service to the nation and

to all the segments of science and technology, and particularly for its pioneering efforts in nuclear research and radiation standards and in appreciation of

its leadership in the formation of TRTR."

As part of preparing for another 20 years of operation past 2004, we have been assessing the present cooling tower. During the

past year, a contract for construction of a hybrid wet/dry tower was

signed. This new tower will not only meet our cooling needs; it

will also reduce the visible plume given off by the tower during the

winter months, a substantial additional benefit. The new tower will be erected adjacent to the current one, and will not require an outage

until the switch is made. This outage will be scheduled when the new

tower is fully ready for use, so as to minimize down time. Extensive

planning for the piping changes that will be needed is now underway.

It is expected that the new second-generation cold source will be

installed at the same time, so as to maximize operating time. During the coming year, we will take advantage of the normal

Christmas shutdown to replace the shim control arms. This operation

is required every 4 to 5 years, since the cadmium in the control arms is burned up in service. By utilizing the time period of the

holiday shutdown, the entire operation will be done with only 3 weeks of additional shutdown time. Since this period will also be

used for required training and requalification of operations personnel,

there will be little lost operating time compared to our best possible

schedule. A major highlight of the year was the annual conference of

the National Organization of Test, Research and Training Reactors (TRTR) held at NIST, chaired and organized by the group. By all

accounts, it was highly successful with the largest number of participants ever. Many distinguished speakers addressed the conference

including the Chairman of the Nuclear Regulatory Commission and

the Under Secretary of Energy. Also, TRTR became the first professional organization to honor NIST on its forthcoming centennial.

Finally, preparations for a license renewal application are

proceeding as planned. We are fortunate to have attracted Dr. Seymour H. (Sy) Weiss to our staff, as Deputy to NCNR Director. He

will be leading the relicensing effort and associated reactor upgrades

for the coming years, and has already started several tasks related

to this effort.

50
INSTRUMENTATION

DEVELOPMENTS

IMPROVEMENTS TO THE

PERFORMANCE OF HFBS

The recent commissioning of the high flux backscattering spectrometer (HFBS) has opened up opportunities to a variety of users from

around the country to study the dynamics of condensed matter

systems with time scales on the order of nanoseconds (10 9 s) and

length scales up to 10 A. A careful design which incorporates stateof-the-art neutron optics has resulted in a flux on sample as high

as that of any other backscattering spectrometer in the world with

comparable energy resolution. The first call for proposals for the HFBS was made in FY 1999 and the response was outstanding.

Several successful user experiments have already been performed

(see Fig. 1) with more scheduled in the near future. Although the

initial performance of the instrument was impressive, improvements

continue to be made.

One of the recent changes to the instrument has been a modification to the data acquisition system. Initially the data were binned

to the velocity of the reciprocating silicon monochromator. However

the method in which the velocity was determined overemphasized

local details of the monochromator motion which were not observed

FIGURE 1. Measurement of quasi-elastic scattering from monolayer coverage

of alkanes on grafoil performed on the HFBS by H. Taub, D. Fuhrmann, L. Criswell, and K. Herwig. The low temperature data (blue) is resolution limited with a full-width at half maximum of 0.96 \ie\l. The higher temperature data

(red) clearly displays broadening indicative of the diffusive motion of the

alkanes.

in the neutron data. A detailed analysis of the performance of the monochromator system indicated that the quality of the data could be improved by making a rather simple change in the way that

data is collected and stored, namely by binning data versus time

during a period of the Doppler monochromator motion. The data

are later re-binned to velocity using the average monochromator

motion profile. This straightforward change to the way that the data

are collected has improved the quality of the data, suppressing the

spurious effects observed in the velocity-binning mode.

Improvements have also been made to the Doppler monochromator system which have improved its reliability and perfor- mance. One of the problems encountered is associated with the

fact that the monochromator is being driven to higher energy transfers than any other Doppler monochromator system in the world. The monochromator, which is vibrated over a distance of 9 cm at

high frequencies, can experience accelerations in excess of 100 g's. Prolonged vibration of the monochromator resulted in the silicon

wafers coming off of the monochromator surface. Recent changes

in the gluing method have dramatically increased the lifetime of the

silicon wafers on the monochromator.

Efforts to optimize shielding in various parts of the instru- ment have resulted in improvements in the signal to noise ratio in

the detectors. During normal operation the instrument vessel (which

is made up of the sample, analyzer crystals, and the detectors) is evacuated in order to reduce the background due to air scattering.

Additional shielding has been installed on the detector assembly

and on parts of the analyzer system in the vessel. Improvements

have also been made to the shielding on the phase space transform chopper to handle the highly divergent beam from the converging

neutron guide. This has resulted in a substantial increase of the

signal to noise ratio to almost 600 to 1

.

THE DISK CHOPPER SPECTROMETER

The Disk Chopper Spectrometer (DCS) is an extremely versatile

time-of-flight instrument, designed to achieve a broad range of

energy resolution full widths, from 12 jxeV to 1 meV, by changing

chopper speed, wavelength, and/or beam width. Once commissioned, the DCS will be in high demand for experiments on a

variety of systems such as proteins, molecular crystals, disordered

materials, and metal-hydrogen systems. The instrument is to be

NIST CENTER FOR NEUTRON RESEARCH 51
FIGURE 2. Photograph of the DCS detector bank and flight chamber.

included, on a limited basis, in the first Call for Proposals in FY2000.

Over the past twelve months the DCS has seen major progress in a number of important areas. The sample chamber and flight chamber were equipped with beam-handling components, and the

insides of both chambers were lined with cadmium. Flow tests were

performed in order to complete the design of the gas handling

system for the sample and flight chambers; the system had been

fabricated and had largely been assembled by the end of the fiscal

year. An overhead platform, to be used for sample environment

preparation and installation into the sample chamber, has also been

designed.

Problems with some of the amplifiers for the DCS detectors prompted us to send the complete inventory to the manufacturer

for mutually agreed modifications. On their return discriminator

thresholds were individually set, and the full complement of 913

detectors and amplifiers was installed on the detector racks, which

were then installed and aligned at the spectrometer. The detectors and voltage distribution assemblies were cabled and fully tested

prior to installation of the outer shields. Much work was devoted

to troubleshooting and greatly improving the reliability and perfor- mance of the VME data acquisition electronics, and to the develop- ment of data acquisition software.

PERFECT CRYSTAL SANS DIFFRACTOMETER

A perfect crystal diffractometer (PCD) used for very high resolution

small angle neutron scattering (SANS) is being developed jointly by

the NCNR and NSF as part of the CHRNS facility. The higher resolution obtained by using perfect silicon crystals increases the maximum size of features that can be measured from 0. 1 \im obtained

using the current NCNR's two 30 m, pinhole geometry SANS

instruments, to 10 \xm with the new instrument. The monochromator and analyzer use triple reflections before and after the sample.

Using large channel-cut silicon crystals suppresses the "wings"

of the beam profile, improving the signal-to-noise ratio to values comparable to that obtained from the pinhole instruments. The PCD

will cover a Q-range from 0.0004 nnr' to 0.1 nrrr

1 with an expected

beam current of 50,000 s '. Located on the BT-5 beam tube in the Confinement Building,

the layout of the instrument is shown in Fig. 3. A vertically and

horizontally focusing graphite premonochromator directs the neutron beam away from the main reactor beam towards the perfect

crystal monochromator. The monochromator reflects a highly collimated beam to the sample. After the sample, a high precision

rotation stage rotates the analyzer crystal to scan the small angle

scattering obtained from the sample, which is then collected by

the detector. The shields supporting the premonochromator are set on kinematic mounts for accurate repositioning. The monochromator and analyzer are isolated from room vibrations using a heavy

pneumatic vibration isolation table.

Triple-bounce Premonochromator

Close-up Sample Collimator

Position FIGURE 3. Schematic layout of the BT-5 perfect crystal diffractometer.

S2 INSTRUMENTATION DEVELOPMENTS
In 1999, all detailed design work was finished and all pur- chased parts received. The beam shutter and premonochromator

shielding have been installed. Major components yet to be installed

are the detector housing, sample position table, and the small monochromator shield. Preliminary characterization measurements leading to instrument commissioning are planned for early 2000.

THE FILTER ANALYZER NEUTRON

SPECTROMETER

The new Filter Analyzer Neutron Spectrometer (FANS) is designed

to give U.S. researchers access to unprecedented sensitivity for measuring the vibrational spectra of a wide variety of materials.

This spectrometer, which will replace the current BT-4 instrument,

uses cryogenically cooled polycrystals as low energy band-pass

filters for neutrons scattered from the sample. A dramatic gain in

signal over the existing filter analyzer is achieved primarily through

a large increase in the solid angle covered by the secondary spectrometer. The FANS instrument is being developed in two phases.

Phase I includes the first of two new filter assemblies, and Phase II

includes the second filter analyzer and a new monochromator and

monochromator drum system.

FIGURE 4. The FANS filter assembly. The first Be filter is in the foreground with the PG filter second and the final Be filter in the background just before the detector bank. A radial collimator is visible in the middle of the assembly.

During the past year, the detailed design of the first filter wedge was completed, the vacuum chamber which encloses the Be and graphite filters was delivered, and the Be and graphite

filter wedges were assembled (see Fig. 4). Recent tests demonstrated that these filters can be cooled to cryogenic temperatures

which is necessary to maximize the performance of the instrument. Furthermore all of the parts for the undercarriage for Phase I have

been received, assembled, and operated successfully under load. Most of the shielding and data acquisition system have also been

received. Major assembly and installation of Phase I will begin early

in 2000.

DEVELOPMENT OF AN ACTIVE DOUBLE

FOCUSSING MONOCHROMATOR SYSTEM

The use of vertical or horizontal focussing monochromators to

increase the intensity of selected neutrons incident on the sample

is well known and widespread. Less common are systems combining these features. Often the machinery employed to do this is cumbersome and results in extraneous material in the beam, increasing the background from unwanted neutrons. For horizontal focussing it is desirable to have maximum flexibility by adjusting many

FIGURE 5. A drawing of the active double focussing monochromator system.

NIST CENTER FOR NEUTRON RESEARCH S3
monochromator elements while keeping the corresponding mechanical components away from the beam area. By contrast, vertical

focussing can be confined to the problem of adjusting only one

parameter, the radius of curvature of the array, and admits a correspondingly simpler mechanical solution. We are currently developing a system that combines completely flexible horizontal focussing with vertical focussing that is achieved by buckling the entire system of separately controllable

vertical crystal arrays. Cylindrical curvature is to be accomplished

by compressing the system of specially shaped strips upon which

the individual monochromating crystals are mounted. This design

eliminates extraneous material in the beam, which should result in

greatly reduced background.

AN ADVANCED LIQUID HYDROGEN

COLD SOURCE

The NIST liquid hydrogen cold source has completed over four

years of service. It was installed with three goals: at least double

the cold neutron intensity with respect to its predecessor (D,0

ice); operate simply and reliably; and pose no safety threat to the

reactor or personnel. It has successfully met or exceeded all these

goals. The cold neutron flux increased by a factor of 4 to 6, for wavelengths in the range of 0.2 nm to 2 nm. The availability of

the source has been nearly 99 % of the time that the reactor was

available (the reactor is shut down if the source is inoperable). And

there have been no hydrogen leaks, nor have any of the insulating vacuums or helium containments been compromised.

Even as Unit 1 was being installed in 1995, however,

improvements in the MCNP model (used for Monte Carlo simulations) of the NIST reactor were pointing toward a new, but more

complicated cryostat assembly, with a possible additional gain of a

factor of two. Better coupling between the reactor fuel and the cold

source can be achieved by expanding the cooling jacket into the volume now occupied by the insulating vacuum, so that it partially surrounds the moderator vessel. In this way, the D2 0 coolant also

serves as an extension of the reactor reflector. Additional changes

in the new source are based on our operating experience with the

existing LH2 source and extensive MCNP calculations. Unit 2 will be an ellipsoidal shell rather than spherical, it will have an evacuated

inner vessel, rather than vapor-filled, and the LH2 layer will be up

FIGURE 6. NCNR Mechanical Engineering Technician Scott Slifer welds the aluminum moderator vessel for the advanced hydrogen cold source.

to 30 mm thick, rather than 20 mm, without increasing the LH2 volume.

The advanced liquid hydrogen cold source is currently being

fabricated and will be installed in the NIST reactor next year. Enhanced mechanical design and manufacturing tools are exploited

in the fabrication of the advanced source. Components of the hydrogen, insulating vacuum, helium containment, and D2 0 vessels are

cut from solid blocks of Al 6061 on a computer-controlled, highspeed mill at the NIST Instrumentation shop, and are then welded

and thoroughly tested by NCNR staff (see Fig. 6). It is expected that

the flux of cold neutrons will increase by a factor of 1.8.

IMPROVEMENTS TO NCNR SAMPLE

ENVIRONMENT EQUIPMENT

The sample environment equipment has seen a number of changes in FY1999 at the NCNR. One of the most visible accomplishments has been the development of informative webpages

that detail sample environment resources, specifications, and even

the current operating condition and location for specific devices.

This information is easily accessible through the NCNR homepage

(http://www.ncnr.nist.gov/), allowing guest researchers to plan their

experiments and design appropriate sample holders.

54 INSTRUMENTATION DEVELOPMENTS
Commissioning has begun on a new high magnetic field/ low temperature superconducting magnet system which is financed

through a joint collaboration of Johns Hopkins University, NCNR,

NEC Research Institute, Princeton, the University of Maryland, and

a National Science Foundation IMR grant. The 0.022 K dilution

refrigerator of this new system has already been tested and used on

triple axis spectrometers. A 7 T magnet has been temporarily outfitted in the system at this time, with replacement by a much stronger

superconducting magnet of 10 T to 12 T in the coming months. The magnet is capable of operating with either a homogeneous

magnetic field at the sample position or with a field gradient, a

great aid for polarized neutron beam experiments. This system is

Table 1 Recent Sample Environment Acquisitions

Helium flow cryostat 1.5 K to 300 K, dedicated to backscattering spectrometer Helium flow cryostat 1 .5 K to 300 K, dedicated to disk chopper

time-of-flight spectrometer

Helium flow cryostat 1.5 Kto 300 K Pumped helium-3 cryostat insert 0.30 K to 300 K, for use with 7 T

vertical field magnet

Closed-cycle helium refrigerator 7 K to 320 K

Closed-cycle helium refrigerator 10 Kto 320 K, modified for backscattering spectrometer

Poiseuilte flow shear cell shear rate up to 130,000 s

1 near surface

Light scattering particle sizer 2 nm to 100 nm diameter Rheometer 1.7 x 10 3 Pasto2.7x108 Pas,

-60 °C to 600 °C, for in-situ measurement

during SANS experiments

Lyophilizer freeze dryer for sample preparation

Kare Fisher titrator quantitative analysis of water in a sample

Freezer -20 °C, for longer term storage of biological samples

Superconducting magnet OA to 120 A, bi-directional power supply

Dual channel lock-in amplifier 1 mHz to 1 02 kHz frequency range

Four temperature controllers programmable, remote operation

Dual channel lock-in amplifier OA to 120 A, bi-directional

Four temperature controllers programmable, remote operation

Single-crystal windowed tail for SANS low-temperature

electromagnet experiments

Sensitive equipment custom-designed to protect transport carts valuable equipment

top loading, which provides an important capability for experiments

requiring multiple sample changes or for quick changeover between

consecutive experiments.

From new capabilities to improved sample preparation and

screening, the sample environment resources have been significantly

expanded during the past year. Listed in Table 1 are further acquisitions, notable modifications, and improvements that combine to

offer the researcher more control over the sample conditions. Fig.

7 displays a typical cryorefrigerator sample environment. More

details are available at the web site mentioned above.

NCNR Sample Environment Geometry

Cryorefrigerators

First Stage

Aluminum

FIGURE 7. Schematic diagram of the sample environment in a

cryorefrigerator in the neutron beam.

NIST CENTER FOR NEUTRON RESEARCH 5S
RESEARCH

TITLES

MATERIALS SCIENCE/

CRYSTALLOGRAPHY

Acid Sites in Zeolite ZSM-5

A. Peters34

, R.-H. Hu214

, S. Purnell 214

, B. H. Toby102

, R. Senesi 150

, D. A. Neumann102 and

D. H. Olson197

Aerogels Investigated by SANS with

Contrast Masking Solutions

C. Merzbacher", M. Anderson"

V. Cepak" and J. G. Barker102 Amorphous Content Determination Methodology

J. K. Stalick102

, R. Senesi150 and

B. H. Toby102

Cation Location in Ion Exchanged

(Li,Na) Chabazite

L. J. Smith 175 and A. K. Cheetham 175

Characterization of Ag and Mixed

Li/Ag Faujasite Zeolites Using Neutron Diffraction

N. Hutson190

, R. Yang190

, B. A. Reisner102 and B. H. Toby102

Characterization of Microcracking in Iron Titanate by SANS

A. J. Allen 105 and E. Fuller105 Chemical Ordering in Ni-Mn-Ga

Heusler Alloys

R. Overholser188

, M. Wuttig 188 and

D. A. Neumann102 Comparison of Residual Stress Measurement Techniques T Gnaupel-Herold 188102

,

P. C. Brand102

, H. J. Prask102

, S. Spooner123

, B. Pardue152

, D. Nelson 149 and S. Foss70 Complex Oxide Structures

A. Sleight128

, 1. Radosavljevic128 and T Amos128 CONV and STRESS': New Codes for Data Reduction in Neutron Diffraction Residual Stress Measurements

P C. Brand 102 and

T. Gnaupel-Herold 188102 CPD Round Robin on Quantitative Phase Analysis

J. K. Stalick102

Crystal Chemistry of Protonic Centers

in Zeolites

D. H. Olson 197 and B. H. Toby102

Crystal Structure of Ba4 CaCu2 06 (C03

) Q. Z. Huang 102188 and F. Izumi 94

Crystal Structure of Dehydrated LaD-LSX

D. H. Olson 197

, B. A. Reisner102 and

B. H. Toby102

Crystal Structure of Ferroelectric Tetragonal Tungsten Bronze Lead Barium Niobate

Q. Z. Huang102188 and R. Guo133 The Crystal Structure of Pb5 Bi

18 P4 042 H. Steinfink157 and S. Giraud 157

Crystal Structure of Sr

2 Nb07 Q. Z. Huang 102188

,

T. Vanderah 104 and I. Levin 105

Defect Structure of (Cu,Zn)lnSe

2 B. A. Reisner102

, M. Knox169

, A. Stacy169 and G. Ron169

Effect of Annealing on Zr02 Phase

Composition

J. K. Stalick102 and J. Ilavsky33

Fast Ion Conductors

J. K. Stalick102

, B. Wuensch83 and

E. Ku83

Field and Temperature Dependent

Neutron Scattering Study of Mn 1? Magnetic Molecules T Yildirim 102 and S.-H. Lee188102

Grazing Incidence SANS from Plasma

Sprayed Coatings

A. J. Allen 105 and H. Boukari 105 Hydrogen Location in Graphite Nano-Fibers

S. F. Trevino 102 ' 8 and

P Anderson 118

Internally Oxidized Palladium Alloys:

Particle Size Determination by SANS

J. G. Barker102

Intermetallic Compounds of the A3 B

4 Structure

J. K. Stalick102 and R. Waterstrat102

Investigation of the Zr

g Pt

1t Structure Type

J. K. Stalick102 and R. Waterstrat 102

In Situ Neutron Reflectivity Measurements of Deuterium

Absorption in Pd Films

B. Heuser184

, A. Munter184

, N. Barber184

, J. A. Dura102 and

C. F. Majkrzak102

Kinetics of Gellation of Silica Under

Shear

C. D. Muzny116

, H. J. M. Hanley116 and G. C. Straty 116 Low Temperature Structure of Methyl

Halide Films on MgO

J. Larese 18

, M. Sprung 18 and

A. Freitag 18 Magnetic Cluster Sizes in Thin Film Magnetic Recording Disks M. Toney52

, S.-M. Choi 102 and

C. J. Glinka 102

Microstructure Evolution of Fly Ash

Blended Cements

A. J. Allen 105 and R. A. Livingston41

Modelling of Texture-Strain Relation- ships Using Neutron Diffraction Data

H. Sitepu 150102

, J. K. Stalick102 and

H. J. Prask102

Morphological and Kinetic Study of Early Calcium-Sificate-Hydrate Gel Development During the Hydration of Cement and Tricalcium Silicate

