Nist Center for Neutron Research Accomplishments and Opportunities

RXC NATL INST. OF STAND & TECH WIST PUBLICATIONS A111QS 6=11773-

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 Fe /NiO Superlattices 8 3 0 4 Spin Density Wave Order in the Superconducting State of La Cu0 10 2 4+y Local Spin Resonance and Spin-Peierls-Like Phase Transition in ZnCr 12 2 0 4 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 Si0 Films 28 2 Certification of an Ion-Implanted Arsenic in Silicon Standard Reference Material 30

The Rotational Dynamics of H in Porous Vycor Glass 32 2 First-Principles Computational and Neutron Scattering Study of Protonic Conductors 34 Magnetic Trapping of Ultracold Neutrons 36

Charge Disproportionation and Magnetic Ordering in CaFe0 38 3 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 accom- strains on our resources, but we can now look forward to many years plishments of the NIST Center for Neutron Research over of benefit from the results. the past year. In the reactor operations area, 1999 was another Finally, as always, the results are seen in the output of the outstanding year. In spite of an unsheduled maintenance shutdown, researchers who use the facility. As was done last year, we are the reactor operated 250 days, with a reliability factor of better than presenting highlights of this work in the following chapters of this

90 %. The cold source availability for the period was 98 %; i.e., the report. I think all can agree that the results truly speak for them- cold source held the reactor from operation 4 days during the year. selves.

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

0¥ INTRODUCTION TO THE NIST CENTER FOR NEUTRON RESEARCH (NCNR)

Modern technological society is dependent upon increasingly details of which are stringent tests of nuclear theory; and the effects

sophisticated use of materials, many of whose attributes are of various external influences such as gravity or magnetic fields on dictated by their sub-microscopic structural and dynamical proper- neutrons. ties. Our knowledge of these properties is provided by a wide range The NCNR utilizes neutrons produced by the 20 MW NIST of scientific techniques of which the many types of scattering (for Research Reactor to provide facilities, including the nation's only example. X-rays, light, electrons, neutrons) are arguably the most internationally competitive cold neutron facility, for all of the above important. Of these probes, neutrons are perhaps least familiar, but types of measurements to a national user community. There are they provide important advantages for many types of measurements. approximately 35 stations in the reactor and its associated beams that

Neutrons, as prepared for use at modern sources, are moving can provide neutrons for experiments. At the present time 26 of these at speeds comparable to those of atoms moving at room temperature, are in active use, of which 6 provide high neutron flux positions in thus providing the ability to probe dynamical behavior. At the same the reactor for irradiation, and 20 are beam facilities. A schematic time, neutrons are well matched to measurements at length scales layout of the beam facilities and brief descriptions of available ranging from the distances between atoms to the size of biological instrumentation are given below. More complete descriptions can be or polymer macromolecules. Neutrons are sensitive to the magnetic found at http://www.ncnr.nist.gov/. properties of atoms and molecules, allowing study of the underlying These facilities are operated both to serve NIST mission needs magnetic properties of materials. They also scatter quite differently and as a national facility, with many different modes of access. Some from normal hydrogen atoms than they do from heavy hydrogen instrumentation was built years ago, and is not suited to general

(deuterium), allowing selective study of individual regions of molec- user access; however, time is available for collaborative research. ular systems. Finally, neutrons interact only weakly with materials, NIST has recently built new instrumentation, and reserves 33 % of providing the opportunity to study samples in different environments available time for mission needs with the balance available to general more easily (at high pressures, in shear, in reaction vessels, etc.), and users. In other cases, instrumentation was built and is operated making them a non-destructive probe. These favorable properties are by Participating Research Teams (PRT). PRT members have access offset by the relative weakness of the best neutron sources compared to 75 % of available time, with the balance available to general to X-ray or electron sources, and by the relatively large facilities users. In a special case, NIST and the National Science Foundation required to produce neutrons. As a result, major neutron sources established the Center for High Resolution Neutron Scattering at the are operated as national user facilities to which researchers come NCNR, with a 30 m Small Angle Scattering (SANS) instrument, a from all over the United States (and abroad) to perform small scale cold neutron triple axis spectrometer, and a perfect crystal SANS science using the special measurement capabilities provided. under construction. For these facilities, most time is available for

In addition to scattering measurements, neutrons can be used general users. While most access is for research, whose results are to probe the atomic composition of materials by means of capture freely available to the general public, proprietary research can be and resultant radioactive decay. The characteristics of the decay act performed under full cost recovery. Each year, approximately 1600 as "fingerprints" for particular atomic nuclei, allowing studies of researchers (persons who participated in experiments at the facility, environmental samples for pollutants (e.g., heavy metals), character- but did not necessarily come here) from all areas of the country, from ization of Standard Reference Materials, and many other essential industry, academe, and government use the facility for measurements measurements. While the scattering and capture users of neutrons not otherwise possible. The research covers a broad spectrum of are little concerned with understanding the inherent properties of the disciplines, including chemistry, physics, biology, materials science, neutron, there are important areas in physics that can be explored and engineering. 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

NIST CENTER FOR NEUTRON RESEARCH 1 NIST CENTER FOR NEUTRON RESEARCH LAYOUT

1 Horizontal Sample 3 Prompt Gamma Activation 6 Fermi Chopper TOF Reflectometer Analysis Spectrometer

Horizontal surface of sample Cold neutron fluxes allow A hybrid time-of-flight spec-

allows reflectivity measure- detection limit for H of 1 i^g trometer for inelastic scatter- ments of free surfaces, liquid to 10 (jug. Focused beams are ing, with wavelengths between vapor interfaces, as well as available for profiling. 0.23 nm and 0.61 nm. The

polymer coatings. wavelength is chosen by a 4 NG-7 30 m SANS focusing pyrolytic graphite 2 Neutron Interferometry and Small Angle Neutron Scattering crystal, while the beam is Optics Station instrument for microstructure pulsed by a simple Fermi Includes perfect silicon inter- measurement sponsored by chopper. ferometer; vibration isolation NIST, the ExxonMobil Research system provides exceptional and Engineering Co., the 7 Spin Echo Spectrometer phase stability and fringe University of Minnesota, and A neutron spin echo spec-

visibility. Texaco R&D. trometer offering neV energy resolution, based upon Julich 5 Neutron Physics Station design, sponsored by NIST, A cold neutron beam Jiilich and ExxonMobil. 150 mm x 60 mm, available for fundamental neutron physics experiments. 0

11 10

10 NG-3 30 m SANS 13 Vertical Sample Reflectometer 16 BT-1 Powder Diffractometer 19 Cold Neutron Depth Profiling

Instrument for microstructure Instrument for measuring Powder diffractometer with 32 A station for quantitative measurement sponsored by the subsurface structure with detectors; incident wavelengths profiling of subsurface National Science Foundation polarization analysis capability. of 0.208 nm, 0.154 nm, and impurities and coatings, based and NIST; part of CHRNS. Reflectivities down to 10" 8 can 0.159 nm, with highest resolu- on neutron capture and 4 be measured. tion of 5d/d = 8x1 . emission of a charged particle. 11 Backscattering Spectrometer

High intensity, very high 14 BT-8 Residual Stress 17 BT-2 Triple Axis Spectrometer 20 Thermal Column resolution backscattering Diffractometer Triple axis crystal spectrometer A very well-thermalized beam spectrometer, with many Diffractometer optimized for with polarized beam capability of neutrons used for radiog- innovative features, and energy depth profiling of residual for measurement of magnetic raphy, tomography, dosimetry,

resolution of approximately stress in large components. dynamics and structure. and other experiments.

1 |xeV. 15 BT-9 Triple Axis Spectrometer 18 BT-4 Filter Spectrometer

12 8 m SANS Triple axis crystal spectrometer A triple axis crystal Instrument for polymer for measurements of excita- spectrometer with a Be or

characterization, sponsored by tions and structure. Be/Graphite filter analyzer Polymers Division. option for chemical spectroscopy.

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

powerful technique for optimizing material properties is to Only inelastic magnetic scattering techniques can provide this infor- Adeposit alternating layers of different materials to form a thin mation, but with current neutron scattering sources the intensities film superlattice. In particular, magnetic and non-magnetic materi- from such measurements can be prohibitively low, because the als grown as a superlattice exhibit a variety of tunable couplings amount of magnetic material in the films is so small. between the magnetic layers. Control of these couplings by varying In order to overcome this difficulty we have made neutron the layer materials and thicknesses has lead to dramatic increases in inelastic scattering measurements on a very large superlattice of performance in certain device applications. A prime example is the alternating layers of dysprosium and yttrium. Dysprosium is the recent use of layered magneto-resistive films in high-performance magnetic constituent, and it has the strongest neutron magnetic- magnetic recording heads and sensors. The inter-layer magnetic scattering of all the elements. In order to maximize the amount coupling can survive across as many as 30 non-magnetic atomic of Dy, 350 bilayers composed of 43 A of Dy and 28 A of Y planes due to its one-dimensional nature, but the coupling strength (designated [Dy /Y, ) were grown by MBE techniques on a 2.5 43 g ] 350 is always much weaker than bulk material magnetic interactions. cm x 1.3 cm substrate resulting in 3 mg of Dy in the sample.

The behavior of the magnetic fluctuations (magnons) in these The magnetic structure of this superlattice has previously weakly coupled layer systems is of interest because it provides a been determined to be the basal-plane helical structure of bulk direct measure of the magnetic interactions responsible for the magnetic struc- DyY Superlattice Magnon Dispersion ture, 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 measurements have found interesting resonances associated with the superlattice structure. 1

It is important to directly measure the magnons at shorter wavelengths in order to determine the dispersion, which 0 directly relates to the magnetic interac- 1.70 1.75 1.80 1.85 1.9 tions, both within and between layers, Q(A"1 ) and whether or not the magnetic fluctuation waves propagate between layers.

FIGURE 1. Inelastic magnetic scattering from a [Dy /Y superlattice, 43 28 ] 350 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

1 Q = 1.97 A .

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 background. The resulting magnetic signal is shown in Fig. 1 as progresses remarkably undisturbed through the conduction electrons a color-coded intensity map in Q-energy space. There is a clear of the non-magnetic yttrium, but with a turn-angle that is different ridge of intensity which moves to higher energies as Q moves away than in the 1 dysprosium. The coupling strength across the yttrium from the magnetic Bragg peak at 1.97 A" . We have concentrated has been measured by applying a uniform external magnetic field. on the magnon branches that extend towards smaller Q since they

The coupling breaks down when the external field provides 0.2 meV move away from the intense magnetic and nuclear Bragg peaks per Dy atom in the basal-plane, while the equivalent zone-boundary that produce a large elastic background. This measured dispersion is magnetic fluctuation in bulk Dy is greater than 5 meV per Dy atom. compared with bulk Dy in Fig. 2, which also shows the diffraction

The inelastic neutron scattering measurements were per- pattern along the growth direction (c-axis) of the superlattice. The formed at the NIST Center for Neutron Research on the cold- bulk Dy dispersion is shown as lines originating from the magnetic

1 1 neutron spectrometer SPINS. A multi-component crystal was used Bragg peaks at Q = 1.97 A and Q = 2.06 A . The measured to analyze the energy of the scattered neutrons in order to enhance magnons are shown as bars centered on the measured peak posi- the measured intensity while sacrificing wave-vector (Q) resolution. tions and with lengths representing the full-width-at-half-maximum-

Measurements were performed at 75 K as a compromise between intensity. The agreement with the bulk dispersion is quite good. the size of the ordered magnetic moment and the thermal population There is no evidence in these data of the influence of the yttrium of magnons. The magnons of interest are those propagating along layers other than possibly the splitting of the dispersion into two the superlattice growth direction or the c-axis of the hep rare-earth branches because of the superlattice structure as shown by separate

1 1 structure. Lower magnon energies produce higher thermal popula- bars at both Q = 1.8 A and at Q = 1.75 A" . The observed modes tions, but become contaminated with elastic background scattering, are not over-damped, but we cannot measure the damping under so it is necessary to subtract scans taken at low temperatures where the current experimental conditions. Also, these data would have the magnons have become depopulated in order to remove this to be extended to smaller Q, in order to approach the interface

thickness. We are currently designing additional focusing configura-

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

displaced along the field axis as a result of magnetic exchange axis. Figure 1 shows a typical growth-axis (00/) scan through the coupling to an antiferromagnet. This "exchange-biasing" phenom- (111) reflection for the superlattice. Structural stacking faults [5] at enon was discovered over 40 years ago in oxidized Co particles [1] the NiO/Fe,0, interfaces limit the coherence of the Fe,0, structural 3 4 3 4 and has been observed in a variety of thin films and multilayers. and magnetic order to a single Fe,0 layer. As a result, we can 4

Artificial spin-valve structures with exchange-biased layers show easily separate the broad Fe 0 and narrow NiO contributions to the 3 4 great promise for applications as magnetoresistive sensors in read reflection and track the latter as a function of field. heads. Recent theories [2-4] make specific predictions about the ori- The neutron scattering data reveal that the magnetic domain gin of exchange biasing and the response of the antiferromagnetic sizes in the antiferromagnetic NiO depend on the presence or layer. absence of exchange biasing. Figure 2 shows the full-width-at-half-

High-angle neutron diffraction is an ideal probe as the anti- maximum (FWHM) for the ( 1 1 1 ) NiO peak scanned along the (00/) ferromagnet gives rise to distinct reflections of magnetic origin. and (//0) directions after cooling in a 6 T field (i.e., exchange-biased

We have performed neutron diffraction studies of exchange-biased state) and cooling in zero field (i.e., unbiased state). After field

[001] Fe,0/NiO superlattices on the SPINS and BT-9 triple-axis cooling, the FWHM of the NiO reflection scanned along the (00/)

spectrometers. These measurements confirm that the NiO layers growth direction shows no dependence on field. 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 applica-

tion 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,0 (6 nm)/NiO( 1 1 nm) superlattice 4 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 0.68 0.72 0.76 0.80 0.84 applied in the sample plane. In this configuration, the (1 1 1) and Q (A" 1 Z ) (111) NiO antiferromagnetic reflections lie in the scattering plane.

Using a horizontal-field magnet, the (1 1 1) and (1 1 1) reflections FIGURE 1 . Zero-field growth-axis (00/) scan through the (111) reflection for the

Fe 0 nm)/Ni0(11 nm) superlattice after cooling to 78 K in a 6 T field parallel 3 4(6 to [110]. The broad Fe 0 peak is shown in red, and the remaining scattering 3 4 is from the NiO. The green arrow marks the FWHM of the NiO peak. The inset shows the scattering diagram.

8 RESEARCH HIGHLIGHTS A. J. Borchers and R. W. Erwin S.-H. Lee D. M. Lind and P. G. Ivanov

NIST Center for Neutron Research NIST Center for Neutron Research Department of Physics, Florida State University National Institute of Standards and Technology National Institute of Standards and Technology Tallahassee, FL 32306 Gaithersburg, MD 20899-8562 Gaithersburg, MD 20899-8562 Aron Qasba and Y. Ijiri Department of Physics University of Maryland Department of Physics, Oberlin College Massachusetts Institute of Technology College Park, MD 20742 Oberlin, OH 44074 Cambridge, MA 02139

The antiferromagnetic domain size along the growth direc- larger, but reversibly decrease in size in high fields (Fig. 2) as the tion, determined from the inverse of the FWHM, remains constant magnetic frustration increases. Consistent with several theoretical near 750 A after field cooling. This contrasts with the pronounced predictions [2,3] we believe that exchange biasing may originate field-dependence of the FWHM observed after cooling in zero field from magnetic frustration that leads to "frozen" domain walls in the

(Fig. 2). In this state, the FWHM is smallest near zero field, but field-cooled state. approaches the constant field-cooled value when the magnitude of We also observe that the magnitude of the ordered NiO the field is greater than 2 T The corresponding domain size varies moments in all four of the {111} domains in the Fe 0 /NiO super- 3 4 from approximately 1200 A in zero field to 800 A in high fields. lattices depends upon applied field. After cooling in a large vertical

Growth-plane (7/0) scans through the NiO reflection show a similar field, the intensity of the antiferromagnetic (111) NiO reflection difference between the field dependence of the FWHM after cooling reversibly decreases as the field is increased. (The behavior is in zero field and cooling in a 6 T field (Fig. 2). qualitatively similar after cooling in zero field.) Analogous field-

Upon field cooling, domain walls both parallel and perpen- cooled measurements of the (111) NiO peak were performed in dicular to the growth direction lock into the antiferromagnetic layer, a horizontal field and surprisingly show a comparable intensity presumably due to the exchange coupling between the NiO antifer- decrease. Some of the NiO moments thus seem to disappear out romagnetic moments and the Fe,0 moments that are aligned paral- of all four {111 } domains. We speculate that these NiO spins 4 lel to the cooling field. After cooling in zero field, the domains are may become disordered as a result of the high internal fields.

Simultaneously, some of the NiO moments reorient perpendicular

to the Fe,0 magnetization direction in high fields [6]. While this 4

Field Cooled Zero Field Cooled "spin-flop" response is favored by some theoretical models [4], it (Exchange Biased) (Unbiased) does not appear to be directly responsible for the exchange biasing

0.015 for these samples.

Future studies will focus on the characteristics and origin 0.014 of the "spin-flop" response of the NiO spin structure to large mag- 0.013 X netic fields. In addition, we will further explore the differences

0.012 between the antiferromagnetic domains for the exchange-biased and 5 o unbiased conditions. <3 0.011 (00/) Scan (00/) Scan

0.024 REFERENCES:

[1] W. H. Meiklejohn and C. P. Bean, Phys. Rev. 102, 1413 (1956); 105, 904 0.022 (1957).

[2] A. P. Malozemoff, J. Appl. Phys. 63, 3874 (1988). 0.020 [3] T. C. Schulthess and W. H. Butler. Phys. Rev. Lett. 81, 4516 (1998).

(110) Scan (110) Scan N. C. Koon, Phys. Rev. Lett. 78, 4865 (1997). o 0.018 [4] CD J. A. Borchers, R. W. Erwin, S. D. Berry, D. M. Lind. J. F. Ankner, E. -60 -40 -20 0 20 40 60 •60-40 -20 0 20 40 60 [5] Lochner, K. A. Shaw and D. Hilton, Phys. Rev. B 51, 8276 (1995). Field (kG) Field (kG) [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).

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.

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 (a) 0 00.-. superconducting -0 structures with Cu0 planes, in which the electrons on neighboring 05 1 2 diamagnetism -o .10 copper ions are strongly coupled magnetically. In systems based \ i H = 5G 0 15 on La,Cu0 antiferromagnetism is a dominant feature of the phase | 4 , 0 20 diagram at low doping levels, and conventional itinerant-electron I J -0 .25 ^ behavior dominates in the high doping regime. Intermediate doping h- 0 .30 levels are described by neither, but this is where the superconduct- (BCS order param.

• E, = 13.7 meV ing properties are optimal. In our experiments, we focus on the evo- • E = 5.0 f meV lution 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 10 20 30 40 50 magnetic ordering coexisting with superconductivity in Temperature (K)

La, Nd ,Sr CuO, and recently in La, Sr CuO, [1,L 2].J Further 1.6-x, 0.4n x 4 > 2-x x 4 experiments are needed to understand the coexistence of the incommensurate spin density waves (SDW) and superconductivity, the FIGURE 1. (a) Magnetic susceptibility measured after cooling in zero field, (b) Peak intensity of the incommensurate elastic scattering as a details of the spin structure, and the influence of pinning potentials. function of temperature. The measurement was performed with two different A crystal of La,Cu0 with a superconducting transition neutron energies of 13.7 meV and 5 meV. The solid line denotes the BCS 4+y superconducting order parameter squared, with a T of 41 K. at = 42 K was produced by doping pure La Cu0 electrochemi- 2 4 cally with a large quantity of excess oxygen (y « 0.12). The the peaks disappear. The solid lines in the figure are Gaussians superconducting shielding signal measured after cooling in zero convolved with the instrumental resolution which indicate that the field is shown in Fig. la. The transition is very sharp with an onset in-plane static magnetic order is correlated over distances larger T = 42 K. Our initial characterization suggests that the crystal is than 400 A. From this, we conclude that static long-range magnetic a bulk superconductor with a hole concentration similar in density order exists in the superconducting state of La,Cu0 . Also, the 4+y and homogeneity to that of La SrCu0 crystals with x 0.15. 2 4 SDW order is not specific to a tetragonal crystal structure as previ-

At temperatures below the superconducting T , we observe ously believed since this crystal is orthorhombic; it is a more elastic magnetic scattering at a quartet of incommensurate positions general phenomenon. centered around (100), which is the Bragg position for the antifer- We then investigated how the static spin arrangement is romagnetism in the undoped insulator. Surprisingly, we find that the correlated between CuO, planes. The /-dependence of the incom- incommensurate wavevectors are not precisely along the Cu-O-Cu mensurate scattering is shown in Fig. 2b. The intensity modulation bond direction, but are rotated by about 3°. of both the (10/)- and (01/)-centered scattering is reminiscent of the In Fig. 2a we show elastic scans along the in-plane h spin structure of the undoped parent compound La,Cu0 . The solid 4 direction through an incommensurate position for various tempera- lines in both panels represent fits to Gaussian lineshapes convolved tures using 5 meV neutrons. Below 42 K, the observed peaks with the instrumental resolution, assuming a model for the stacking are extremely sharp and are resolution-limited, while above 42 K arrangement and spin direction identical to that of pure La,Cu0 . 4

10 RESEARCH HIGHLIGHTS —

Y. S. Lee, Ft. J. Birgeneau, and M. A. Kastner Y. Endoh, S. Wakimoto, and K. Yamada R. W. Erwin and S.-H. Lee Department of Physics Department of Physics NIST Center for Neutron Research Massachusetts Institute of Technology Tohoku University National Institute of Standards and Technology Cambridge. MA 02139 Aramaki Aoba Gaithersburg, MD 20899-8562 Sendai 980-77, Japan G. Shirane

Department of Physics Brookhaven National Laboratory Upton, NY 11973

Here, the only free parameters are the width and a single overall 800 i i i i i i i intensity scale factor. The agreement is clearly satisfactory, with the

- (a) 700 fit indicating that the spins are correlated across » 3 CuO, planes. • 45K (O=0 min) m We conclude that the stacking arrangement of the magnetically 600 0 A 30 K ordered planes in our La,Cu0 sample follows that of undoped 4+y 1.3 K

iunts/1 500 insulating La,Cu0 , even though the magnetic order in the CuO, 4

o planes is incommensurate. This is the first direct evidence that the >, 400 magnetism of the doped superconductor mimics the magnetism in

300 the undoped insulator in such a specific way.

••gf»l We show in Fig. lb the peak intensity of the elastic signal 200 as a function of temperature measured using both 13.7 meV and

100 5 meV neutrons. The fact that one obtains identical results for the 1.08 1.10 1.12 1.14 temperature dependences of the intensities with these two different

{h, 0.128, 0) neutron energies and, concomitantly, energy resolutions indicates

that the scattering is truly elastic. The intensity of the elastic scat-

tering turns on at approximately the same transition temperature as

superconductivity. Noting that the intensity of the magnetic scatter- (10/)centered ing is proportional to the square of the magnetic order parameter, - 400 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 200 exhibits mean field behavior just like conventional superconductiv-

ity. This is very surprising given the two dimensionality of the

— 0 ordered magnetism. The size of the ordered moment is 0.15 [x & B ,

which is 25 % of the ordered moment in pure La,Cu0 . Our 4

(01/)centered results argue against an itinerant electron description of the incom- 400 mensurate 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 La Cu0 . It appears 2 4

that the spins are localized and ordered in this high temperature

superconductor.

0 2 4 REFERENCES

/(r.l.u.) [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 degen-

eracy and offers the possibility of qualitatively new states of matter.

Theoretical studies have in fact shown that spins with nearest neigh- Frustrated

bor antiferromagnetic Heisenberg interactions on the pyrochlore lat-

tice 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, T , into a glassy FIGURE 1 . A network of corner-sharing tetrahedra. When two spins in a f tetrahedron are aligned antiparallel to each other then the third spin phase with static short range correlations [1]. Spinel antiferromag- can not satisfy its antiferromagnetic interaction with the other two spins

nets, AB,0 , in which the octahedral B site forms the same mag- simultaneously. 4

netic lattice as in the pyrochlore structure, however behave quite indicates the presence of weakly interacting spin clusters within the

differently. For instance, ZnCr,0 exhibits a first order phase transi- 4 ordered phase, which is a key feature of geometrically frustrated tion to = a long-range ordered Neel phase at T 12.5 K , much less magnets.

than the Curie-Weiss temperature 10 I = 393 K. have explored We Theoretical work indicates that magnetic order cannot devel-

this ordered phase and the corresponding phase transition through op in an isotropic spin system with nearest neighbor antiferromag-

inelastic neutron scattering [2], netic Heisenberg interactions on the pyrochlore lattice. It is natural Figure 2 provides an overview of our neutron scattering to ask what deviation from this model causes order to develop

results as a color image of / w) at three temperatures. For (Q, in ZnCr 0 ? To answer the question we probed the temperature 2 4 > Figures 2a and 2b show a constant-Q ridge centered at T T , dependence of static and dynamic features of this system in the * 1.5 1 and extending beyond 10 meV. The ridge indicates Q A vicinity of the phase transition. Figure 3 shows that long range

quantum critical fluctuations of small clusters, most likely AFM antiferromagnetic order (blue squares in frame (b)) and the local antiferromagnetically correlated tetrahedra, and closely resembles spin resonance (frame (a)) appear simultaneously in a spectacular those obtained in similar experiments on other frustrated AFM. first order transition. It also shows that magnetic ordering is accom-

For T < T , however, the low energy spectral weight concentrates panied by a cubic to tetragonal lattice distortion (red circles in

into a sharp constant-energy mode centered at fid) = 4.5 meV frame (b)). The lattice distortion plays a crucial role in relieving

= IJI » k T.. The wave vector dependence of this resonance B frustration and allowing long-range order to develop. It is well

intensity reveals that it is an excitation among antiferromagnetically 3+ known that exchange interaction between Cr ions whose oxygen correlated nearest neighbor spins. they can not be seen Though coordination octahedra share an edge are strongly dependent on the

in Fig. 2c, there are in fact magnetic Bragg peaks in the elastic oxygen bond angles and hence the metal ion spacing. As a conse- scattering channel (see Fig. 3b), which provide evidence for long- quence the tetragonal strain e > 0 and e < 0 yields weaker AFM a c

range order for < . It is unusual that excitations of such local- T T interactions between spins occupying the same basal plane and ized character exist in a long-range ordered phase. The resonance stronger AFM interactions between all other spin pairs. This reduces

1 2 S.-H. Lee C. Broholm, NCNR and S. W. Cheong W. Ratcliff II NIST Center for Neutron Research Department of Physics and Astronomy Department of Physics and Astronomy Department of Physics and Astronomy National Institute of Standards and Technology The Johns Hopkins University Rutgers University Rutgers University Gaithersburg, MD 20899-8562 Baltimore, MD 21218 Piscataway, NJ 08854 Piscataway, NJ 08854 and and T.H. Kim University of Maryland Bell Laboratories, Lucent Technologies Francis Bitter Magnet Laboratory Park, College MD 20742 Murray Hill, NJ 07974 Massachusetts Institute of Technology Cambridge, MA 02139

the energy of a particular long range ordered spin configuration with 1 (Q = 1.5A- ,u)) (1/meV/Cr)

respect to the low energy degenerate manifold thus allowing the 0.5

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 3 2

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 (3/2,3/2,0) - (1/2,1/2,2) disordered cubic paramagnet. 1 ' (1,2,1/2) There are strong analogies between the phase transition in o II ZnCr,0 and the spin-Peierls (SP) transition. In both cases the 3 4

high T phase is nearly quantum critical and can lower its energy (b) through a lattice distortion. In both cases the transition occurs from 0 10 20 30 T(K) I (Q, hw) (1/meV/Cr)

1 0 0.1 0.2 FIGURE 3. (a) Image of inelastic neutron scattering for Q = 1.5 A , (b) T- of scattering

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

energy spectral weight is moved into a finite energy peak. 4 - There are also important differences between the two transi-

tions. The low T phases are qualitatively different, the transition in 0

ZnCr,0 is a first order one, while the SP transition is second order, 12 4

and the change in entropy at T plays an important role in ZnCr 0 , 2 4

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 4 - should be relevant for any frustrated magnet when other symmetry

0 breaking interactions are sufficiently weak.

12 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 Source Sample aperture aperture Detector 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 small- angle 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 com-

FIGURE 2. Upper panel, conventional SANS pinhole collimation. The source and parisons with reflection optics or pinhole collimation for application sample apertures, A and A respectively, determine the shape and extent 1p 2p , in SANS instruments. Measurements made recently at the NCNR of the beam profile, l(x), at the detector plane. Lower panel, focusing lens

geometry. Ideally, the source aperture, A , alone determines the beam profile. in collaboration with the Bell Labs scientists [2] have addressed u these issues and have demonstrated and quantified the significant improvement in resolution that can be achieved with compound

refractive optics.

Our tests were made with the same set of cylindrical bicon-

cave 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 two-

dimensional 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 FIGURE 1 . Now installed in the pre-sample flight path of the NG-7 30 m SANS instrument are two sets of MgF biconcave lenses that can be inserted 2 the source aperture, than is possible with pinhole collimation where into the beam under computer control. The 28-lens array in the foreground propor- focuses 8.44 A neutrons at a distance of 15 m from the lenses, and the both the source aperture and sample size must be reduced

6-lens set focuses 18 A neutrons at the same distance. Each lens is 25 mm tionally to improve angular resolution. Aberrations and small-angle in diameter, has a radius of curvature of 25 mm, and is 1 mm thick in the center. scattering by the lenses could, however, blur the image to such

14 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 10 0.0001 0.001 0.01 Q (A 1 Y(mm) )

FIGURE 3. Red dots are measured points along the vertical profile of the image FIGURE 4. Small-angle scattering from voids in a single crystal (2.5 cm in formed by the 28 lens array shown in Fig. 1 of a 9.5 mm diameter source of diameter and 1 cm thick) of fast-neutron-irradiated aluminum. The measure- neutrons 15 m upstream from the lenses. The blue dots are a Monte Carlo ments were made under equivalent resolution conditions (i.e. nearly identical calculation of the profile that includes the effects of spherical and chromatic beam spot size at the detector) using both simple pinhole collimation and the aberrations as well as the broadening caused by gravity. The shoulder in the 28 biconcave lens array shown in Fig. 1. The integrated gain in intensity due measured profile at Y = 0 is due to a residual fast neutron component in to the lenses is approximately 26. the beam. a degree that any advantage over pinhole collimation, which does Fig. 4. The measurements were made under equivalent resolution produce a sharply defined beam spot at the detector, would conditions (i.e., nearly identical beam spot size at the detector) be lost. using both simple pinhole collimation and the 28 biconcave lens

To accurately measure the intensity profile produced by the array shown in Fig. 1. The first data point unaffected by the beam lenses, «= 1 a dysprosium foil was positioned at the focal plane and stop in both data sets occurs at Q 0.001 A" , but the scattered

2 exposed to the focused beam for approximately 2 h. The activated intensity at the detector (counts/cm /s) is more than 10 times higher foil was then placed in contact with a high resolution image plate by using the lenses to illuminate a much larger area of the sample. which stored the image produced by the emitted gamma rays with a The focusing lenses shown in Fig. 1 are now installed for spatial resolution of better than 0. 1 mm. A typical profile obtained routine use in the NCNR's 30 m SANS instrument on guide NG-7. from reading out the image plate is shown in Fig. 3. Also plotted in Further testing is planned to understand, and hopefully eliminate, the figure is a Monte Carlo calculation of the profile that includes the sources of parasitic scattering that contribute to the tails of the the effects of spherical and chromatic aberrations as well as the beam profile seen in Fig. 3, prior to installing a lens system in the broadening caused by gravity. The measured profile agrees with the NIST/NSF 30 m SANS instrument on guide NG-3. simulation down to intensity levels of 10' 3 of the peak intensity and has an overall signal-to-background ratio in the wings approaching REFERENCES

5 [1] M. R. Eskildsen, P. L. Gammel, E. D. Isaacs, C. Detlefs, K. Mortensen. D. 10 , which is highly satisfactory for most SANS measurements. J. Bishop, Nature 391, 563-566 (1998). The practical benefit provided by the lenses is demonstrated [2] S. -M. Choi, J. G. Baker, C. J. Glinka, P. L. Gammel, Proceedings of the

J. Appl. by the SANS data from voids in a single crystal (2.5 cm in diameter Xlth International Conference on Small-Angle Scattering, 1999, Cryst. (in press) and 1 cm thick) of fast-neutron-irradiated aluminum shown in

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 non- FIGURE 1. Schematic illustrating the effect of shear on grafted brushes equilibrium properties of polymer brushes are still under intense predicted by Miao et al. [8] Such an effect would be consistent with the present data. 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 1 pump and head Si crystal medical implant devices, and for permeation flow through polymer- containing porous media [1]. it"

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 solvent reservoir SS shear base competition between two opposing tendencies: 1) elastic contraction, as the chains attempts to maximize their entropy by adopting FIGURE 2. Shear cell. Arrows denote solvent flow direction. The polystyrene

brush is grafted onto the Si crystal. random walk configurations, and 2) monomer-monomer interactions, such as polymer-polymer repulsions, and polymer-solvent brushes have a tendency to come off the surface at higher shear wetting [2, 3]. rates. Polymer chain stretching in densely grafted brushes has been Predictions from theoretical calculations of brush profiles studied by many different techniques including surface forces appa- under shear span the gamut of possibilities, ranging from brush ratus [4], neutron reflectivity [5], and small angle neutron scattering thickening to brush compression, including no effect of shear flow (SANS) [6]. In general, there is good agreement with results from on the density profile [3]. Miao et al. [8] predict that the response of experiment, simulations and analytical calculations [3]. a brush to the solvent shear flow is displayed as chain tilting toward Oscillatory shear measurements performed with a surface and chain stretching along the direction of flow. However, the forces apparatus suggest that the normal forces between a pair of overall conformational properties such as brush thickness remain brush surfaces are altered when sheared. However, these measure-

essentially unaffected (Fig. 1 ). ments do not give the actual brush profile either with or without We have performed neutron reflectivity measurements on a shear. Effective hydrodynamic thickness measurements of polymer chemically grafted polymer in both good and poor solvents at shear brushes under shear indicate a thickening of the brush; whereas neu- rates over an order of magnitude greater than previously reported. tron reflectivity experiments on adsorbed PS-PEO block copolymer Our neutron reflectivity experiments measure the segment density brushes on a silica surface show no effect of shear on the brush profile of the polymer brushes under shear in an experimental density profile in good solvent, and a slight increase in poor solvent. cell similar to the one used by Baker et al. [9], (Fig. 2). We These earlier reflectivity measurements were limited to shear rates use deuterated polystyrene (d-PS), 83 kg/mol, with a trichloro- 1 of 10,000 s" [7] since the adsorbed PS-PEO block copolymer silane 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 0.01 0.02 0.03 0.04 0.05

1 (A" 1 Q ) Q(A" )

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

1 at 30,000 s .

solvent, cyclohexane, as the solvent media. The dry brush height display an effect. We cannot at this time determine if the brush was measured by X-ray reflectivity to be 17.5 nm. Without shear responds as predicted by Miao et al. [8], or if there is insufficient the brush extends to 31 nm in cyclohexane and 75 nm in toluene. solvent penetration into the brush to exert enough force on the

We measured the brush profile at several shear rates, up to 130,000 chains to induce conformational changes. Future measurements will

1 s yet we see effect of shear the brush density profiles in distinguish between these cases. , no on either solvent (Fig. 3). No desorption of the polymer brush was

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

J. L. Harden and E. Cates, J. Phys. II France 5, 1093 (1995). 1 [1] M. 130,000 s" look identical, indicating less than a 2 % to 3 % change [2] P.-G. de Gennes, Macromolecules 13, 1069 (1980). in the brush density profile. [3] S. Grest, Adv. Polym. Sci., in press. We have also been able to establish that the slight shear [4] G. Hadziannou, S. Patel, S. Granick, and M. Tirrell, J. Am. Chem. Soc. induced swelling reported by Baker et al. [7] for a poor solvent 108, 2869 (1986).

J. Fetters, Phys. (cyclohexane), was probably due to frictional heating of the solvent. [5] A. Karim, S. K. Satija, J. F. Douglas, J. F. Ankner, and L. Rev. Lett. 73, 3407 (1994). In high shear fields, heat generated from friction between the [6] P. Auroy, Y. Mir, and L. Auvray, Phys. Rev. Lett. 69, 93 (1992). solvent and interior surfaces of the apparatus does not readily [7] S. M. Baker, A. Callahan, G. Smith, C. Toprakcioglu, and A. Vradis, dissipate, causing a = 2 °C to 3 °C rise in the temperature of Physica B 241-243, 1041 (1997).

M. L. Miao, H. Guo, M. J. Zuckermann, Macromolecules 29, 2289 (1996). the shear cell. We were able to demonstrate that the brush height [8]

[9] S. M. Baker, G. S. Smith, R. Pynn, P. Butler, J. Hayter, W Hamilton, and L. in cyclohexane is unaffected by shear when the cell temperature Magid, Rev. Sci. Instrum. 65, 412 (1994). 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

NIST CENTER FOR NEUTRON RESEARCH 17 — MACROMOLECULAR CONFORMATION IN ULTRATHIN POLYMER FILMS

Since thin polymeric films are ubiquitous in technological appli- The scattered intensity for a 15 nm thick film of the 270k

cations such as paints, lubricants, and adhesives, a critical blend is compared to an analogous bulk sample in Fig. 1. It is clear characterization of their thermophysical properties is essential. A from the figure that, on a unit volume basis, the thin film scattering central premise in the development of theories for predicting the is higher than that of the bulk. We postulated that this difference is properties of polymer melts in confined geometries is that chains attributable to the scattering from the imperfections at both the air maintain their unperturbed Gaussian conformation, which they and the substrate interfaces, which is driven by the relatively high adopt in the bulk, in the direction parallel to the surfaces under all neutron contrast at these boundaries. To evaluate this component, conditions [1,2]. These assumptions, which form the foundations of films of pure d-PS were spin cast under identical conditions and the important field of polymer thin films, have been questioned on their scattering measured. the basis of indirect experimental findings [3,4]. We have utilized The pure d-PS film data were fit with a simple Debye-Bueche the power of small angle neutron scattering, especially the high form factor to obtain parameters for a roughness term. The blend neutron flux at NCNR, to unequivocally characterize the chain film data were then fit by scaling this roughness term and adding a structure and conformation in ultrathin polymer films, and thus have component obtained from the Random Phase Approximation (RPA) resolved this important fundamental question. model. In the fitting, two RPA model parameters were also varied:

The experimental measurements of chain conformations and the blend chain radius of gyration (R ) and the Flory interaction g system thermodynamics in thin films have remained elusive due parameter. The combined model is illustrated as the solid line in to the small amounts of sample material involved. To illustrate Fig. 1 along with the roughness term (long dashed line) and RPA this point, a thin film of 10 nm incurs a decrease in signal by term (short dashed line). The fact that the RPA term is very close

4 lxl0 from a typical bulk polymer sample. In this case, the noise to the data for the bulk blend illustrates that the film and bulk

is comparable to the signal, complicating the experiments. Prior to

, , , 400.0 | upgrades of the cold neutron source at the NCNR, data collection 1 times were prohibitive. Improvements in sample preparation, which are discussed in detail elsewhere [5,6], have allowed us to measure 300.0 - 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).

1 0.0 1 ' = ' 1 0.000 0.010 0.020 0.030 0.040

1 Q(A- )

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

have nearly the same this the samples . Using model, thinnest films, Rc combined R Our results clearly show that, in the g was determined for films ranging in thickness over two decades volume pervaded by a coil is decreased as compared to the bulk.

(0.5 R < D < 50 The molecular size was found to be indepen- This is because the in the direction parallel to the surfaces is o RJ. R g dent of film thickness (Fig. 2). Since the scattering vector is primar- unaffected, while the corresponding quantity in the third direction is ily in the surface plane, this conclusion is consistent with theoretical strongly reduced. In conjunction with other studies, which indicate assumptions and suggests that chain conformation in the direction a thickness-independent density in ultrathin polymer films, these parallel to the surfaces are unaffected by confinement. 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

2.00 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 increas-

es in cold neutron flux, SANS at the NCNR is now an appropriate

tool to study a host of problems involving interfacial structure,

nano-patterning in systems as far 1.00 finite size phase behavior, and

ranging as engineering thermoplastics to biological systems. These,

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

groups.

REFERENCES 0.00 [1] D. N. Theodorou, Macromolecules 21, 1400 (1988).

[2] S. K. Kumar, M. Vacatello, D. Y. Yoon, J. Chem. Phys. 89, 5206 (1988). 2.00 [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).

§ 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 . Data are displayed for blends with Mn = 270k (filled g circles) and Mn = 650k (open circles).

NIST CENTER FOR NEUTRON RESEARCH 19 .

PROBING THE LOCATION OF THE TERMINAL GROUPS OF A DENDRIMER

Dendrimers represent a new class of macromolecules developed The location of the terminal units can be determined by label-

in recent years. Typically, a dendrimer structure has a tri- or ing the last generation of the dendrimer with deuterium and using tetrafunctional core, which is surrounded by several "generations" contrast matching techniques. Figure 1 shows the labeled groups in of stepwise added trifunctional monomers, leaving the last genera- red and the rest of the dendrimer in blue. By choosing the proper tion with a large number of terminal units as shown in Fig. 1 mix of h- and d- solvents, the interior of the dendrimer will be

The molecular weight doubles with each generation, leading to matched, making only the labeled end groups visible in small angle high molecular weights, and causing the dendrimer to become very neutron scattering (SANS). compact and crowded. A sixth generation polyamidoamine (PAMAM) dendrimer

Many of the potential technological applications of den- was reacted with acrylonitrile (vinyl-d3) to give the deuterium drimers depend on their segment density distribution. Previous scat- labeling for the SANS. Ethylene diamine was reacted with the tering studies have shown that dendrimers have uniform interiors dendrimer to give a labeled seventh generation dendrimer. A similar and are quite spherelike in their shape [1]. The location of the reaction was used to make a seventh and eighth generation den- terminal groups is also of importance, since they are usually differ- drimer without labeling. Solutions of unlabeled eighth generation ent chemically from the rest of the dendrimer. This invites a number dendrimer were made in mixtures of CH OH and CD^OH for deter- ? of applications such as the support of catalysts or drugs or their mination of the match point. Three samples were analyzed, an use as hyperfunctional crosslink sites. The accessibility of these unlabeled dendrimer in CD,OH (high contrast), an unlabeled den- terminal groups depends on their location compared to the other drimer in the match mixture (dendrimer matched), and the labeled dendrimer units. dendrimer in the match mixture (interior matched).

0 0.05 0.1 0.15 0.2

1 Q(A" )

FIGURE 1 . Dendrimer structure with labeled terminal units. FIGURE 2. SANS from G8 dendrimer in CD,0H/CH 0H mixtures. 3

20 RESEARCH HIGHLIGHTS Andreas Topp, Barry J. Bauer, and June W. Klimash, Ralph Spindler, and Eric. J. Amis Donald A. Tomalia

Polymers Division Michigan Molecular Institute National Institute of Standards and Technology 1910 West Saint Andrews Road Gaithersburg, MD 20899-8542 Midland, Ml 48640

SANS was performed at the 30 m facilities at NIST. The nal, demonstrating that the match conditions have been achieved.

spectrometers were operated at a wavelength of X - 6 A, and a The labeled dendrimer SANS is given by the squares. The scattering wavelength spread of AA./A. = 0.15. is weak because only the labeled terminal groups scatter.

Figure 2 is a plot of SANS of dendrimer solutions with differ- A Guinier analysis of the scattering of the high contrast ent CD,OH contents. The intensity is the strongest in pure CD,OH, sample gives the radius of gyration (R ) of the whole dendrimer, and g

as is added and increases again when pure the labeled - contrast match sample gives the of only the terminal weakens CH,OH CH,OH R o

2 is used. The coherent scattering intensity varies as I « (b - b groups. The R of the whole dendrimer is (34.2 ± 0.2) A, while the s D ) o

where b is the contrast of the dendrimer and b is the average R of the terminal groups is (39.3 ± 1.0) A. D s g contrast of the solvent mixture. The terminal groups of a seventh generation PAMAM den-

Figure 3 is a plot of the square root of the scattered intensity drimer are 15 % larger than the average of all of the units.

versus solvent composition with the values to the right made nega- Therefore, the terminal units of a dendrimer are concentrated in the tive so that a straight line can be put through all of the data points. outer shell of a dendrimer.

The zero intersection is at a mass fraction of 60.5 CH,OH which

was the composition used in the matching experiments. REFERENCES

[1] T. J. Prosa, B. J. Bauer, E. J. Amis, D. A. Tomalia, R. Scherrenberg, J. Figure 4 is a plot of the SANS of the three G7 samples. Polym. Sci.: Polym. Phys. 35, 2213, (1997). The circles give the scattering from the high contrast sample, show-

ing 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 sig-

" 0.35

- o [H] in CD OH 0.30 G7 3

G7 [D] in contrast match solvent 0.25 -

o contrast match solvent 0.20 - Eo a 0.15 -

0.10 -

0.05 -

0 -

-0.05

0.02 0.04 0.06 0.08 0.10 0.12

1 Q(A" )

dendrimer in match and FIGURE 3. Location of the match point. FIGURE 4. SANS of labeled and unlabeled G7 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 1 in a major structural challenge, namely in detecting and analyz- ing the structures of peptide assemblies in fluid membranes [1,2]. 0.8

These experiments were performed with membranes in the form 0.6 of oriented multilayers. Originally the samples were investigated in full hydration so that the physical properties of the lipid bilayers N 0.4 were close to those at physiological conditions. However, it was + + + § 0.2 ± * * _ o soon realized that new phenomena involving peptide-lipid inter- + actions occur when the sample hydration is varied. In general, 0

+ ° in full hydration, the peptide organization in each membrane " ° + -0.2 % + 4 is uncorrected to the neighboring membranes. As the hydration 0 0.1 0.2 0.3 0.4 0.5 level decreases, the peptides become correlated between bilayers, Q(A-1) even though the membranes are still fluid. In many cases, further dehydration strengthens the correlation such that the peptide orga-

(b) nization in the multilayers crystallizes [2]. The crystallization 1.5 - provides the possibility for high-resolution diffractional studies.