H. M. Jennings118

, J. J. Thomas118 and A. J. Allen 105 MSANS Study of Effects of Feedstock

Preparation on the Microstructure of Plasma-Sprayed Ceramic Coatings

A. J. Allen 105

, H. Boukari105 and

A. Kulkarni 150

Negative Thermal Expansion in A0P04 Compounds

A. W. Sleight128 and T. Amos128

Neutron Diffraction of Heusler Alloys

V. G. Harris99 and Q. Z. Huang102188

Neutron Diffraction of Single-Wall Carbon Nanotubes

P Papanek102

, J. Fischer197

, Z. Benes197

, D. Colbert138 and

M. Heben 138

Neutron Diffraction Study of Hydronium Ions in Zeolite ND4 D3 OX

D. H. Olson 197 and B. H.Toby102

Neutron Scattering and the Low

Energy Excitations in Polycarbonate

Copolymers

C. Soles111

, R. M. Dimeo102

, J. Liu 190

, A. Yee190 and A. Sokolov166 A New Phase of Silver Fluoride? No,

lt'sAg

10 C2

! R. L. Harlow35

Order-Disorder in CoFe/Carbon Composites

J. H. Scott115

, M. E. McHenry22

, Z. Turgut22 and M. Storch22 Phase Analysis of Sintered Yttria- Stabilized Zirconia

J. K. Stalick102 and A. Slifka 108 Phase Composition Analysis of Plasma-Sprayed Partially Stabilized Zirconia Coatings by Neutron Powder

Diffraction Data

H. Sitepu 150 102 H. J. Prask102

, J. K. Stalick102

, R. Goswani 150 and

S. Sampath 150

Polymerized Fullerenes

S. F. Trevino 102 8

, N. Beck-Tan8 and

L. Balogh89

Radiation-Induced Microstructure in Reactor Pressure Vessel Steels

G. R. Odette 175

, B. Wirth175 and

D. Klingensmith 175

Residual Stresses in Powder

Metallurgy Test Specimens

T Gnaupel-Herold 188102

, H. J. Prask102

, M.-J. Yang 133 and

R. German 133

Residual Stresses in Ti Rib Implants

for Children T Gnaupel-Herold 188102

, H. J. Prask102 and R. Roberts4

Residual Stress Measurements on

Railroad Rails I Gnaupel-Herold 188102

, R C. Brand102

, J. Gordon164

, J. Magiera32

, J. Orkisz32 and

H. J. Prask102 SANS and SAXS Determination of the Dispersion in Organic Solvents

of Organically Modified Clays for Polymer/Clay Nanocomposites

D. Ho188

, R. M. Briber188 and

C. J. Glinka102 SANS Characterization of Hydrides in Uranium

S. Spooner123

, G. Ludtka123 and

J. G. Barker102 SANS Investigation of Hydrogen

Trapping at Lattice Defects in Palladium

B. Heuser183 and J. S. King190 SANS Study of Fire Retardant Polymer-Clay Nanocomposites

H. J. M. Hanley116

, C. D. Muzny116 and J. Gilman 123 SANS Study of Oil Bearing

Sedimentary Rocks

A. Radlinski 10 and G. D. Wignall 123

Site Distributions in the Structure of Ba

2 Sn2 ZnGa10„Cr

x 022 (x = 3 and 4)

Q. Z. Huang102188 and R. Cava136

Single-Crystal Elastic Constants from Measurements on Polycrystals

T. Gnaupel-Herold188 102

, H. J. Prask102 and P. C. Brand102

Si02 Ultra Thin Films Round Robin

J. A. Dura102

, C. F. Majkrzak102 and

J. Ehrstein 112

Size Distribution and Volume Fraction

of Copper-Rich Precipitates in Model

Reactor Pressure Vessel Steels

D. Balzar109 and C. J. Glinka102

Solute Effects on Membrane

Thickness in DOPG and DOPC

J. Pencer183 and R. Hallett

183

Structural Ordering in Erbium Doped

Bi

2 03 B. A. Reisner102

, E. Wachsman180

, T J. Udovic102 and D. A. Neumann102

Structural Studies of Fullerene Superconductors

K. Prassides203 and

D. A. Neumann102

Structural Study of Sr

4 Nb2 0g Compound

I. Levin 105

, J. Chan105 and I Vanderah105

Structural Distortions in the NaSr3 M06 (M = Ru,Rh) Family

B. A. Reisner102

, A. Prieto169 and

A. Stacy169

Structural Distortions in Titanites

B. A. Reisner102 and D. Xirouchakis92

56
Structural Distortions in Zeolite RHO

B. A. Reisner102

Structural Studies of Germanium

Zeolites

J. B. Parise150

, G. M. Johnson150 and

A. Tripathi 150 and S. Park150

Structural Studies of High Silica Zeolite RHO

J. B. Parise150

, A. Tripathi 150 and

Y.-J. Lee150

Structural Studies of Iodine-Loaded ZSM-5

D. H. Olson197

Structural Studies of S^Rh^R^O,

Layered Perovskites

P. Woodward18

, B. Kennedy204 and

T. Vogt18

Structural Studies of Strontium Niobium Oxides

W. Wong-Ng 105

, W. Greenwood188 and B. H.Toby102 A Structural Sudy of the Ruddlesden- Popper Calcium Manganate Ca4 Mn3 O10 M. Greenblatt143 and I. Fawcett143

Structure of Barium Titanate Thin

Films on Silicon

C. Bouldin 105, B. Revel 105 and

J. A. Borchers102

Structure, Cation Ordering, and Magnetism in Manganate Spinels M. Green 140 and D. A, Neumann102

Structure of Ca2 Ta

2 Nb 0 . (x = 0.05 and 0.1)

Q. Z. Huang102 ' 188 and R. Roth102

Structure Determination of Ca2 RhD5 by Powder Neutron Diffraction

R. Mover162 and B. H. Toby102

Structure Determination of Framework

Materials with the RHO Topology

B. A, Reisner102

Structure Determination of Lao78 Sr

o 22 Ru03 Q. Z. Huang 102 188

, 1. Natali Sora168

, A. Santoro102 and F, T, Vanderah105

Structure Determination of Sr

2 lrD5 by Powder Neutron Diffraction

R. Moyer162 and B. H.Toby102

Structure Refinement of a Ferromagnetic Vanadium(lll) Sulfate

D. Grohol83

, D. Nocera83

, B. H. To by102 and Q. Z. Huang102 ' 188

Structure of Ca.AINbO, and CaTiO, Compounds

I. Levin 105

, J. Chan105 and

T. Vanderah 105

Structure of the Layered Cobalt Oxychlorides Sr

3 Co2 05 CI2 and Sr2 Co03 CI

Q. Z. Huang102 - 188

, N. McGlothlin 136

, D. Ho136 and R. J. Cava136 The Structure of a Lithium Substituted Aluminosilicate RHO

B. A. Reisner102 and J. B. Parise150

Structure and Oxygen Disorder in

Q. Z. Huang102 188 and W. Wong-Ng105

Structure of Porous Silica Thin Films W. Wu111 and D. Pochan111

Structure of 75.25:24.75 Ca0-Nb2 05 J. Chan 105

, 1. Levin 105, R. Roth105

, T. Vanderah 105 and B. A. Reisner102

Structure Refinements of Alumo- and

Gallo-Germanates Using Neutron

Scattering Techniques

S. Park150

, J. B. Parise 150 and

B. H.Toby102

Structure of Srt ^Dy, 125 Cu2 0,

Q. Z. Huang 102 - 188 and W. Wong-Ng105

Study of Hydronium Ions In Zeolites

D. H. Olson197 and B. H.Toby102 Temperature Dependence in the

Structure of Yttrium Tungstate

A. Sleight128

, P. Forster128 and

A. Yokochi128 Temperature-Dependent Structure Determination of Ca2 lrD

5 by Powder

Neutron Diffraction

R. Moyer162 and B. H. Toby102 Thermal Expansion of ll-VI Semiconductors

R. Reeber117 9 and K. Wang117 Thermal Expansion of Alpha SiC from 15 to 298K

R. Reeber117 - 9

, K. Wang117 and

B. H.Toby102 Thermal Expanion of HgSe

R. Reeber117 9 and K. Wang117

Zeolite SRM Characterization

B. H.Toby102 and R. Senesi150 X-Ray Reflectometry Analysis of Alkanethiol Deposited on AuO

K. T. Forstner102

, J. A. Dura102

, C. F. Majkrzak102

, J. Woodward104 and A. L. Plant104

Zeolite SRM Characterization

B. H.Toby102 and R. Senesi 150

Zirconium Tungstate Studies

A. W. Sleight128 and N. Duan128

POLYMERS

Behavior of Polymer Chains in Porous Media

M. Nieh133

, S. Kumar133 and

R. M. Briber188

Chain Conformation in Deformed

Elastomers

D. Peiffer40

, M. Rabeony40 and

M. Lin40

Chain Conformation in Self-Assembled, Layer-by-Layer Polyelectrolyte Thin Films

M.-P. Nieh 133

, S. Kumar133 and

R. M. Briber188

Characterization of Dye Distribution in Polymer Thin Films

C. White111

, E. Lin 111 and W. L. Wu111

Characterization of Organically Modified Clays

L.-T. Ho188

, R. M. Briber188 and

C. J. Glinka102 Conformation of Chains in Strained Polymer Networks

C. Cohen31 and R. M. Briber188 Conformation of Polymer Chains

Confined in Controlled Pore Glass

R. M. Briber188

, D. Ho183 and

I. Teraoka135

Conformation of Random Copolymers

in Solution M. Y. Lin40 and D. Peiffer40

Critical Neutron Reflection Tests of Polymer Interdiffusion Dynamics

R. P. Wool 179

, K. A. Welp179 and W. Dozier179 Demixing Kinetics of Polyolefin Blends

N. Balsara135

, H. Wang135 and

B. Hammouda102 Dynamics of Polymer Interdiffusion

S. K. Satija102

Effects of Polymer Additives on the Formation of Hydrate Crystals

J. M. Hutter40

, H. King 40 and M. Lin40

Effects of Pressure on the Lower

Critical Ordering Temperature of Diblock Copolymers

A.-V. Ruzette83 and A. M. Mayes83

Effects of Shear on the Phase

Behavior of Polyolefin Blends

N. Balsara135 and A. Lefebvre 135

Effects of Substrate Interactions on

the Ordering of Block Copolymer

Films

E. Huang 189

, J. DeRouchey189 and

T. P. Russell 189

Effects of Supercritical CO, on the Phase Behavior of Block Copolymer

Melts

J. Watkins189, M. Pollard 189

, G. Brown 189

, S. Kumar133 and

T. P. Russell 189

Effects of Surfactants on the Confor- mation of Grafted Polymer Brushes

T. Cosgrove166

, J. Hone166 and

R. Wesley166

Electric Field-Induced Orientation of Diblock Copolymers in Thin Films

J. DeRouchey189 and T. P. Russell 189

Glass-Transition Effects on Microphase Separation in PS/PVME

Polymer Blends

S. Kumar133

, R. Jones133, S. Kanath 133

, R. M. Briber188 and

L. Ho133

Inelastic Neutron Scattering from

Filled Elastomers

A. I. Makatani 111

, R. D. Ivkov102

,

P. Papanek102

- 197

, H. Yang 146 and

M. Gerspacher146

In-Plane Structure of PSAN/dPMMA

Blends in Thin Films

M.-P. Nieh 133

, S. Kumar133

, R. Jones133 and R. M. Briber188

Interdiffusion of Crosslinked Polymer

Films

U. Perez-Salas188

, R. M. Birber188

, M. Rafailovich 150

, J. Sokolov150 and

N. F. Berk102

Interfacial Scattering from Phase-Separated Polymer Blends

H. Jinnai 78

, M. Hayashi78 and

C. C. Han111

Investigation of the Concentration

Profile Between Crosslinked Thin Films

R. M. Briber188

, U. A. Perez-Salas188

, M. Rafailovich 150 and J. Sokolov150 Low Energy Excitations in Deuterated

Polystyrene

R. M. Dimeo102 and J. F. Douglas111

Kinetics of Shear Alignment of Block Copolymer Blends

R. Krishnamoorti183

, S. Rai 183 and

B. Hammouda102

Marginal Solvent Scaling of Polystyrene in Naphthalene

J. G. Barker102 Membrane Mediated Polymer

Interdiffusion

H. Gruell 111

, A. Esker111 and

C. C. Han 111

. Microstructure and Properties of Hyperbranched Polymers

N. Wagner179 and Y. Kim36 Morphology of Self-Assembled Aggregates of Amphiphilic Peptides

with Applications in Bioengineering

T. Gore191

, H. Bianco191

, Y. Dori 191 and M. Tirrell 191 Morphology of Single Graft Block Copolymers

S. F. Trevino 102 8

, N. Beck-Tan8

S. Guido189 and C. Lee189

Neutron Reflectivity from the Monolayers of SAN Random

Copolymers

E. Kim50

, H. Kim77

, K. Char145 and

S. H. Lee145

NIST CENTER FOR NEUTRON RESEARCH
Neutron Reflectivity Study of the Phase Separation in dPB/PI Blends

Using a Unique Back Transformation Technique

A. Schreyer102

, C. F. Majkrzak102

, N. Berk102

, H. Gruell 111 and

C. C. Han111

Neutron Studies of Polymer Dynamics

in Intercalated Polymer-Clay NanoComposites

R. D. Ivkov111

, P. M.Gehring102

, N. Maliszewskyj102

, P. Papanek102197 and R. Krishnamoorti 183

Nucleation and Growth in Binary

Polymer Mixtures Initiated by Pressure Jumps

N. Balsara 135

, A Lefebvre 135, H. Lee135 and B. Hammouda102 Phase Behavior of Multi-Component

Polymer Systems in Compressible

Solvents

J. Watkins189

, G. Brown 189

, V. RamachandraRao189

, B. Vogt189 and T. P. Russell 189 Phase Behavior of Polystyrene/ Polybutadiene Blends with Added Random Copolymer Studied via Small

Angle Neutron Scattering

D. Waldow131 and R. M. Briber188 Phase Separation in Polymer Thin Films

H. Gruell 111

, C. C. Han111 and

S. Kumar133 Phase Separation in Polyolefin Blends M. Modi 183 and R. Krishnamoorti 183

Polyethylene/Polymethylene Blends: Wetting and Phase Transitions

Y. Akpalu 111 and A. Karim 111 Polymer Brushes Under Shear

R. D. Ivkov 102

, P. D. Butler102 and

S. K. Satija 102 Polymer Chain Conformation in Thin

Films: Deviations from Bulk Behavior

in dPS/PS Films

S. Kumar133

, R. Jones133

R. M. Briber188

, L. Ho183 and

T. P. Russell 189 Polymer Interdiffusion Near the Polymer/Solid Interface

E. K. Lin 111

, D. J. Pochan 111

, W. Wu111

, S. K. Satija102 and R. Kolb40 Polymer Liquid-Crystal Ordering at an

Interface

G. Lynn205

, E. Lin 111

, W. L. Wu111 and

M. Dadmun205 Polymer Materials for Medical

Implants

A. Bellare49

, A. Gomoll49 and

R. Myers49 Polymer Supercritical Fluid Solutions M. McHugh71

, T. diNoia71

, J. van

Zanten71

, C. Kirby71, T. Kermis71 and

S. Conroy71

Polyolefin Polymer Blend Tie Chain

Structures

D. Lohse40

, M. Rabeony40 and

R. Garner40

Pressure Dependence of the Order- Disorder Transition in Diblock Copolymers

M. Pollard 189 and T. P. Russell 189

Pressure Effects on Crystallization and Phase Behavior of Binary Polyolefin Blends

R. Krishnamoorti183

, M. Modi 183 and

B. Hammouda102

Pressure Induced Phase Transitions in Multicomponent Polymer Systems

N. Balsara135 and A. Lefebvre 135 SANS from Dendrimer-Hydrophobe

Complexes

G. Nisato 111 and E. Amis111 SANS Investigations of a New Class of Nylon-6 Polymers

M. Kreitschmann 59 and

S. Rathgeber188 SANS Study of Phase Separation in Model Polymer Networks

B. Viers 178 SANS Study of the Thermodynamics of Blends of Star and Linear Polymers

M. D. Foster166 T. Zook166 and

C. Greenberg166

Self-Assembly of Polyethylene- Propylene-Ethylene Triblock Copolymers in Selective Solvents

L. Fetters40

, D. Richter59

, M. Monkenbush59 and W. Leube59

Shear-Induced Order-Disorder

Transition in Diblock Copolymer

Solutions

C.-l. Huang 191

, T. Lodge191 and C. C. Han 111 Shear Induced Polymer Desorption

E. Lin 111

, R. Kolb111 and W. L. Wu111

Shear-Induced Polymer Melt

Desorption from an Attractive Solid Surface

E. K. Lin 111

, D. J. Pochan 111

, W. Wu111

, S. K. Satija102 and R. Kolb40

Small Angle Neutron Scattering of Water Dispersable Arborescent

S. Yun188

, R. M. Briber188

, M. Gauthier215 and B. J. Bauer102

Solvent Vapor Induced Swelling of a Polymer Brush

S. K. Satija102

, R. D. Ivkov102

,

P. D. Gallagher102 and J. A. Dura102

Solution Structure of Arborescent

Graft Polymers

R. M. Briber188

, S.-W. Choi 188 ' 102

, S.-M. Choi102

, M. Gauthier215 and

B. Bauer111

Spinodal Decomposition in PS/PI Blends

H. Jinnai 78

, Hayashi78 and

C. C. Han111

Strain-Induced Interfacial Fracture Between Epoxy and Silicon Oxide M. Kent74 and W. F. McNamara74

Strained Polymer Networks

N. Gilra31

, C. Cohen31, R. M. Briber188 and T. Panagiotopolis188

Structure and Characterization of Ultrathin Polymer Films

R. L. Jones133

, S. Kumar133

, L.-T. Ho188 and R. M. Briber188

Structure of Filled Elastomer Thin Films

Y. Zuang150

, B. Tan150

, M. Rafailovich 150

, J. Sokolov150 and

M. Lin 40' 102

Structure of Fluorosilicone Networks

F Horkay45 and E. Geissler181

Structure of Genetically Engineered

Triblock Copolymer Gels

S. Kennedy189 and T. P. Russell 189

Structure of Nafion in Various

Solvents

S. F. Trevino 102 8

, S. Young8 and

N. Beck-Tan8

Surface Segregation in Binary Blends

of Topological^ Distinct Polymers

M. D. Foster166

, C. C. Greenberg166 and D. M. Teale166

Static Characterization of Star-Like Dendrimers

S. Rathgeber188 A. Gast149 and

J. Hedrick

Structure and Aggregation Kinetics of Asphaltenes

T. Mason40 and M. Lin 40

Structure of Adsorbed Polyelectrolyte Multilayer Thin Films

C. Barrett83 and A. M. Mayes83

Structure and Morphology of SemiCrystalline Polymer Thin Films

D. J. Pochan 111

, E. K. Lin 111

, W. L. Wu111

, S. K. Satija102

, C. F. Majkrzak102 and R. Kolb40

Structure of Polystyrene/Polyisoprene

Diblock Copolymer Micelles in Decane

J. Pople149

, J. Hur149, A. Lee149

, A. Gast149 and K. Barnes111 Temperature Induced Contrast

Variation Method in Semicrystalline

Polymers

J.Barnes111

, A.Nakatani 111, K. Barnes111

, B. Hammouda102 and

R. Kolb40 Thermal Expansion and Glass

Transition Behavior of Polymer Films:

Effect of the Free Surface and

Confinement Between Non-Interacting Surfaces

D. J. Pochan 111

, E. K. Lin 111

, W. Wu111

, S. K. Satija102 and

S. Z. D. Cheng166 Thermal Expansion and Glass

Transition of Thin Polymer Films Sandwiched Between Polymer Layers

D. J. Pochan 111

, E. K. Lin 111 and

W. L. Wu111 Thermodynamics of Mixing in Ternary Polymer Blend Mixtures

D. Waldow131 and R. M. Briber188 Two-Stage Spinodal Decomposition in a Rubber Blend

M. Hayashi78 and C. C. Han 111

COMPLEX FLUIDS

Compatibility of Oil Mixtures at High Temperatures

H. Aldrich 40 and M. Y. Lin40

Effect of Shear Combined with a Proximate Surface on Surfactant Sponge Phases and the Sponge to Lamellar Transition W. A. Hamilton 123

, P. D. Butler102

, G. Warr204 and L. Porcar123

Effects of Shear on Phase Boundaries

of Bicontinuous Microemulsions

S.-M. Choi102 and S.-H. Chen83

Electrostatic and Counterion-Specific

Effects on Micelle Morphology Probed

with SANS

L. J. Magid205

, P. D. Butler102 and

Z. Han 111

Field Driven Phase Transitions in Monolayers and Bilayers of Amphiphiles at Electrode Surfaces

J. Lipkowski182

, J. Majewski80 and

G. Smith80

Flow-Induced Microstructural

Transitions in Polyampholyte-Polymer

Colloid Mixtures

N. Wagner179

, K. A. Vaynberg179 and

R. Sharma179

High Pressure Study of Hydrophobic

Interactions M. Lesemann71

, C. Kirby71

, M. Paulaitis71 and J. VanZanten71

Kinetics of Poiseuille Flow-Induced

Structures in Solutions of Thread-Like

Micelles W. A. Hamilton 122

, P. D. Butler102

, Z. Han156 and L. J. Magid205

Kinetics of Polymerization of Rod-Like

Micelles

S. R. Kline 102

Micellar Fluids Near a Solid Interface

C. Sommer39

, W. A. Hamilton123 and

L. J. Magid205 Microemulsion Structure at an

Interface

G. Warr204

, J. Schulz204, P. D. Butler102 and W. A. Hamilton123

Microstructure of Alkylpolyglucoside Micelles and Microemulsions

L. D. Ryan 179

, D. lanspetro 179

, C. McKelvey179

, J. Silas 179 and

E. W. Kaler179

Microstructure and Properties of Hyperbranched Polymers

l\l. Wagner179

, B. Tande179 and Y. Kim 179

Microstructure of Shear Thickening and Shear Thinning Suspensions

N. Wagner179

, B. Moranzano179

, B. Schubert179

, B. Tunde179

,

P. Middhu179

, A. Vaynberg179 and

R. Butera37 Mixed Cationic/Anionic Vesicle Formation Kinetics Using TimeResolved SANS

P. Huibers83

, L. Shen83 and

I. Goldmints83 Octane Wetting of an Air/Water

Interface

S. Satija 102 and R. D. Ivkov102

Ordered Structures of Pluronic Micelles in Formamide Solutions

P. Alexandridis150

, L. Yang150

, S. Ann 150 and Y. Lin 150

58 RESEARCH UTILES
Percolation Transition in L-64 Triblock Copolymer Micelles

S.-M. Choi102

Polymeric Surfactants on Modified

Surfaces

A. Rennie16

, A. Jackson130 and

R. Thomas130

Poiseuille-Flow-lnduced Changes in the Structure of Surfactant Micelles

L. Walker22

, B. Poore22

, M. Truong22

, Y. Christanti22 and B. Hammouda102

Pressure-Induced Swelling of Polymer

Micelles in Supercritical Fluids M. McHugh71

, T. diNoia71

, J. van Zanten71

, C. Kirby71

, T. Kermis71 and S. Conroy71

Prewetting at a Hydrophobic Surface

in Phenol/Water Mixtures

A. Rennie16

, Z. X. Li

130 and

R. Thomas130 SANS Characterization of Wax

Modifiers for Diesel Fuel

L. Fetters40

, D. Richter59 and

W. Leube59 SANS Determination of the Persistence Length in Rod-Like

Micelles

L.J. Magid205 and P. D. Butler102 SANS Determination of the Structure

of Vitrified Emicroemulsions

G. Warr203

, P.R. Harrowell 204

, A. Widmer-Cooper204 and

P. D. Butler102 SANS from Nanodroplet Aerosols

B. Wyslouzil 219

, C. Heath219

, K Streletzky2 ' 9

, G. Wilemski 193 and

R. Strey58 SANS Investigation of Stimuli Responsive Hybrid Linear-Dendrimer Copolymers in Various Solvents M. Diallo20

, B. Bauer111 and

B. Hammouda102 SANS Measurements of Liposome

Size Distributions

S. F. Trevino102 - 8

, F. Lebeda216 and

G. R. Matyas7 SANS Study of the Factors Affecting

the Crystallization of Wax in Fractionated Petroleum

J. Hsu 156 and E. Sheu156 SANS Study of Interfacial Curvature in Microemulsions

S.-H. Chen83 and S.-M. Choi83 SANS Study of Organic-TemplateDriven Synthesis of Transition Metal Mesoporous Oxides

S. Elder123 and P. D. Butler102 Search for Micelle Formation in Caustic Solutions Used in Bauxite Processing

J. Watson 11

, H.J. M. Hanley116 and

M. Lin 40

Search for Surface Enrichment in Ultrafine Aerosol Droplets Using SANS

B. Wyslouzil 219

, G. Wilemski193 and

R. Strey58

Shear-Induced Structure in Rodlike

Micelles

P. D. Butler102 and C. Sommer39

Structural Evolution During Synthesis

of SBA-15 and MCF-Type Mesoporous

Silica

P. Schmidt-Winkel175

, G. D. Stucky175

, S. R. Kline 102 and C. J. Glinka102

Structure and Aggregation Behavior of Aqueous Solutions of Fulvic Acid

M. Diallo 51 and C. J. Glinka102

Structure and Aggregation of Soot in Flowing Motor Oil M. Y. Lin40 and M. Francisco40

Structure of Dendritic Diblock Copolymer Langmuir Films

P. Hammond83 and J. Iyer

83

Structure of Oil in Water Micro- Emulsions Stabilized by Triblock Copolymer Amphiphiles

J. Lettow83

, A. Zarur83 and J. Ying83

Structure of Ni(OH)2 Sheared

Dispersions of Colloidal Hard Plates

A. Rennie21 and A. Brown21

Solvent Effects on the Size and Shape

of Dendrimers

S. F. Trevino 102 8 and N. Beck-Tan102- 8 Temperature and Concentration Dependence of Polymer(PEO)-

Surfactant (SDS) Complexes in Aqueous Solutions

K. Chari38 and M. Lin40 Time-Resolved SANS Study of Microemulsion Polymerization

C. Co179 and E. W. Kaler179

CONDENSED MATTER

PHYSICS

Antiferromagnetic Ordering of La„

33 Ca0 67 Mn03 Thin Films

Y. Ijiri 124

, J. A. Borchers102

, J. W. Lynn 102

, R. W. Erwin102

, M. Rajeswari 188

, M. C. Robson188

, R. Ramesh188 and V. Venkatesan 188

Antiferromagnetic Structure Determination: Exchange-Based MnPd-Based Thin Films

J. A. Borchers102

, R. F. Farrow52

, M. Toney52 A Bond-Valence Analysis of the

Structure of YBa2 Fe

3 08

I. Natali Sora168 and A. Santoro102

Characterization of the Antiferro- magnetic Order in Exchange-Biased

Ni

8D Fe20/CoO Bilayers

N. Gokemeijer69

, C. L. Chien69

, Y. Ijiri 124

, J. A. Borchers102 and

R. W. Erwin102

Characterization of Thin Si0

2 on Si by Spectroscopic Ellipsometry, Neutron

Reflectivity and X-Ray Reflectivity

J. A. Dura102

, C. A. Richter59

, N. V. Nguyen18 and C. F. Majkrzak102

Charge, Orbital Magnetic Ordering and Two-Phase Coexistence in La

1/2 Ca1/2 Mn03 Q. Z. Huang 102 188

, J. W. Lynn102

, V. Smolyaninova188

, K. Ghosh188

, R. L. Greene188

, D. C. Dender102

, R. W. Erwin102 and A. Santoro102

Crystal and Magnetic Structure of ZnCr,

4 Ga„ 6 04 S.-H. Lee188 - 102

, W. Retcliff143

, T. H. Kim143 and S. Cheong143

Crystal and Magnetic Structures in C°

2 2 5 RU0 75 04 31,(1 CO2 25 Sn0 25 RU0 50 04 Q. Z. Huang102 - 188

, J. W. Lynn 102

, R. W. Erwin 102

, M. Crawford35

, R. L. Harlow35 and E. M. McCarron35

Crystal and Magnetic Structures of FeOCI

W.-H. Li

93

, S. Y. Wu93

, C. G. Wu93 and

J. W. Lynn102

Crystal and Magnetic Structures of La

3 Ru07 and La7 Ru8 026 Q. Z. Huang 102- 188

, R. Cava136

, R. W. Erwin102 and J. W. Lynn102

Crystal and Magnetic Structures of La

5 R2 °i 2 Q. Z. Huang 102 - 188

, R. Cava136

, R. W. Erwin 102 and J. W. Lynn 102

Crystal and Magnetic Structures of Sr

4 Fe2 C09 Q. Z. Huang102 - 188

, R. Cava136

, R. W. Erwin102 and J. W. Lynn 102

Crystal and Magnetic Structures of TbBaCo2 06 Q. Z. Huang 102 - ,88

, I. Troyanchuk13 and J. W. Lynn 102

Crystal Structure and Magnetic

Ordering in CoMo03 Q. Z. Huang102 188

, J. W. Lynn 102

, R. W. Erwin102 and M. Crawford35

Crystal Structure and Magnetic

Ordering in Co2 25 (Sn

0 25 )Ru0 75 O4 Q. Z. Huang 102 - 188 and M. Crawford35

Crystal Structure and Magnetic

Ordering in the Perovskite SrRu0 33 Mn0 67 O3 Q. Z.Huang 102 - 188 and R.J. Cava136

Crystal Structure and Magnetic

Properties of Th3 (Fe

1 .CoJ^Ti, s Alloy

V. G. Harris99 and Q. Z. Huang 102 - 188

Crystal Structure and Magnetic Order LaCaMnRu06 and LaSrMnRu06 J. W. Lynn 102

, Q. Z. Huang102 and

J. Gopalakrishnan188

Crystal Structure Determinations of the CeMnOj Compound

W.-C. Li

93

Crystal Structure of LitMn^Co,^

W.-C. Li

93

Crystal Structure of PrBa2 Cu4 08 W.-C. Li

93 and S. Y. Wu93

Crystallographic and Magnetic

Structure of a Series of Lanthanide Copper Oxides: LnCu2 04 B. A. Reisner102 - 150

, A. Stacy169 and

J. Luce169

Crystallographic and Magnetic

Structure of Tb2 Ni

3 Si5

F. Bourdarot102

, J. W. Lynn102 and

L. Gupta151 TIFR

Crystallographic Study of La0.67 Wl g33 MnO3 C. Adams102- 168

, J. W. Lynn102

, R.G. Williams187 and G. Zhao188

Determination of the Spin Hamiltonian

for a Spin-1/2 Antiferromagnetic with

a Spin Gap

M. Stone71

, J. Rittner71, D. H. Reich71 and C. Broholm 71 - 102

Effect of Superconductivity on the

Lattice Dynamics of Ba06 K

04BiO3 C. P. Adams102 - 188

, J. W. Lynn 102 and

S. N. Barilo 13 The Effects of Confinement of the

Collective Excitations in Superfluid Helium

R. M. Dimeo102

, P. Sokol133 and

D. Silva133

Effects of Field Cycling on Co/Cu and

Co/Ag Multilayers

J. A. Borchers102

, J. A. Dura102

, C. F. Majkrzak102

, S. Y. Hsu90

, R. Loloee90

, W. P. Pratt, Jr.

90 and J. Bass90

Effects of H on Magnetic Coupling in FeV Superlattices

B. Horvarsson 139

, G. Andersson139

, J. A. Dura102

, T. Udovic102 and

C. F Majkrzak102

Feasibility Studies of He3 Polarizers

for Magnetic SANS Measurements

T. R. Gentile 102

, G. L. Jones107

, A. K. Thompson 107

, J. W. Lynn102

, D. C. Dender102

, J. A. Borchers102 and

M. Toney52

Flux Lattice Structure in Nb and BaKBiO

D. C. Dender102 - 188

, C. Adams 102- 188

, J. W. Lynn 102 and X. Ling 19

Ground-State Selection in FCC and BCT Antiferromagnets due to Quantum

Disorder

T. Yildirim 102

, A. B. Harris197 and

E. F. Shender169 Incommensurate and Commensurate

Magnetic Structures in the Magnetoresistive R.Ni jSr Materials

F. Bourdarot30

, S. Skanthakumar5

, J. W. Lynn102 and L. C. Gupta151 Incommensurate Spin Fluctuations and Structural Transitions in Excess Oxygen-Doped La

2 Cu04+y R. J. Birgeneau83

, Y. S. Lee83

, R. J. Christianson 83

, M. A. Kastner83 and R. W. Erwin102

Influence of Interface Structure on the Magnetic Polarizability of a Pd-Co

Alloy Overlayer in Close Proximity to CoPt3 M. Fitzsimmons80

, F. Hellman173

, B. Maran 173 and A. Shapiro173

Interfacial Spin States in Magnetic

Tunnel Junction Multilayers

C. Piatt173

, A. E. Berkowitz173

, J. A. Borchers102

, J. A. Dura102 and

C. F. Majkrzak102

Interlayer Spin Coupling in FeMn-Based Spin Valves

J. A. Borchers102

, C. F. Majkrzak102

, A. Reilly29

, W. P. Pratt, Jr.

90

, J. Bass90 and D. C. Dender102

Lattice Dynamics of a Material with Negative Thermal Expansion, ZrW2 08 G. Ernst82

, C. Broholm71 - 102

, A. P. Ramirez82

, G. Kovac82 and

G. Gasparovic71

NIST CENTER FOR NEUTRON RESEARCH 31
Local Spin Resonance in a Frustrated Antiferromagnetic ZnCr2 04 S.-H. Lee188- 102

, C. Broholm71 ' 102

, T H. Kim83

, W. Ratcliff II 143 and

S-W. Cheong143 Low-Temperature Neutron Diffraction Studies of Pr

3 (Fe,Co)27 5Ti,5 Permanent Magnets

V. G. Harris" and Q. Z. Huang 102188 Magnetic and Crystal Structure Phase

Transitions in f?1j Ba i Co03 (R = Nd.Gd)

I. 0. Troyanchuk13

, D. D. Khalyavin 13

, T K. Solovykh13

, H. Szymczak13

, Q. Z.Huang 102 188 and J. W. Lynn 102 Magnetic Correlations and Lattice Distortions in the Bilayer Manganite

La,

2 Sr18Mn2 07 L. Vasiliu-Doloc 119

, S. Rosenbranz5

, R. Osborn5

, S. K. Sinha5

, J. W. Lynn102 and J. F.Mitchell5 Magnetic Correlations in Discontinuous Co-SiO, Thin Films and

Multilayers

S. Sankar188

, A. E. Berkowitz173

, D. C. Dender102 188

, J. A. Borchers102

, R. W. Erwin 102

, S. R. Kline 102

, J. A. Dura102 and C. F. Majkrzak102 Magnetic Correlations in a Geometrically Frustrated Magnet ZnV2 04 S.-H. Lee188 102

, C. Broholm71 102 and

Y. Ueda207 Magnetic Correlations in the Heavy

Fermion System LiV

2 04 S.-H. Lee188- 102

, C. Broholm71102 and

Y. Ueda207 Magnetic Depth Profile of CMR

Perovskite Films and Spin Valves

Y. Ijiri 124

, J. A. Borchers102

, J. W. Lynn102

, R. W. Erwin102

, C. F. Majkrzak102

, M. Robeson 188

, R. Ramesh 188

, V. Venkatesan 188 and

R. L. Greene188 Magnetic Domains in Co/Cu

Multilayers

J. A. Borchers102

, J. A. Dura102

, C. F. Majkrzak102

, J. Unguris106

, D. Tulchinsky106

, M. H. Kelley106

, R. Celotta 106

, S. Y. Hsu90, R. Loloee90

, W. P. Pratt, Jr. 90 and J. Bass90 Magnetic Domain Structure in CoPt

Thin Films

C. J. Glinka102 and M. Toney52 Magnetic Domain Structure of Thermally Treated Nanocrystalline

Ni

3 Fe

H. Frase20 and L. Robertson 123 Magnetic Order in EuMn2 P

J. Y. Chan105

, J. W. Lynn 102

, S. M. Kauzlarich 170

, A. Payne 170 and

B. A. Reisner102 Magnetic Ordering in the Spin-Ladder

Compound CaCu2 03 V. Kiryukhin83

, Y.-J. Kim83

, R. W. Erwin102 and R. J. Birgeneau83 Magnetic Ordering in the System

La, .P^BaCuFeOj

W. Mombru198

, F. Araujo-Moreira188

L. Suescun210

Magnetic Field Effects on Antifer- romagnetic Ordering in a Fe/FeF2 Bilayer

Y. Ijiri 124

, J. A. Borchers102

, R. W. Erwin102

, M.-C. Cyrille173

,

I. K. Schuller173

, J. Nogues167 and

D. Lederman218 Magnetic Order and Crystal Field

Effects in RNiBC

F. Bourdarot24 102

, J. W. Lynn 102

, Q. Z. Huang 102188

, D. R. Sanchez26

, M. B. Fontes26

, J. C. Trochez26 and

E. Baggio-Saitovitch 26 Magnetic Order and Fluctuations in a Zig-Zag Spin-1/2 Chain

I. A. Zaliznyak71 ' 102

, C. Broholm71102

, M. Kibune207 and H. Takagi207 Magnetic Order in Pr-Containing Cuprate Superconductors

W.-H. Li

93

, K. C. Lee93, H. C. Ku98 and

J. W. Lynn102 Magnetic Order in the Ferromagnetic

Superconductors RuSr2

160 GdCu2 08 B. Keimer84 ' 136 and J. W. Lynn102 Magnetic Order in the Superconductor

RNi2 B

2 C

J. W. Lynn102

, S. Skanthakumar5

, Z. Hossain151

, L. C. Gupta151

, R. IMagarajan 151 and C. Godart25 Magnetic Order, Structure, and Spin

Dynamics of (La,

K CaJMn03 J. W. Lynn 102

, R. W. Erwin 102

, J. A. Borchers102

, Q. Z. Huang102'

188

, A. Santoro102, K. Ghosh188 and

R. L. Greene188 Magnetic Properties of HoV04 C. K. Loong5

, S. Skanthakumar5

, J. W. Lynn102 and G. K. Liu 188 The Magnetic Structure of [MnTPPHTCNE] 2PhMe by High-Resolution Neutron Powder Diffraction

C. R. Kmety-Stevenson 125

, A. J. Epstein 125 and J. S. Miller211

, E. J. Brandon211 Magnetic Ordering and Structure of PrBa2 Fe

3 08 N. Rosov102

, J. W. Lynn102

, M. Seyedahmadian82 and T. Yeun82 Magnetic Ordering of ExchangeBiased Fe

3 04/Ni0 Superlattices

J. A. Borchers102

, R. W. Erwin102

, Y. Ijir 124

, D. M. Y. Lind42 and

P. G. Ivanov42 Magnetic Ordering of Mn in Nd, „Ca Mn03 S. Y. Wu93

, W-H. Li

93

, K. C. Lee93

, J. W. Lynn102

, R. S. Liu 97, J. B. Wu97 and C. Y. Huang 102188 Magnetic Structure in ZnV2 04 S.-H. Lee1W02 , C. Broholm 71102 and

Y. Ueda161 Magnetic Structure of Charge Ordered CaFe03 E. Moshopoulou18

, D. E. Cox18 and

P. Woodward125 Magnetic Structure Transition of AlFe, ,Mn, Under a Magnetic Field

Q. Z. Huang 102 ' 188 ,V. G. Harris99

, R. W. Erwin 102 and J. W. Lynn102

Magnetism of Ferrihydrite Nanoparticles M. S. Seehra218

, V. Suresh Babu218 and J. W. Lynn 102 Neutron Coherence Length and NonSpecular Scattering from Diffraction Gratings

C. F. Majkrzak102 and N. F. Berk102

Neutron and X-Ray Diffraction Study

of the Crystal Structure of Bi,

a Sr8 0,

Q. Z. Huang102188 and W. Wong-l\lg 105

Neutron and X-Ray Diffraction Study

of the Crystal Structure of Sr

0 495 Ca0 , 65 B'„.