Investigations along this line might also lead to useful information ~ 1 for crystallization of membrane proteins. E

Antimicrobial peptides are inducible innate host defense mol- 0.5 - ecules 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 0.2 0.3 the molecular mechanisms of their actions are still not clear. We Q(A"1) have found that all peptides, when they are bound to lipid bilayers, exhibit two distinct oriented circular dichroism spectra, one at low FIGURE 1. In-piane SANS from alamethicin in DLPC lipid bilayers at a high peptide-to-lipid ratios (P/L) and another at high P/L. This indicates 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 that each peptide has two different physical states of binding to a were filled with either D 0 giving strong scattering contrast, or H 0 (o). In 2 (+), 2 membrane. the lower panel the lipid was deuterated, providing stronger scattering contrast with H 0 in the channels compared with D (o). These data were taken (+) 2 0 The transition from the low to the high P/L spectrum occurs 2 atANL. 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 embed- Argonne National Laboratory (ANL) of alamethicin in protonated ded in the headgroup region, as suggested by the peptide orientation lipid bilayers (Fig. la) and in deuterated lipid bilayers (Fig. lb), and the membrane thinning effect. At concentrations above P/L*, with D,0 or H,0 filling the pore channels. The peak in these data neutron in-plane scattering showed that the peptides form pores

is due to the fairly regular pore spacing and is most pronounced in the membranes, while no pores were detected below P/L*. The

when there is a strong contrast, either between D 0 and protonated detection was achieved by exploiting the sensitivity of neutrons 2 lipid, or between H,0 and deuterated lipid. All four sets of data are to D,0, which had replaced the water in the membrane pores. consistent with the model shown in Fig. 2 once the differences in As an example, Fig. 1 shows neutron in-plane scattering taken at 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

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 instrument that includes both the FIGURE 2. Model for the channels formed by octamers of alamethicin in DLPC SANS bi layers that is consistent with the in-plane SANS data shown in Fig. 1. 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

") '5 changed to the top middle panel. Our analysis [2] showed that the

C 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

a * 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 > i I » ( ) biology.

REFERENCES FIGURE 3. Examples of SANS patterns from channel-forming peptides in lipid [1] K. He, S. J. Ludtke, D. L. Worcester, and H. W. Huang. Biochemistry bilayers at various temperatures and stages of dehydration. The upper left 34, 16764 (1995); Biophys. J. 70, 2659 (1996); S. J. Ludtke, K. He, W. panel is for magainin pores in fully hydrated fluid bilayers. As this and other T. Heller, T. A. Harroun, L. Yang, and H. W. Huang. Biochemistry 35, peptide/lipid systems studied are dehydrated, the pores in adjacent bilayers 13723 (1996). become correlated and eventually crystallize. [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 anisotro-

pic 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 -100 study a solution of the synthetic hectorite type clay, Laponite LRD

6 (Laporte Industries Ltd.), and poly(efhylene-oxide) (PEO) = 10 (Mw -50 0 50 100 150 200 250 300 350 400 450 g/mol). The results reported here are for a highly viscoelastic solu-

dydt (s" 1 tion containing a mass fraction of 3 % LRD and 2 % PEO at room ) temperature. The clay particles produce transparent dispersions of

FIGURE 1 . Optical birefringence as a function of shear rate. The arrow disk shaped particles ca. 300 A in diameter and ca. 10 A thick [5,6]. indicates the shear rate where the minimum in the birefringence occurs.

The pH and ionic strength of the solutions were controlled by the addition of NaOH and NaCl, respectively. SANS experiment used to detect the orientation of the clay platelets

1 the rate the birefringence Figure shows shear dependence of and polymer chains under shear is between D 0 and the other 2 of the clay-polymer solution. A distinct minimum in the birefrin- solution components.

1 gence is observed at a critical shear rate of approximately 40 s . The results obtained from the polymer-clay solutions in the

The source of the shear dependence of the birefringence is due to "radial" and "tangential" beam configurations are summarized in the alignment of the clay particles and the PEO. Previous work Fig. 2. At low shear rates, a diffuse isotropic ring of SANS intensity demonstrated that the sign of the birefringence of the clay particles is observed (Fig. 2a). The diffuse ring corresponds to an average oriented along a flow field is negative, therefore at low shear rates, spacing between platelets of 800 A to 1100 A. With increasing shear the orientation of the clay dominates the birefringence. Above the rate, the ring becomes more diffuse (Fig. 2b) and an anisotropic critical shear rate, the birefringence due to the orientation of the streak develops parallel to the vorticity axis of the flow field (the polymer chains dominates. cylinder axis). If we neglect the main reflected beam which appears

A double logarithmic plot of viscosity, v\, versus shear rate as a background streak in the gradient direction for tangential beam shows that the solution is shear-thinning over the entire range measurements (Fig. 2d), the anisotropic streak becomes the domi- according to a power law with exponent m = -0.65. No signature of nant feature in both scattering geometries with increasing shear rate the critical shear rate is observed in the viscosity behavior. After cessation of shear, the streaks relaxed to an isotropic state in |

The SANS shear cell utilized has been described previ- less than 2 min. ously [2]. It consists of a cylinder that rotates within an outer To account for the SANS and birefringence results, our cur cylinder with the sample in the gap between them. The instrument rent understanding is that the polymer chains are in a dynamic was configured in both "radial" (incident beam parallel to the adsorption/desorption equilibrium with the clay particles to form shear gradient along the cylinder diameter) and "tangential" (inciT a network. The peak position in the quiescent scattering pattern dent beam passing between the cylinders, parallel to the flow direc- in Fig. 2a is an indication of the mesh size of this network tion) geometries. Using 9 A wavelength neutrons gives a Q range (<=» 1000 A). A 2 % solution of only PEO, at the same pH, polymer

1 1 between 0.0027 A" and 0.0199 A . The primary contrast in the 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

1 shear rates up to 100 s . Similarly a 3 % aqueous clay solution tion of the flow field, however, the type of orientation observed shows no evidence of an anisotropic SANS pattern. Therefore, we in these clay-polymer solutions is also observed in some liquid can conclude that the anisotropic SANS pattern observed in the crystalline lamellar phases, block copolymer solutions, and melts. clay-polymer solutions is due to this coupling between clay platelets The critical shear rate is the shear rate at which the rate of chain and polymer, allowing a higher orientation than either single com- desorption is slower than the terminal relaxation time of the chain, ponent in solution can produce. From the birefringence data, the hence chain extension is observed in the birefringence. clay particles orient at low shear rates, while strong orientation of On cessation of shear, the stress on the network decays the PEO does not occur until the critical shear rate is exceeded. almost immediately, and the recovery of the isotropic structure is

Since the clay platelets and the PEO chains are of comparable size controlled by the relaxation of the stretched chains. As the chains

(both about 300 A), the lack of internal flexibility of the rigid clay retract, the coupling of the chains to the clay allows the platelets particles makes them much easier to align than the flexible polymer to randomize in orientation in the local viscous environment. The chains. recovery from anisotropy is much faster than expected from simple

According to SANS patterns from both beam configurations Brownian motion of only the clay particles in a medium of the

(Fig. 2) the shear flow results in an alignment of clay platelets same viscosity as the clay-polymer solution exhibited macroscopi- orienting with their surface normals in the vorticity direction. One cally, and is indicative of the dynamic coupling of the polymer would expect the surface normals to orient along the gradient direc- 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. a) radial beam b) radial beam

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).

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

1 1 1 1 a) 0.5 s" . , b) 20 s , c) 90 s , d) 90 s

NIST CENTER FOR NEUTRON RESEARCH 25 UNIQUE DETERMINATION OF BIOMIMETIC MEMBRANE PROFILES BY NEUTRON REFLECTIVITY

ew biomimetic membrane materials, of fundamental impor- The existence of multiple solutions, only one of which can be

tance in understanding such key biological processes as physical, is especially problematic in cases where a key additional molecular recognition, conformational changes, and molecular self- piece of structural or compositional information is lacking as can assembly, can be characterized using neutron reflectometry. In par- happen in the investigation of these biological membrane systems. ticular, scattering length density (SLD) depth profiles along the Why this inherent uncertainty? The neutron specular reflection normal to the surface of a model biological bilayer, which mimics amplitude for a model SLD can be computed exactly from first the structure and function of a genuine cell membrane, can be principles; the square of its modulus gives the measurable reflectiv- deduced from specular neutron reflectivity data collected as a func- ity. It is firmly established, however, that the complex amplitude tion of wavevector transfer Q. Specifically, this depth profile can be is necessary and sufficient for a unique solution of the inverse obtained by numerically fitting a computed to a measured reflectiv- problem, that of recovering the SLD from reflection measurements. ity. The profile generating the best fitting reflectivity curve can Unambiguous inversion requires both the magnitude and phase of then be compared to cross-sectional slices of the film's chemical reflection. Once these are known, practical methods [3] exist for composition predicted, for example, by molecular dynamics simula- extracting the desired SLD. tions [1]. However, the uniqueness of a profile obtained by conven- In fact, considerable efforts were made about a quarter century tional analysis of the film's reflectivity alone cannot be established ago to solve the analogous "phase problem" in X-ray crystallography definitively without additional information. In practice, significantly using known constraints on the scattering electron density [4] and by different SLD profiles have been shown to yield calculated reflectiv- the technique of isomorphic substitution [5]. Variations of the latter ity curves with essentially equivalent goodness-of-fit to measured approach have been applied to reflectivity, using a known reference data [2], as illustrated in Fig. 1. layer in a composite film in place of atomic substitutions. These

0.1 . 0.2 1 Q(A" )

FIGURE 1 . Family of scattering length density profiles obtained by model- FIGURE 2. Reflectivity curves for the thin film system depicted schematically in

reflectivity in inset. profile represented the inset, one for a Si fronting (red triangles), the other for Al 0 (black circles). independent fitting of the data the The 2 3 by the blue dashed line is unphysical for this Ti/TiO film system yet generates The curve in the lower part of the figure (blue squares) is the real part of the a reflectivity curve that fits the data with essentially equivalent goodness-of-fit complex reflection amplitude for the films obtained from the reflectivity curves

(all the reflectivity curves corresponding to the SLD's shown are plotted in the by the method described in the text. inset but are practically indistinguishable from one another).

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, reflectometry has been successfully applied to the challenging type which generally is valid in crystal structure determination but which of biological membrane depth profiling described earlier. fails catastrophic ally at low Q (low glancing angles) in reflection In Fig. 2 are plotted a pair of neutron reflectivity curves from slab-shaped samples such as thin films. Exact inversion measured for the layered film structure schematically depicted in requires accurate knowledge of the reflection amplitude over the the upper right inset, one with Si and the other with A1 0 as the 2 3 entire Q-range, especially at low Q. fronting medium. The lower part of Fig. 2 shows the real part of

In this decade the reflection phase problem has been exactly the complex reflection amplitude for the multilayer as extracted from solved using a protocol of three reflectivity measurements on com- the reflectivity data, according to the method described above, and posite films consisting of the film of interest in intimate contact with which was subsequently used to perform the inversion to obtain each of three known reference layers [6, 7]. Subsequently, variations the SLD shown in Fig. 3. For comparison, the SLD predicted by using only two measurements have been shown to partially solve a molecular dynamics simulation is also shown in Fig. 3, in a the phase problem, an additional procedure being required to choose slightly distorted version, corresponding to a truncated reflectivity between two solution branches, only one of which is physical [8, data set, which indicates the spatial resolution of an SLD obtainable

9]. In the past year [10], an exact solution has been found for a in practice. This latter SLD was obtained by inversion of the reflec- two measurement strategy in which the film surround, either the tion amplitude computed for the exact model SLD, but using values

1 fronting (incident) or backing (transmitting) medium, is varied. This only up to the same maximum Q value (0.3 A ) over which new approach is simpler to apply than reference layer methods the actual reflectivity data sets were collected. Overall, agreement and is adaptable to many experiments. Surround variation neutron 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).

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.

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 characterization methods, while remaining thin enough that the

few nm thick. Optical techniques such as ellipsometry are results are relevant to film of technological interest. Figure 1 shows

used to monitor film thicknesses and optical properties in produc- spectroscopic ellipsometry (SE) data and corresponding best fits for

tion. However, for the current integrated circuit (IC) generation the sample with surface contamination and after an organic cleans-

the accuracy of ellipsometry degrades because parameters such ing. Nominally, the only change is a decrease in the thickness of the

as thickness and index of refraction (which reflects the composi- contamination layer [1].

tion) become strongly correlated. Thus, it is difficult to unambigu- In XR data (Fig. 2) two oscillation periods are observed

ously determine these parameters simultaneously, and the accuracy for the contaminated sample. The high frequency oscillation corre-

of ellipsometry would benefit from an independent calibration. In sponds to the SiO, film, whereas the low frequency modulation is

reflectometry techniques, on the other hand, these parameters are due to the thinner contamination layer (which is not present after

nearly decoupled. The thickness of a layer is approximately inverse- cleaning, indicating removal of the contamination.)

ly proportional to the oscillation period of the reflected intensity, The NR measurements (Fig. 3) were done in a vacuum to

whereas the differences in scattering length density SLD (also an reduce the air scattering background. This allowed us to achieve 8 indicator of composition) between the layers is related to the ampli- a very large range in reflectivity, over 10 , which is among the

tude of the oscillations. Neutron reflectometry (NR) is better suited best examples in NR measurements to date. A slightly thinner

than X-ray reflectometry (XR) for the study of the Si0 /Si system contamination layer in NR is consistent with the fact that the XR 2

because there is a relatively large contrast (or difference in SLD) was done in air, during which the contamination was growing. This

between the scattering length densities of the two materials: 65 %, was confirmed by changes in XR scans immediately following those

vs. 7.6 % for X-rays. in Fig. 2.

Consider as an example a sample with a nominally 10 nm The average of the 5 measurements of the SiO, film thickness

thick thermal oxide film on silicon. This moderate thickness was was 10.27 ±0.13 nm. The excellent agreement among the results

chosen to increase our confidence in the results of the various for the three different techniques increases our confidence in the

0 1.00

-1 L-fa 2.0 03 :

<^S -2 CXJ 1.5 " C o.5o E 1.0 -£ -3 E= _ . c 0.5 O -O CJ> 000 0.0 CJ> 5 10 15 g -5 CD Depth (nm) ^ -6

3 -7

-8

-9

-10 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

Photon Energy (eV)

x 2. reflectivity and best fits for the clean and surface FIGURE 1. Comparison of spectroscopic ellipsometry experimental data, \' FIGURE X-ray contaminated sample. The inset shows the scattering length density profile and A, to the fits (solid line) for the clean and surface contaminated sample. determined by the fits. The inset shows < e,> and > as a function of depth determined by the fit.

28 RESEARCH HIGHLIGHTS J. A. Dura and C. F. Majkrzak C. A. Richter, N. V. Nguyen and J. R. Ehrstein NIST Center for Neutron Research Semiconductor Electronics Division National Institute of Standards and Technology National Institute of Standards and Technology Gaithersburg, MD, 20899-8562 Gaithersburg, MD, 20899-8122

40.0 160 7(a) —~~~~~ , \ 140 30.0

1 •' s 120 — / / s A"\-*

2.0 3.0 4.0 5.0 6.0

Photon Energy (eV)

1.0

-1.0 IVMb) FIGURE 3. Neutron Reflectivity data and best fit for a sample with surface contamination. The inset is the scattering length density profile determined -3.0 ^^enmXR by the fit.

-5.0 parameters extracted via these models. Thus the XR and particularly

\ , o-/ \ / the NR corroborate the correct analysis required in SE (which is the -7.0 v\ 4 nm NRX^/-— technique most practical in monitoring production). \2 nm NR To further investigate the applicability of these techniques to -9.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 thinner SiO, layers, we simulated the SE and the XR and NR curves Q (nm" 1 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

FIGURE 4. Model calculations for thin S1O2 Alms of thickness indicated in the average values obtained from the actual measurements previously figure, on Si. a) Spectroscopic ellipsometry, and b) unless otherwise noted discussed. The SE simulation, Fig. 4a, shows distinct differences 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 in both the magnitude and shape of A among the three thicknesses == 2.4 nm film. shown. In models of XR, shown in Fig. 4b, only very weak oscilla- have shown that three different techniques can offer com- tions are seen for even the thickest of the SiO, layers because of We

plimentary information on the structure of thin SiO, films on Si. the low contrast between SiO, and Si. However, in NR, for SiO, All offer a significant degree of sub-monolayer thickness sensitivity, layers as thin as 2 nm strong oscillations are clearly seen above

8 although in NR there is a much higher contrast between SiO, and the 10" lower limit, demonstrated in Fig. 3. Therefore both NR and Si than in XR. 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, REFERENCES 2.4 nm, sample. While these data are not yet fit to a model curve, [1] For details see: "Neutron Reflectivity, X-ray Reflectivity, and Spectroscopic we note that both the reflected intensities oscillation amplitude and Ellipsometry Characterization of Thin Si0 on Si," J. A. Dura, C. A. 2 F. Majkrzak, and N. V. Nguyen" Appl. Phys. Lett. 73, 2131 are similar to those of the 2.0 nm model, indicating similar interface Richter, C. (1998). widths.

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 10 5 the United States recently undertook a round-robin study to 559.08 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 stan-

dards. By contrast, in an international round-robin exercise spon-

sored 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 pos-

sible because all the laboratories used SRM 2137 Boron Implant in

Silicon as a common reference material. These results demonstrate 560 570 the need for a common arsenic reference material to improve inter- Energy, keV

laboratory reproducibility. Furthermore, SEMATECH (a consortium of semiconductor manufacturers) recently listed SRM implants of 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. phosphorus and arsenic in silicon as high priority industrial needs.

Consequently, a Standard Reference Material (SRM 2134 Ion- air-dried. Each was weighed and heat-sealed in a polyethylene bag Implanted Arsenic in Silicon) was produced at NIST, using a wafer that had been cleaned in high purity nitric acid. from the SIMS intercomparison. The material for this SRM was A dilute solution standard was prepared by gravimetrically provided by a major ion implanter manufacturer who supplied three diluting a 10 mg/g solution of As^O., in dilute ammonia to about 2 200 mm diameter wafers that had been implanted with arsenic at mg/kg. Another solution was prepared similarly from SRM 3103a an energy of 100 keV (in the same batch). One of the wafers was Arsenic Spectrometric Solution. Aliquants of both solutions were diced and distributed to 12 participating laboratories for the arsenic weighed from a polyethylene pipette onto 1-cm disks of acid- round-robin study described above. Each of the remaining wafers leached Whatman 41 filter paper and dried to produce standards could provide 221 SRM units, enough for an estimated 10 year sup- with about 200 ng arsenic each. Two standards from each solution ply. One of the remaining wafers was therefore diced into 1 cm x 1 were irradiated with the samples. A blank filter paper was shown in cm pieces with a wafer saw for use as SRM 2134. Because of the a separate experiment to contain no significant arsenic (« 0.01 % specificity and matrix independence of instrumental neutron activa- of the amount in the standards). tion analysis (INAA), this technique was chosen as the primary Samples, standards, and blanks were stacked in the irra- method for certification of the arsenic implanted dose. diation container in the following sequence: standard, blank, five Ten analytical specimens of silicon were selected from samples, two standards, five samples, blank, and standard. The among the 22 1 pieces cut from the wafer to determine arsenic stack was irradiated for four hours in the RT- 1 pneumatic tube of content and test for homogeneity. Two blank chips of silicon were 3 the NIST research reactor, at a thermal fluence rate of 7.7 x 10' analyzed in parallel. Pre-irradiation handling was done on a class 2 cnr s'. The container was inverted halfway through the irradiation 100 clean bench. In a Teflon TFE beaker, the specimens and blanks to equalize to the first order for the axial fluence rate gradient along were rinsed together in ultrapure (UP) water, rinsed with 95 % the container. ethanol, cleaned ultrasonically for one minute in ethanol, and rinsed After irradiation the silicon samples were cleaned ultra- twice with UP water. The samples and blanks were then agitated for sonically for one minute in de-ionized water, blotted dry, and one minute in UP water, blotted on Whatman 41 filter paper, 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 detec- Certification using a primary method is only possible when tor with a 1.71 keV resolution and 40 % relative efficiency at 1333 all potentially significant sources of uncertainty have been evaluated keV. Each sample and standard was counted at least twice, after explicitly for the application of the method and the matrix under

31 the 2.62 h Si matrix activity had substantially decayed. The 559 investigation. In addition, confirmation of measurements by a pri-

76 + 563 keV doublet of As in each spectrum was integrated with mary NIST method may be accomplished by one or more of the the SUM computer program [1]. See Fig. 1. No evidence indicating following: determination of certified constituents in other SRM(s) significant heterogeneity among samples could be seen when the or CRM(s) of similar matrix and constituent concentration range; observed sample-to-sample precision was compared to what was a second NIST technique with appropriate controls; or results of expected from counting statistics combined with other sources of measurements from selected outside collaborating laboratories with analytical variability. appropriate experience.

NIST currently certifies elemental concentrations in SRMs In order to certify the arsenic concentration in SRM 2134 using one of three modes: (1) a primary method at NIST with using INAA as a primary method it is therefore necessary to evalu- confirmation by other method(s); (2) two independent critically ate all significant sources of uncertainty explicitly. For this set of evaluated methods at NIST, and (3) one method at NIST and differ- measurements, we considered sources of uncertainty greater than ent methods by outside collaborating laboratories [2]. 0.01 % relative to be significant. The results of a complete evalua-

tion of all sources of uncertainty are listed in Table 1. This evalua-

Table 1. Individual Uncertainty Components for Determination of tion yielded an expanded relative uncertainty of 0.38 % (as defined Arsenic in SRM 2134. by ISO and NIST) and gives an approximate level of confidence Source of Uncertainty Individual Uncert. (1s) % of 95 %. The arsenic concentration observed was 91.20 ng/cnr ±

- Basis Measure Sample Area / Micrometer Accuracy 0.012 2 0.35 ng/cm .

1 Basis Measure - Sample Area / Precision (n = 26) 0.0089 In conclusion, we have successfully applied INAA as a

Concentrations of Comparators (Standards) 0.106 primary method for the certification of this new SRM. The observed

Mass Determination - Comparators 0.041 relative expanded uncertainty of 0.38 % is considerably smaller Isotopic Variability 0 than the 1 % value desired by the semiconductor industry. This

Blank and Blank Correction (n = 10 2 1 0.013 ) new SRM should greatly enhance the U.S. semiconductor industry's Irradiation Geometry Differences 0.039 ability to achieve accurate and reproducible analytical results for

Neutron Self - Shielding/Scattering Differences 0.024 this key dopant in silicon. Timing 0

Irradiation Interferences Negligible REFERENCES

1 Measurement Replication (n = 9) 0.081 [1] R. M. Lindstrom, Biol. Trace Elem. Res. 43-45, 438 (1994).

Counting - = 5 1 0.073 [2] W. May, R. Parris, C. Beck, J. Fassett, R. Greenberg, F. Guenther, G. Statistics Standards (n 10 ) Kramer, S. Wise, T. Gills, J. Colbert, R. Gettings, B. MacDonald, NIST Counting Geometry Differences 0.009 Spec. Pub. 260-136, 2000.