39°,

Q. Z. Huang102 188 and W. Wong-l\lg 105

Neutron Diffraction Measurements of Nanostructured, Non-Equilibrium

Spinel Ferrites

V. G. Harris99

Neutron Reflectivity Studies of Fe

3 04/Ni0 Exchange-Biased Bilayers

D. M. Lind42

, J. A. Dura102 and

C. F. Majkrzak102

Neutron Scattering Study of the Nuclear and Magnetic Structure of RD3 T J. Udovic102

, Q. Z. Huang102 - 188

, J. W. Lynn102

, R. W. Erwin 102 and

J. J. Rush 102

Neutron Studies of New Incommensurate Magnetic Correlations Near the Lower Critical Concentration for Stripe Order in La,

6 i Nd04Sri CuO4 J. M. Tranquada18

, N. Ichikawa207

,

P. M. Gehring 102 and S.-H. Lee102 - 188 Oxygen Isotope Effect on the Spin and

Lattice Dynamics of La

5/8 Ca 3

, 8 Mn03 C. P. Adams102188

, J. W. Lynn 102

, V. Smolyaninova188

, G. M. Zhao188

, R. L. Greene188 and

S.-W. Cheong82143

Polarized Neutron Diffraction Studies

of Magnetic Ordering in ExchangeBiased Fe

3 04/CoO Superlattices

Y. Ijiri 124

, J. A. Borchers102

, R. W. Erwin102

, S.-H. Lee102 188

, C. F. Majkrzak102

, P. J. van der Zaag134 and R. M. Wolf134

Polarized Neutron Reflectrometry Measurements of CoPt Thin Films M. Toney52

, A. Schreyer102141

, J. A. Borchers102

, C. Majkrzak102

Polarized-Neutron Scattering Measurements of the Oxygen Moment in (La.Sr)MnO

P. M. Gehring 102

, G. Shirane18 and

H. Hirota159

Polarized Neutron Studies of Magnetic

Interfacial Roughness in EuTe/PbTe

Superlattices

H. Kepa128 102

, T. Giebultowicz128

, G. Bauer128 and C. F. Majkrzak102

Pressure Dependence of the Nuclear and Magnetic Structures in La

0 67 Ca0 33 MnO3 Q. Z. Huang 102 188

, J. W. Lynn102

, A. Santoro 102

, S. F. Trevino 1028

Pr Magnetic Order and Spin Dynamics

in the Cuprates

J. W. Lynn102

, Rosov102, S. N. Barilo13

, L. Kurnevitch 13 and

A. Zhokhov142

Q-Dependence of the Spin Flip Scattering from Exchange Coupling

across Fe-FeF2 Interfaces Measured

with Spin Polarized Neutron

Diffraction with Polarization Analysis M. Fitzsimmons81 and I. Schuller173

Reflectivity Measurements on Spin Valve Structures

D. Sarkisov199 and M. Dabaghian199 Refinement of the Ordered Moment in the QuasMD Antiferromegnet CsNiCI,

I. Zaliznyak71 ' 102 and C. Broholm71 102

Single-Ion Anisotropy and Crystal

Field Effects in R2 Cu04 (R = Nd, Sm,

Pr, ...) I Yildirim 102

, R. Sachidanandam 155

, A. Aharony155 and A. B. Harris197

Site Ditributions and Magnetic

Structures in AI 05 Fe05 Mn , x = 0.05, 0.1,0.15

V. Harris99

, D. J. Faremi99

, K. B. Hathaway99

, Q. Z. Huang 102 188

, A. Mohan193 and G. J. Long 193

Sites Distribution and Magnetic

Structure in La

2 (Co, FeJ^Ti

(x = 0,0.2,0.4)

J. K. Liang 57

, Q. Z. Huang102 188 and

A. Santoro102

Small-Angle Magnetic Scattering from

Nanocrystalline Cobalt

J. Weismuller200

, R. D. Shull 105

, R. McMichael105

, U. Erb137 and

J. G. Barker102

Spin Chain Direction in Copper

Pyrazine Nitrate M. Stone71

, D. H. Reich71 and

C. Broholm71102

Spin Dynamics of the Mn Ions in La^Ba^nO., and Pr^BaJVInO.,

J. W. Lynn102

, L. Vasiliu-Doloc119

, K. Ghosh188

, R. L. Greene188 and

S. Barilo 13

Spin Dynamics in LaTi03 B. Keimer84 136

, A. Ivanov65

, J. W. Lynn 102

, Y. Taguchi207 and

Y. Tokura207

Spin Dynamics in Single Crystal La

7 Ca 3 Mn03 CP. Adams188 102

, J. W.Lynn102 and

Y. M. Mukovskii91

Spin Dynamics of Strongly Doped

La,

x SrMn03 L. Vasiliu-Doloc 119

, J. W. Lynn102

.

Y. M. Mukovskii91

, A. A. Arsenov91 and D. A. Shulyatev91

Spin Freezing in a Geometrically

Frustrated Antiferromagnet, Y2 Mo2 07 J. Gardner87

, B. Gaulin87

, C. Broholm71102 and S.-H. Lee102188

Spin-Flop Tendencies in Exchangebiased Co/CoO Thin Films

J. A. Borchers102

, Y. Ijiri 102

, S.-H. Lee102 188

, C. F. Majkrzak102

, G. Felcher5

, R. Kodama99

, K. Takano173 and A. E. Berkowitz173

Static and Dynamic Properties of Spin and Charge Ordering in La2lSr

x Ni04 S.-H. Lee102 - 188

, S-W. Cheong82 and

G. Aeppli 100

60 RESEARCH TITILES
Strain-Induced Changes to the NiO

Spin Structure in NiO Thin Films I Regan 149

, R. White149 and

J. Stohr52

Structural Change and Magnetic

Ordering in Bilayered La

2 2i SrU2iMn2 07 W.-H. Li 93

, S. Y. Wu93

, H. D. Yang96 and J. W. Lynn102

Structural and Magnetic Ordering in

T. J. Udovic102

, Q. Z. Huang102- m, J. W. Lynn102 and R. W. Erwin102

Structural and Magnetic Ordering in

T J. Udovic102

, Q. Z. Huang102- 188

, J. W. Lynn102 and R. W. Erwin102

Structural Phase Transition and Magnetic Order in Heavy Fermion Compounds Ce3 M with M = Al. In and Sn

W.-H. Li 93

, K. C. Lee93 and

Y. Y. Chen82

Structure and Magnetic Order in Ba3 MRu2 Og

, M = Cu, Fe, Co, Ni, In

J. T. Rijssenbeek133

, Q. Z. Huang'02 188

, R. W. Erwin102 and

R. J. Cava136

Structure and Magnetic Order in Sr

3 CaRu2 09 Q.Z.Huang102 188 and R.J. Cava136

Structure and Magnetic Order in Sr

2 Y0 ,Ca , 2 Co2 06 Q. Z. Huang102 188

, J. W. Lynn102

, R. W. Erwin102 and R. J. Cava136

Structure and Magnetic Properties

in the SrJLa, 5Na05)IRu03 Solid Solution

Q. Z. Huang 102 188 and R. J. Cava136

Structure of YCo0 5 Mn0 5 03 T

»o5 Bao5 C ° 0, and Nd05 Ba05 CoO,

Q. Z. Huang102 188

, J. W. Lynn102

R. W. Erwin102 and I. Troyanchuk4

Structures of HgMo^BajCuO^ High T Superconductor

Q. Z. Huang102- 188

, M. Marezio63

,

F. Licci63 and A. Santoro102

Structures of Ba0 8 Sr

0 2 CoO

y Compounds

Q. Z. Huang102- 188 and R.J. Cava136

Structures of YM2 Cu2 85 Re015O7ti (M = Ba and Sr) High T Superconductors

Q. Z. Huang102 188

, M. Marezio63

,

F. Licci 63 and A. Santoro102

Structure Change of BaRuO, Under

High Pressure

Q. Z. Huang102- 188

, S. F. Trevino102- 8

A. Santoro102

, R. J. Cava136

Structure and Magnetic Ordering of M"[N(CN)

2

] 2 (M = Co, Ni, Mn)

J. L. Manson211

, C. R. Kmety-Stevenson125

, Q. Z. Huang 102 188

, J. W. Lynn 102

, G. Bendele150

, S. Pagola150

,

P. W. Stephens150

, L. M. Kiable-Sands18

, A. L. Rheingold 18

, A. J. Epstein 125 and J. S. Miller211

Studies of Charge, Spin and Orbital Ordering in the System

Bi1xCaxIVIn0

3

P. Woodward125

, J. Goldberger125 and

P. Santosh125

Studies of Magnetic Critical Scattering in Strained and Lattice- Matched (Y/Lu)IHol(Y/Lu) Films

P. M. Gehring 102

, C. F. Majkrzak102

, L. D. Gibbs18

, A. Vigliante 18

, A. C. Lake130

, J. Goff130 and

R. A. Cowley130

Studies of Spin Waves in the Ladder Compound La

5 Ca9 Cu24 041 M. Matsuda67

, G. Shirane18

, S.-H. Lee102- 188 and P. M. Gehring 102

Study of Low-Energy Excitations in a Weakly-Coupled Quantum Spin Chain System

A. Zheludev18

, K. Uchinokura60

, C. Broholm71

, 102 and S.-H. Lee188- 102

Study of the Relax or Based

Ferroelectric PZN-PT

P. M. Gehring102

, G. Shirane18

, R. E. Park133 and T. R. Shnut133

Superconductivity in La^S^CuO,,

S. Wakimoto159

, S. Ueki 159

, K. Hirota159

, K. Yamada159

, Y. Endoh 159

, R. J. Birgeneau83

, Y. S. Lee83

, M. A. Kastner83

, G. Shirane18

, S.-H. Lee102 - 188 and

P. M. Gehring102

Superconductivity, Magnetic Fluc- tuations and Magnetic Order in TbSr2 Cu269 Mo0 31 07 W.-H. Li 93

, W. Y. Chuang, S. Y. Wu93

, K. C. Lee93

, J. W. Lynn 102, H. L. Tsay96 and H. D. Yang96

Surface Spin Ordering in LaFe03 Thin Films

J. A. Borchers102

, J. Stohr52 and M. Toney52 TbNiBC Diffraction and Critical Scattering

F. Bourdaut102

, Q. Z. Huang 102 - 188 and

J. W. Lynn102 Temperature Dependence of the Exchange Coupling in Fe/Cr

Superlattices

A. Schreyer188

, C. F. Majkrzak102, T Schmitte141 Temperature-Dependent Crystallogra- phy and Zero-Field Magnetic Order of Mn[N(CN)2

] 2 (pyrazine-d

4)

J. L. Manson211

, J. W. Lynn102 and

J. S. Miller211 Temperature Evolution of the Spin

Excitation Spectrum in a Reentrant

Spin Glass Fe07AI 03 W. Bao80

, S. Shapiro18 and

S.-H. Lee188102 Three-Dimensional Spin Structure of Sr CuO CI : Field Dependent Neutron

Scattering Study T Yildirim 102

, S. Skanthakumai^and

J. W. Lynn102

Ultra-High Energy Resolution Studies

of the Second Length Scale in Single

Crystal Terbium

J. E. Lorenzo65, B. Farago65

, B. F. Frick65

, P. M. Gehring 102

, C. F. Majkrzak102 and G. Shirane18

Vortex Lattice in ErNi

2 BrC

P. Gamme182

, S. Lopez 182

, D. C. Dender102

, S. Choi188 - 102

, J. W. Lynn 102

, P. Cawield69

Vortex Lattice Structure in High-T

Bi-2212

B. Keimer136 - 84

, T. Fong 136 and

J. W. Lynn102

BIOMOLECULAR

SCIENCE

Conformational Changes of Chaperonin Complexes Involved in Protein Refolding

E. Eisenstein23

, J. Zondlo23 and

S. T. Krueger102

Determination of the Bending of DNA

Bound to Cyclic AMP Receptor Protein

in Solution

F. Schwarz23 and S. T. Krueger102

Determination of the Location of the

Lipid Anchor in Outer Surface Protein A of Borrelia Burgdorfei by SANS

D. Schneider18

, C. Lawson18 and

V. Graziano18

Gelation of Methylcellulose

C.-l. Huang191 and T. Lodge191

Interaction of the Peptide Penetration

with Phospholipid Double Bilayers

G. Fragneto65, E. Bellet-Amalric65

,

F. Graner65 and L. Perino

Interfacial Morphologies of Phospholipid Membrane Systems

B. Gaulin 87

, P. Mason27 and

R. Epand87

Internal Organization of Peptide- Nucleic Acid Complexes Derived from SANS

F. Schwarz23 and S. T. Krueger102

Interpretation of Specular and Off- Specular Reflectivity Data from

Patterned Thiahexaethyleneoxide Alkane Surfaces

N. F. Berk102

, C. F. Majkrzak102

, A. Munter102

, J. Woodward104

, C.W. Meuse104

, A. L. Plant104 and

S. T. Krueger102

In-Situ Measurements of Melittin Insertion into Hybrid Bilayer Membranes

S. T. Krueger102

, C. F. Majkrzak102

, J. A. Dura102

, A. L. Plant104 and

C. Meuse104 Lysozyme Adsorption at the Air/Water

Interface

J. Erickson 71 and K. J. Stebe71

Magnetic Field Alignment of Mixed

Lipid Discotic Micelles

J. Katsaras27

, R. Prosser74

, S. T. Krueger102 and C. J. Glinka102 Membrane Active Peptides: Phase

Transitions and Supramolecular Assemblies of Peptides in Membranes

H. W. Huang138

, W. Heller138

, T Harroun138 and L. Yang 138

Motion in Alpha-Lactalbumin and

Alpha-Lactalbumin Molten double

Studied by Quasielastic Neutron

Scattering

B. Zimei111

, D. A. Neumann102 and

C. C. Han111

Neutron Diffraction Studies of Peptides in Fluid Lipid Bilayers

S. White171 and K. Hristova171

Neutron Reflectivity Studies of Protein Adsorption/Desorption on the Surfaces

of Self-Assembled Monolayers

M. D. Foster166

, S. Petrash 166 and

C. F. Majkrzak102

Ordering in Protein/Polelectrolyte Multilayers

J. Rusling 177 and Y. Lvov99

Protein Adsorption at Solid/Liquid

Interfaces

J. R. Lu202

, T. J. Su202 and B. Green202

Quasielastic Neutron Scattering Study

of the Dynamics of Water in Saccharide Solutions

A. Tsai23

, M. Feeney136

,

P. G. Debenedetti136 and

D. A. Neumann102 Rnase-A Dynamics by Time of Flight Neutron Scattering: A Case Study in Protein Dynamics and its implications

for Drug Design, Formulation, and

Delivery

A. Tsai 23

, T. J. Udovic102

, J. R. D. Copley102

, D. A. Neumann102, J.J. Rush102

, M.Tarek102 - 197, D. Tobias171 and G. Gilliland 104 SANS Studies of Calmodulin/Target

Enzyme Interactions

S. J. Krueger80, J. Trewhella80

, N. Bishop80 and A. Wang104 SANS Study of Catechol Dioxygenases

from Pseudomonas Putida SH1

S.-L Huang93

, W.-H. Li

93 and

J. W. Lynn 102 SANS Study of Colloidal Interactions

of Proteins

0. Velev179

, P. Hinderliter179

, J. Silas179 and E. W. Kaler179 SANS Study of Cyclic-AMP-Dependent

Protein Kinase

J. Zhao80

, J. Trewhella80

, D. Walsh170 and R. Bruschia170 SANS Study of the DNA/Flap Endonuclease Complex

J. Trewhella80

, C. Kim80 and

S. Gallagher80 SANS Study of Protein Folding Mechanisms

R. M. Briber188

, R. Perez-Salaz188 and

S. T. Krueger102 SANS Study of the Ferredoxin TOL

Component of Toluence Dioxygenase

from Pseudomonas Putida F1

S.-L. Huang93

, D. T. Gibson 186, W.-H. Li

93 and J. W. Lynn102

Self Assembly of Peptide Amphiphiles

H. Bianco191

, T. Gore191, Y. Dori191 and

M. Tirrell191

Structural Investigation of the High Temperature Protonic Conductors

C. Karmonik206, Q. Z. Huang102- 188

, T J. Udovic102 and J. J. Rush102

NIST CENTER FOR NEUTRON RESEARCH ?-:
Structure of Hybrid Bilayer Membranes by Direct Inversion of Neutron Reflectivity Data

C. Majkrzak102, N. F. Berk102

, C. W. Meuse104

, V. Silin

104

, A. L. Plant104 and S. T. Krueger102

Structure of Intact Influenza Hemagglutinin Protein Containing the Viral Membrane Spanning Region

R. Blumenthal95

, D. Remeta143

, S. Durell 95 and S. T. Krueger102

Structure of Microtubule-Based

Cellular Motors Investigated by SANS

R. Mendelson 174

, D. Stone174 and

R. Hjelm80

Vectorially-Oriented Protein Monolayers: Neutron Reflectivity Studies

J. K. Blasie 197

, L. Kneller197

, E. Nordgren 197

, J. Strzalka 197 and

A. Edwards197

CHEMICAL PHYSICS OF

MATERIALS

A Quasi-Elastic and Inelastic Neutron

Scattering Study of Hydrogen in Zeolite R Sokol 133 and R. M. Dimeo102 Bond Lengths and Ground State Structure of the Fulleride Polymer

G. M. Bendele80

, A. Huq150 and

R W. Stephens150

Deposition Interdiffusion at Room

Temperature and the Kinetics of Interlayer Diffusion in Barium

Stearate Langmuir-Blodgett Films at the Temperature Just Below the Melting Point

L. A. Feigin 66 and I. I. Samoilenko66 Dynamics of Arsenic-Selenium

Glasses

B. Effey126

, R. L Cappelletti 126 and

W. A. Kamitakahara102 The Dynamics of Hydrogen Bonded

Guanidinium Based Materials

A. Pivovar191 D. A. Neumann102

, M. Ward and J. J. Rush 102 Dynamics of Hydrogen in Laves Phase

Hydrides

A. V. Skripov88

, J. C. Cook188102

, T J. Udovic102 and D. A. Neumann102 The Dynamics of Hydrogen in Single- Walled Nanotubes

W. M. Brown 188102

, T. Yildirim 102 and

D. A. Neumann102 Dynamics of Hydrogen Trapped by

Defects in Pd

R. Kirchheim201

, T. J. Udovic102 and

J. J. Rush102 Dynamics of Layered Silicates: Inter- calated Water

N. Wada160 and

W. A. Kamitakahara102 Dynamics of Li-Doped Carbon

Electrode Materials R Papanek102- 197

, J. E. Fischer191197 and W. A. Kamitakahara102

The Dynamics of Potassium Crytand

Complexes

N. C. Maliszewskyj102

, D. A. Neumann102

, D. J. Gilbert90 and

J. L. Dye90 Dynamics of Selenium-Arsenic- Bromine Glasses

R. L. Cappelletti 102 and

B. E. Schwickert169 The Effects of Confinement on

Tunneling in Methyl Iodide

R. M. Dimeo102

Evolution of the Structure of the K2 NiF4 Phases of La^S^NiO^ with Oxidation State: Octahedral Distortion and Phase Separation (0.2 < x < 1.0)

J. E. Millburn 130

, M. A. Green 130

, M. J. Rosseinsky130 and

D. A. Neumann102

First-Principles Calculations and

Neutron Scattering T Yildirim 102 and 0. Gulseren 197

First-Principles Calculations of Structural, Vibrational, and Electronic Properties of Solid Cubane

T Yildirim 102

, C. Kilic15 and S. Ciraci 15

First-Principles Investigation of Structure and Dynamics of NegativeThermal-Expansion Materials T Yildirim 102

Fulleride Superconductors I Yildirim 102

High Resolution Powder Diffraction of CeRh2 Si

2 G. M. Bendele80

, W. Bao80

, R. A. Robinson80 and J. L. Sarrao80 Hydrogen Dynamics in K3 MnH5 G. Auffermann165

, T. J. Udovic102

, J. J. Rush102 and T. Yildirim 102 Hydrogen Dynamics in ZrBeH, 5 I J. Udovic102 and B. Hauback61

Incoherent Scattering from Lipid Bilayers and Bilayers with Channel

Proteins Imbedded

H. H. Chen83

, C. Liao83 and T Weiss138

Inelastic Neutron Scattering Study of the Dynamics of Crown Ethers in Potassium Electrides

N. C. Maliszewskyj 102

, D. A. Neumann102

, M. Wagner47 and

J. L. Dye90

Inelastic Neutron Scattering Study of the Dynamics of Guanidinium-Based

Clathrate Materials

A. Pivovar191

, M. Ward 191

, D. A. Neumann102

, T. Yildirim 102 and

J. J. Rush102

Inelastic Neutron Scattering Study of the Hydration of Tricalcium Silicate

S. A. FitzGerald 124

, J. J. Thomas120

, J. C. McLaughlin120

, D. A. Neumann102 and

R. A. Livingston 41

Inelastic Neutron Scattering Study

of Rare Earth Trihydrides and

Trideuterides T J. Udovic102

, J. J. Rush102 and

Q. Z. Huang102- 188

Inelastic Neutron Scattering Study of Al Charged with Hydrogen

I J. Udovic102

, J. J. Rush 102

, C. Buckley184 and H. K. Birnbaum 184

Inelastic Scattering in Ce- and U-Based Non-Fermi Liquid Systems

W. Beyermann172

, T. Kelly172

, R. Robinson80 and B. Maple 173

In Situ Neutron Reflectometry Study

of Self-Assembled Poly(Dimethyl

Siloxane) Film M.-W. Tsao179

, J. Rabolt179

, A. Kalambur179

, L. Sung102 - 188 and

C. F. Majkrzak102

Investigation of Slow Motion Dynamics in Selective Adsorption

H. Taub192

, D. Fuhrmann192

, L. Criswell 192

, K. Herwig5 and R. M. Dimeo102

Isotopic Ordering in La(Dx H, ,) 3 T J. Udovic102

, Q. Z. Huang 102 188 and

J. J. Rush 102

Location of K and/or D Dissolved in Crystalline Pd3 P

08 T J. Udovic102

, Q. Z. Huang 102 - 188 and

Y. Andersson209 The Microscopic Glass Transition in Viscous Metallic Liquids

A. Meyer102188

, R. Busch20

, J. Neuhaus153 and H. Schober65

Neutron and X-Ray Reflectometry

Studies of Rough Interfaces in a Langmuir Blodgett Film

H. Kepa128

, L. J. Kleinwalks 158

, N. F. Berk102

, C. F. Majkrzak102

, I S. Berzina, V. I. Troitsky154

, R. Antolini 208 and L. A. Feigin 66

Neutron Investigation of Molecular

Reorientations in Solid Cubane

T Yildirim 102

, P. M. Gehring 102

, D. A. Neumann102

, P. E. Eaton 176 and

T. E. Emrick176

Neutron Scattering Studies of Hydration Reaction of Tricalcium

Silicate and Portland Cement

S. A. FitzGerald 124

, J. J. Thomas120

, D. A. Neumann102

, R. A. Livingston41 and J. McLanghlin120

Neutron Scattering Studies of the Dynamics of Hydrofluorocarbons

Encaged in NaX and NaY Zeolites

C. Karmonik206

, N. C. Maliszewskyj 102

, T. J. Udovic102

, J. J. Rush102

, M. K. Crawford35

, D. R. Corbin3 and R. R. Cavanagh 115

Neutron Scattering Studies on the

Vibrational Excitations and the

Structure of Ordered Niobium

Hydrides

B. Hauer59

, E. Jansen59

, W. Kockelmann59

, W. Schafer59

, D. Richter59

, R. Hempelmann200

, T J. Udovic102 and J. J. Rush 102

Neutron Scattering Study of the

Structure of Na2 C60 as a Function of Pressure and Temperature

I Yildirim 102

, D. A. Neumann102

, S. F. Trevino 102 8 and J. E. Fischer197

Neutron Scattering Study of the Dynamics of Hydrogen and Deuterium

Solved in Crystalline Pdg Si

2 C. Karmonik206

, T. J. Udovic102

, Q.Z.Huang 102188

, J.J. Rush102

, Y. Andersson212 and T. B. Flanagan212 Neutron Scattering Study of the Role

of Diffusion in the Hydration Reaction

of Tricalcium Silicate

S. A. FitzGerald 124

, J. J. Thomas120

, D. A. Neumann102 and

R. A. Livingston41

Neutron Scattering Study of the

Vibrational Modes of Cubane

T. Yildirim 102

, P. M. Gehring102

, D. A. Neumann102

, P. E. Eaton176 and

T. E. Emrick176

Neutron Spectroscopy of Single- Walled Nanotubes

R Papanek102

, J. Fischer197 and

A. Clay197

Neutron Vibrational Spectroscopy of Poy^HtD),

T J. Udovic102

, Q. Z. Huang102 - 188 and Y Andersson212

Neutron Vibrational Spectroscopy of Sr

2 lrH5 T J. Udovic102 and R. 0. Moyer162

Layer Shearing Modes in Li-Graphite Compounds

W. A. Kamitakahara102 C. Bindra197 and J. E. Fischer191 Low Energy Dynamics of Alkali

Silicate Glasses

J. Toulouse79 and D. A. Neumann102

Orientational Dynamics of P

4 Molecules in White Phosphorus

W. A. Kamitakahara102

, T. Yildirim 102

, D. A. Neumann102 and F. Gompf73

Preferential Isotopic Site Occupation

in Rare-Earth Hydrides

T. J. Udovic102

, Q. Z. Huang102 - 188 and

J. J. Rush102 Phonon Density of States in Sc2 (W04

) 3 C. Broholm71

, C. Urich 71 and

G. Gasparovic71

Pressure Dependence of Phonon

Density of States in Zr,W,0,

C. Broholm71

, C. Ulrich71 and

A. P. Ramirez82

Proton Dynamics in Hydrated Nations T J. Udovic102

, S. F. Trevino 102 - 8 and

M. K. Crawford35

Proton Dynamics in Strontium Cerate and Zirconate Ceramics

C. Karmonik206

, T. Yildirim 102

, T J. Udovic102

, J. J. Rush102 and

R. L. Paul 103

Quasielastic Scattering Study of the Liquid-Glass Transition Intertramethyl-Heptane

J. Toulouse79

, H. Cummins28 and

S. Goiqing28

Relaxational Dynamics in GeO,

A. Meyer102 - 188

, J. Neuhaus153 and

H. Schober65

Rotational Dynamics of C60 in (ND3 )K

3 C60 S. Margadonna203

, K. Prassides203

, D. A. Neumann102

, H. Shimoda2 and

Y. Iwasa2

G 2 RESEARCH TITILES
Rotational Excitations of Methane

Confined to Porous Glass

B. Asmussen75, R. M. Dimeo102 and

D. A. Neumann102

Search for Bragg Peaks in Se-As-Br Glasses

R. Cappelletti 102 and B. Schwickert169

Search for Su b lattice Ordering in PrD2+1 T. J. Udovic102 and Q. Z. Huang102 188 Slow Motion in Bulk-Glass Forming

Zr

46 8Ti82 CU7 5 Ni

10 Be27. 5 A. Meyer102 18S

, J. Wuttke153

, W. Petry 153 and H. Schober65

Structural Ordering in LaD3i

T. J. Udovic102

, Q. Z. Huang 102 188 and

J. J. Rush 102

Structure and Dynamics of Amorphous

Carbon

P. Papanek102 ' 197

, W. A. Kamitakahara102 and

J. E. Fischer197

Structure and Dynamics of Hydrogen

S. A. FitzGerald 124

. T. Yildirim 102

, L. J. Santodonato102

, D. A. Neumann102

, J. R. D. Copley102

, J.J. Rush102 andF. Trouw5

Structure and Dynamics of Hydrogen

in Nax CM

S. A. FitzGerald 124. T. Yildirim 102

, L. J. Santodonato102 and

D. A. Neumann102

Structure and Dynamics of an

Ultrahard Carbon

W. A. Kamitakahara102

, S. F. Trevino 102 3 and S. G. Buga64

Structure of the Ruddlesdon-Popper,

(Ln,Ca)n+1 Mnn 03n+1 Series

(Ln = Lanthanide)

M. Green140 and J. Waldron 140

Vibrational Densitites of States for Cubic and Hexagonal Boron Nitride W. A. Kamitakahara102

, D. A. Neumann102

, G. Doll46

, B Sweeting46 and A. W. Moore1 The Vibrational Isocoordinate Rule in Se-As-Ge Glasses

B. Effey126

, R. L Cappelletti 126 and

W. A. Kamitakahara102

INSTRUMENTATION

Assembly and Testing of the Filter Analyzer Spectrometer

A. W. Clarkson 102

, D. J. Pierce102

J. Reardon102

, S. Slifer102 and

G. M. Baltic102

Characterization of Fe/Si Reference

Layers for Reflectivity Data Inversion

C. F. Majkrzak102 "DARTS": A New Neutron

Diffractometer for Residual Stress Measurement, Texture Determination, and Single Crystal Diffraction

P. C. Brand 102

, H.J. Prask102 and

T. Gnaupel-Herold 188102

Data Acquisition and Analysis Software for the Backscattering Spectrometer

N. C. Maliszewskyj102 and R. M. Dimeo 102

Data Analysis Software for the Fermi Chopper Spectrometer

T. Yildirim 102 and C. M. Brown 188 Design of a Cable and Hose Management System for the NSE

Spectrometer

D. B. Fulford 102

Design of the Disk Chopper

Spectrometer

C. W. Brocker102 ' 188

Design of the Filter Analyzer Spectrometer

D. J. Pierce102

, R. Christman102 and

J. T. Kenney102

Design and Performance Testing of the DCS Data Acquisition System

Electronics

J. B. Ziegler102

. J. Raebiger59

,

P. Klosowski 102 N. C. Maliszewskyj102 and H. Layer102

Design and Testing of Vertically Polarized Heusler Alloy Monochrometer/

Analyzer

J. W. Lynn 102

, J. A. Borchers 102 and

K. T. Forstner102

Design of the Perfect Crystal SANS

Diffractometer

J. J. Mover102 and J. T. Kenney102 Development and Design of the Next- Generation Triple-Axis Spectrometer

C. W. Wrenn 188 102, M. Murbach 188102

,

P. C. Brand102 and J. W. Lynn102 Development and Installation of a Leak-Tight, Top-Loading, Horizontal

Field Superconducting Magnet

D. C. Dender102 '

'

88 and R. W. Erwin102 Development and Installation of a Radial Collimator and Horizontally Focussed Pb Analyzer for BT-2

J. G. LaRock102 and A. W. Carkson 102 Development and Testing of Fe/Si Supermirror Plates for the NSE

Analyzer

N. Rosov102

, S. Rathgeber188102

, C. F. Majkrzak102 and J. L. Wood129 Development of a Radially-Focussed

Polarizing Supermirror Analyzer Array M. Murbach 188 102

, P. C. Brand 102 and

N. Rosov102 Development of a Robust Static Thermal Switch for Fixed Sample

Environment Temperatures from

15 Kto 650 K

L. Santodonato102 Development of the HFBS Doppler

Drive

R. M. Dimeo102

, A. Meyer188102

, R. Christman102 and P. C. Brand102 Development of Synthetic Mica Monochromators

K. T. Forstner102 and L. Passell 18 Development of a Vacuum Rated

Preamplifier/Amplifier/-Discriminator

for 3 He Neutron Detectors

J. B. Ziegler102

Dy/SPP Neutron Detector

Y.-T. Cheng 101

, 102 and J. K. Stalick 102 and B. H. Toby102 The Disk Chopper Time-of-Flight Spectrometer(DCS)

J. R. D. Copley102

, J. C. Cook188102 and F. B. Altofer102132

Evaluation of New Neutron AreaDetectors

Y. T. Cheng 103' 101

Evaluation of a Beryllium Single

Crystal as a Monochromator

for'DARTS"

P. C. Brand102 and

T. Gnaupel-Herold 188102 The Filter Analyzer Spectrometer

D. A. Neumann102

, P. Papanek197

, J. E. Fischer197

, J. J. Rush102

, M. L. Klein 197 and A. C. Cheetham 175 The High Flux Backscattering Spectrometer (HFBS)

R. M. Dimeo 102

, D. A. Neumann102

, C. Karmonik206

, A. Meyer188 102 and

P. M. Gehring 102 Hydrogen Cold Source Development

R. E. Williams102

, P. A. Kopetka102 and J. M. Rowe102

In-Situ Real-Time Neutron Beam

Imaging

K. T. Fortner102 and

N. C. Maliszewskyj102

Installation and Testing of the New

Thermal Beam Tube Shutter Design

Using a Remote Actuated Cast System

J. J. Moyer102

, C. W. Wrenn188102

,

P. C. Brand102

, A. W. Clarkson 102

, G. M. Baltic102

, D. L. Clem102

, M. J. Rinehart102 and S. Slifer102

Installation of a New Heusler Alloy

Polarizing Analyzer for BT-2

K. T. Forstner102

, J. A. Borchers102 and J. W. Lynn102

Installation of Dedicated Crystal Alignment Spectrometer at BT-7 Beamline for Construction of FANS

Double Focusing Copper Monochromator

K. T. Forstner102 and

A. W. Clarkson 102

Installation of the Sample Chamber,

Flight Chamber, and Detector Assembly for the DCS

C. W. Brocker102- 188

, M. J. Rinehart102

, G. M. Baltic 102 and

S. Slifer102 Laue Focussing and its Applications

V. K. Kvardakov76, V. A. Somenkov76

, S. S. Shilstein 76

, J. W. Lynn 102

, D. F. R. Mildner103 and

H. H. Chen-Meyer103 MBE Chamber for in-situ Neutron

Scattering: Instrument Development

J. A. Dura102 Mica and Ge Reflectivity

K. T. Forstner102 and C. F Majkrzak102 Monte Carlo Methods for Nuclear

Applications

R. E. Williams102 Monte Carlo Simulation of the NIST

Cold Neutron Beamlines

J. C. Cook188 - 102

Neutron Scattering Properties and

Materials Properties Testing of the

Null Scattering Titanium Alloy to be used for High Pressure Cells

S. F. Trevino102 - 8

, K. T. Forstner102 and

R. Fields 110 The NIST Neutron Spin Echo Spectrometer (NSE)

N. Rosov102

, S. Rathgeber188 102 and

M. Monkenbusch59 Osmic and Mica Supermirror Tests

K. T. Forstner102 and C. F. Majkrzak102 The Perfect Crystal SANS Diffractomeeter

J. G. Barker102

, M. Agamalian 1 " and

C. J. Glinka102 Performance Tests of the Phase Space

Transform Chopper on NG-2

P. M. Gehring 102

, D. A. Neumann102 and C. Karmonik206 102 SANS Polarization Analysis with Nuclear-Spin-Polarized 3 He

T. R. Gentile 107

, G. L. Jones107

, A. K. Thompson107

, J. G. Barker102

, C. J. Glinka102

, B. Hammouda102 and

J. W. Lynn 102

Search for Effects on Neutron Trans- mission due to Multiple Reflection by Glass Capillary Walls

R. E. Beneson22 - 24

, H. H. Chen-Mayer22 and J. W. Lynn 102

Spin Echo Supermirror Development

N. Rosov102 and C. F. Majkrzak102

Supermirror Reflectivity Measure- ments

C. F. Majkrzak102 TANQENS-A New Utility for the Analysis of Quasiolate Neutron

Scattering Data

T. Yildirim 102

NEUTRON PHYSICS

Accurate Determination of Neutron

Capture Flux M. S. Dewey107

, M. Arif107

, D. M. Gilliam 107

, G. L. Greene80

, W. M. Snow56

, J. Pauwels62 and

R. Scott85 Benchmark Measurements and

Calculations of Neutron Transport

D. M. Gilliam 107

, M. S. Dewey107,

J. S. Nico107

, C. M. Eisenhauer107

, J. A. Grundl 107 and H. Gerstenberg6

Certified Neutron Fluence Standards from the Cavity Fission Source

J. A. Adams107 and J. A. Grundl107

Defined-Geometry Alpha Counting

D. M. Gilliam 107 and J. S. Nico107

Determination of the Neutron Lifetime M. S. Dewey107

, J. S. Nico107

, D. M. Gilliam 107

, W. M. Snow56

, G. L. Greene80 and X. Fei56

Highly Accurate Neutron Wavelength Measurements

M. S. Dewey107

, K. J. Coakley114

, W. M. Snow56 and M. Arif107

Intercomparison of NIST and PNL

Calibration Facilities

A. K. Thompson 107

, R. B.Schwartz107

, J. McDonald 12 and M. Murphy12

NIST CENTER FOR NEUTRON RESEARCH 33
LASER Polarization of 3 He for Neutron

Spin Filters and Medical MRI

A. K. Thompson107

, T. R. Gentile107

, M. S. Dewey107

, G. L. Jones'07 56

, E E. Wietfeldt10749

, W. M. Snow56 and R. Rizi 197

Neutron Calorimetry

W. M. Snow56

, Z. Chowdhuri56

, X. Fei 56 and M. S. Dewey107

Neutron Fluence Rate Measurements

D. M. Gilliam 107

, J. S. Nico107 and

J. A. Adams107

Neutron Interferometry and Optics M. Arif107

, D. L. Jacobson 107

, R. Clothier14

, A. K. Thompson107

, S. A. Werner192

, A. loffe 192107

, A. Zeilinger185

, K. Raum 194

, B. Schillinger194

, C. Rausch 194 and

W. Richards85

Neutron Radiography/Tomography

T. R. Gentile 107

, M. Arif107 and

D. L. Jacobson 107

Parity Non-Conserving Neutron Spin

Rotation

B. Heckel214

, D. Markoff214

, E. Adelberger214

, S. Penn214 and

F E. Wietfeldi107 ' 49

Quality Assurance Checks on Masses

and Impurities in Neutron Dosimeters

for NRC Reactor Pressure Vessel Embrittlement Surveillance

J. A. Adams107

, D. M. Gilliam 107 and

J. A. Grundl107 Response of Albedo Dosimeters

Versus Distance from a Neutron Source

R. B. Schwartz107 and

A. K. Thompson107 Response of Albedo Neutron Dosimeters as a Function of Angle

R. B. Schwartz107

Study of Time Reversal Invariance in Neutron Beta Decay

J. Wilkerson217

, E. Wasserman169

, J. S. Nico107

, R. G. H. Robertson169

, S. Freedman169

, A. Garcia195

, T Chupp23

, K. Coulter23

, M. S. Dewey107

, G. L. Greene80

, A. K. Thompson107

, B, Fujikawa169

, G. L. Jones 107 56

, J. A. Adams107

, E E. Wietfeldt10749

, L. Using 169

, S. Hwang23 and T. Steiger214

Trapping of Ultra Cold Neutrons

J. M. Doyle49

, S. K. Lamoreaux80

, R. Golub48

, G. L. Greene80

, M. S. Dewey107

, P. R. Huffman49

, C. R. Brome49

, C. E. H. Mattoni 49

, J. Butterworth49 and

D. N. McKinsey49

Utilization of the Materials Dosimetry

Reference Facility-Tests of New IRMM

237 Np and 238 U Fast Neutron Dosimeters

J. A. Adams107

, J. A. Grundl 107

, C. M. Eisenhauer107

, D. M. Gilliam 107 and P. Simpson23

MATERIALS ANALYSIS

A Bender-Focuser for Prompt Gamma

Activation Analysis

E. A. Mackey103

, H. H. Chen-Mayer103

, R. M. Lindstrom 103

, D. F. R. Mildner103

, R. L. Paul 103, Q.-F Xiao213 and V. A. Sharov220

Analytical Applications of Cold Neutrons

H. H. Chen-Mayer103

, R. Demiralp103

, R. R. Greenberg103

, G. P. Lamaze103

, J. K. Langland 103

, R. M. Lindstrom103

, E. A. Mackey103

, D. F. R. Mildner103

, R. L. Paul 103 and V. A. Sharov220

Application of Radioisotope-lnduced

X-Ray Emission to the Identification of Lead and Other Elements in Ceramic

Glazes and Housewares

D. L. Anderson43 and

W. C. Cunningham43

Archeological Applications of NAA

R. Bishop147 and M. J. Blackman 103 Bromation in Breadmaking

W. C. Cunningham43 and

C. R. Warner43

Bio-Analytical and Specimen Bank

Research

R. R. Greenberg 103

, G. V, Iyengar113

, J. K. Langland 103

, E, A, Mackey103

, B. J. Porter103 and R. Zeisler103

Certification of Standard Reference

Materials by Neutron Activation Analysis

D. A, Becker103

, R. Demiralp103

, R. R. Greenberg 103

, R. M.