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.

NIST CENTER FOR NEUTRON RESEARCH 31 THE ROTATIONAL DYNAMICS OF H IN POROUS VYCOR GLASS 2

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. H is 2 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 FIGURE 1 . The top panel shows a contour plot of the inelastic scattering from

H in Vycor at various pore fillings at 6 K. The bottom panel is a cut through the pores). As can be seen in Fig. 1, at low filling fractions only a single 2 contour plot at f = 0.65 (indicated by the line). 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 of this potential is quite large, comparable to that seen in alpha surface. The appearance of scattering at 14 meV, corresponding to alumina, a catalyst used for ortho-H, enrichment [3], and on leached the free molecule transition, for fillings above 0.45 is associated glass [4]. with the appearance of "bulk"-like material in the pore center. Careful inspection of the data reveals that the peak due to

The clear separation of the scattering from molecules adsorbed the bound state actually shifts from 9.1 meV to 10.1 meV between on the walls and in the pore center suggests that these are quite filling fractions, f, of 0.20 and 0.27. Thus for f between 0.27 and distinct states which we refer to as the bound and bulk-like states, 0.45, the bound state may be separated into a layer in direct contact respectively. with the pore wall and a layer that feels a weaker orientational

The shift in the energy of the rotational transition at low potential. The scattering from these two layers can be separately fillings can be directly related to the interaction of the molecules determined assuming the intensity from the first layer varies linearly with the surface [2]. Figure 2 shows the shift of the J = 1 to with filling.

J = 0 transition as a function of the rotational energy barrier for The scattering from the second surface layer can be obtained the molecule. From Fig. 2 one finds that the observed rotational from the difference of the monolayer and bilayer spectra. The scat- energy of 10 meV corresponds to an orientational potential with tering from the second layer is centered at E = 11.3 meV, compared a barrier height of V /B = 2.7 (V = 19.8 meV). The magnitude B H B

32 RESEARCH HIGHLIGHTS -

D. W. Brown P. E. Sokol S. A. FitzGerald Lujan Jr. Neutron Scattering Manual Center Department of Physics Department of Physics Los Alamos National Laboratory The Pennsylvania State University Oberlin College Los Alamos, NM 87545 University Park, PA 16802 Oberlin, OH 44074

—I

First Layer Second Layer

E = 41.7 meV H Full Pore 2

H 9 Monolayer

-4 -2 4 10 12 V/B

FIGURE 3. Distribution of potential barriers felt by the molecules in the first - (red) and second (blue) layers. 1 Full Pore Monolayer V = 19.8 meV 25.7 meV orientational potential for the first layer is broad, asymmetric, and

i centered at V = 3.5B , whereas the potential of the second layer is 3 B H relatively narrow and centered at V = 2.0B indicating a weaker V/B B H , interaction with the surface. FIGURE 2. Shift of the rotational energy levels of H as a function of 2 barrier height. The data allow us to draw the following picture of the adsorp-

tion of molecular hydrogen on a porous glass surface. The first to the first layer which is centered at 9.1 meV, indicating that the monolayer is bound tightly to the rough pore surface. The rough second layer interacts less strongly with the wall. surface prevents free rotation of the molecule, altering the rotational The width of the peak we associate with the bulk-like mol- energy states. The second layer perceives the surface roughness ecules is due entirely to instrumental resolution. This is consistent smoothed by the presence of the first layer, and accordingly, the with the view of these molecules as being free rotors with a rotational transitions are affected to a lesser degree. Subsequent to single well defined value for B. On the other hand, the width of the completion of the second monolayer, the H, molecules sense the peak which we attribute to the bound layer is much broader no significant orientational interaction from the glass surface. This than the instrumental resolution. A single well defined orientational is in agreement with the picture presented by Katsaros et al. [5], potential would yield a shift in the peak location, as observed, but in which surface roughness is created by dangling bonds on the no additional broadening, since the energy levels would still be well pore surface. defined. Thus, we attribute this additional width to a distribution of orientational potentials which can also be directly extracted using REFERENCES the model of White and Lassettre (Fig. correcting [2] 2). After [1] J. Dekinder, A. Bouwen and D. Schoemaker, Phys Rev B 52, 15872 (1995).

for instrumental effects, the strength of the scattering at a given [2] D. White and E. N. Lassettre, J. of Chem. Phys. 32, 72 (1960).

I. F. Silvera, Rev. of Phys. 52, 393 (1980). energy is directly proportional to the number of molecules which [3] Mod.

[4] M. Mohnke and W Saffert, Gas Chromatography, edited by M. Swaay feel the corresponding orientational potential. Thus, plotting the (Butterworths, London, 1962), p. 216. scattering as a function of V/B directly yields the distribution H , [5] F. Katsaros, et al., Physica B 234, 402 (1997).

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

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 dopants. The bending-mode energy could be correlated with the water, have emerged in the last decade as one of the key size of the dopant cation, generally increasing for smaller cations. technologies for meeting the world's energy needs well into the NVS measurements of SrZr M H (M = Sc, Y, and Nd) 095 005 0,_ 5 21 st century. Solid-oxide fuel cells (SOFCs) are the most promising indicated differences in the OH bending-mode energies between among the many different types of fuel cells being developed. the cerates and zirconates. These differences reflect changes in the

However, the required high operating temperature of an SOFC lattice potential experienced by the protons, which ultimately effects places stringent requirements on its component materials. Potential the proton jump rates and therefore the performance of these materi- candidates to replace the oxygen-conducting electrolyte used in cur- als for use in fuel cells. rent SOFCs include the perovskite-based high-temperature protonic An understanding of the dynamics of the undoped conductors (HTPCs), since switching from anionic to protonic con- perovskites is the first step towards a comprehensive picture of duction can lower the practical operating temperature from 1300 K the protonated doped materials. To explore this in more detail, we to around 1000 K. performed ab initio total-energy calculations using the CAmbridge

We undertook neutron vibrational spectroscopy (NVS) mea- Serial Total Energy Package (CASTEP). We calculated the surements of various HTPCs (namely, SrCeO, and SrZr0 aliova- = 0 phonons in the primitive unit cell (i.e., Zr Sr 0 ) of undoped 3 Q 4 4 12 lently doped with different rare earth cations) in order to probe the strontium zirconate and compared with the experimental density of bonding potentials experienced by the residual protons incorporated states (DOS) at room temperature, as shown in Fig. 1. While at low as OH" species via steaming. At high temperatures, these protons energies, the calculated modes are almost at the same energies as migrate from site to site, giving rise to protonic conduction. The observed modes, at high energies, we overestimate the energies of

NVS measurements revealed the existence of dopant-related pertur- the modes by about 10 %. However there is still a one-to-one cor-

bations to the bending-mode energies of OH in SrCe„„sM„„M O, , respondence between the main experimental and calculated spectral ° ° 0.95 0.05 x 3-6 (M = Sc, Ho, and Nd), confirming the trapping effects of the

30 60 90 120 Neutron Energy Gain (meV)

FIGURE 1. LEFT: A view of the structure of undoped SrZr0 in the [001] direc- 3 tion. RIGHT: Vibrational spectra for SrZr0 measured by neutron time-of-flight 3 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 while some portion of the peak near 80 meV is due to protons at measurements. the undoped sites. Thus NVS can be used to determine the hydrogen

In order to model the dynamics of protons trapped in occupancy of the various sites.

Sc-doped SrZrO,, we replaced one of the Zr atoms in the For a better understanding of the protonic conduction in

supercell (Sc H), \flX\flX 1 by + which yields a cell formula these materials, we calculated the total energy of the system as the

Sr Zr.ScHO, (See Fig. 2). We performed calculations for protons proton migrates from Zr to Sc sites. We found that the doped site s 4 at either the "undoped" (U) or "doped" (D) sites. Even though the has a much lower energy (-1.13 eV) than the undoped site. The

MO octahedra are quite rigid, the distortions due to the presence of two sites are separated by an energy barrier of 1.5 eV. Hence, we fe the proton at these sites are quite large. expect that most of the protons are trapped at the dopant site. This

These distortions are also reflected by the vibrational spec- is primarily because the proton prefers to be closer to the Sc cation, trum of the proton. The two tangential OH- bending modes depend which has a charge of +3 compared to +4 for Zr. Yet, one also strongly on the proton siting. At the Sc site, the lowest tangential has to consider steric effects; i.e., if the dopant cation has a larger mode is found at 122.9 meV However at the Zr site, the mode is radius, then the proton may prefer to occupy the Zr site, despite much softer at 88.5 meV Interestingly, we observe new features the larger Coulomb interaction. Thus these calculations indicate in our NVS spectra at these energies upon proton addition. To that the protonic transport is sensitive to the competition between further investigate this effect, we performed "embedded cluster" short-range repulsive and Coulomb interactions, and suggest that calculations in which the vibrational spectrum of the H-M0 cluster the use of a large dopant cation is one important step in developing 6 is calculated while all other atoms are kept at their equilibrium a HTPC with increased protonic conductivity. We are currently positions. The similarity between experiment and the calculated testing the usefulness of the calculated proton potentials for predict- spectrum from H-Zr0 + H-Sc0 clusters suggests that the mode ing the protonic diffusional motions observed experimentally via 6 6 observed near 120 meV is due to protons trapped at the Sc sites quasielastic scattering measurements.

: H at the undoped site

60 85 110 Energy (meV) Distance from U-site (A)

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-M0 clusters, where = Zr (undoped site) and Sc (doped site), respectively. S M RIGHT: Potential energy of the crystal as the proton migrates from the undoped site (U) to the doped site (D).

NIST CENTER FOR NEUTRON RESEARCH 35 MAGNETIC TRAPPING OF ULTRACOLD NEUTRONS

The demonstration of three-dimensional magnetic trapping of scattering medium. A neutron with kinetic energy near 1 1 K (where neutrons was performed this past year at NIST [1]. The tech- the free neutron and Landau-Feynman dispersion curves cross) that niques developed should lead to improved precision in the measure- passes through the helium can lose nearly all of its energy in a ment of the neutron beta-decay lifetime, thereby expanding our single scattering event. Neutrons that scatter to energies less than

knowledge of the weak nuclear force and our understanding of the the trap depth ( 1 mK) and in the appropriate spin state are trapped. creation of matter during the Big Bang. Neutrons in this energy range are called ultracold neutrons (UCN).

Magnetic traps are formed by creating a magnetic field mini- Isotopically pure superfluid helium is contained in a tube mum in free space. The confining potential depth is determined by located inside the superconducting magnet and centered axially the magnetic moment of the neutron and the difference between the within its trapping field (see Fig. 1). The superconducting magnet, magnitude of the field at the edge of the trap and at the minimum. A trapping region, and other key parts of the apparatus reside within neutron in a low-field-seeking state (one with its magnetic moment a cryogenic dewar. The incident neutron beam is collimated, passes anti-aligned with the local magnetic field vector) feels a force push- through the trapping region, and is absorbed by the beam stop. As ing it towards the trap minimum and will remain confined within the beam traverses the trapping region, about 1 % of the neutrons the trapping region. scatter in the helium. Some of these neutrons are trapped and the

In order to load a neutron into a static conservative trap, its remainder are absorbed by shielding materials that surround the energy must be lowered while it is in the potential well. We rely helium. Low-field-seeking UCN are trapped and remain in the trap- on a loading technique that employs the "superthermal process" [2]. ping region until they decay.

Superfluid helium fills the trapping region and serves as a neutron

Acrylic lightguide

Magnet form Trapping region

Racetrack coil

Cupronickel tube

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 C. R. Brome, J. S. Butterworth, S. N. Dzhosyuk, K. J. Coakley Radiation Division Ionizing C. E. H. Mattoni, D. N. McKinsey and J. M. Doyle Statistical Engineering Division National Institute of Standards and Technology Department of Physics, Harvard University National Institute of Standards and Technology Gaithersburg, MD 20899-8461 Cambridge, MA 02138 Boulder, CO 80303

R. Golub and K. Habicht G. L. Greene and S. K. Lamoreaux Hahn-Meitner-lnstitut Los Alamos Neutron Science Center Glienicker Strasse 100 Los Alamos National Laboratory D-14109 Berlin, Germany Los Alamos, NM 87545

The trapped neutrons are detected when they decay. When a where the magnetic field is on during the initial loading phase, so trapped neutron decays (into an electron, proton and anti-neutrino), that UCN are confined by the trap and subtracting data where the the resulting high-energy electron travels through the helium leav- magnetic field is off initially, so that no neutrons are trapped. Equal ing a trail of ionized helium atoms. These ions quickly combine numbers of each data set were taken, pooled and subtracted to give with neutral helium atoms to form metastable diatomic molecules. the background subtracted data.

Most of these molecules decay within 10 ns, emitting a pulse of Two sets of background subtracted data were collected: set light in the extreme ultraviolet (EUV), X «= 70 nm to 90 nm. This I with a trap depth of 0.76 mK (Fig. 2a) and set II with a lower pulse of scintillation light is the signal of a neutron decaying in trap depth of 0.50 mK (Fig. 2b) due to problems with the magnet. the trap. For each set, the pooled background subtracted data are modeled to

In an experimental run, the cold neutron beam is allowed to extract the amplitude and lifetime of the decaying neutron signal. pass through the trapping region, after which the beam is blocked The best fit values for the initial counting rates combined with the and pulses of light are counted. background signal, with both measured detection efficiency gives = 560 ± 160 and N = 240 A N n constant and time-varying components, obscures the trapped neu- ± 65. Calculations using the known beam flux, trap geometry and tron signal. These backgrounds are subtracted by collecting data 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

4 doped the isotopically pure He with 'He at a concentration of 2 x

10"7 3 He/4He. This amount of 'He absorbs the trapped neutrons in

0.1 less than 1 s without affecting anything else in the experiment (less

3 than 1 % of the cold neutron beam is absorbed by He). The data

- 0 (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.

0.1 Magnetic trapping of neutrons is a new technique that should

allow a higher precision measurement of the neutron lifetime, and 0 offers the prospect of precision much greater than the current limit

3 of one part in 10 . In order to realize the potential of this technique, 0.1 we are in the process of improving our apparatus in many ways,

including increasing the size and depth of the trap. We expect to 0 make a competitive neutron lifetime measurement in the near future.

-0.1 1000 2000 3000 REFERENCES: Time (s) [1] P. R. Huffman et al. Nature 403, 62 (2000). FIGURE 2. Counting rate as a function of time after the neutron beam is [2] R. Golub, D. Richardson, and S. K. Lamoreaux Ultra-Cold Neutrons turned off (pooled background subtracted data), (a) Trapping data set I, (Adam Hilger, Bristol, UK 1991). N. = 560 ± 160, (b) Trapping data set II, N = 240 ± 65, (c) Combined trapping M Particle Physics," Eur. Phys. J. 3, 1 3 [3] Particle Data Group, "Review of C signal, t = 750:^ s, (d) Combined He data, N = 53 ± 63. 3He (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 the dielectric BaTiO v following World War H, 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 YBa Cu 0 triggered an unprecedented 2 3 ? , avalanche of scientific activity in the late 1980's and early

1990's. More recently, phenomena such as collosal magnetoresi- tance (CMR), charge, orbital and spin ordering, and phase separation in the manganate perovskites, (Ln A )Mn0 (Ln = lanthanide ( x x 3 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

FIGURE 1 . The low temperature structure of CaFe0 . The green spheres depict structure the oxygen atoms are arranged in an octahedral geometry 3 the calcium ions. The other shaded objects represent iron centered octahedra, about the transitional ion; is metal each oxygen then shared by where an oxygen atom can be found at each vertex and an iron atom at 3* two transition metal ions to form a three dimensional network of the center of each octahedron. The purple and blue objects represent Fe centered and Fe5+ centered octahedra respectively. corner sharing M0 octahedra. The octahedral coordination removes 6 the energetic degeneracy of the 3d orbitals, forming the familiar electrons and metallic conductivity are seen at higher temperatures triply degenerate t and doubly degenerate e set of orbitals. The 2g g but give way to a magnetically ordered, insulating ground state e orbitals point directly at the oxygen ligands to form a strongly o upon cooling. antibonding a* bond. In contrast, the t orbitals have a smaller 2g LaMn0 SrFe0 and CaFe0 are isolectronic; they each have overlap with the oxygen 2p orbitals, which leads to a weakly 3 , 3 3 3 an electronic configuration of t e '. According to the Jahn-Teller antibonding it* band. If this covalent bonding interaction between 2g g theorem, the presence of a single localized electron in the doubly the transition metal and oxygen is weak, the valence electrons

degenerate e set of orbitals is not a stable situation. LaMn0 are localized and a magnetic insulator is typically observed. If g 3 responds to this instability by undergoing a cooperative Jahn-Teller we increase the strength of the interaction sufficiently, either by distortion of the Mn0 octahedra, producing two long and four short increasing the electronegativity of the transition metal ion or the 6 Mn-0 bonds, Thereby, removing the degeneracy of the e orbitals. spatial overlap of the metal 3d and oxygen 2p orbitals, partial g SrFe0 takes a different approach, by delocalizing its e electrons derealization of the valence electrons can occur. Frequently, this 3 g to form a a* band. The contrasting behavior of these two materials leads to metallic conductivity. In a number of transition metal can be understood in terms of the strength of the metal-oxygen oxides the metal-oxygen interaction strength is such that delocalized

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 tures observed in the (La Ca )Mn0 system was vital in the devel- 1 x x 3 the transition metal increases from +3 to +4, which leads to an opment of the Goodenough-Kanamori rules of superexchange [2]. increase in the metal-oxygen interaction strength, increasing the These rules correctly predict an A-type antiferromagnetic structure width of the a* band and stabilizing a metallic ground state. Since for LaMnO,. Using the same rules, we would expect CaFe0 to 3 4 they both contain Fe *, one might expect that CaFeO, and SrFeO, have a simple ferromagnetic ground state. Perhaps not surprisingly,

" 2+ 2 1 would behave very much alike. However, Ca is smaller than Sr ", our investigation showed that again CaFeO, defies expectations.

which causes a tilting of the Fe0 octahedra to satisfy the valence Low temperature neutron powder diffraction data reveals instead 6 This subtle distortion has sev- an incommensurate antiferromagnetic ground state (T 120 K). requirements of calcium. seemingly N eral important consequences. The Fe-O-Fe bond is distorted away Analysis of the data shows the magnetic structure to be either from the linear geometry observed in SrFeO, (the Fe-O-Fe angle a screw spiral or a sinusoidal amplitude-modulated structure. In is 158° in CaFe0 ). This reduces the spatial overlap of the Fe e either case, it would appear that a long range AFM interaction 3 g and 0 2p orbitals, and the width of the a* band decreases. The (probably between next-neighbors) is present in addition to the reduction in bandwidth triggers an electron localization that occurs nearest neighbor FM superexchange interaction. just below room temperature (290 K). Once electron localization

occurs, a cooperative Jahn-Teller distortion to the LaMn0 crystal REFERENCES 3 [1] M. Takano, N. Nakanishi, Y. Takeda, S. Naka and T. Takada, Mater. Res. structure is expected. Bull. 12, 923 (1977). However, CaFeO, refuses to conform with expectations. [2] J. B. Goodenough, Magnetism and the Chemical Bond, Interscience, New 4* Instead CaFeO, undergoes a charge disproportionation (CD), IFe York (1963).

-> 3+ 2 5+ 3 (t V) Fe (t Je ) + Fe (t e °). Evidence for a CD in CaFe0 2 e 2g 3

was first proposed over 20 years ago, based on Mossbauer studies

[1]. However, crystallographic confirmation of this rare phenom-

enon 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 CaFe0 in its CD state 3

for the first time. The resulting structure (Fig. 1) clearly shows

the presence of two chemically and crystallographically distinct Fe

5+ " sites. The average Fe-0 bond length about the "Fe site is 1.872(6)

3+" A, while the same distance about the "Fe site is 1.974(6) A.

3+ 5+ 3+ The ordered arrangement of Fe /Fe is such that each Fe is sur-

5+ rounded by six Fe 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 struc-

NIST CENTER FOR NEUTRON RESEARCH 3 9 BOND VALENCE ANALYSIS OF RUTHENATES

I ond valence analysis allows us to evaluate, for any compound

B'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 (a) n(i) n(j)

.V -7(0 and (1) e Ru o • 0 2 ; v

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 FIGURE 1 . Schematic representation of (a) the 4-layer structure of TRu0 3 balance in ionic crystals, and is known as the valence sum rule [1]. [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 Ru0 octahedra share corners and faces, respectively. ( ii) The sum of the bond valences around any loop in the 6

structure, taken with alternating signs, is equal to zero ration. These distances satisfy exactly the valence requirements of

v„ =0. the atoms and, in general, differ significantly from those determined loop 'J (2) experimentally. The discrepancies are in some cases due to the elec-

Equation (2) expresses the mathematical conditions that result tronic behavior of particular cations, which may cause distortions in the most regular distribution of the valences among the bonds in not accounted for by the bond valence model (for example, lone a structure and is known as the equal valence rule [1]. The system 3+ 2+ pair distortions around cations such as Bi and Pb , or Jahn-Teller of equations and allows us to evaluate the valences of all the 3+ 2+ (1) (2) distortions around Mn and Cu ). In the majority of cases, how- individual bonds if we know how the atoms are bonded together in ever, the bond lengths calculated with equations (1-3) are incom- a structure [2]. The description of atomic bonding in terms of bond mensurate under the constraints imposed by the crystal geometry, valences is useful because the length d of a bond between atoms and have to be stretched or compressed in order to fit them into a

i and j is a function only of the bond valence v... The relationship particular configuration. Since these changes introduce strains into between these two quantities is expressed by the empirical formula the structure, the process of adapting the theoretical model to the

requirements of a space group symmetry must be carried out in -0.37 lnv„ (3) such a way that the violations of the bond valence sum rule and

where the bond valence parameter R.. depends on the nature and the of the equal valence rule are kept as small as possible. We have oxidation states of atoms /' and j forming the bond, and expresses recently applied the concepts discussed above to the determination the length of a bond of unit valence. Values of/? can be evaluated of the crystal structures of IRu0 (T = 0.875Ba + 0.125Sr) [5] and 3 the distances of known structures are tabulated for from bond and BaRuO, [6], using initially only the information obtained from the

most chemical species [3,4]. By means of equations (1-3) we may indexing of the neutron diffraction patterns of these materials (i.e.,

evaluate the expected bond lengths for any known atomic configu- 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

2+ other structural details obtained in the experimental work. Since T Ru-0 bonds have to be stretched. This process of relaxation of

2+ 2 and Ba have ionic radii similar to that of O , we may expect that the initial model is carried out by modifying the structural param- the structures of IRuO, and BaRuO, are built with some sphere eters obtained from sphere packing geometry in such way that the packing mechanism. This assumption is corroborated by the fact violations of equations (1) and (2) are contained within reasonable that in both cases the a-parameter calculated from the average r bounds [7]. The results of the bond valence analysis of BaRu0 are 3

of the ionic radii of A and O (A = T, Ba) for the composition reported in Table 1 , where they are compared with the correspond-

AO, is in good agreement with the experimental values, and by the ing values determined experimentally. Similar results, reported in

4+ fact that the ionic radius of is quite close to the radius of reference were obtained for The agreement between Ru [5], 7RuOr the octahedral void formed by the close packing of oxygen anions. the observed and calculated structures is quite good for both com-

The periodicity n of the stacking sequences of the AO, layers pounds, and the differences between bond distances are well within in the vertical direction of the c-axis, evaluated with the formula 0.02 A. This result proves that, at least in favorable cases, the n = c/(2r\/2/3), shows that 7TtuO, and BaRuO, have 4- and 9-layer bond valence method may yield an accurate model of the structure

structures, respectively, in which the Ru0 octahedra are related to without requiring more information than that needed to index a 6 one another as indicated in Fig. la and lb. powder pattern. More importantly, however, it shows that the need

In order to fit this configuration, the theoretical bond lengths to satisfy the valence requirements of the atoms with an acceptably calculated with equations (1-3) have to be changed, and in particular regular distribution of the bond valences is the driving force in the A-0 bonds have to be compressed, on the average, and the determining the magnitude and the direction of the atomic shifts

allowed by the symmetry, and that, as a consequence, non-bonded Table 1. Models of the Structure of BaRu0 (R 3 m) 3 metal-metal and oxygen-oxygen interactions do not play an impor-

3 4 12 tant role in the way in which the structures of these ruthenates are

Lattice parameters (A) and atomic positions built. In particular, the shifts that pull together the oxygen atoms

5.754 5.754 0.007 a 5.747(1) forming the shared faces of the Ru0 octahedra (thus providing a 6 c 21.142 21.626 21.602(1) 0.024 shielding effect to Ru-Ru interactions) are specifically designed to

X 0.1769 0.0000 1/6 0.1769(1) improve the local valence balance of the Ru and O atoms involved

z 1/9 0.1087 0.1082(1) 0.0005 , in the Ru-0 bonds. Application of the method to structural types

Z 2/9 0.2185 0.2175(1) 0.0010 2 other than perovskites is now under consideration.

Z 7/18 0.3844 0.3829(1) 0.0015 3

Bond distances (A) REFERENCES

Ba(1)-0(1) 2.877 2.877 2.8733(1) 0.004 [1] D. Brown, Acta Cryst. B48, 553 (1992).

M. O'Keeffe, Structure and Bonding 71, 161 (1989). -0(2) 2.877 2.938 2.926(2) 0.012 [2]

[3] D. Altermatt and I. D. Brown, Acta Cryst. B41, 240 (1985); I. D. Brown Ba(2)-0(1) 2.877 2.988 3.002(2) -0.014 and D. Altermatt, Acta Cryst. B41, 244 (1985). -0(2) 2.877 2.882 2.880(2) 0.002 [4] N. E. Breese and M. O'Keeffe, Acta Cryst. B47, 192 (1991).

-0(2') 2.877 2.957 2.945(3) 0.012 [5] A. Santoro, I. Natali Sora and Q. Huang, J. Solid State Chem. 143, 69 (1999). Ru(1)-0(1) 2.034 2.001 2.005(2) -0.004

[6] A. Santoro, I. Natali Sora and Q. Huang, (in preparation). Ru(2)-0(1) 2.034 1.995 1.974(1) 0.021 [7] I. D. Brown, Z. Kristall. 199, 255 (1992). -0(2) 2.034 1.995 2.007(2) -0.012

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 well-

established 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 FIGURE 1. Experimental setup. The three arrows indicate three directions of and cold-coiling. Hot coiling implies that the spring is wound from measured lattice spacing with respect to the specimen: A = axial, R = radial,

T = tangential. In the current configuration, the spacing of planes whose stock at or above the recrystallization temperature. The strength normal is parallel to T is being measured. The sampling volume is defined by and fatigue resistance are controlled afterwards by an appropriate the primary aperture P and secondary aperture S, respectively.

heat treatment. Cold-coiling means that the helical winding takes

place at a low temperature after the spring has been hardened and number of windings times the wire thickness. After this the spring tempered. Cold-coiling allows the high temperature heat treatments was allowed to relax. A small part of this torsion strain is in the to take place on the bar stock, which is easier to handle than the plastic region, so this spring is slightly shorter than all the others. In coiled end-product. The resulting residual stresses can be essentially the automotive industry this process is known as "bulldozing". eliminated by a relatively low temperature tempering treatment fol- The measurements were carried out on the Double Axis lowing the cold coiling. system for Residual stress, Texture and Single crystal analysis The idea is to measure the residual stress field in a number of (DARTS) at beam tube 8 (BT-8) in the NIST Center for Neutron specimens that represent various stages of the production process. Research. This instrument is specifically designed for residual stress Using neutron diffraction one can determine the effect of the prior measurements, and to that effect is equipped with very accurately processing on the residual stress state of that particular stage in positioned apertures as is shown in Fig. 1 the process. Of equal importance, these measurements can serve to For these experiments the apertures were chosen to allow

verify well established elasto-plastic models that are being used to 3 a sampling volume of 2 x 2 x 2 mm . The residual stress in predict the formation of residual stress. Finally one can look for a the three springs across the cross-section of the originally 14 mm way to correlate the residual stress at the surface to the stress field thick wire stock was determined by detecting the diffracted mono- as a whole. chromatic neutron intensity with a position sensitive detector. The We have looked at three cold-coiled springs. The first spring neutron wavelength was chosen such that the [211] Fe planes would

is an as-cold coiled spring. The second one is cold-coiled followed scatter diffracted intensity over approximately 90°. The specimen

by a relatively low temper. The third one is identical to the second was rotated and translated in this geometry, such that the sampling one, but in addition to being tempered the spring has been com- volume was scanned across this cross-section allowing the elastic

pressed to the point where the length of the spring is equal to the (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

Annealed 1.5 coil tangential stress 1000 c m O 800

600 4 400 2 200

0 0

-200 -2 -400

-4 -600

-800 -6

i -1000

-6 -4 -2 0 2 4 -6 -4 -2 0 2 4

x (mm) x (mm)

FIGURE 2. Contour map of the residual stress in the direction of the length of FIGURE 3. Same as Fig. 2, these data representing the as-tempered spring. the coiled bar stock, plotted on the bar stock cross-section. With reference The data for the as-bulldozed spring, though not given here, look essentially to Fig. 1 , this is the tangential direction. This map represents the as-cold- the same. coiled 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. the pattern is roughly the same, albeit at a much reduced level. The

These strain measurements allowed us to calculate the residual stress range being from -170 to +160 MPa as depicted in Fig. 3. stress in three perpendicular directions from the equations published The uncertainties in these stress levels are around ± 30 MPa. by Allen et al. [1] in each of the three specimens. For every speci- This means that the bulldozing process does not introduce addi- men, the stress free lattice parameter was determined on the basis tional residual stresses, a fact that can be well understood consider- that the net force on the cross-section under investigation had to ing that the plastic deformation under pure torsion is essentially be zero. uniform and thus cannot contribute to the residual stress state.

From these experiments a set of interesting observations can These results will allow Ford to correlate their model pre- be made. First is the notion that the residual stress pattern across the dictions and X-ray residual stress measurements to the complete wire stock in the as-coiled spring is very pronounced and exactly residual stress field. This constitutes a powerful tool in optimizing matches what one would expect when a cylindrical bar is plastically the parameters of the spring manufacturing process. bent into a hoop, a process much resembling helical coiling. With reference to Fig. 2 we note essentially uniaxial residual stress in the

[1] A. J. Allen, M. T. Hutchings, C. G. Windsor, and C. Andreani: "Neutron length direction of the original wire stock. Through the diameter of Diffraction Methods for the Study of Residual Stress Fields," Advances in the stock, the stress goes from highly compressive at the convex Physics, 34, 445-473 (1985). 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

NIST CENTER FOR NEUTRON RESEARCH 43 THE NCNR NEUTRON SPIN ECHO SPECTROMETER

The first experiments have been performed on the NCNR's lengths greater than 5 A. The neutrons precess, from the first tt/2 Neutron Spin Echo (NSE) Spectrometer, which is the only flipper (1) to the sample, through a phase angle that is determined spectrometer of its kind in the United States. This cold neutron by the time that the neutron spends in the solenoidal magnetic field spectrometer allows studies of dynamic processes in macromolecu- (4) and the field integral along the neutron path. Near the sample, a lar systems that are relevant to, among others, polymer [1] and it flipper (2) rotates the spin by 180° around the vertical axis. If the biomedical [2] sciences. It covers a time-scale of 0.01 ns to 100 ns solenoid on the second arm of the spectrometer provides the same and a length-scale of 2 A to 200 A with the equivalent of extremely field integral for the scattered neutron and if the scattering is elastic, high energy resolution and moderate Q-resolution. Unlike the other the neutron will precess through the same phase angle as along the high-resolution inelastic instruments at the NCNR, which measure first arm and will end up with the original spin orientation at the in the energy domain, the NSE spectrometer measures, in the time final tt/2 flipper (3). This tt/2 flipper rotates the spin back into the domain, the real part of the intermediate scattering function, I(Q,t). horizontal plane. If the neutron is scattered quasielastically, it will

This is done by using the neutron's spin precession in a magnetic precess a slightly different number of times in the second arm of the field as a clock to determine the energy transfer in the scattering spectrometer and end up at the second tt/2 flipper rotated by some process. angle that is proportional to the wavelength shift. The analyzer (7)

The NSE spectrometer, developed in partnership with Exxon projects the component of the neutron spin that is parallel to the

Research and Engineering and the Forschungszentrum Julich in field direction onto the detector.

Germany [3], is located at the end position of the NG-5 guide. Figure 2 shows the detector count rate as a function of current

The guide is tapered horizontally and then deviated so that the in the phase coil (5), which changes the field integral on one arm spectrometer is out of the direct line of sight of the reactor core, of the spectrometer. The field integrals for the first and second arms thereby reducing the background and the radiation load on the of the spectrometer are equal at the echo point where the amplitude sample region [4]. The taper is followed by a Neutron Velocity is at a maximum, since for an elastic scatterer the neutrons all

Selector (NVS), which transmits a A\/\ = 10 % FWHM band arrive at the analyzer in phase. As the phase current is changed, of neutrons to the spectrometer. The last element of the guide the neutron spins rotate away from the polarization axis of the is a transmission polarizer [5], which produces a polarized beam analyzer (7) and the count rate is changed. The period of this oscil- of neutrons with spin anti-parallel to the beam direction for wave- lation is proportional to the mean wavelength. The envelope of the

+ (2I\I"IT+Cf>) 4l\llT+

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

oscillations gives the wavelength distribution. The amplitude A is

proportional to I(Q,t), which can be normalized by measuring the

difference in intensity the tt flipper on and off, For with NQN - N0FF

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.

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 As an example of the science that is available through NSE, Phase Current (A) we have reproduced the measurements of Hayter and Penfold [6] on

a micellar solution of 10 % sodium dodecylsulfate (SDS) in D,0.

FIGURE 2. Phase scan of an echo for an elastic scatterer (Grafoil). A is the Fig. 3 shows the normalized intermediate scattering function versus amplitude at the echo point; N and N are counting rates with the it flipper 0H 0FF time at several Q values at, well below, and well above the interac- on and off, respectively, and the rr/2 flippers off. tion peak in the structure factor. The effective diffusion constant

2 I(Q,t) t), varies inversely D (Q), obtained from ; exp(-D (Q)Q eff cfl 1 —-0.0905 A ,X = 10A n 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). 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 D 0 2 at room temperature. The resolution curve is a normalized measurement of an elastic scatterer (Grafoil) at 10 A.

NIST CENTER FOR NEUTRON RESEARCH SERVING THE SCIENTIFIC AND TECHNOLOGICAL COMMUNITIES

Providing neutron beam methods to the U.S. research com- THE USER PROGRAM

munity is a central purpose of the NCNR. Intense neutron NIST has always relied on advice from accomplished scientists instruments sources are scarce, as are the advanced needed to fully to assist in formulating policy. The Program Advisory Committee exploit Expert scientists will always recognize opportunities them. (PAC) is the body primarily responsible for proposal review and to perform research with the most powerful tools available, so recommending user policies for the NCNR, working closely with that the existence of the as the Nation's premier reactor- NCNR the Center's Director and staff. Its current membership includes based neutron facility stimulates considerable demand from the Sanat Kumar (Penn State University, chair), Robert M. Briber community. However, in order to foster the best possible science, (University of Maryland), Michael K. Crawford (DuPont), Dieter

of our procedures and activities are designed to encourage many K. Schneider (Brookhaven National Laboratory), Thomas P. Russell researchers to learn more about our capabilities, and eventually to (University of Massachusetts), Sunil K. Sinha (Argonne National obtain instrument time through proposals and collaborations. The Laboratory), Emile A. Schweikert (Texas A&M University), first instruments became operational in the NCNR guide hall in Laurence Passell (Brookhaven National Laboratory), and Gabrielle

1991, and a formal proposal system was started to accommodate G. Long (NIST). users from universities, industry, and government laboratories. At their meeting in May 1999, the PAC made several recom- diversity Since then, the quantity and the of research carried out mendations for improving the current system. They felt that pro-

at the NCNR has grown steadily, and the number of research gram proposals for longer-term projects had not had their intended participants (Fig. 1) is now several times larger than it was just a effect of reducing the burden for external reviewers, and should

few years ago. 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 2000 in that area was recommended. The PAC discussed the results of In FY99 Research Participants were from:

23 NIST Divisions and Offices a recent independent survey of user satisfaction, coordinated by 34 U.S. Government Laboratories 1500 105 U.S. Universities Anne Mayes of MIT. Ideas for obtaining more feedback from users 55 U.S. Industrial Laboratories were also considered. Incidentally, Professor Mayes, the head of the t: NCNR User's Group, recently won the American Physical Society's t 1000 Dillon Medal, partly for work carried out using NCNR instruments.

Most of the PAC meeting was devoted to proposal review.

500 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

86 87 88 89 90 91 92 93 94 95 96 97 98 99 for SANS, reflectometry, SPINS, and time-of-flight instruments. Fiscal Year The PAC usually meets twice a year, but because of a planned FIGURE 1. Research participants at the NCNR. shutdown for cold source and reactor upgrades, only one meeting

was held in 1999.

4 6 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 tri-

ple-axis spectrometer, and a double-crystal, high-resolution SANS.

FIGURE 2. Nick Rosov explains the operation of the Neutron Spin Echo The last of these is under construction. Approximately 40 % of the Spectrometer to summer school participants. instrument time allocated by the PAC goes to experiments carried

out on CHRNS instruments. The NSF is currently reviewing the SUMMER SCHOOL ON METHODS AND CHRNS renewal proposal, which requests support for upgrading APPLICATIONS OF NEUTRON SPECTROSCOPY existing instruments and including an improved 9 m SANS instru-

ment within CHRNS. Approval would mean an increase of more Each summer for the past five years, the NCNR has held a one- than in capacity to serve users. week school to introduce researchers to the methods of neutron 50 % CHRNS'

scattering. Organized by senior staff members John Copley and COLLABORATIONS Peter Gehring, the 1999 summer school was devoted to spectrosco-

collaborations on specific experiments remain a common py with neutrons, with an emphasis on the opportunities afforded by Direct facilities, account- new instruments in the guide hall. Most of the 32 participants, cho- way for users to pursue their ideas using NCNR

sen from almost 60 who applied, were graduate students and post- ing for approximately 60 % of the number of instrument-days. The

doctoral fellows. The curriculum consisted of lectures by NCNR thermal-neutron triple-axis spectrometers are mainly scheduled in

staff and experts from other institutions, tours of the facility, and this way. Most of the time reserved for NIST on these and all

devoted to experiments that are four three-hour, hands-on, sessions at instruments in the guide hall. other NCNR instruments is also

Informal discussions among students and the resident staff were collaborations with non-NIST users. Participating also an important part of the school's activities. Another mode of access to the NCNR is through researchers Beginning with lectures on the fundamental concepts of Research Teams (PRTs). In this case, groups of from operate an instrument. nuclear and magnetic scattering, the agenda turned to talks on appli- various institutions join forces to build and

instrument is then cations of neutron spectroscopy to a wide range of research topics. Typically, 50 % to 75 % of the time on the

is allocated to general Subsequent presentations covered the reactor and cold source, reserved for the PRT, and the remaining time a involving ExxonMobil, the specific scattering techniques, computer modeling and ab initio user proposals. For example, PRT cooperates on calculations, and the operating principles of various spectrometers University of Minnesota, Texaco R&D and NIST instrument. Similar arrangements involving used in the experimental sessions. In the latter, students and staff the NG-7 30 m SANS the horizontal-sample refiectometer, the high- used time-of-flight, backscattering, triple-axis, and neutron spin- other PRTs apply to powder diffractometer, and the neutron spin-echo spec- echo spectrometers to measure, respectively, quasielastic scattering resolution trometer. from water, rotational tunneling in solid methyl iodide, magnetic

excitations in a geometrically frustrated antiferromagnet, and

NIST CENTER FOR NEUTRON RESEARCH *7 INDEPENDENT PROGRAMS other neutron scattering techniques, in activities that complement

There are a number of programs of long standing located at the research at ExxonMobil's main laboratories as well as at its affili-

NCNR which involve other parts of NIST, universities, industrial ates' laboratories around the world. The aim of these activities is

laboratories, or other government agencies. to deepen understanding of the nature of ExxonMobil's products

The Polymers Division of the Materials Science and and processes, so as to improve customer service and to improve

Engineering Laboratory has two major program elements at the the return on shareholders' investment. Accordingly, and taking full

advantage of the unique properties of neutrons, most of the experi- NCNR. In the first, the purpose is to help the U.S. microelectronics

industry in addressing their most pressing materials measurement ments use SANS or other neutron techniques to study the structure

and standards issues. In today's ICs and packages, the feature size and dynamics of hydrocarbon materials, especially in the fields

on a chip is ever shrinking, approaching 250 nm, while the size of polymers, complex fluids, and petroleum mixtures. ExxonMobil

regards its participation in the collaborations with of a polymer molecule is typically 5 nm to 10 nm. As feature size NCNR and NIST

shrinks, the structure and properties of interfaces play an increas- and other PRT members not only as an excellent investment for the

ingly important role in controlling the properties of the polymer company, but also as a good way to contribute to the scientific health

layers used in interconnects and packages. NIST scientists use both of the Nation.

neutron reflectivity and other neutron scattering methods to charac- The Nuclear Methods Group (Analytical Chemistry

terize polymer/metal interfaces with regard to local chain mobility, Division, Chemical Science and Technology Laboratory) has as its

moisture absorption, glass transition temperature, and crystalline principal goals the development and application of nuclear analytical

for the with structure. In the second program element, the objective is to under- techniques determination of elemental compositions

stand underlying principles of phase behavior and phase separation greater accuracy, higher sensitivity, and better selectivity. A high

kinetics of polymer blends, both in the bulk and on surfaces, in level of competence has been developed in both instrumental and

order to help control morphology and structure during processing. radiochemical neutron activation analysis (INAA and RNAA). In

SANS and reflectivity measurements in equilibrium, in transient addition, the group has pioneered the use of cold neutron beams

conditions, and under external fields provide essential information as analytical probes with both prompt gamma activation analysis

for general understanding as well as for specific application of (PGAA) and neutron depth profiling (NDP). PGAA measures the

polymer blend/alloy systems. Customers include material producers total amount of a particular analyte present throughout a sample

and users, ranging from chemical, rubber, the, and automotive com- by the analysis of the prompt gamma-rays emitted during neutron concentrations of panies, to small molding and compounding companies. The focus capture. NDP on the other hand, determines

of research on polymeric materials includes commodity, engineering several important elements (isotopes) as a function of depth within

and specialty plastic resins, elastomers, coatings, adhesives, films, the first few micrometers of a surface by energy analysis of bombardment. foams, and fibers. the prompt charged-particles emitted during neutron The ExxonMobil Research and Engineering Company These techniques (INAA, RNAA, PGAA, and NDP) provide a powerful combination of complementary tools to address a wide is a member of the Participating Research Team (PRT) that operates, variety analytical problems of great importance in science and maintains, and conducts research at the NG-7 30 m SANS instru- of

ment and the recently commissioned NG-5 Neutron Spin Echo technology, and are used to help certify a large number of NIST Materials. the past several years, a large Spectrometer. The mission is to use those instruments, as well as Standard Reference During

48 SERVING THE SCIENTIFIC AND TECHNOLOGICAL COMMUNITIES part of the Group's efforts has been directed towards the exploitation to neutron technology and neutron physics. The national and indus- of the analytical applications of the guided cold-neutron beams trial interests served include scientific instrument calibration, elec- available at the NIST Center for Neutron Research. The Group's tric power production, radiation protection, defense nuclear energy involvement has been to design and construct state-of-the-art cold systems, radiation therapy, neutron radiography, and magnetic reso- neutron instruments for both PGAA and NDP and provide facilities nance imaging. The Group's activities may be represented as three and measurements for outside users, while retaining and utilizing major activities. The first is Fundamental Neutron Physics - includ- our existing expertise in INAA and RNAA. ing operation of a neutron interferometry and optics facility, devel-

The Center for Food Safety and Applied Nutrition of the opment of neutron spin filters based on laser polarization of -He,

U. S. Food and Drug Administration (FDA) directs and maintains measurement of the beta decay lifetime of the neutron, and investi- a neutron activation analysis (NAA) facility at the NCNR. This gations of other coupling constants and symmetries of the weak facility provides agency-wide analytical support for special investi- interaction. This project involves a large number of collaborators gations and applications research, complementing other analytical from universities and national laboratories. The second is Standard techniques used at FDA with instrumental (INAA), neutron-capture Neutron Fields and Applications - utilizing both thermal and fast prompt-gamma (PGAA), and Radiochemical Neutron Activation neutron fields for materials dosimetry in nuclear reactor applications

Analysis (RNAA) procedures, radioisotope X-ray fluorescence spec- and for personnel dosimetry in radiation protection. These neutron trometry (RXRFS), and low-level gamma-ray detection. This combi- fields include thermal neutron beams, "white" and monochromatic

235 nation of analytical techniques enables diverse multi-element and cold neutron beams, a thermal-neutron-induced U fission neutron

252 radiological information to be obtained for foods and related materi- field, and Cf fission neutron fields, both moderated and unmoder- als. The NAA facility supports agency quality assurance programs ated. The third is Neutron Cross Section Standards - including by developing in-house reference materials, by characterizing food- experimental advancement of the accuracy of neutron cross section related reference materials with NIST and other agencies, and by standards, as well as evaluation, compilation and dissemination of verifying analyses for FDA's Total Diet Study Program annually. these standards.