Lindstrom 103

, E. A. Mackey103 and

R. Zeisler103

Characterization of Sources and

Fluxes of Particulate Pollutants Depositing to Great Waters

P. F. Caffrey188

, A. E. Suarez188 and

J. M, Ondov188

Characterization of Submicrometer

Aerosol Particles

J. M. Ondov188

, S. F. Heller-Zeisler188 and R. Zeisler103

Determination of Hydrogen by PGAA

R. R. Greenberg 103

, R. M. Lindstrom103

, E, A. Mackey103 and R. L. Paul 103

Determination of Phosphorus via RNAA with Beta Counting

R. L. Paul 103 Development of Radiochemical

Separation for NAA

D. A. Becker103

, R. R. Greenberg 103 and E. A. Mackey103

Evaluation of Accuracy and Precision

in INAA of Botanical Materials

D. A. Becker103

Evaluation of Errors and Interferences

in NAA

D. A. Becker103

, M. J. Blackman 147

, R. R. Greenberg 103

, R. M. Lindstrom103 and R. Zeisler103

Focusing Methods for Radiography and Topography

H. H. Chen-Mayer103

, D. F. R, Mildner103

, K. M. Podurets76

V. A. Sharov220 and S. S. Shilstein 76

High Sensitivity Gamma-Ray Spectrometry

R. M. Lindstrom 103 Homogeneity and Composition of Small Solid Samples

R. Zeisler103 Hydrogen Detection in Industrial Materials by Incoherent Neutron

Scattering

H. H. Chen-Mayer103

, V. V. Kvardakov76 D. F. R. Mildner103

, V. A. Somenkov76 and D. Kozlenko72 Improvements to INAA Methodology

D. A. Becker103

, R. Demiralp103

, R. R. Greenberg 103

, R. M.

Lindstrom 103

, E. A. Mackey103 and

R. Zeisler103 Improvements to PGAA Methodology

D. L. Anderson43

, R. M. Lindstrom 103

, E. A. Mackey103 and R. L. Paul 103

Lithium Migration in Electrochromic

Thin Films

G. P. Lamaze103

, H. H. Chen-Mayer103

, M. Badding144

, A. Gerouk163 and

R. Goldner163

Multielement Analysis of Foods and

Related Materials by NAA

D. L. Anderson43 and

W. C. Cunningham43

Neutron Absorption Measurements

Using Converging Beams

H. H. Chen-Mayer103

, E. A. Mackey103

, D. F, R. Mildner103 and R. L. Paul 103

Neutron Autoradiography of Paintings

Y.-T Cheng 101 103 and J. Olin 127

Neutron Beam Spatial Distributions Using Imaging Plate Technology

H. J. Bahre44

, H. H. Chen-Mayer103

, Y.-T Cheng101103

, D. F. R. Mildner103 and V. A. Sharov220

Neutron Depth Profiling of AIN Thin Films

H. H. Chen-Mayer103

, G. P. Lamaze103 and S. McGuire31

Neutron Depth Profiling of c-BN

H. H. Chen-Mayer103

, G. P. Lamaze103 and L. Pilione12

Nitrogen Profiling of Thin Titanium

Nitride Films

G. P. Lamaze103

, H. H, Chen-Mayer103

, N. Cox68 and E. B. Steel 115

Neutron Focusing for Analytical Chemistry

H. Chen-Mayer103

, G. P. Lamaze103

, J. K. Langland 103

, R. M. Lindstrom 103

, E. A. Mackey103

, D. F. R. Mildner103

, V. A. Sharov220 and J. R, Swider115

Neutron Distribution Measurements

by Neutron Induced Autoradiography

Z. En213

, J. S. Brenizer213 and

D. A. Becker103

Neutron Dosimetry for Instrument Development

R. M. Lindstrom 103

Neutron Scattering Effects on PGAA

R. R. Greenberg 103

, R. M.

Lindstrom 103

, E. A. Mackey103

, R. L. Paul 103 and M. Blaauw213

Neutron Transmission Through

Tapered Capillaries

H. H. Chen-Mayer103

, D. F. R. Mildner103 and

V. A. Sharov220 New Developments in Monitor

Activation Analysis

G. P. Lamaze103

, R. M. Lindstrom 103

, E. A. Mackey103 and R. L, Paul 103 New Developments in NDP

H. H. Chen-Mayer103

, G. P. Lamaze103 and J. K. Langland103

Quality Assurance Improvements for NAA

D. A. Becker103

, R. Demiralp103

, R. R. Greenberg103

, R. M.

Lindstrom 103

, E. A. Mackey103 and

R. Zeisler103

Quality Assurance Programs

D. L. Anderson43 and

W. C. Cunningham43

Reactor Characterization for NAA

D. A. Becker103

Radionuclides in Foods

D. L. Anderson43 and

W. C. Cunningham43

Revalidation of Food SRMs

D. L. Anderson43 and

W. C. Cunningham43

Size Distribution and Deposition of Toxic Elements to Lake Michigan, by

Size and by Source

P. F. Caffrey188 and J, M. Ondov188

Studies in Elemental Speciation

D, A. Becker103

, E. A. Mackey103 and

R. Zeisler103

Test of a Novel High Sensitivity Neutron Detector

B. Feller121

, H. H. Chen-Mayer103 and

G. Lamaze103

Trace Elemental Characterization of Silicon Semiconductor Materials

D. A. Becker103and R. M.

Lindstrom 103

64 RESEARCH TITILES
AFFILIATIONS:

I Advanced Ceramics Corporation

: Advanced Institute of Science and

Technology, Japan

3 AEA Technology, United Kingdom

4 American Manufacturing Technology

5 Argonne National Laboratory

6 Armed Forces Radiobiology Research Institute

7 Army Medical Research Institute

8 Army Research Laboratory

9 Army Research Office

10 Australian Geological Survey,

Australia

II Australian Nuclear Science and

Technology Organization, Australia

12 Battelle Pacific Northwest

Laboratory

13 Belarus Academy of Sciences,

Belarus

14 Bethany College

15 Bilkent University, Turkey

16 Birbeck College, United Kingdom

17 Boeing Helicopter Group

18 Brookhaven National Laboratory

19 Brown University

20 California Institute of Technology

21 Cambridge University, United Kingdom

22 Carnegie Mellon University

23 Center for Advanced Research in Biotechnology

24 Centre d'Etudes Nucleaires de

Grenoble, France

25 Centre National de la Recherche

Scientifique, France

26 Centra Brasileiro de Pesquisas

Fisicas, Brazil Chalk River Laboratories, Canada

City College of New York

College of William and Mary

Commissariat d'Energie Atomique,

France

Cornell University Cracow University of Technology, Poland Czech Academy of Sciences, Czech

Republic Davidson Chemical Company

Dupont Company

Dupont Experimental Station Dupont Marshall Laboratory Eastman Kodak

Eidgenossische Technische

Hochschule, Switzerland ExxonMobil Research and

Engineering Company

Federal Highway Administration

Florida State University Food and Drug Administration

Fuji Medical Systems USA,

Incorporated

General Electric Corporate Research

General Motors Research and Development Center George Washington University Hahn-Meitner Institute, Germany

Harvard University Hongik University, South Korea Howard University IBM, Almaden

Idaho National Engineering and

Environment Laboratory Imaging and Sensing Technology

55 Imperial College, United Kingdom

56 Indiana University

57 Insitute of Physics, Peoples

Republic of China

58 Institut fur Physikalische Chemie, Germany

59 Institut fur Festkorperforschung, Germany

60 Institute for Chemical Research, Japan

61 Institute for Energiteknikk, Norway

62 Institute for Reference Materials and Measurements, Belgium

63 Institute for Special Materials, Italy

64 Institute for Superhard and Novel Carbon Materials, Russia

65 Institut Laue-Langevin, France

66 Institute of Crystallography, Russia

67 Institute of Physical and Chemical

Research, Japan

68 Intel Corporation

69 Iowa State University

70 John Deere Corporation

71 Johns Hopkins University

72 Joint Institute of Nuclear Research, Russia

73 Karlsruhe Nuclear Research Center, Germany

74 Kent State University

75 Kiel University, Germany

76 Kurchatov Institute, Russia

77 Kyunghee University

78 Kyoto University, Japan

79 Lehigh University

80 Los Alamos National Laboratory

81 Los Alamos Neutron Science Center

82 Lucent Technologies, Bell Laboratories

83 Massachusetts Institute of Technology

84 Max-Planck Institut, Germany

85 McClellan Nuclear Radiation Center

86 McGill University, Canada

87 McMaster University, Canada

88 Metal Physics Institute, Russia

89 Michigan Molecular Institute

90 Michigan State University

91 Moscow Steel and Alloys Institute, Russia

92 National Aeronautics and Space

Administration, Johnson Space

Center

93 National Central University, Taiwan

94 National Institute for Research in Inorganic Materials, Japan

95 National Institute of Health

96 National Sun Yat-Sen University, Taiwan

97 National Taiwan University, Taiwan

98 National Tsing Hua University, Taiwan

99 Naval Research Laboratory

100 NEC Research Institute Incorporated

101 Neutek Incorporated

102 NIST Center for Neutron Research

103 NIST, Analytical Chemistry Division

104 NIST, Biotechnology Division

105 NIST, Ceramics Division

106 NIST, Electron and Optical Physics

Division

107 NIST, Ionizing Radiation Division

108 NIST, Materials Reliability Division

109 NIST, Materials Reliability Division

110 NIST, Metallurgy Division

11 NIST, Polymers Division

12 NIST, Semiconductor Electronicis Division

13 NIST, Standard Reference Materials Program

14 NIST, Statistical Engineering Division

15 NIST, Surface and Microanalysis Science Division

16 NIST, Thermophysics Division

17 North Carolina State University

18 Northeastern University

19 Northern Illinois University

20 Northwestern University

21 Nova Scientific

22 Oak Ridge Institute for Science and

Education

23 Oak Ridge National Laboratory

24 Oberlin College

25 Ohio State University

26 Ohio University

27 Olin Conservation Incorporated

28 Oregon State University

29 OSMIC, Incorporated

30 Oxford University, United Kingdom

31 Pacific Lutheran University

32 Paul Scherrer Institute, Switzerland

33 Pennsylvania State University

34 Philips Research Laboratories, The

Netherlands

35 Polytechnic University

36 Princeton University

37 Queen's University, Canada

38 Rice University

39 Royal Institute of Technology, Sweden

40 Royal Institution, United Kingdom

41 Ruhr University, Germany

42 Russian Academy of Sciences, Russia

43 Rutgers University

44 SAGE Electrochromics

45 Seoul National University

46 Sid Richardson Carbon Company

47 Smithsonian Institute

48 Stanford Linear Accelerator

49 Stanford University

50 State University of New York, Stony Brook

51 Tata Institute of Fundamental

Research, India

52 TEC

"Technical University Munchen,

Germany

54 Technobiochip

55 Tel Aviv University, Israel

56 Texaco Research and Development

Center "Texas Materials Institute

58 Thomas Jefferson High School

59 Tohoku University, Japan

60 Toyo University, Japan

61 Tokyo University, Japan

62 Trinity College

63 Tufts University

64 U. S. Department of Transporation

65 University of Aachen, Germany

66 University of Akron

67 Universitat Autonoma de Barcelona, Spain

68 Universita di Brescia, Italy

69 University of California at Berkeley

70 University of California at Davis

71 University of California at Irvine

72 University of California at Riverside

73 University of California at San Diego

74 University of California at San

Francisco

75 University of California at Santa

Barbara

76 University of Chicago

77 University of Connecticut

78 University of Cincinnati

79 University of Delaware

80 University of Florida

81 University of Grenoble, France

82 University of Guelph, Canada

83 University of Houston

84 University of Illinois

85 University of Innsbruck, Austria

86 University of Iowa

87 University of Manitoba

88 University of Maryland at College Park

89 University of Massachusetts

University of Michigan

University of Minnesota

University of Missouri at Columbia

University of Missouri-Rolla

University of Munich, Germany

University of Notre Dame

University of Oklahoma

University of Pennsylvania

Universidad de la Republica

Argentina

199 University of Rhode Island

200 Universtat des Saarlandes, Germany

201 University of Stuttgart, Germany

202 University of Surrey, United Kingdom

203 University of Sussex, United Kingdom

204 University of Sydney, Australia

205 University of Tennessee

206 University of Texas

207 University of Tokyo, Japan

208 University of Trento, Italy

209 Unversity of Uppsala

210 University of Uruguay

211 University of Utah

212 University of Vermont

213 University of Virginia

214 University of Washington

215 University of Waterloo, Canada

216 Walter Reed Army Institute of Research

217 Washington University

218 West Virginia University

219 Worcester Polytechnic Institute

220 X-Ray Optical Systems

NIST CENTER FOR NEUTRON RESEARCH 65
PUBLICATIONS

Abdurashitov, J. N., Gavrin, V N., Girin, S. V, Gorbachev, V V, Ibragimova,

T. V, Kalikhov, A.V., Khairnasov, N. G., Knodel, V N., Kornoukhov,

V N., Mirmov, I. N., Shikhin, A. A., Verentenkin, E. P., Vermul, V. M., Yants, V E., Zatsepin, G. T. , Khomyakov, Y S., Zvonarev, A. V , Bowles, T. J., Nico, J. S., Teasdale, W. A., Wark, D. L„ Cherry, M. L., Karaulov, V. N.,

Levitin, V. L., Maev, P. I., Nazarenko, P. I., Shkol'nik, V S., Skorikov, N.V., Cleveland, B. T., Daily, T., Davis, R., Lande, K., Lee, C. K., Wildenhain, P S., Elliott, S. R., Wilkerson, J. F., "Measurement of the Response of a Gallium Metal Solar Neutrino Experiment to Neutrinos from a

51 Cr Neutrino

Source," Phys. Rev. C 59, 2246 (1999).

Abdurashitov, J. N., Gavrin, V N., Girin, S. V , Gorbachev, V V , Ibragimova,

T. V, Kalikhov, A.V., Khairnasov, N. G, Knodel, V N., Mirmov, I. N., Shikhin, A. 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., Nico,

J. S., Cleveland, B. T., Davis, R., Lande, K., Wildenhain, P. S., Elliott,

S. R., Wilkerson, J. E, "Measurement of the Solar Neutrino Capture Rate

with Gallium Metal," Phys. Rev. C 60, 55801 (1999).

Abdurashitov, J. N., Gavrin, V N., Girin, S. V , Gorbachev, V V , Ibragimova,

T. V, Kalikhov, A.V., Khairnasov, N. G„ Knodel, V N„ Mirmov, I. N„

Shikhin, A. 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., Nico,

J. S., Cleveland, B. T, Davis, R., Lande, K„ Wildenhain, P. S., Elliott,

S. R., Wilkerson, J. E, "Measurement of the Solar Neutrino Capture Rate by SAGE and Implications for Neutrino Oscillations in Vacuum," Phys. Rev.

Lett., in press. Adams, J. M., "Results from the NIST Round Robin Test of Fissionable Dosimeters in a Reactor Leakage Spectrum," in Reactor Dosimetry, edited by J. G. Williams, D. W. Vehar, F H. Ruddy, and D. M. Gilliam, in press.

Aeppli, G, Bishop, D. J., Broholm, C, Bucher, E„ Cheong, S. W, Dai, P., Fisk,

Z., Haysedn, S. M., Kleiman, R., Mason, T. E., Mook, H. A., Perring, T. G, Schoeder, A., "Neutron Scattering and the Search for Mechanisms of

Superconductivity," Physica C 318, 9 (1999). Agnew, S. R., Elliott, B. R., Youngdahl, C. J., Hernker, K. J., Weertman, J. R., "Structure and Mechanical Properties of Nanocrystalline," in Metals with Opportunities for Modeling 19"' Ris0 International Symposium on Materials

Science (Ris0 National Laboratory, Roskilde, Denmark), in press. Amis, E. J., Bauer, B. J., Groehn, F. I., Prosa, T. J., Liu, D. W, Barnes, K.

A., Jackson, C. L., Viers, B. D., Karim, A, Douglas, J. D., "Preparation and

Characterization of Polymer/Dendrimer Blends Progress Report for 1999," NISTIR 6353. Amos, T. G., Yokochi, A., Sleight, A. W, "Phase Transition and Negative Thermal Expansion in Tetragonal NbOP04 ," J. Solid State Chem. 141, 303

(1998). Anderson, C. R., Andersen, K. H., Bossy, J., Stirling, W. G, Dimeo, R. M., Sokol, P. E., Cook, J. C, Brown, D. W , " High Resolution Neutron

Scattering Study of the Roton in Confined Superfluid 4He," Phys. Rev. B

59, 13588 (1999). Anderson, M. L., Morris, C. A., Stroud, R. M., Merzbacher, C. I., Rolison, D.

R., "Colloidal Gold Aerogels: Preparation, Properties, and Characterization," Langmuir 15, 674 (1999). Armstrong, D. W, Schneiderheinze, J., Nair, U., Magid, L. L, Butler, P D., "Self-Association of Rifamycin B: Possible Effects on Molecular

Recognition," J. Phys. Chem. B 103, 4338 (1999). Balbach, J. J., Conradi, M. S., Hoffmann, M. M., Udovic, T. J., Adolphi,

N. L., "NMR Evidence of Disorder and Motion in Yttrium Trideuteride," Phys. Rev. B 58, 14823 (1998).

Balsara, N. P., "Multicomponent Polyolefin Blends with Ordered and Disordered

Microstructures," Curr. Opin. Sid. St. Mtls. Sci. 3, 589 (1998).

Balsara, N. P., Lefebvre. A. A., Lee, J. H., Lin, C. C, Hammouda, B., "The

Search for a Model Polymer Blend," AIChE J. 44, 2515 (1998). Bandyopadhyay, S., Klein, M. L., Martyna, G. L, Tarek, M., "Molecular Dynamics Studies of the Hexagonal Mesophase of Sodium Dodecylsulfate in Aqueous Solution," Mol. Phys. 95, 377 (1998). Bandyopadhyay, S., Tarek, M., Klein, M. L., "Nature of Lipid-DNA Interactions: A Molecular Dynamics Study of DNA Intercalated into a Lipid Bilayer," J. Phys. Chem., in press. Bandyopadhyay, S., Tarek, M., Lynch, M. L., Klein, M. L., "C 12EO,/Water System: A Molecular Dynamics Study," Langmuir, in press.