Other studies include the development of RXRFS methods for Several universities have also established long term programs screening foodware for the presence of Pb, Cd, and other potentially at the NCNR. The University of Maryland is heavily involved toxic elements, use of INAA to investigate bromate residues in in the use of the NCNR, and maintains several researchers at bread products, and use of PGAA to investigate boron nutrition the facility. Johns Hopkins University participates in research

and its relation to bone strength. The FDA's NAA laboratory person- programs in solid state physics and in instrument development at the

nel frequently provide intra-agency technical assistance, the most NCNR. The University of Pennsylvania is working to help develop

recent example being participation in the production of the docu- biological applications of neutron scattering. It is also participating

ment "Accidental Radioactive Contamination of Human Food and in the construction of a new filter analyzer neutron spectrometer,

Animal Feeds: Recommendations for State and Local Agencies" by along with the University of California at Santa Barbara, DuPont,

the Center for Devices and Radiological Health. Hughes, and Allied Signal. The University of Minnesota partici-

The Neutron Interactions and Dosimetry Group pates in two PRTs, the NG-7 30 m SANS and the NG-7 refiectom-

(Physics Laboratory) provides measurement services, standards, and eter. The University of Massachusetts also participates in the latter

fundamental research in support of NIST's mission as it relates PRT

NIST CENTER FOR NEUTRON RESEARCH , REACTOR OPERATIONS AND ENGINEERING

! he reactor operated for 250 full power (20 MW) days during the As part of preparing for another 20 years of operation past

past year, or 68 % of real time. This meets our goal, and was 2004, we have been assessing the present cooling tower. During the

achieved in spite of a shutdown for maintenance early in the fiscal past year, a contract for construction of a hybrid wet/dry tower was

year. The reactor operated with better than 90 % predictability—i.e. signed. This new tower will not only meet our cooling needs; it

days operated on the day originally scheduled. This is substantially will also reduce the visible plume given off by the tower during the

better operation than is specified in national goal of 85 % reliability winter months, a substantial additional benefit. The new tower will

for user facilities. Just after the end of the fiscal year, another fuel be erected adjacent to the current one, and will not require an outage

shipment was made, thus clearing additional space in the spent fuel until the switch is made. This outage will be scheduled when the new

storage pool. This completes our current round of scheduled spent tower is fully ready for use, so as to minimize down time. Extensive

fuel shipments. There is now ample storage space for at least 5 years planning for the piping changes that will be needed is now underway.

of continuous 20 MW operation. 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 partici-

pants ever. Many distinguished speakers addressed the conference

including the Chairman of the Nuclear Regulatory Commission and TRTR Chairman-Elect, Pedro Perez, presents NIST Director, Raymond G. Kammer, with a plaque stating: the Under Secretary of Energy. Also, TRTR became the first profes-

sional organization to honor NIST on its forthcoming centennial. "The National Organization of Test, Research and Training Reactors recognizes the National Institute of Standards and Technology on the occasion of its Finally, preparations for a license renewal application are centennial as the foremost measurements and standards laboratory in the proceeding as planned. We are fortunate to have attracted Dr. 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 pioneer- Seymour H. (Sy) Weiss to our staff, as Deputy to NCNR Director. He ing efforts in nuclear research and radiation standards and in appreciation of will be leading the relicensing effort and associated reactor upgrades its leadership in the formation of TRTR." for the coming years, and has already started several tasks related

to this effort.

50 .

INSTRUMENTATION DEVELOPMENTS

IMPROVEMENTS TO THE in the neutron data. A detailed analysis of the performance of the PERFORMANCE OF HFBS monochromator system indicated that the quality of the data could recent commissioning of the high flux backscattering spectrom- The be improved by making a rather simple change in the way that eter (HFBS) has opened up opportunities to a variety of users from data is collected and stored, namely by binning data versus time the of around the country to study dynamics condensed matter during a period of the Doppler monochromator motion. The data 9 with time scales the order of nanoseconds s) systems on (10 and are later re-binned to velocity using the average monochromator

scales up to 10 A. careful design which incorporates state- length A motion profile. This straightforward change to the way that the data

resulted in a flux as of-the-art neutron optics has on sample high are collected has improved the quality of the data, suppressing the

backscattering in the with as that of any other spectrometer world spurious effects observed in the velocity-binning mode. comparable energy resolution. The first call for proposals for the Improvements have also been made to the Doppler mono-

in 1999 and the response was outstanding. HFBS was made FY chromator system which have improved its reliability and perfor- Several successful user experiments have already been performed mance. One of the problems encountered is associated with the

Fig. with scheduled in the near future. Although the (see 1) more fact that the monochromator is being driven to higher energy trans- impressive, initial performance of the instrument was improvements fers than any other Doppler monochromator system in the world. continue to be made. The monochromator, which is vibrated over a distance of 9 cm at has a One of the recent changes to the instrument been modi- high frequencies, can experience accelerations in excess of 100 g's. fication to the data acquisition system. Initially the data were binned Prolonged vibration of the monochromator resulted in the silicon to the velocity of the reciprocating silicon monochromator. However wafers coming off of the monochromator surface. Recent changes velocity the method in which the was determined overemphasized in the gluing method have dramatically increased the lifetime of the local details of the monochromator motion which were not observed 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

FIGURE 1. Measurement of quasi-elastic scattering from monolayer coverage chopper speed, wavelength, and/or beam width. Once commis- of alkanes on grafoil performed on the HFBS by H. Taub, D. Fuhrmann, L. for a Criswell, and K. Herwig. The low temperature data (blue) is resolution limited sioned, the DCS will be in high demand experiments on with a full-width at half of 0.96 \ie\l. The higher temperature data maximum variety of systems such as proteins, molecular crystals, disordered (red) clearly displays broadening indicative of the diffusive motion of the alkanes. materials, and metal-hydrogen systems. The instrument is to be

NIST CENTER FOR NEUTRON RESEARCH 51 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 reso-

lution obtained by using perfect silicon crystals increases the maxi-

mum 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 monochroma-

tor 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 FIGURE 2. Photograph of the DCS detector bank and flight chamber. will cover a Q-range from 0.0004 nnr' to 0.1 nrrr 1 with an expected

beam current of 50,000 s '. included, on a limited basis, in the first Call for Proposals in Located on the BT-5 beam tube in the Confinement Building, FY2000. the layout of the instrument is shown in Fig. 3. A vertically and Over the past twelve months the DCS has seen major prog- horizontally focusing graphite premonochromator directs the neu- ress in a number of important areas. The sample chamber and flight tron beam away from the main reactor beam towards the perfect chamber were equipped with beam-handling components, and the crystal monochromator. The monochromator reflects a highly col- insides of both chambers were lined with cadmium. Flow tests were limated beam to the sample. After the sample, a high precision performed in order to complete the design of the gas handling rotation stage rotates the analyzer crystal to scan the small angle system for the sample and flight chambers; the system had been scattering obtained from the sample, which is then collected by fabricated and had largely been assembled by the end of the fiscal the detector. The shields supporting the premonochromator are set year. An overhead platform, to be used for sample environment on kinematic mounts for accurate repositioning. The monochroma- preparation and installation into the sample chamber, has also been tor and analyzer are isolated from room vibrations using a heavy designed. pneumatic vibration isolation table. Problems with some of the amplifiers for the DCS detectors Triple-bounce prompted us to send the complete inventory to the manufacturer Premonochromator

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.

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- During the past year, the detailed design of the first filter

chased parts received. The beam shutter and premonochromator wedge was completed, the vacuum chamber which encloses the

shielding have been installed. Major components yet to be installed Be and graphite filters was delivered, and the Be and graphite

are the detector housing, sample position table, and the small mono- filter wedges were assembled (see Fig. 4). Recent tests demon-

chromator shield. Preliminary characterization measurements lead- strated that these filters can be cooled to cryogenic temperatures

ing to instrument commissioning are planned for early 2000. which is necessary to maximize the performance of the instrument.

Furthermore all of the parts for the undercarriage for Phase I have

THE FILTER ANALYZER NEUTRON been received, and operated successfully under load. SPECTROMETER assembled, Most of the shielding and data acquisition system have also been

The new Filter Analyzer Neutron Spectrometer (FANS) is designed received. Major assembly and installation of Phase I will begin early to give U.S. researchers access to unprecedented sensitivity for in 2000. measuring the vibrational spectra of a wide variety of materials.

This spectrometer, which will replace the current BT-4 instrument, DEVELOPMENT OF AN ACTIVE DOUBLE

uses cryogenically cooled polycrystals as low energy band-pass FOCUSSING MONOCHROMATOR SYSTEM

filters for neutrons scattered from the sample. A dramatic gain in The use of vertical or horizontal focussing monochromators to

signal over the existing filter analyzer is achieved primarily through increase the intensity of selected neutrons incident on the sample

a large increase in the solid angle covered by the secondary spec- is well known and widespread. Less common are systems combin-

trometer. The FANS instrument is being developed in two phases. ing these features. Often the machinery employed to do this is

Phase I includes the first of two new filter assemblies, and Phase II cumbersome and results in extraneous material in the beam, increas-

includes the second filter analyzer and a new monochromator and ing the background from unwanted neutrons. For horizontal focus-

monochromator drum system. sing it is desirable to have maximum flexibility by adjusting many

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.

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 cor- respondingly simpler mechanical solution.

We are currently developing a system that combines com- pletely 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 FIGURE 6. NCNR Mechanical Engineering Technician Scott Slifer welds the aluminum moderator vessel for the advanced 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 to 30 mm thick, rather than 20 mm, without increasing the LH 2 the cold neutron intensity with respect to its predecessor (D,0 volume. ice); operate simply and reliably; and pose no safety threat to the The advanced liquid hydrogen cold source is currently being reactor or personnel. It has successfully met or exceeded all these fabricated and will be installed in the NIST reactor next year. goals. The cold neutron flux increased by a factor of 4 to 6, for Enhanced mechanical design and manufacturing tools are exploited wavelengths in the range of 0.2 nm to 2 nm. The availability of in the fabrication of the advanced source. Components of the hydro- the source has been nearly 99 % of the time that the reactor was gen, insulating vacuum, helium containment, and D 0 vessels are 2 available (the reactor is shut down if the source is inoperable). And cut from solid blocks of Al 6061 on a computer-controlled, high- there have been no hydrogen leaks, nor have any of the insulating speed mill at the NIST Instrumentation shop, and are then welded vacuums or helium containments been compromised. and thoroughly tested by NCNR staff (see Fig. 6). It is expected that Even as Unit 1 was being installed in 1995, however, the flux of cold neutrons will increase by a factor of 1.8. improvements in the MCNP model (used for Monte Carlo simulations) of the NIST reactor were pointing toward a new, but more IMPROVEMENTS TO NCNR SAMPLE complicated cryostat assembly, with a possible additional gain of a ENVIRONMENT EQUIPMENT factor of two. Better coupling between the reactor fuel and the cold The sample environment equipment has seen a number of source can be achieved by expanding the cooling jacket into the changes in FY 1999 at the NCNR. One of the most visible accom-

occupied insulating that it partially volume now by the vacuum, so plishments has been the development of informative webpages surrounds the moderator vessel. In this way, the D 0 coolant also 2 that detail sample environment resources, specifications, and even serves as an extension of the reactor reflector. Additional changes the current operating condition and location for specific devices. in the new source are based on our operating experience with the This information is easily accessible through the NCNR homepage existing LH source and extensive MCNP calculations. Unit 2 will 2 (http://www.ncnr.nist.gov/), allowing guest researchers to plan their be an ellipsoidal shell rather than spherical, it will have an evacuated experiments and design appropriate sample holders. inner vessel, rather than vapor-filled, and the LH layer will be up 2

54 INSTRUMENTATION DEVELOPMENTS Commissioning has begun on a new high magnetic field/ top loading, which provides an important capability for experiments low temperature superconducting magnet system which is financed requiring multiple sample changes or for quick changeover between through a joint collaboration of Johns Hopkins University, NCNR, consecutive experiments.

NEC Research Institute, Princeton, the University of Maryland, and From new capabilities to improved sample preparation and a National Science Foundation IMR grant. The 0.022 K dilution screening, the sample environment resources have been significantly refrigerator of this new system has already been tested and used on expanded during the past year. Listed in Table 1 are further acquisi- triple axis spectrometers. A 7 T magnet has been temporarily outfit- tions, notable modifications, and improvements that combine to ted in the system at this time, with replacement by a much stronger offer the researcher more control over the sample conditions. Fig. superconducting magnet of 10 T to 12 T in the coming months. 7 displays a typical cryorefrigerator sample environment. More

The magnet is capable of operating with either a homogeneous details are available at the web site mentioned above. 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 NCNR Sample Environment Geometry Cryorefrigerators

Helium flow cryostat 1.5 K to 300 K, dedicated to First Stage 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

1 Poiseuilte flow shear cell shear rate up to 130,000 s near surface

Light scattering particle sizer 2 nm to 100 nm diameter

Rheometer 1.7 x 10 3 Pasto2.7x10 8 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 Aluminum transport carts valuable equipment

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/ Crystal Structure of Sr Nb0 Morphological and Kinetic Study of Residual Stress Measurements on 2 7 102188 Q. Z. Huang Early Calcium-Sificate-Hydrate Gel Railroad Rails CRYSTALLOGRAPHY , 104 105 188102 T. Vanderah and I. Levin Development During the Hydration of I Gnaupel-Herold Acid Sites in Zeolite ZSM-5 , Cement and Tricalcium Silicate 102 164 R C. Brand , J. Gordon 34 214 Defect Structure of (Cu,Zn)lnSe , 2 A. Peters , R.-H. Hu , 118 118 32 32 102 169 J. J. 102 H. M. Jennings , Thomas J. Magiera , J. Orkisz and 214 B. A. Reisner , M. Knox , S. Purnell , B. H. Toby , 105 102 169 169 and A. J. Allen H. J. Prask 150 102 A. Stacy and G. Ron R. Senesi , D. A. Neumann and 197 MSANS Study of Effects of Feedstock SANS and SAXS Determination of H. Effect of Annealing on Zr0 Phase D. Olson 2 Preparation on the Microstructure of the Dispersion in Organic Solvents Aerogels Investigated by SANS with Composition 102 33 Plasma-Sprayed Ceramic Coatings of Organically Modified Clays for Contrast Masking Solutions J. K. Stalick and J. Ilavsky 105 105 Polymer/Clay Nanocomposites A. J. Allen , H. Boukari and Fast Ion Conductors C. Merzbacher", M. Anderson" 150 188 188 A. Kulkarni D. Ho , R. M. Briber and 102 102 83 V. J. G. Barker Cepak" and J. K. Stalick , B. Wuensch and 102 C. J. Glinka 83 Negative Thermal Expansion in A0P0 Amorphous Content Determination E. Ku 4 Compounds SANS Characterization of Hydrides in Methodology Field and Temperature Dependent 128 128 A. W. Sleight and T. Amos Uranium 102 150 Neutron Scattering Study of Mn J. K. Stalick , R. Senesi and 1? 123 123

S. Spooner , G. Ludtka and 102 Magnetic Molecules Neutron Diffraction of Heusler Alloys B. H. Toby 102 99 102188 J. G. Barker 102 188102 V. G. Harris and Q. Z. Huang Cation Location in Ion Exchanged T Yildirim and S.-H. Lee SANS Investigation of Hydrogen (Li,Na) Chabazite Grazing Incidence SANS from Plasma Neutron Diffraction of Single-Wall Trapping at Lattice Defects in 175 175 Carbon Nanotubes L. J. Smith and A. K. Cheetham Sprayed Coatings 102 197 Palladium 105 105 P Papanek , J. Fischer , Characterization of Ag and Mixed A. J. Allen and H. Boukari 183 190 197 138 B. Heuser and J. S. King Z. Benes , D. Colbert and Li/Ag Faujasite Zeolites Using Hydrogen Location in Graphite M. Heben 138 SANS Study of Fire Retardant Neutron Diffraction Nano-Fibers Polymer-Clay Nanocomposites 190 190 102 Neutron Diffraction Study of ' 8 N. Hutson , R. Yang F. , S. Trevino and 116 116 H. J. M. Hanley , C. D. Muzny 102 102 118 Hydronium Ions in Zeolite ND D OX 4 3 B. A. Reisner and B. H. Toby P Anderson 123 197 102 and J. Gilman D. H. Olson and B. H.Toby Characterization of Microcracking in Internally Oxidized Palladium Alloys: Neutron Scattering and the SANS Study of Oil Bearing Iron Titanate by SANS Particle Size Determination by SANS Low Sedimentary Rocks 105 105 102 Energy Excitations in Polycarbonate A. J. Allen and E. Fuller J. G. Barker 10 123 Copolymers A. Radlinski and G. D. Wignall Chemical Ordering in Ni-Mn-Ga Intermetallic Compounds of the A B 3 4 111 102 190 Site Distributions in the Structure of C. Soles , R. M. Dimeo , J. Liu Heusler Alloys , Structure 166 A. Yee 190 and A. Sokolov Ba Sn ZnGa „Cr 0 (x = 3 and 4) 188 188 102 102 2 2 10 x 22 R. Overholser , M. Wuttig and J. K. Stalick and R. Waterstrat 102188 136 Q. Z. and R. Cava 102 A New Phase of Silver Fluoride? No, Huang D. A. Neumann Investigation of the Zr Pt Structure g 1t lt'sAg C ! Single-Crystal Elastic Constants from Comparison of Residual Stress Type 10 2 35 R. L. Harlow Measurements on Polycrystals Measurement Techniques 102 102 J. K. Stalick and R. Waterstrat 188 102 T. Gnaupel-Herold Order-Disorder in CoFe/Carbon , T Gnaupel-Herold 188102 , In Situ Neutron Reflectivity 102 102 H. P. C. 102 102 Composites J. Prask and Brand P. C. Brand , H. J. Prask , Measurements of Deuterium 115 22 123 Si0 Ultra Thin Films Round Robin 152 J. H. , E. Scott M. McHenry , 2 S. Spooner , B. Pardue , Absorption in Pd Films 22 22 102 102 149 70 Z. Turgut and M. Storch J. A. Dura , C. F. Majkrzak and D. Nelson and S. Foss 184 184 B. Heuser , A. Munter , 112 J. Ehrstein Complex Oxide Structures 184 102 Phase Analysis of Sintered Yttria- N. Barber , J. A. Dura and 128 128 102 Stabilized Zirconia Size Distribution and Volume Fraction A. Sleight , 1. Radosavljevic and C. F. Majkrzak 102 108 128 J. K. Stalick and A. Slifka of Copper-Rich Precipitates in Model T Amos Kinetics of Gellation of Silica Under Reactor Pressure Vessel Steels and STRESS': New Codes for Phase Composition Analysis of CONV Shear 109 102 Partially Stabilized D. Balzar and C. J. Glinka Data Reduction in Neutron Diffraction 116 116 Plasma-Sprayed C. D. Muzny , H. J. M. Hanley 116 Zirconia Coatings by Neutron Powder Solute Effects on Membrane Residual Stress Measurements and G. C. Straty 102 Diffraction Data Thickness in DOPG and DOPC P C. Brand and Temperature Structure of Methyl Low 150 102 102 183 183 188102 H. Sitepu H. J. Prask J. Pencer and R. Hallett T. Gnaupel-Herold Halide Films on , MgO 102 150 J. K. Stalick , R. Goswani and Structural Ordering in Erbium CPD Round Robin on Quantitative 18 18 Doped J. Larese , M. Sprung and S. Sampath 150 18 Bi 0 Phase Analysis A. Freitag 2 3 Polymerized Fullerenes 102 180 102 Reisner , E. B. A. Wachsman , J. K. Stalick Magnetic Cluster Sizes in Thin Film 102 8 8 102 102 F. N. J. Udovic and D. A. S. Trevino , Beck-Tan and T Neumann Crystal Chemistry of Protonic Centers Recording Disks Magnetic 89 L. Balogh Structural Studies of Fullerene in Zeolites 52 102 M. Toney , S.-M. Choi and 197 102 102 Radiation-Induced Microstructure in Superconductors D. H. Olson and B. H. Toby C. J. Glinka 203 Reactor Pressure Vessel Steels K. Prassides and Crystal Structure of Ba (C0 CaCu 0 ) Microstructure Evolution of Fly Ash 102 4 2 6 3 175 175 D. A. R. , B. Wirth and Neumann 102188 94 G. Odette Q. Z. Huang and F. Izumi Blended Cements 175 D. Klingensmith 105 41 Structural Study of Sr Nb 0 Crystal Structure of Dehydrated A. J. Allen and R. A. Livingston 4 2 g Residual Stresses in Powder Compound LaD-LSX Modelling of Texture-Strain Relation- Metallurgy Test Specimens 105 105 I. Levin , J. Chan and 197 102 ships Using Neutron Diffraction Data D. H. Olson , B. A. Reisner and T Gnaupel-Herold 188102 I Vanderah 105 102 150102 102 , B. H. Toby H. Sitepu , J. K. Stalick and 102 133 J. M.-J. H. Prask , Yang and Structural Distortions in the NaSr M0 102 3 6 Crystal Structure of Ferroelectric H. J. Prask 133 R. German (M = Ru,Rh) Family Tetragonal Tungsten Bronze Lead Residual Stresses in Ti Rib Implants 102 169 B. A. Reisner , A. Prieto and Barium Niobate 169 for Children A. Stacy 102188 133 Q. Z. Huang and R. Guo 188102 T Gnaupel-Herold , Structural Distortions in Titanites The Crystal Structure of Pb Bi P 0 102 4 5 18 4 42 H. J. and R. Roberts 102 92 Prask B. A. Reisner and D. Xirouchakis 157 157 H. Steinfink and S. Giraud

56 Structural Distortions in Zeolite RHO Structure and Oxygen Disorder in Characterization of Dye Distribution in Inelastic Neutron Scattering from 102 B. A. Reisner Polymer Thin Films Filled Elastomers 102 188 111 111 111 111 102 Q. Z. Huang and I. C. White , E. Lin and W. L. A. Makatani , R. D. Ivkov Structural Studies of Germanium Wu , 105 102 197 146

- Zeolites W. Wong-Ng Characterization of Organically P. Papanek , H. Yang and 146 150 150 Structure of Porous Silica Thin Films Modified Clays M. Gerspacher J. B. Parise , G. M. Johnson and 150 150 111 111 188 188 Tripathi W. and D. Pochan L.-T. In-Plane Structure of PSAN/dPMMA A. and S. Park Wu Ho , R. M. Briber and 102 Blends in Thin Films Structural Studies of High Silica Structure of 75.25:24.75 Ca0-Nb 0 C. J. Glinka 2 5 133 133 105 105 105 M.-P. Nieh , S. Kumar Zeolite RHO Conformation of Chains in Strained , J. Chan , 1. Levin , R. Roth , 133 188 150 150 105 102 Polymer Networks R. Jones and R. M. Briber J. B. Parise , A. Tripathi and T. Vanderah and B. A. Reisner 150 31 188 Interdiffusion of Crosslinked Polymer Y.-J. Lee Structure Refinements of Alumo- and C. Cohen and R. M. Briber Structural Studies of Iodine-Loaded Gallo-Germanates Using Neutron Conformation of Polymer Chains Films 188 188

U. Perez-Salas , R. M. Birber ZSM-5 Scattering Techniques Confined in Controlled Pore Glass , 150 150

197 150 150 188 183 M. Rafailovich , J. Sokolov and D. H. Olson S. Park , J. B. Parise and R. M. Briber , D. Ho and 102 102 135 N. F. Berk Structural Studies of S^Rh^R^O, B. H.Toby I. Teraoka Interfacial Scattering from Layered Perovskites Structure of Sr ^Dy, Cu Conformation of Random Copolymers t 125 2 0, 204 102 188 105 Phase-Separated Polymer Blends 18 - in Solution P. Woodward , B. Kennedy and Q. Z. Huang and W. Wong-Ng 78 78