Balizer, E., DeReggi, A. S., Neumann, D. A., Bateman, F, "Polarization and Structural Transitions of Irradiated Vinylidene Fluoride-Trifluorethylene Copolymer," in 1999 Conference on Electrical Insulation and Dielectric Phenomena, Vol. 1, (IEEE Publ. No 99CH36319, 1999), p. 104. Bao, W, Broholm, C, Aeppli, G, Carter, S. A., Dai, P., Rosenbaum, T. F, Honig, J. M., Metcalf, P., Trevino, S. F, "Magnetic Correlations and Quantum Criticality in the Insulating Antiferromagnetic, Insulating Spin

Liquid, Renormalized Fermi Liquid, and Metallic Antiferromagnetic Phases

of the Mott System V2 0,," Phys. Rev. B 58, 12727 (1999).

Barilo, S. N., Bychkov, G. L., Kurnevich, L. A., Shiryaev, S. V, Lynn, J. W , Vasiliu-Doloc, L., "Seeded Growth from Flux and Neutron Study of La,

x BaxMnO, (0.2 < x < 0.5) Single Crystals," J. Cryst. Growth, in press.

Barilo, S. N., Shiryaev, S. V, Gatalskaya, V. I., Lynn, J. W, Baran, M., Szymczak, H., Szymczak, R., Dew-Hughes, D., "Scaling of Magnetization and Some Basic Parameters of Ba,

x Kx BiO,+ Superconductors near T,"

Phys. Rev. B 58, 12355 (1998). '

X * +y

Barilo, S. N., Shiryaev, S.V., Gatalskaya, V I., Zhigunov, D. I., Pushkarev, A. V, Fedotova, V. V, Szymczak, H., Szymczak, R., Baran, M., Lynn, J. W,

Rosov, N., Skanthakumar, S., "A New Method for Growing Ba,^KFiiO,

Single Crystals and Investigation of their Properties," J. Cryst. Growth 199, 636(1999).

Barilo, S. N, Shiryaev, S. V , Zhigunov, D. I., Pushkarev, A. V , Gatalskaya, V.

I., Fedotova, V V, Lynn, J. W, Skanthakumar, S., Rosov, N., Szymczak, H., Szymczak, R., Baran, M„ Nabyalek, A., "Investigation of Electrochemical Growth Conditions for Ba,

x KBi03 Single Crystal Superconductor and

its Magnetic Properties," in International Conference on Crystal Growth,

(OBNIS, 1998), p. 30.

Barker, J. G, Weertman, J. R., Pedersen, J. S., "Strain Rate Dependence of

the Growth Rate of Grain Boundary Cavities During the High Cycle High

Temperature Fatigue of Copper," in Advanced Materials for the 21" Century: The 1999 Julia R. Weetman Symposium, edited by Y W Chung, D. C. Dunand, P. K. Liaw, G. B. Olson (The Minerals, Metals & Materials Society, Pennsylvania, 1999), p. 71.

Barnes, K. A., Morrison, F A., Nakatani, A. I., "The Effects of Steady Shear on the Order and Orientation of Diblock Copolymer Melt Using In-Situ Small-Angle Neutron Scattering," SPE ANTEC, in press. Bateman, F. B., Boukharouba, N., Brient, C. E., Carlson, A. D., Grimes, S. M.,

Haight, R. C, Massey, T. N., Wasson, O. A., "New Measurements of the H (n, n) H Angular Distribution," in Reactor Dosimetry, edited by J. G.

Williams, D. W Vehar, F. H. Ruddy and D. M. Gilliam, in press.

Bauer, B. J., Prosa, T. L, Liu, D. W. , Jackson, C. L., Tomalia, D. A., Amis,

E. J., "Molecularly Dispersed Dendrimers in a Polymeric Matrix," ACS

reprint 40, 406 (1999).

66
Bauer, B. J., Ramzi, A., Liu, D. W , Scherrenberg, R. L., Froehling, P., Joosten,

J.. "Blends of Fatty Acid Modified Dendrimers with Polyolefins," J. Polym.

Sci. Phys.. in press.

Becker, D. A., "30 Years of Reactor Characterization on the NBSR," J. Radioanal. Nucl. Chem., in press.

Becker, D. A.. "Accurate Determination of Trace Elements in Sediment CRMs

by Instrumental Neutron Activation Analysis," Czech. J. Phys. 49. 271

(1999).

Becker, D. A., Porter, B. J., Mackey, E. A., Schantz, M. M., Demiralp, R., "National Marine Mammal Tissue Bank and Quality Assurance Program:

Protocols, Inventory, and Analytical Results," NISTIR 6279.

Bellows, R. J., Lin, M. Y, Arif, M., Thompson, A. K., Jacobson, D., "Neutron Imaging Technique for In-Situ Measurement of Water Transport Gradients

within Nation in Polymer Electrolyte Fuel Cells," J. Electrochem. Soc. 146, 1099 (1999). Benenson, R. E., Chen-Mayer, H. H., Lynn, J. W., "Search for Effects on

Neutron Transmission due to Multiple Reflection by Glass Capillary Walls,"

in Proceedings of SPIE Annual Meeting, in press. Blackman, M. J„ Badaljan, R. S., Kikodze, Z. K., Kohl, P. L, "Chemical

Characterization of Caucasian Obsidian: Geological Sources," in Synthese Sur I'Obsidienne an Proche-Orient: Du Volcan a I'Outil (BAR Publication, London), in press. Blackman, M. J., Redford, S., "Northern Syrian Luster and Fritware: Petrographic and Chemical Implications for Productions and Distribution." Antiquity, in press. Bode, P.. de Nadai Fernandes, E. A., Greenberg, R., "INAA as a Primary Method

in Metrology for Chemical Measurements," Proceedings Metrolsul. '99. in press. Bode, P., de Nadai Fernandes, E. A., Greenberg, R. R., "Metrology for Chemical Measurements and the Position of INAA," J. Radioanal. Nucl. Chem.. in press.

Bbdeker, K., Schreyer, A., Zabel, H., "Spin Density Waves and Reorientation

Effects in Thin Epitaxial Cr Films Covered with Ferromagnetic and

Paramgnetic Layers," Phys. Rev. B 59, 9408 (1999).

Borchers, J. A., Dura, J. A., Majkrzak. C. F, Hsu, S. Y, Lolee, R., Pratt, W P,

Bass, J., "Polarized Neutron Reflectivity Characterization of Weakly Coupled

Co/Cu Multilayers," Physica B, in press.

Borchers, J. A.. Dura, J. A., Unguris, J., Tulchinsky. D., Kelley, M. H., Majkrzak,

C. F, Hsu. S. Y, Loloee, R., Pratt Jr., W. P., Bass, J., "Observation of

Antiparallel Magnetic Order in Weakly Coupled Co/Cu Multilayers," Phys. Rev. Lett. 82, 2796 (1999).

Borchers, J. A., Ijiri. Y, Lind, D. M., Ivanov, P. G., Erwin, R. W. , Lee, S. -H, Majkrzak, C. F, "Polarized Neutron Diffraction Studies of ExchangeCoupled Fe,04/NiO Superlattices," J. Appl. Phys. 85, 5883 (1999).

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Fischer, P, Ioffe, A., Jacobson, D. L., Arif, M., Mezei, F, "4*-Periodicity of

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68 PUBLICATIONS
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Nucl. Soc.80, 101 (1999). Goldmints, I.. Yu. G., Booth, C, Smith, K. A., Hatton, T. A., "Structure of

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Green, M. A., Neumann, D. A., "Synthesis, Structure and Electronic Properties of LaCa,Mn.07 ," Chem. Mater., in press.

Green, M. A., Prassides, K„ Stalick, J. K., Day, P., "The Crystal Structure of SrSnO,," Inorg. Chem., in press.

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Greenberg. R. R., Lindstrom, R. M., Simons, D. S., "Instrumental Neutron

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Griffith. P. C, Cosgrove. T. Shar, J., King, S. M., Yu, G. E., Booth, C,

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Hanley, H. J. M., Muzny, C. D., Butler, B. D., Straty, G. C, Bartlett, J., Drabarek, E., "Shear-Induced Restructuring of Concentrated Colloidal Silica Gels," J. Phys. Condens. Matt. 11, 1369 (1999).

Harris, V. G., Fatemi, D. J., Hathaway, K. B., Huang, Q., Mohan, A., Long, G. J., "Atomic Structure and Magnetism of Ordered and Disordered A1

Q 5 Fe

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Harris, V. G., Huang, Q., Shah, V.R., Markandeyulu, G., Rao, K. V. S. R., Huang. M. Q., Sirisha, K., McHenry, M. E., "Neutron Diffraction and Extended X-Ray Absorption Fine Structure Studies of Pr, (Fe, Co)27 5Ti

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Heller-Zeisler, S., Ondov, J., Zeisler, R., "Collection and Characterization of a Bulk PM, 5 Air Particulate Matter Material for Use in Reference Materials,"

J. Bio. Trace Ele. Res. 71, 195 (1999).

Henrickson, R. C, Blackman, M. J., "Hellenistic Production of Terra Cotta Roof

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Heuser, B. J., King, J. S., Chen, W. C, "SANS Measurements of Deuteride

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20, 2303 (1998). Huang, C. -I., Chapman, B. R., Lodge, T. P., Balsara, N. P., "Quantifying

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Hunt, W. J., Zukoski, C. F, "The Equilibrium Properties and Microstructure of Mixture of Colloidal Particles with Long Range, Soft Repulsions," JCIS

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Idemoto, Y, Izumi, F, Huang, Q., Santoro, A., Matsuzawa, M., Koura, N, "Effects of Sr Substitution on the Tc and Crystal Structure of T^Ba, x Sr

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Ilavsky, J., Long, G. G., Allen, A. J., Herman, H., Berndt, C. C, "Use of Small Angle Neutron Scattering for the Characterization of Anisotropic Structures Produced by Thermal Spraying," Ceramics-Silikaty 42, 81 (1998).

Ilavsky, J., Stalick, J. K., "Phase Composition and its Changes During Annealing

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Ivkov, R., Gehring, P. M., Maliszewskyj, N. C, Krishnamoorti, R., "Structure and Dynamics of Polymers in Confined Geometries: Neutron Studies

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NIST CENTER FOR NEUTRON RESEARCH 69
Jeon, H. S., Lee, J. H., Balsara, N. P., Newstein, M. C, "An Experimental

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Kesler, O., Matejicek, J., Sampath, S., Suresh, S., T, Brand, P. C, Prask, H. J., "Measurement of Residual Stress in Plasma-Sprayed Metallic, Ceramic, and Composite Coatings," J. Mater. Sci. Eng. 257, 215 (1998).

Kessler, E. G., Dewey, M. S., Deslattes, R. D., Henins, A., Borner, H. G.,

Jentschel, M., Doll, C, Lehmann, H., "The Deuteron Binding Energy and

the Neutron Mass," Phys. Rev. Lett. 255, 221 (1999).

Kholifah, P., Erwin, R. W., Lynn, J. W., Huang, Q., Batlogg, B., Cava, R. J., "The Magnetic and Electronic Characterization of Quasi-One-Dimensional La3RuO? ," Phys. Rev. B 60, 9573 (1999).

Kilic, C, Yildirim, T, Mehrez, H., Ciraci, S., "A First-Principles Study of the Structure and Dynamics of CgH8

, Si

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(1999).

Kitade, S., Ochiai, N., Takahashi, Y, Noda, I., Matsushita, Y, Karim, A., Nakatani, A. I., Kim, H., Han, C. C, "Lamellar Orientation of Diblock Copolymer Solutions Under Steady Shear Flow," Macromol. 31, 8083

(1998).

Kline, S. R., "Polymerization of Rod-Like Micelles," Langmuir 15, 2726 (1999).

Kline, S. R., "Structural Evolution During Micelle Polymerization," J. Appl.

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M[N(CN)2

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J. S., Epstein, A. J., "Magnetic Phase Transitions in M"[N(CN),L," J. Mol.

Liq. Cryst., in press.

Kossuth, M. B., Morse, D. C, Bates, F. S., "Viscoelastic Behavior of Cubic

Phases in Block Copolymer Melts," J. Rheology 43, 167 (1999). Koubi, L., Tarek, M., Klein, M. L., Scharf, D., "Distribution of Volatile General

Anesthetics in a Model Membrane from Molecular Dynamics Simulation," Biophy. J., in press.

Krishnamoorti, R., Silva, A. S., Modi, M. A., Hammouda, B., "Small Angle

Neutron Scattering Study of a Cylinder to Sphere Order-Order Transition in Block Copolymers," Macromol, in press. Krone, C. A., Robisch, P. A„ Tilbury, K. L., Stein, J. E„ Mackey, E. A., Becker, P R., O'Hara, T. M., Philo, L. M., "Elements in Liver Tissues of Bowhead

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Using Cold Neutron Depth Profiling," J. Surf. Interface Anal. 27, 644 (1999). Lamaze, G. P., Chen-Mayer, H. H., Langland, J. K., "Recent Developments in Neutron Depth Profiling at NIST," in Proceedings of the 1998 International Conference on Characterization and Metrology for Ultra Large Scale

Integration Technology, edited by D. G. Deiler, A. C. Diebold, W. M. Bulis,

T. J., Shaffner, R. McDonald, E. J. Walter, (American Institute of Physics,

1998), p. 883.

Lee, S.-H., Broholm, C, Aeppli, G., Cheong, S.-W., "Short-Range Spin

Correlations in a Geometrically Frustrated Magnet, SrCr

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Lee, S.-H., Broholm, C, Cheong, S.-W, Kim, T. H., Ratcliff II, W, "Local

Spin Resonance and Spin-Peirls Like Phase Transition in the Geometrically

Frustrated Antiferromagnet ZnCr2 04

," Phys. Rev. Lett., in press.

Lee, S.-H., Majkrzak, C. F, "A New Technique for Polarized Neutron

Diffraction," Physica B 268, 341 (1999).

Lee, S.-H., Majkrzak, C. F, "Polarized Neutron Diffraction with an AreaSensitive Detector," J. Neutron Res. 7, 131 (1999).

7 D PUBLICATIONS
Lee, S.-H., Majkrzak, C. E, Sinha, S. K., Stassis, C, Kawano, H., Lander, G.

H., Brown. P. J., Fong, H. F. Cheong, S. W. . Matsushita, H., Yamada, K., Endoh, Y., "Search for Orbital Moments in Underdoped Cuprate Metals—

A

Sisyphian Task," Phys. Rev. B 60, 10405 (1999).

Lee, Y. S., Birgeneau, R. I, Kastner, M. A., Endoh, Y , Wakimoto, S., Yamada,

K., Erwin, R. W., Lee, S. H.. Shirane, G., "Neutron Scattering Study of Spin

Density Wave Order in the Superconducting State of Excess-Oxygen-Doped

LajCuO^," Phys. Rev. B 60, 3643 ( 1 999).

Lefebrve, A. A., Balsara, N. P., Hammouda, B., Jeon, H. S., La, R. J., Lee, J. H., "Initial Stages of Nucleation During Liquid-Liquid Phase Separation in Polymer Blends," J. Chem. Phys. Ill , 6082 (1999).

Lefebrve, A. A., Lee, J. H., Balsara, N. P., Hammouda, B.. Krishnamoorti, R., "Relationship Between Internal Energy and Volume Change on Mixing in Pressurized Polymer Blends," Macromol. 32, 5460 (1999).

Lefebvre, K. K., Lee, J. H., Balsara, N. P., Hammouda, B., Krishnamoorti, R., Kumar, S., "Relationship Between Internal Energy and Volume Change of Mixing in Pressurized Polymer Blends," Macromol. 32, 5460 (1999). Leheny, R.L., Christianson, R. J., Birgeneau, R. J., Erwin, R. W, "Spin

Correlations in an Isotropic Spin - 5/2 Two-Dimensional Antiferromagnetic," Phys. Rev. Lett. 82,418 (1999).

Leheny, R. L., Nagel, S. R., "Dielectric Susecptibility Studies of the High- Frequency Shape of the Primary Relaxation in Supercooled Liquids," J. NonCryst. Solids 235, 278 (1998).

Li, W.-H., Wu, S. Y , Lee, K. C, Lynn, J. W. , "Magnetic Ordering of Mn in Ca-Doped NdMnO,," Physica B, in press.

Li, W.-H.. Wu, S. Y, Lee, K. C, Lynn, J. W, Liu, R. S., Wu, J. B., Huang, C. Y, "Magnetic Order and Spin Reorientation in Nd045Ca055MnO3 ," J. Appl.

Phys. 85, 5588 (1999).

Li, W.-H, Wu, S. Y, Lin, Y. C, Lee, K. C, Lynn, J. W, Weng, S. S„ Hong, I. P., Lin, J. -Y, Yang, H. D., "Magnetic Ordering in Double-Chain PrBa,Cu4Og ," Phys. Rev. B 60, 4212 (1999).

Li, Z. G., Harlow, R. L., Foris, C. M., Li, H., Ma, P., Vickery, R. D., Maunn,

M. B., Toby, B. H., "Polymorph Determination for the GPIIb/IIIa Antagonist,

Roxifiban, Using a Combination of Electron Diffraction and Synchrotron

X-Ray Powder Diffraction Techniques," J. Pharmctl. Sci. 88, 297 (1999).

Liang, J. K., Huang, Q., Santoro, A., Liu, Q. L., Chen, X. L., "A Neutron Powder Diffraction Study of the System La^COj x Fe

s

) 16Ti for x = 0.0, 0.2, and 0.4," J. Appl. Phys. 86, 1226 (1999).

Liang, J. K„ Huang. Q., Santoro, A., Wang, J. L., Yang, F. M., "Magnetic

Structure, and Site Occupancies in YFe n CoTi (x = 1, 3, 7, 9)," J. Appl.

Phys. 86, 2155 (1999).

Licci. F, Marezio, M., Huang, Q., Santoro, A., Bougerol-Chaillout, C, Masini, R, "Synthesis, Structure, and Superconductivity of Hg075Mof)15 Ba,CuO4+6 ," Physica C, in press.

Lin. E. K., Kolb, R., Satija, S. K., Wu, L. U., "Reduced Polymer Mobility Near the Polymer/Solid Interface as Measured by Neutron Reflectivity," Macromol. 32, 3753 (1999).

Lin, E. K, Kolb, R, Wu, W. L., Satija, S. K., "Enhanced Polymer Segment

Exchange Kinetics due to an Applied Shear Field," Macromol. 32, 4741

(1999).

Lin, E. K., Pochan, D. J.. Kolb, R., Wu, W. L., Satija, S. K., "Neutron

Reflectivity for Interfacial Materials Characterization," in Characterization and Metrology for VLSI Technology, edited by D. G. Seiler, A. C, Diebold, W. M. Bullis, T. J. Shaffner, R. McDonlad, E. I. Watters, AIP Conference

Series 449 (American Institute of Physics, Woodbury, NY 1998), p. 879.

Liu, Y, Chen, S.-H., Huang, J. S., "Small-Angle Neutron Scattering Analysis of

the Structure and Interaction of Tri-Block Copolymer Micelles in Aqueous

Solution," Macromol. 31, 2236 (1998). Long, G. G., Krueger, S., Allen, A. J., "Multiple Small-Angle Neutron

Scattering," J. Neutron Res. 7, 195 (1999).

Lynn, J. W. , "Magnetic Neutron Scattering," in Methods in Materials Research,

edited by Kaufman (lohn Wiley & Sons), in press. Lynn, J. W , "Spin Dynamics of Magnetoresistive Oxides," in The Physics of

Manganites, edited by Kaplan and Mahanti (Plenum Publishing, 1999), p. 149. Lynn, J. W , "Spin Dynamics of the Magnetoresistive Oxides," Int. J. Mod. Phys.