18 40 40 H. Jinnai , M. Hayashi and T. Vogt Study of Hydronium Ions In Zeolites M. Y. Lin and D. Peiffer 111 C. C. Han 197 102 Structural Studies of Strontium D. H. Olson and B. H.Toby Critical Neutron Reflection Tests of Investigation of the Concentration Niobium Oxides Polymer Interdiffusion Dynamics Temperature Dependence in the 105 188 179 179 Profile Between Crosslinked Thin R. P. Wool , K. A. Welp and W. Wong-Ng , W. Greenwood Structure of Yttrium Tungstate 102 179 Films and B. H.Toby 128 128 W. Dozier A. Sleight , P. Forster and 188 188

R. Briber , U. A. Perez-Salas M. , 128 Kinetics of Polyolefin A Structural Sudy of the Ruddlesden- A. Yokochi Demixing 150 150 M. Rafailovich and J. Sokolov Popper Calcium Manganate Ca Mn O Blends 4 3 10 Temperature-Dependent Structure 143 143 135 135 Low Energy Excitations in Deuterated M. Greenblatt and I. Fawcett Determination of Ca lrD by Powder N. Balsara , H. Wang and 2 5 102 Polystyrene Diffraction B. Hammouda Structure of Barium Titanate Thin Neutron 102 111 R. M. Dimeo and J. F. Douglas 162 102 Films on Silicon R. Moyer and B. H. Toby Dynamics of Polymer Interdiffusion 105 105 102 Kinetics of Shear Alignment of Block K. Satija C. Bouldin , B. Revel and Thermal Expansion of ll-VI S. 102 Copolymer Blends J. A. Borchers Effects of on the Semiconductors Polymer Additives 183 183 R. Krishnamoorti , S. Rai and 117 9 117 of Crystals Structure, Cation Ordering, and R. Reeber and K. Wang Formation Hydrate 102 B. 40 Hammouda Magnetism in Manganate Spinels 40 40 Thermal Expansion of Alpha SiC from J. M. Hutter , H. King and M. Lin 140 102 Marginal Solvent Scaling of M. Green and D. A, Neumann 15 to 298K Effects of Pressure on the Lower Polystyrene in Naphthalene 117 9 117 - Structure of Ca Ta Nb 0 . (x = 0.05 Critical Ordering Temperature of R. Reeber , K. Wang and 102 2 2 J. G. Barker 102 and 0.1) B. H.Toby Diblock Copolymers 83 83 Membrane Mediated Polymer 102 ' 188 102 Q. Z. Huang and R. Roth Thermal Expanion of HgSe A.-V. Ruzette and A. M. Mayes Interdiffusion 117 9 117 Structure Determination of Ca RhD R. K. Effects of Shear on the Phase 2 5 Reeber and Wang 111 111 H. Gruell , A. Esker and by Powder Neutron Diffraction Behavior of Polyolefin Blends Zeolite SRM Characterization 111 C. C. Han . 162 102 135 135 102 150 N. Balsara and A. Lefebvre R. Mover and B. H. Toby R. Senesi B. H.Toby and Microstructure and Properties of Structure Determination of Framework Effects of Substrate Interactions on X-Ray Reflectometry Analysis of Hyperbranched Polymers Materials with the RHO Topology the Ordering of Block Copolymer 179 36 Alkanethiol Deposited on AuO N. Wagner and Y. Kim 102 B. A, Reisner 102 102 Films K. T. Forstner , J. A. Dura , 189 189 Morphology of Self-Assembled 102 104 Structure Determination of E. Huang , J. DeRouchey and C. F. Majkrzak , J. Woodward 189 Aggregates of Amphiphilic Peptides 104 T. P. Russell La Sr Ru0 and A. L. Plant o7 8 o 22 3 with Applications in Bioengineering 102 188 168 Effects of Supercritical CO, on the Q. Z. Huang , 1. Natali Sora 191 191 191 , Zeolite SRM Characterization T. Gore , H. Bianco , Y. Dori 102 105 Behavior of Block A. Santoro and F, T, Vanderah 102 150 Phase Copolymer 191 B. H.Toby and R. Senesi and M. Tirrell Melts Structure Determination of Sr lrD by 2 5 Zirconium Tungstate Studies 189 189 Morphology of Single Graft Block J. Watkins , M. Pollard Powder Neutron Diffraction 128 128 , A. W. Sleight and N. Duan 189 133 Copolymers 162 102 G. Brown , S. Kumar and R. Moyer and B. H.Toby 102 8 8 189 S. F. Trevino , N. Beck-Tan T. P. Russell 189 189 Structure Refinement of a S. Guido and C. Lee Effects of Surfactants on the Confor- Ferromagnetic Vanadium(lll) Sulfate POLYMERS Neutron Reflectivity from the 83 83 mation of Grafted Polymer Brushes

D. Grohol , D. Nocera , Monolayers of SAN Random Behavior of Polymer Chains in Porous 166 166 102 102 188 T. Cosgrove , J. Hone and B. H. To by and Q. Z. Huang ' 166 Copolymers Media R. Wesley Structure of Ca.AINbO, and CaTiO, 50 77 145 133 133 E. Kim , H. Kim , K. Char and M. Nieh , S. Kumar and Electric Field-Induced Orientation of Compounds 145 188 S. H. Lee R. M. Briber 105 105 Diblock Copolymers in Thin Films I. Levin , J. Chan and 189 189 105 Chain Conformation in Deformed J. DeRouchey and T. P. Russell T. Vanderah Elastomers Glass-Transition Effects on Structure of the Layered Cobalt Oxy- 40 40 D. Peiffer , M. Rabeony and Microphase Separation in PS/PVME chlorides CI CI Sr Co 0 and Sr Co0 40 3 2 5 2 2 3 M. Lin Polymer Blends 102 - 188 136 Q. Z. Huang , N. McGlothlin , 133 133 in Self-Assem- R. Jones 136 136 Chain Conformation S. Kumar , , D. Ho and R. J. Cava 133 188 bled, Layer-by-Layer Polyelectrolyte S. Kanath , R. M. Briber and The Structure of a Lithium Substituted 133 Thin Films L. Ho Aluminosilicate RHO 133 133 and M.-P. Nieh , S. Kumar 102 150 B. A. Reisner and J. B. Parise 188 R. M. Briber

NIST CENTER FOR NEUTRON RESEARCH Neutron Reflectivity Study of the Pressure Effects on Crystallization and Structure of Fluorosilicone Networks Effect of Shear Combined with a

45 181 Phase Separation in dPB/PI Blends Phase Behavior of Binary Polyolefin F Horkay and E. Geissler Proximate Surface on Surfactant Using a Unique Back Transformation Blends Structure of Genetically Engineered Sponge Phases and the Sponge to Technique 183 183 Lamellar Transition R. Krishnamoorti , M. Modi and Triblock Copolymer Gels 102 102 102 123 102 A. Schreyer , C. F. Majkrzak B. 189 189 A. , Hammouda W. Hamilton , P. D. Butler S. Kennedy and T. P. Russell , N. 102 H. Gruell 111 204 123 Berk , and Pressure Induced Phase Transitions in G. Warr and L. Porcar Structure of Nafion in Various 111 C. C. Han Multicomponent Polymer Systems Solvents Effects of Shear on Phase Boundaries 135 135 Neutron Studies of Polymer Dynamics N. Balsara and A. Lefebvre 102 8 8 of Bicontinuous Microemulsions S. F. Trevino , S. Young and in Intercalated Polymer-Clay Nano- 102 83 SANS from Dendrimer-Hydrophobe N. Beck-Tan 8 S.-M. Choi and S.-H. Chen Composites Complexes Electrostatic and Counterion-Specific Surface Segregation in Binary Blends 111 102 111 R. D. Ivkov , P. M.Gehring 111 , Effects G. Nisato and E. Amis of Topological^ Distinct Polymers on Micelle Morphology Probed 102 102197 P. N. Maliszewskyj , Papanek with SANS Investigations of a New Class of 166 166 SANS 183 M. D. Foster , C. C. Greenberg and R. Krishnamoorti 205 102 166 L. J. , P. D. Nylon-6 Polymers and D. M. Teale Magid Butler and 111 Nucleation and Growth in Binary 59 Z. Han M. Kreitschmann and Static Characterization of Star-Like Polymer Mixtures Initiated by 188 S. Rathgeber Dendrimers Field Driven Phase Transitions in Pressure Jumps Bilayers of Study of Phase Separation in 188 149 Monolayers and 135 135 135 SANS S. Rathgeber A. Gast and

N. Balsara , A Lefebvre , H. Lee Model Polymer Networks Amphiphiles at Electrode Surfaces 102 J. Hedrick and B. 182 80 Hammouda 178 J. Lipkowski , J. Majewski and B. Viers Structure and Aggregation Kinetics of Phase Behavior of Multi-Component G. Smith 80 SANS Study of the Thermodynamics of Asphaltenes Polymer Systems in Compressible 40 40 Flow-Induced Microstructural Blends of Star and Linear Polymers T. Mason and M. Lin Solvents 166 166 Transitions in Polyampholyte-Polymer 189 189 M. D. Foster T. Zook and Structure of Adsorbed Polyelectrolyte J. Watkins , G. Brown , 166 Colloid Mixtures 189 189 C. Greenberg Multilayer Thin Films V. RamachandraRao , B. Vogt 179 179 N. Wagner , K. A. Vaynberg and 189 Self-Assembly of Polyethylene- 83 83 and T. P. Russell C. Barrett and A. M. Mayes 179 R. Sharma Propylene-Ethylene Triblock Phase Behavior of Polystyrene/ Structure and Morphology of Semi- High Pressure Study of Hydrophobic Copolymers in Selective Solvents Polybutadiene Blends with Added Crystalline Polymer Thin Films 40 59 Interactions L. Fetters , D. Richter 111 111 , D. J. Pochan , E. K. Lin Random Copolymer Studied via Small , 71 71 59 59 M. Lesemann , C. Kirby M. Monkenbush and W. Leube 111 102 , W. L. , S. K. Satija Angle Neutron Scattering Wu , 71 71 M. Paulaitis and J. VanZanten 102 40 131 188 Shear-Induced Order-Disorder D. Waldow and R. M. Briber C. F. Majkrzak and R. Kolb Kinetics of Poiseuille Flow-Induced Transition in Diblock Copolymer Phase Separation in Polymer Thin Structure of Polystyrene/Polyisoprene Solutions Structures in Solutions of Thread-Like Films Diblock Copolymer Micelles in 191 191 Micelles T. 111 111 C.-l. Huang , Lodge and C. C. Decane H. Gruell , C. C. Han and 122 102 111 W. A. Hamilton , P. D. Butler , 133 Han 149 149 149 J. Pople , J. Hur , A. Lee S. Kumar , 156 205 Z. and L. J. Magid 149 111 Han Shear Induced Polymer Desorption A. Gast and K. Barnes Phase Separation in Polyolefin Blends 111 111 111 Kinetics of Polymerization of Rod-Like E. L. 183 183 Lin , R. Kolb and W. Wu Temperature Induced Contrast M. Modi and R. Krishnamoorti Micelles Shear-Induced Polymer Melt Variation Method in Semicrystalline 102 Polyethylene/Polymethylene Blends: S. R. Kline Desorption from an Attractive Solid Polymers Wetting Transitions and Phase Micellar Fluids Near a Solid Interface Surface J.Barnes 111 111 111 111 , A.Nakatani , Y. Akpalu and A. Karim 39 123 111 111 111 102 C. Sommer , W. A. Hamilton and E. K. Lin , D. J. Pochan K. Barnes , B. Hammouda and , 205 Polymer Brushes Under Shear 111 102 40 40 L. J. Magid W. Wu , S. K. Satija and R. Kolb R. Kolb 102 102 P. R. D. Ivkov , D. Butler and Microemulsion Structure at an Small Angle Neutron Scattering of Thermal Expansion and Glass 102 S. K. Satija Interface Water Dispersable Arborescent Transition Behavior of Polymer Films: 204 204 102 Polymer Chain Conformation in Thin 188 188 J. P. Effect of the Free Surface and G. Warr , Schulz , D. Butler S. Yun , R. M. Briber , 123 Films: Deviations from Bulk Behavior 215 102 and W. A. Hamilton M. Gauthier and B. J. Bauer Confinement Between Non-Interacting in Films dPS/PS Surfaces Microstructure of Alkylpolyglucoside Solvent Vapor Induced Swelling of a 133 133 111 111 S. Kumar , R. Jones Micelles and Microemulsions D. J. Pochan , E. K. Lin Polymer Brush , 188 183 111 179 179 R. M. Briber , L. Ho and 102 102 102 W. , S. K. Satija and L. D. Ryan , D. lanspetro Wu , S. K. Satija , R. D. 189 Ivkov , T. P. Russell 166 179 179 102 102 S. Z. D. Cheng C. McKelvey , J. Silas and P. D. Gallagher and J. A. Dura 179 Polymer Interdiffusion Near the Thermal Expansion and Glass E. W. Kaler Solution Structure of Arborescent Interface Polymer/Solid of Microstructure and Properties of Graft Polymers Transition Thin Polymer Films 111 111

E. K. Lin , D. J. Pochan , Sandwiched Between Polymer Layers Hyperbranched Polymers 188 188 ' 102

R. M. Briber , Choi 111 102 40 S.-W. , K. Satija 111 111 179 179 W. Wu , S. and R. Kolb 102 215 D. J. Pochan , E. K. Lin and l\l. Wagner , B. Tande and Y. S.-M. Choi , M. Gauthier and 111 179 Polymer Liquid-Crystal Ordering at an 111 W. L. Kim B. Bauer Wu Interface Thermodynamics of Mixing in Ternary Microstructure of Shear Thickening Spinodal Decomposition in PS/PI 205 111 111 G. Lynn , E. Lin , W. L. Wu and Blends Polymer Blend Mixtures and Shear Thinning Suspensions 205 M. Dadmun 131 188 179 179 78 78 D. R. N. , B. Waldow and M. Briber Wagner Moranzano , H. Jinnai Hayashi and , Polymer Materials for Medical 179 179 111 B. Schubert , B. Tunde C. C. Han Two-Stage Spinodal Decomposition in , Implants 179 179 P. Middhu , A. Vaynberg and Strain-Induced Interfacial Fracture a Rubber Blend 49 49 37 Bellare 78 111 R. Butera A. , A. Gomoll and Between Epoxy and Silicon Oxide M. Hayashi and C. C. Han 49 R. Myers 74 74 Mixed Cationic/Anionic Vesicle M. Kent and W. F. McNamara Polymer Supercritical Fluid Solutions Formation Kinetics Using Time- Strained Polymer Networks 71 71 Resolved SANS M. McHugh , T. diNoia , J. van Gilra 31 31 R. 188 71 71 71 N. , C. Cohen , M. Briber 83 83

P. Huibers , L. Shen and Zanten , C. Kirby , T. Kermis and 188 71 and T. Panagiotopolis COMPLEX FLUIDS 83 S. Conroy I. Goldmints Structure and Characterization of Polyolefin Polymer Blend Tie Chain Octane Wetting of an Air/Water Ultrathin Polymer Films Structures Compatibility of Oil Mixtures at High Interface 133 133 R. L. Jones , S. Kumar 40 , 102 102 40 S. Satija and R. D. Ivkov D. Lohse , M. Rabeony and Temperatures 188 188 L.-T. Ho and R. M. Briber 40 40 40 R. Garner H. Aldrich and M. Y. Lin Ordered Structures of Pluronic Structure of Filled Elastomer Thin Pressure Dependence of the Order- Micelles in Formamide Solutions Films Disorder Transition in Diblock 150 150 P. Alexandridis , L. Yang 150 150 , Y. Zuang , B. Tan , 150 150 Copolymers S. Ann and Y. Lin 150 150 189 189 M. Rafailovich , J. Sokolov and M. Pollard and T. P. Russell 40 102 M. Lin '

58 RESEARCH UTILES Percolation Transition in L-64 Triblock Structural Evolution During Synthesis Crystal and Magnetic Structure of Determination of the Spin Hamiltonian Copolymer Micelles of SBA-15 and MCF-Type Mesoporous ZnCr, Ga„ 0 for a Spin-1/2 Antiferromagnetic with 4 6 4 102 188 102 S.-M. Choi Silica - 143 a Spin Gap S.-H. Lee , W. Retcliff , 175 175 143 71 P. 143 71 71 Schmidt-Winkel , G. D. Stucky T. H. Polymeric Surfactants on Modified , Kim and S. Cheong M. Stone , J. Rittner , D. H. Reich 102 102 71 102 S. R. Kline C. Glinka - Surfaces and J. Crystal and Magnetic Structures in and C. Broholm 16 130 Structure and Aggregation Behavior of A. Rennie , A. Jackson and C ° RU 0 31,(1 CO Sn RU 0 Effect of Superconductivity on the 2 2 5 0 7 5 4 2 2 5 0 25 0 50 4 130 102 188 R. Thomas Aqueous Solutions of Fulvic Acid Z. - 102 Lattice Dynamics of Ba K BiO Q. Huang , J. W. Lynn , 06 04 3 51 102 102 M. Diallo and C. J. Glinka 35 102 - 188 102 R. W. Erwin , M. Crawford C. P. Adams , J. W. Lynn and Poiseuille-Flow-lnduced Changes in , 35 35 13 the Structure of Surfactant Micelles Structure and Aggregation of Soot in R. L. Harlow and E. M. McCarron S. N. Barilo 22 22 22 Flowing Motor Oil Crystal and Magnetic Structures of Effects of Confinement of the , The L. Walker , B. Poore M. Truong , 22 102 40 40 Y. Christanti and B. Hammouda M. Y. Lin and M. Francisco FeOCI Collective Excitations in Superfluid 93 93 93 Helium W.-H. Li , Y. Pressure-Induced Swelling of Polymer Structure of Dendritic Diblock S. Wu , C. G. Wu and 102 102 133 P. Micelles in Supercritical Fluids Copolymer Langmuir Films J. W. Lynn R. M. Dimeo , Sokol and 133 71 71 83 83 Crystal and Magnetic Structures of D. Silva , T. diNoia P. Hammond and J. Iyer M. McHugh , 71 71 La Ru0 and La Ru 0 Effects of Field Cycling on Co/Cu and J. van Zanten , C. Kirby , Structure of Oil in Water Micro- 3 7 7 8 26 71 71 102 188 136 T. and S. Conroy Q. Z. - Co/Ag Multilayers Kermis Huang , R. Cava Emulsions Stabilized by Triblock , 102 102 102 102 R. A. J. A. W. Erwin J. Lynn J. Borchers , Dura Prewetting at a Hydrophobic Surface Copolymer Amphiphiles and W. , 102 90 83 83 83 C. F. Majkrzak , S. Y. Hsu in Phenol/Water Mixtures Crystal and Magnetic Structures of , J. Lettow , A. Zarur and J. Ying 90 90 16 130 P. Pratt, Jr. J. La R R. Loloee , W. and Rennie , Z. X. Li and A. Structure of Ni(OH) Sheared 5 2 °i 2 2 90 130 102 - 188 136 Bass R. Thomas Q. Z. Huang , R. Cava Dispersions of Colloidal Hard Plates , 102 102 21 21 R. Effects of H on Magnetic Coupling in SANS Characterization of Wax A. Rennie and A. Brown W. Erwin and J. W. Lynn FeV Superlattices Modifiers for Diesel Fuel Solvent Effects on the Size and Shape Crystal and Magnetic Structures of 139 139 40 59 B. Horvarsson , G. Andersson Sr Fe C0 , L. Fetters , D. Richter and of Dendrimers 4 2 9 102 102

59 102 - 188 136 J. A. Dura , T. Udovic and W. Leube 102 8 102 - 8 Q. Z. Huang , R. Cava , S. F. Trevino and N. Beck-Tan 102 102 102 C. F Majkrzak R. W. Erwin and J. W. Lynn SANS Determination of the Temperature and Concentration Feasibility Studies of He 3 Polarizers Persistence in Rod-Like Crystal Structures of Length Dependence of Polymer(PEO)- and Magnetic Micelles TbBaCo 0 for Magnetic SANS Measurements Surfactant (SDS) Complexes in 2 6 102 107 102 205 102 - ,88 13 T. R. Gentile , G. L. Jones , P. I. L.J. Magid and D. Butler Aqueous Solutions Q. Z. Huang , Troyanchuk 107 102 102 A. K. Thompson , J. W. Lynn Determination of the Structure 38 40 and J. W. Lynn , SANS K. Chari and M. Lin 102 102 D. C. Dender , J. A. Borchers and of Vitrified Emicroemulsions Crystal Structure and Magnetic Time-Resolved SANS Study of M. Toney 52 203 204 Ordering in CoMo0 , P.R. G. Warr Harrowell , Microemulsion Polymerization 3 204 102 188 102 Flux Lattice Structure in Nb and

A. Widmer-Cooper and 179 179 Q. Z. Huang , J. W. Lynn C. Co and E. W. Kaler , 102 102 35 BaKBiO P. D. Butler R. W. Erwin and M. Crawford

102 - 188 102 - 188 D. C. Dender , C. Adams , Crystal Structure SANS from Nanodroplet Aerosols and Magnetic 102 19 J. W. Lynn and X. Ling 219 219 Ordering in Co (Sn )Ru O B. Wyslouzil , C. Heath , 2 25 0 25 0 75 4 CONDENSED MATTER Ground-State Selection in FCC and 2 ' 9 193 102 - 188 35 K Streletzky , G. Wilemski and PHYSICS Q. Z. Huang and M. Crawford 58 BCT Antiferromagnets due to Quantum R. Strey Crystal Structure and Magnetic Antiferromagnetic Ordering of Disorder in SANS Investigation of Stimuli Ordering the Perovskite 102 197 La„ Ca Mn0 Thin Films T. Yildirim , A. B. Harris and Responsive Hybrid Linear-Dendrimer 33 0 67 3 SrRu Mn O 124 102 0 33 0 67 3 169 E. F. Shender Y. Ijiri , J. A. Borchers , Copolymers in Various Solvents Q. Z.Huang 102 - 188 and R.J. Cava 136 102 102 , R. 20 111 J. W. Lynn W. Erwin , Incommensurate and Commensurate

Diallo , B. M. Bauer and 188 188 Crystal Structure and Magnetic

Rajeswari , 102 M. M. C. Robson , Magnetic Structures in the Magnetore- B. Hammouda 188 188 Properties of Th (Fe .CoJ^Ti, Alloy R. Ramesh and V. Venkatesan 3 1 s sistive R.Ni jSr Materials 102 of 99 - 188 SANS Measurements Liposome V. G. Harris and Q. Z. Huang 30 5

F. Bourdarot , S. Skanthakumar Antiferromagnetic Structure , Size Distributions Crystal Structure and Magnetic Order 102 151 Determination: Exchange-Based J. W. Lynn and L. C. Gupta