12, 3355 (1998). Lynn, I. W, Rosov, N., Barilo, S. N, Kurnevitch, L., Zhokhov, A., "Pr Magnetic Order and Spin Dynamics in the Cuprates," Chin. J. Phys., in press. Lynn, J. W. , Skanthakumar, S., "Neutron Scattering Studies of Rare Earth Magnetic Ordering," Handbook on the Physics and Chemistry of Rare

Earths, edited by K. A. Gschneider, Jr., L. Eyring, M. B. Maple (Elsevier Science), in press. Mackey, E. A., Demiralp, R., Fitzpatrick, K. A., Porter, B. J., Wise, S. A., Greenberg, R. R., "Quality Assurance in Analysis of Cryogenically Stored Specimens from the NIST National Biomonitoring Specimen Bank," Sci. Total Environ. 226, 165 (1999). Magid, L. J., "The Surfactant-Polyelectrolyte Analogy," J. Phys. Chem. B. 102, 4064 (1998). Magid. L. J., Han, Z., Li, Z., Butler, P.D., "Tuning Microstructure of Cationic Micelles on Multiple Length Scales: The Role of Electrostatics and Specific Ion Binding," Langmuir, in press. Majkrzak, C. F, "Neutron Applications in Materials Science and Engineering,"

J. Neut. Res., in press. Majkrzak, C. F, "Neutron Reflectometry Studies of Thin Films and Multilayered

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Reflectometry by Variation of the Surrounding Media," Phys. Rev. B 58, R15416 (1998). Majkrzak, C. F, Berk, N. F, "Experimental Demonstration of Phase

Determination in Neutron Reflectometry by Variation of the Surrounding

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Structures Using Polarized Beams," Physica B 268, 168 (1999). Mang, J. T, Hjelm, R. P., "Small Angle Neutron Scattering Studies of Vesicle

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"Rotational Dynamics of C6(l in (ND} )Kfm

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Matejicek, J., Sampath, S., Brand, P. C, Prask, H. J., "Quenching, Thermal, and

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J. M., "Radiative Decay of the Metastable Molecule He2 (a32u

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Merfeld, G. D., Karim, A., Majumdar, B., Satija, S. K., Paul, D. R., "Interfacial Thickness Between Immiscible Bilayers of Poly(phenylene oxide) and

Styrenic Copolymers," J. Poly. Sci. Part B, in press.

Merzbacher, C. I., Barker, J. G., Long, J. W , Rolison, D. R., "The Morphology of Nanoscale Deposits of Ruthenium Oxide in Silica Aerogels," Nanostructured Mater., in press.

NIST CENTER FOR NEUTRON RESEARCH 71
Meyer, A., Busch, R., Schober, H., "Time-Temperature Superposition of

Structural Relaxation in a Viscous Metallic Liquid," Phys. Rev. Lett., in

press. Meyer, A., Wuttke, J., Petry, W., "Two-Step Relaxation in a Viscous Metallic Liquid," J. Non-Cryst. Solids, in press.

Migler, K. B., Han, C. C, "Pressure Effects on Diblock Copolymers: Optical

Birefringence and Neutron Scattering," Macromol., in press.

Mildner, D. F. R., "Self Shielding for Thick Slabs in a Converging Neutron Beam," Nucl. Instrum. Meth. A 432, 399 (1999).

Mildner, D. F. R., Chen-Mayer, H. H., "Neutron Absorption Measurements

Using Converging Beams—Increased Reaction Rate," Nucl. Instrum. Meth. A 422, 21 (1999).

Mildner, D. F. R., Lamaze, G. P., "Neutron Transmission of Simple Crystal Sapphire." J. Appl. Crystallogr. 31, 835 (1998). Modi, M. A., Krishnamoorti. R., Tse, M. F, Wang. H. C, "Viscoelastic Characterization of an Order-Order Transition in a Mixture of Di- and

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Nakatani, A. I., "Phase Separation Kinetics During Shear in Compatibilized

Polymer Blends," in Scattering from Polymers, edited by B. S. Hsiao, P. Cebe, D. J. Lohse (ACS Symp. Series, Washington, DC), in press. Newstein, M. C, Wang, H., Balsara, N. P., Lefebvre, A. A., Shnidman,

Y., Watanabe, H., Osaki, K., Shikita, T, Niwa, H., Morishima, Y,

"Microstructural Changes in a Colloidal Liquid in the Shear Thining and

Shear Thickening Regimes," J. Chem. Phys., in press.

Nico, I. S., Abdurashitov, I. N„ Gavrin, V. N., Girin, S. V, Gorbachev, V

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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, I. F, "Solar Neutrino Results from SAGE," in Proceedings of the 10lH International Baksan School: Particles and Cosmology, in press.

Nikolaev, A. V, Michel, K. H., Copley, J. R. D., "Orientational Disorder and

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60 60 Coherence, and Order, edited by D. V Shopova, D. I. Uzunov (Plenum Press, London-New York, 1999), p. 183.

Nisato, G., Ivkov, R., Amis, E. J., "Structure of Charged Dendnmer Solutions as Seen by SANS," Macromol. 32, 5895 (1999). Norman, B. R., Igengar, G. V, "Further Applications of Pre-Irradiation 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. Oakey, I., Marr, D. W. M., Schwartz, K. B., Wartenberg, M., "The Influence of Polyethlene and Carbon Black Morphology on Vo id Formation in Conductive Composite Materials - a SANS Study," Macromol. 32, 5399

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Sinha, S. K„ Mitchell, J. F, Gray, K. E, Bader, S. D., "Neutron Scattering

Investigation of Magnetic Bilayer Correlations in La!

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Overholser, R., Wuttig, M., Neumann, D. A., "Chemical Ordering in Ni-Mn-Ga

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Pan, Y.-M., Page, R. A., Long, G. G., Krueger, S., "The Role of Zirconia Addition in Pore Development and Grain Growth in Alumina Compacts," J. Mater. Res., in press.

Papanek, P., Fischer, I. E., Sauvajol, I. L., Dianoux, A. J., McNeillis, P. M.,

Mathis, C, Francois, B., "Low-Frequency Phonons in Pristine and Doped

Phases of Polyacetylene: An Inelastic Neutron Scattering Study," J. Chem.

Phys., in press.

Pardo, H., Ortiz, W. A., Araujo-Moreira, F. M., Suescun, L., Toby, B. H., Negreira, C. A., Prassides, K., Mombru, A. W., "A New Structure in the REBaCuFeO.+5 Series: LaBaCuFeOJ+6

. Structure and Magnetic Properties in the La,

xPrxBaCuFe5+5 System," Physica C 313, 105 (1999).

Paul, R. L., "Determination of Nitrogen in Some Reference Materials by

Cold Neutron Prompt Gamma-Ray Activation Analysis,"!. Radioanal. Nucl. Chem., in press.

Paul, R. L.. "Determination of Phosphorus in Steels by Radiochemical Neutron

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Paul, R. L., "Measurement of Phosphorus in Metals by Radiochemical Neutron

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with and without a Free Surface via Neutron Reflectometry," in Dynamics

in Small Confining Systems IV, edited by I. M. Drake, G. S. Grest, J. Klafter, R. Kopelman, MRS Symp. Series 543, (Materials Research Society, Warrendale, PA, 1999), in press.

Podurets, K. M., Mildner, D. F. R., Sharov, V. A., "Application of Capillary Optics to Neutron Radiography," Rev. Sci. Instrum. 69, 3541 (1998). Pomme, S., Simonits, A., Lindstrom, R. M., DeCorte, F, Robouch, P., "Determination of Burnup Effects Prior to Reactor Neutron Field

Characterization," I. Radioanal. Nucl. Chem., in press.

Prask, H. I., Choi, C. S., "Nondestructive Determination of Subsurface Residual

Stresses by Means of Neutron Diffraction," in Multiazial Fatiqul of an

Induction Hardened Shaft, edited by T. Cordes, K. Leasly (Society Auto

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Prask, H. J., Gnaupel-Herold, T, Clark, A. V, Hehman, C. S., Nguyen, T. N., "Neutron and Ultrasonic Determination of Residual Stress in an Aluminum

Ring-Plug," in Proceedings of the 26th Annual Review of Progress in Qualitative NDE (Montreal, July 1999), in press.

Prince, E., "Neutron Scattering Instrumentation: A Tutorial Review," App.

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Qi, S., Chakraborty, A. K„ Wang, H., Lefebvre, A. A., Balsara, N. P., Shaknovich, E. I., Xenidou, M., Hadjichristidis, N., "Microphase Ordering in Melts of Randomly Grafted Copolymers," Phy. Rev. Lett., in press. Ramzi, A., Bauer, B. J., Scherrenberg, R., Froehling, P., Joosten, J., Amis, E.

J., "Fatty Acid Modified Dendrimers in Bulk and Solution: Single Chain

Neutron Scattering from Dendrimer Core and Fatty Acid Shell," Macromol. 32,4983 (1999).

Richter, C. A., Nguyen, N. V , Dura, J. A., Majkrzak, C. F, "Characterization of Thin SiO, on Si by Spectroscopic Ellipsometry, Neutron Reflectivity, an X-Ray Reflectivity," in Characterization and Metrology for VLSI

Technology, edited by D. G. Seiler (AIP, New York, 1998), p. 185.

Rijssenbeek, J. T, Huang, Q., Erwin, R. W, Zandbergen, H. W, Cava, R. J., "The Crystal Structure of Ba3 CuRu,09 and Comparison to Ba3 MRu209 (M =

In, Co, Ni, and Fe)," J. Sol. State Chem. 146, 65 (1999).

Rijssenbeek, J. T, Matl, P., Batlogg, B., Huang, Q., Ong, N. P., Cava, R. J., "Crystal Structure and Physical Properties of a Series of Ternary Barium

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72 PUBLICATIONS
Rosov, N.. Rathgeber. S.. Monkenbusch, M., "Neutron Spin Echo Spectroscopy

at the NIST Center for Neutron Research," ACS Proceedings of the PSME

Symposium Scattering and Polymers 216, 4865 (1998).

Rush. J. J.. Udovic. T. J., Berk, N. F., Richter. D., Magerl. A., "Excited-State

Vibrational Tunnel Splitting of Hydrogen Trapped by Nitrogen in Niobium,"

Europhys. Lett., in press.

Russell, T. P., "Neutron Reflectivity on Thin Film Symmetric Diblock

Polymers," Am. Cryst. Assoc. Trans., in press.

Ruzette. A.-V. G., Banerjee, P.. Mayes, A. M. Pollard, M., Russell, T. P, Jerome,

R.. Slawecki, T. Hjelm, R.. Thiyagarajan, P., "Phase Behavior of Diblock Copolymers Between Styrene and N-Alkyl Methacrylates" Macromol. 31, 8509 (1998). Ryan, L. D.. Kaler, E. W., "Microstrucrure Properties of Alkyl Polyglucoside Microemulsions." Langmuir 15, 92 (1999).

Salamat. G.. de Uries, R., Kaler, E. W., Satija, S. K.. Sung. L. P., "Undulations

in Salt-Free Charged Lamellar Phases Detected by Small Angle Neutron

Scattering and Neutron Reflectivity." Langmuir, in press.

Salamat, G., Kaler, E. W., "Colloidad Dispersions in Lyotropic Lamellar

Phases." Langmuir 15, 5414 (1999).

Sanders. P. G., Eastman. J. A.. Weertman, J. R., "Pore Distributions

in Nanocrystalline Metals from Small-Angle Neutron Scattering." Acta

Materialia 46, 4195 (1998).

Santoro. A., Natali Sora. L, Huang, Q.. "Bond-Valence Analysis of the Structure of (Ba

087JSr

0 125)Ru03 ," J. Solid State Chem. 143, 69 (1999).

Sayer, E. V., Yener, A. K., Joel, E. C, Blackman. M. J.. Ozbal, "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-Winkel. P., Glinka, C. J., Stucky, G. D., "Microemulsion Templates for Mesoporous Silica," Langmuir, in press.

Schober. H.. Cook, J. C. Mezei, F, "Upgrade of the IN5 Cold Neutron Time-ofFlight Spectrometer." J. Neutron Res., in press.

Schober, H., Losert, C, Mezei, F, Cook, J. C, "Chopper Cascades: An

Analytical Treatment of the Contamination Problem," J. Neutron Res., in

press.

Schreyer, A., Majkrzak, C. F, Berk, N. F, Griill, H., Han., C. C, "Using

Polarized Neutrons to Determine the Phase Reflection from Thin Film

Structures," J. Phys. Chem. Sol. 60, 1045 (1999).

Schulz, J. C, Warr, G. G.. Hamilton, W. A., Butler, P D., "Neutron

Refiectometry of Adsorbed Surfactant Aggregates," J. Phys. Chem. B. in

press.

Seehra, M. S., Babu, V. S., Lynn, J. W., "Magnetism of Ferrihydrite Nanoparticles Studied by Neutron Scattering and Magnetometry," Phys. Rev.

B. in press.

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Topp, A., Bauer, B. J., Prosa, T. J., Scherrenberg, R., Amis, E. J., "Size Change

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NIST CENTER FOR NEUTRON RESEARCH 73
Topp, A., Bauer, B. J., Tomalia, D. A., Amis, E. J., "Effect of Solvent Quality on the Molecular Dimensions of PAMAM Dendnmers," Macromol. 32, 7232

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Copolymers with Confinement and Interfacial Interactions," in Supramolecular Structures in Confined Geometries (ManneAVarr, 1999), in

press.

Tu, K. C, Tarek, M., Klein, M. L., Scharf, D„ "Effects of Anesthetics on the Structure of a Phospholipid Bilayer: Molecular Dynamics

Investigation of Halothane in the Hydrated Liquid Crystal Phase of

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Scattering Study of the Nuclear and Magnetic Structure of DyD3 and

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C. E, Hsu, S. Y., Loloee, R., Pratt, W. P., Bass, J., "Magnetic Depth Profiling Co/Cu Multilayers to Investigate Magnetoresistance," J. Appl. Phys., in press. van der Zaag, P. J., Feiner, L. F, Wolf, R. M., Borchers, J. A., Ijiri, Y., Erwin,

R. W., "The Blocking and Neel Temperature in Exchange Biased Fe,04/CoO

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I 5 I J 6 45 1/ lUo 11 5 15 Chem. 143, 182 (1999).

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and Chymotrypsinogen," Biophys. J. 75, 2682 (1998).

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74 PUBLICATIONS
Yildirim, T., Kilic, C. Ciraci, S., Gehring, P. M., Neumann, D. A., Eaton, P. E., Emrick, T., "Vibrations of the Cubane Molecule: Inelastic Neutron Scattering Study and Theory," Chem. Phys. Lett. 309, 234 (1999).

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(1999).

Yildirim, T. Zhou. 0.. Fischer, J. E., "Intercalation Compounds of Fullerenes

I: Synthesis, Characterization, and Solid State Properties." in Physics and

Chemistry of Materials with Low-Dimensional Structures, edited by W.

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Yildirim, T. Zhou, O., Fischer, J. E., "Intercalation Compounds of Fullerenes

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Yildirim, T. Zhou. O.. Fischer, J. E., "Intercalation Compounds of Fullerenes

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Zeisler, R., "Investigations by INAA for the Development of Natural Matrix

Standard Reference Materials (SRMs) Suitable for Small Sample Analysis,"

J. Radioanal. Nucl. Chem., in press.

Zeisler, R., "Maintaining Accuracy in Gamma-Ray Spectrometry at High Count

Rates," J. Radioanal. Nucl. Chem., in press.

Zeisler, R., Greenberg, R. R., "Determination of Sub-Nanomole Elemental

Levels by NAA and Their Possible Impact on Human Health Related Issues,"

J. Bio. Trace Ele. Res. 71, 283 (1999). Zhao, J., Wang, J., Chen, D. J., Peterson, S. R., Trewhella, J., "The Solution

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38, 21512 (1999). Zhao, J., Hoye, E., Boylen, S., Walsh, D. A., Trewhella, J., "Quaternary

Structures of a Catalytic Subunit-Regulatory Subunit Dimeric Complex

and the Holoenzyme of the CAMP-Dependent Protein Kinase by Neutron

Contrast Variation," J. Bio. Chem. 273, 30448 (1998). Zheludev, A., Maslov, S., Shirane, G., Tsukada, I., Masuda, T, Uchinokura,

K., Zaliznyak, I., Erwin, R. W, Regnalt, L.P., "Experimental Evidence for Kaplan-Shekhtman-Entin-Wohlman-Aharony Interactions in Ba,CuGe07 ," Phys Rev. Lett. 81,5410 (1998). Zheludev, A., Maslov, S., Shirane, G., Tsukada, I., Masuda, T, Uchinokura,

K., Zaliznyak. I.. Erwin, R. W., Regnault, L. P., "Magnetic Anisotropy and Low-Energy Spin Waves in the Dzyaloshinskii-Moriya Spiral Magnet

Ba,CuGe,07 ," Phys. Rev. B, in press. 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 Interactions in Ba,CuGe,07 ," 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. Polm. Phys., in press.

NIST CENTER FOR NEUTRON RESEARCH 75
INSTRUMENTS AND

CONTACTS

High resolution powder diffractometer (BT-1)

J. K. Stalick, (301) 975-6223, judy.stalick@nist.gov

B. H. Toby, (301) 975-4297, brian.toby@nist.gov

Residual stress and texture diffractometer (BT-8)

H. J. Prask, (301) 975-6226, hank@nist.gov

P. C. Brand, (301) 975-5072, pbrand@nist.gov

30 m SANS instrument (NG-7)

C. J. Glinka, (301) 975-6242, cglinka@nist.gov

J. B. Barker, (301) 975-6732, barker@nist.gov

S.-M. Choi, (301) 975-4863, sungmin@nist.gov

30 m SANS instrument (NG-3) (NIST/NSF-CHRNS)

B. Hammouda, (301) 975-3961, hammouda@nist.gov

S. R. Kline, (301) 975-6243, steven.kline@nist.gov

S. Krueger, (301) 975-6734, krueger@nist.gov

8 m SANS instrument (NG-1)

A. Karim, (301) 975-6588, karim@nist.gov

Perfect crystal SANS (BT-5) (NIST/NSF-CHRNS)

J. B. Barker, (301) 975-6732, barker@nist.gov

Cold neutron reflectometer - vertical sample-polarized beam option (NGC. F. Majkrzak, (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

R. Ivkov, (301) 975-6737, rivkov@nist.gov

Triple-axis polarized-beam spectrometer (BT-2)

J. W. Lynn, (301) 975-6246, jeff.lynn@nist.gov

Triple-axis spectrometer (BT-9)

R. W. Erwin, (301) 975-6245, rerwin@nist.gov

P. M. Gehring, (301) 975-3946, pgehring@nist.gov

Spin-polarized triple-axis spectrometer (NG-5) (NIST/NSF-CHRNS)

P. M. Gehring, (301) 975-3946, pgehring@nist.gov

S. -H. Lee, (301) 975-4257, seung-hun.lee@nist.gov

Filter-analyzer neutron spectrometer (BT-4) T J. Udovic, (301) 975-6241, udovic@nist.gov

P. Papanek, (301) 975-5049, pete@jazz.ncnr.nist.gov

D. A. Neumann, (301) 975-5252, dan@nist.gov

Fermi-chopper time-of-flight spectrometer (NG-6)

C. M. Brown, (301) 975-5134, craig.brown@nist.gov

T. J. Udovic, (301) 975-6241, udovic@nist.gov

Disk-chopper time-of-flight spectrometer (NG-4)

J. R. D. Copley, (301) 975-5133, jcopley@nist.gov

J. C. Cook, (301) 975-6403, jeremy.cook@nist.gov

High-flux backscattering spectrometer (NG-2)

R. M. Dimeo, (301) 975-8135, robert.dimeo@nist.gov

D. A. Neumann, (301) 975-5252, dan@nist.gov

Neutron spin echo spectrometer (NG-5)

N. S. Rosov, (301) 975-5254, nrosov@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-O)

G. Lamaze, (301) 975-6202, lamaze@nist.gov

Instrument development station (NG-O)

D. F. R. Mildner, (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

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 I Yildirim, (301) 975-6228, taner@nist.gov

Sample environment

D. C. Dender, (301) 975-6225, dender@nist.gov

L. J. Santodonato, (301) 975-6657, lsantodonato@nist.gov

76
NIST CENTER

FOR NEUTRON

RESEARCH

For additional information on the facility, contact:

J. Michael Rowe

(301) 975-6210

mike.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 Kamitakahara

(301) 975-6878

william.kamitakahara@nist.gov

Location of all contacts:

National Institute of Standards and Technology 100 Bureau Drive, MS8562

Gaithersburg, MD 20899-8562

Details are also available on the IMCNR Web site: http://www.ncnr.nist.gov/