102 - 8 216 S. F. F. Trevino , Lebeda and LaCaMnRu0 and LaSrMnRu0 MnPd-Based Thin Films 6 6 7 Incommensurate Spin Fluctuations G. R. Matyas 102 102 102 52 J. W. Lynn , Q. Z. Huang and J. A. Borchers , R. F. Farrow Transitions in Excess , and Structural SANS Study of the Factors Affecting 188 M. Toney52 J. Gopalakrishnan Oxygen-Doped La Cu0 2 4+y the Crystallization of Wax in Crystal Structure Determinations of 83 83 A Bond-Valence Analysis of the R. J. Birgeneau , Y. S. Lee , Fractionated Petroleum the CeMnOj Compound 83 83 Structure of YBa Fe 0 R. J. Christianson , M. A. Kastner 156 156 2 3 8 J. Hsu and E. Sheu 93 168 102 W.-C. Li Erwin 102 I. Natali Sora and A. Santoro and R. W. of Interfacial SANS Study Curvature in Crystal Structure of Characterization of the Antiferro- LitMn^Co,^ Influence of Interface Structure on the Microemulsions 93 magnetic Order in Exchange-Biased W.-C. Li Magnetic Polarizability of a Pd-Co S.-H. Chen 83 and S.-M. Choi 83 Ni Fe /CoO Bilayers Crystal Structure of PrBa Cu 0 Alloy Overlayer in Close Proximity to 8D 20 2 4 8 SANS Study of Organic-Template- 69 69 93 93 CoPt N. Gokemeijer , C. L. Chien W.-C. Li and S. Y. 3 , Wu 173 Driven Synthesis of Transition Metal 124 102 80 , F. Hellman Y. M. Fitzsimmons , Ijiri , J. A. Borchers and Crystallographic and Magnetic 173 173 Mesoporous Oxides 102 B. Maran and A. Shapiro R. W. Erwin Structure of a Series of Lanthanide 123 102 S. Elder and P. D. Butler Characterization of Thin Si0 on Si by Copper Oxides: LnCu 0 Interfacial Spin States in Magnetic 2 2 4 Search for Micelle Formation in 102 - 150 169 Multilayers Spectroscopic Ellipsometry, Neutron A. and Tunnel Junction B. A. Reisner , Stacy Caustic Solutions Used in Bauxite 169 173 173 Piatt , A. E. Berkowitz Reflectivity and X-Ray Reflectivity J. Luce C. , 102 102 Processing 102 59 J. A. Borchers , J. A. Dura and J. A. , A. Richter Dura C. , Crystallographic and Magnetic 11 116 102 102 J. Watson , H.J. M. Hanley and 18 C. F. Majkrzak N. V. Nguyen and C. F. Majkrzak Structure of Tb Ni Si M. Lin 40 2 3 5 Charge, Orbital Magnetic Ordering 102 102 Interlayer Spin Coupling in F. Bourdarot , J. W. Lynn and Search for Surface Enrichment in 151 FeMn-Based Spin Valves and Two-Phase Coexistence in L. Gupta TIFR Ultrafine Aerosol Droplets Using SANS 102 102 J. , C. F. Majkrzak La Ca Mn0 A. Borchers , 1/2 1/2 3 Crystallographic Study of 219 193 29 90 90 B. Wyslouzil 102 188 102 Jr. J. , G. Wilemski and A. Reilly , W. P. Pratt, , Bass Q. Z. , J. Huang W. Lynn , La Wl MnO 58 0.67 g33 3 102 R. Strey 188 188 102 and D. C. Dender 102 - 168 V. Smolyaninova , K. Ghosh , C. Adams , J. W. Lynn , Shear-Induced Structure in Rodlike 188 102 187 188 Lattice Dynamics of a Material with R. L. Greene , D. C. Dender , R.G. Williams and G. Zhao Micelles 102 102 Negative Thermal Expansion, ZrW 0 R. W. Erwin and A. Santoro 2 8 71 102 102 39 82 - P. D. Butler and C. Sommer G. Ernst , C. Broholm , 82 82 A. P. Ramirez , G. Kovac and G. Gasparovic71

NIST CENTER FOR NEUTRON RESEARCH 31 Local Spin Resonance in a Frustrated Magnetic Field Effects on Antifer- Magnetism of Ferrihydrite Q-Dependence of the Spin Flip Antiferromagnetic ZnCr 0 romagnetic Ordering in a Fe/FeF Nanoparticles Scattering from Exchange Coupling 2 4 2 71 102 188 - 102 ' Bilayer 218 218 across Fe-FeF Interfaces Measured S.-H. Lee , C. Broholm M. S. Seehra , V. Suresh Babu , 2 83 143 124 102 102 II with Spin Polarized Neutron T H. Kim , W. Ratcliff and Y. Ijiri , J. A. Borchers and J. W. Lynn , 143 102 173 Diffraction with Polarization Analysis S-W. Cheong R. W. Erwin , M.-C. Cyrille , Neutron Coherence Length and Non- 173 167 81 173 I. Low-Temperature Neutron Diffraction K. Schuller , J. Nogues and Specular Scattering from Diffraction M. Fitzsimmons and I. Schuller 218 Studies of Pr (Fe,Co) Ti, D. Lederman Gratings Reflectivity Measurements on Spin 3 27 5 5 102 102 Permanent Magnets Magnetic Order and Crystal Field C. F. Majkrzak and N. F. Berk Valve Structures 102188 Effects in 199 199 V. G. Harris" and Q. Z. Huang RNiBC Neutron and X-Ray Diffraction Study D. Sarkisov and M. Dabaghian 24 102 102

F. Bourdarot , J. W. Lynn Magnetic and Crystal Structure Phase , of the Crystal Structure of Bi, Sr Refinement of the Ordered Moment in a 8 0, 102188 26 Q. Z. Huang , D. R. Sanchez 102188 105 Transitions in f? Ba Co0 , Q. Z. Huang Wong-l\lg the QuasMD Antiferromegnet CsNiCI, 1j i 3 and W. 26 26

B. Fontes , J. C. Trochez 71 71 102 (R = Nd.Gd) M. and ' 102 Neutron and X-Ray Diffraction Study I. Zaliznyak and C. Broholm 26 13 13 E. Baggio-Saitovitch I. 0. Troyanchuk , D. D. Khalyavin , of the Crystal Structure of Sr Ca Single-Ion Anisotropy and Crystal 0 495 0 , 65 13 13 Magnetic Order and Fluctuations in a T K. Solovykh , H. Szymczak , B'„. Field Effects in R Cu0 (R = Nd, Sm, 39°, 2 4 102 188 102 Q. and J. W. Lynn Zig-Zag Spin-1/2 Chain 102 188 105 Z.Huang Q. Z. Huang and W. Wong-l\lg Pr, ...) 71 ' 102 71102 I. A. Zaliznyak , C. Broholm 102 155 Magnetic Correlations and Lattice , I Yildirim , R. Neutron Diffraction of Sachidanandam , 207 207 Measurements M. Kibune and H. Takagi 155 197 Distortions in the Bilayer Manganite Nanostructured, Non-Equilibrium A. Aharony and A. B. Harris La, Sr Mn 0 Magnetic Order in Pr-Containing 2 18 2 7 Spinel Ferrites Site Ditributions and Magnetic 119 5 Cuprate Superconductors L. Vasiliu-Doloc , S. Rosenbranz 99 , Structures in AI Fe , x = V. G. Harris 05 05 Mn 0.05, 5 5 93 93 98

R. Osborn , S. K. Sinha W.-H. Li , K. C. Lee , H. C. Ku and , Neutron Reflectivity Studies of 0.1,0.15 102 5 102 J. W. Lynn and J. F.Mitchell J. W. Lynn 99 99 V. Harris , D. J. Faremi Fe 0 /Ni0 Exchange-Biased Bilayers , 3 4 99 102 188 Magnetic Correlations in Discon- Magnetic Order in the Ferromagnetic 42 102 K. B. Hathaway , Q. Z. Huang , D. M. Lind , J. A. Dura and 160 193 193 tinuous Co-SiO, Thin Films and Superconductors RuSr GdCu 0 102 A. Mohan and G. J. Long 2 2 8 C. F. Majkrzak 84 136 102 Multilayers ' B. Keimer and J. W. Lynn Sites Distribution Neutron Scattering Study of the and Magnetic 188 173 S. Sankar , A. E. Berkowitz , Magnetic Order in the Superconductor Structure in La (Co, FeJ^Ti Nuclear and Magnetic Structure of RD 2 102 188 102 3 D. C. Dender , J. A. Borchers , RNi B C (x = 0,0.2,0.4) 102 102 - 188 2 2 T J. Udovic , Q. Z. Huang 102 102 ,

R. W. Erwin , S. R. Kline 102 5 57 102 188 , J. W. Lynn , S. 102 102 J. K. , Q. Z. Skanthakumar , Liang Huang and 102 102 J. W. Lynn , R. W. Erwin and J. A. Dura and C. F. Majkrzak 151 151 102 Z. Hossain , L. C. Gupta 102 A. Santoro , J. J. Rush 151 25 Magnetic Correlations in a Geometri- R. IMagarajan and C. Godart Small-Angle Magnetic Scattering from Neutron Studies of New Incommensu- cally Frustrated Magnet ZnV 0 2 4 Magnetic Order, Structure, and Spin rate Magnetic Correlations Near the Nanocrystalline Cobalt 188 102 71 102 200 105 S.-H. Lee , C. Broholm and Dynamics of (La, CaJMn0 J. Weismuller , R. D. Shull K 3 Lower Critical Concentration for Stripe , 207 Y. Ueda 102 102 105 137 J. W. Lynn , R. W. Erwin R. McMichael , U. Erb and , Order in La, Nd Sr CuO 6 i 04 i 4

102 102 ' 102 Magnetic Correlations in the Heavy 18 J. A. Borchers , Q. Z. Huang 207 J. G. Barker J. M. Tranquada , N. Ichikawa , Fermion System LiV 0 188 102 188 , A. Santoro , K. Ghosh and 102 102 - 188 2 4 P. M. Gehring and S.-H. Lee Spin Chain Direction in Copper 188 102 71102 188 - R. L. S.-H. Lee , C. Broholm and Greene Pyrazine Nitrate Oxygen Isotope Effect on the Spin and 207 Y. Ueda Magnetic Properties of HoV0 71 71 4 Lattice Dynamics of La Ca Mn0 M. Stone , D. H. Reich and 5/8 3 , 8 3 Magnetic Depth Profile of CMR 5 5 71102 C. K. Loong , S. Skanthakumar 102188 102 C. Broholm , C. P. Adams , J. W. Lynn , Perovskite Films and Spin Valves 102 188 J. W. Lynn and G. K. Liu 188 188 Spin Dynamics of the Mn Ions in V. Smolyaninova , G. M. Zhao , 124 102 Y. Ijiri A. 188 , J. Borchers , The Magnetic Structure of R. L. Greene and La^Ba^nO., and Pr^BaJVInO., 102 102 J. W. Lynn , R. W. Erwin 82143 102 119 , [MnTPPHTCNE] 2PhMe by High-Reso- S.-W. Cheong J. W. Lynn , L. Vasiliu-Doloc , 102 188 C. F. Majkrzak , M. Robeson 188 188 , lution Neutron Powder Diffraction L. Polarized Neutron Diffraction Studies K. Ghosh , R. Greene and 188 188

R. Ramesh , V. Venkatesan and 125 13 C. R. Kmety-Stevenson S. Barilo , of Magnetic Ordering in Exchange- 188 R. L. Greene 125 211 A. J. Epstein and J. S. Miller , Biased Fe 0 /CoO Superlattices Spin Dynamics in LaTi0 3 4 3 211 Magnetic Domains in Co/Cu E. J. Brandon 124 102 84 136 65 Y. Ijiri B. , A. , J. Borchers Keimer Ivanov A. , , Multilayers Magnetic Ordering and Structure of 102 102 188 102 207 R. W. Erwin , S.-H. Lee J. W. Lynn , Y. Taguchi and , 102 102

J. A. Borchers , J. A. Dura 102 207 , PrBa Fe 0 F. P. Y. 2 3 8 C. Majkrzak , J. van der Tokura 102 106

C. F. Majkrzak , J. Unguris 102 102 134 134 , N. Rosov , J. W. Lynn Zaag and R. M. Wolf , Spin Dynamics in Single Crystal 106 106 D. Tulchinsky , M. H. Kelley 82 82 , M. Seyedahmadian and T. Yeun Polarized Neutron Reflectrometry La Ca Mn0 106 90 90 7 3 3 R. Celotta , S. Y. Hsu , R. Loloee , 188 102 102 Magnetic Ordering of Exchange- Measurements of CoPt Thin Films J. 90 90 CP. Adams , W.Lynn and W. P. Pratt, Jr. and J. Bass Biased Fe 0 /Ni0 Superlattices 52 102141 91 M. Toney , A. Schreyer Y. M. Mukovskii 3 4 , Magnetic Domain Structure in CoPt 102 102 102 102 J. A. Borchers , R. W. Erwin J. A. Borchers , C. Majkrzak , Spin Dynamics of Strongly Doped Thin Films 124 42 Y. Ijir Y. , D. M. Lind and Polarized-Neutron Scattering Mea- La, SrMn0 102 52 x 3 C. J. Glinka and M. Toney 42 P. G. Ivanov surements of the Oxygen Moment in 119 102 L. Vasiliu-Doloc , J. W. Lynn . Magnetic Domain Structure of Magnetic Ordering of Mn in (La.Sr)MnO 91 91 Y. M. Mukovskii , A. A. Arsenov Thermally Treated Nanocrystalline Nd, „Ca Mn0 102 18 91 P. , Shulyatev 3 M. Gehring G. Shirane and and D. A. Ni Fe 93 93 93 159 3 S. Y. Wu , W-H. Li , K. C. Lee H. Hirota , Spin Freezing in a Geometrically 20 123 H. Frase and L. Robertson 102 97 97

J. , J. W. Lynn R. S. Liu , B. Wu Polarized Neutron Studies of Magnetic Frustrated Antiferromagnet, Y Mo 0 102188 2 2 7 Magnetic Order in EuMn P C. Y. 87 87 2 and Huang Interfacial Roughness in EuTe/PbTe J. Gardner , B. Gaulin , 105 102 71102 102188 J. Y. Chan , J. W. Lynn , Magnetic Structure in ZnV 0 Superlattices 2 4 C. Broholm and S.-H. Lee 170 170 S. M. Kauzlarich , A. Payne and 1W02 71102 128 102 128 S.-H. Lee , C. Broholm and H. Kepa , T. Giebultowicz , Spin-Flop Tendencies in Exchange- 102 B. A. Reisner 161 128 102 Y. Ueda G. Bauer and C. F. Majkrzak biased Co/CoO Thin Films Magnetic Ordering in the Spin-Ladder Magnetic Structure of Charge Ordered Pressure Dependence of the Nuclear 102 102 J. A. Borchers , Y. Ijiri , Compound CaCu 0 102 188 102 2 3 CaFe0 and Magnetic Structures in S.-H. Lee , C. F. Majkrzak 3 , 83 83 V. Kiryukhin , Y.-J. 18 18 5 99 Kim , La Ca MnO E. , D. E. and G. Felcher , R. Kodama Moshopoulou Cox 0 67 0 33 3 , 102 83 R. W. Erwin and R. J. Birgeneau 125 102 188 102 173 173 P. Woodward Q. Z. Huang , J. W. Lynn K. Takano and A. E. Berkowitz , 102 1028 Magnetic Ordering in the System F. Magnetic Structure Transition of A. Santoro , S. Trevino Static and Dynamic Properties of Spin La, .P^BaCuFeOj AlFe, ,Mn, Under a Magnetic Field Pr Magnetic Order and Spin Dynamics and Charge Ordering in La Sr Ni0 2l x 4 198 188 F. 188 102 - 188 82 102 ' 99 W. Mombru , Araujo-Moreira in the Cuprates Q. Z. Huang ,V. G. Harris S.-H. Lee , S-W. Cheong and , 210 L. Suescun 102 102 102 102 100 R. W. Erwin and J. W. Lynn J. W. Lynn Rosov G. Aeppli , , 13 13 S. N. Barilo , L. Kurnevitch and 142 A. Zhokhov

60 RESEARCH TITILES Strain-Induced Changes to the NiO Studies of Charge, Spin and Orbital Vortex Lattice in ErNi BrC Motion in Alpha-Lactalbumin and 2 Spin Structure in NiO Thin Films Ordering in the System 182 182 Alpha-Lactalbumin Molten double P. Gamme , S. Lopez , 149 149 102 188 102 Bi Ca IVIn0 - Studied by Quasielastic Neutron Regan , R. White and D. C. I Dender , S. Choi 1x x 3 , 52 125 125 102 69 P. Scattering J. Stohr Woodward , J. Goldberger and J. W. Lynn , P. Cawield 125 111 102 P. Structural Change and Magnetic Santosh Vortex Lattice Structure in High-T B. Zimei , D. A. Neumann and 111 Ordering in Bilayered La Sr Mn 0 Studies of Magnetic Critical Bi-2212 C. C. Han 2 2i U2i 2 7 93 96 84 136 93 Scattering in Strained and Lattice- 136 - Neutron Diffraction Studies of W.-H. Li , S. Y. Wu , H. D. Yang B. Keimer , T. Fong and 102 102 and J. W. Lynn Matched (Y/Lu)IHol(Y/Lu) Films J. W. Lynn Peptides in Fluid Lipid Bilayers 102 102 171 171 P. M. Gehring , C. F. Majkrzak S. White and K. Hristova Structural and Magnetic Ordering in , 18 18

L. D. Gibbs , A. Vigliante , Neutron Reflectivity Studies of Protein 130 130

102 A. , J. 102 - m C. Lake Goff and Adsorption/Desorption on the Surfaces T. J. Udovic , Q. Z. Huang , BIOMOLECULAR 130 102 102 R. A. Cowley of Self-Assembled Monolayers J. W. Lynn and R. W. Erwin SCIENCE Studies of Spin Waves in the Ladder 166 166 Ordering in M. D. Foster , S. Petrash and Structural and Magnetic Conformational of Changes 102 Compound La Ca Cu 0 F. 5 9 24 41 C. Majkrzak Chaperonin Complexes Involved in 67 18 102 102 - 188 M. Matsuda , G. Shirane Q. Z. , Ordering in Protein/Polelectrolyte T J. Udovic , Huang , Protein Refolding 102 188 102 102 102 S.-H. Lee - and P. M. Gehring J. W. Lynn and R. W. Erwin 23 23 Multilayers E. Eisenstein , J. Zondlo and 177 99 Study of Low-Energy Excitations in a 102 J. Rusling and Y. Lvov Structural Phase Transition and S. T. Krueger Weakly-Coupled Quantum Spin Chain Protein Adsorption at Solid/Liquid Magnetic Order in Heavy Fermion Determination of the Bending of DNA System Compounds Ce M with M = Al. In and Interfaces 3 Bound to Cyclic AMP Receptor Protein 18 60 202 202 202 A. Zheludev , K. Uchinokura , B. Sn in Solution J. R. Lu , T. J. Su and Green 71 102 188 102 93 93 C. Broholm and S.-H. Lee - , 23 102 W.-H. Li , K. C. Lee and F. Schwarz and S. T. Krueger Quasielastic Neutron Scattering Study 82 of Y. Y. Chen Study the Relax or Based of the Dynamics of Water in Determination of the Location of the Ferroelectric PZN-PT Saccharide Solutions Structure and Magnetic Order in Lipid Anchor in Outer Surface Protein 102 18 23 136 P. M. Gehring , G. Shirane = Ni, In , Ba MRu O , Cu, Fe, Co, A. Tsai , M. Feeney M A of Borrelia Burgdorfei by SANS , 3 2 g 133 133 133 R. E. Park and T. R. Shnut 136 18 18 P. G. Debenedetti and J. T. Rijssenbeek , D. Schneider , C. Lawson and 02 188 102 102 R. Superconductivity in La^S^CuO,, 18 D. A. Neumann Q. Z. Huang' , W. Erwin and V. Graziano 136 159 159 S. , S. Ueki R. J. Cava Wakimoto , Rnase-A Dynamics by Time of Flight Gelation of Methylcellulose 159 159 K. Hirota , K. Yamada Structure and Magnetic Order in , 191 191 Neutron Scattering: A Case Study in 159 83 C.-l. Huang and T. Lodge

Y. Endoh , R. J. Birgeneau Sr CaRu 0 , Protein Dynamics and its implications 9 3 2 83 83 Interaction of the Peptide Penetration

102 188 136 Y. S. Lee , M. A. Kastner Q.Z.Huang and R.J. Cava , for Drug Design, Formulation, and 18 102 - 188 with Phospholipid Double Bilayers G. Shirane , S.-H. Lee and Delivery Structure and Magnetic Order in 102 65 65 G. Fragneto , E. Bellet-Amalric P. M. Gehring , 23 102 A. Tsai , T. J. Udovic Sr Y ,Ca Co 0 65 , 2 0 , 2 2 6 F. Graner and L. Perino Superconductivity, Magnetic Fluc- 102 A. 102 102 188 102 J. R. D. Copley , D. Neumann , Q. Z. Huang , J. W. Lynn ,

102 102 - 197 tuations and Magnetic Order in Interfacial Morphologies of Phospho- J.J. Rush M.Tarek 102 136 , , R. W. Erwin and R. J. Cava 171 104 TbSr Cu Mo 0 lipid Membrane Systems D. Tobias and G. Gilliland 2 269 0 31 7 Structure Magnetic Properties 87 27 and 93 93 B. Gaulin , P. Mason and Li , Y. S. Y. W.-H. W. Chuang, Wu , SANS Studies of Calmodulin/Target in the Sr Na Ru0 Solid 87 JLa, 5 05)I 3 93 102 96 R. Epand K. C. Lee , J. W. Lynn , H. L. Tsay Enzyme Interactions Solution 96 and H. D. Yang Internal Organization of Peptide- 80 80 102 188 136 S. J. Krueger , J. Trewhella , Q. Z. Huang and R. J. Cava Derived 80 104 Surface Spin Ordering in LaFe0 Thin Nucleic Acid Complexes from N. Bishop and A. Wang 3 Structure of YCo Mn 0 SANS 0 5 0 5 3 Films SANS Study of Catechol Dioxygenases 102 T B ao5 C ° 0 and Nd Ba CoO, 102 52 23 »o5 , 05 05 A. and F. Schwarz and S. T. Krueger J. Borchers , J. Stohr 102 188 102 from Pseudomonas Putida SH1

Q. Z. Huang , J. W. Lynn M. Toney52 Interpretation of Specular and Off- 93 93 102 4 S.-L Huang , W.-H. Li and R. W. Erwin and I. Troyanchuk Specular Reflectivity Data from 102 TbNiBC Diffraction and Critical J. W. Lynn Structures of HgMo^BajCuO^ High Patterned Thiahexaethyleneoxide Scattering SANS Study of Colloidal Interactions T Superconductor 102 102 - 188 Alkane Surfaces F. Bourdaut , Q. Z. Huang and 102 188 63 of Proteins - 102 102 , Marezio Q. Z. Huang M. , 102 F. , F. Majkrzak N. Berk C. , 179 179 J. W. Lynn P. 63 102 0. Velev , Hinderliter , F. Licci and A. Santoro 102 104 A. Munter , J. Woodward , 179 179 Temperature Dependence of the J. Silas and E. W. Kaler 104 104 Structures of Ba Sr CoO C. W. Meuse , A. L. Plant and 0 8 0 2 y Exchange Coupling in Fe/Cr 102 SANS Study of Cyclic-AMP-Dependent Compounds S. T. Krueger Superlattices 102 188 136 Protein Kinase Q. Z. - and R.J. Cava Huang 188 102 In-Situ Measurements of Melittin 170 F. Majkrzak 80 80 A. Schreyer , C. , J. Zhao , J. Trewhella , D. Walsh Structures of YM Cu Re O 141 Insertion into Hybrid Bilayer 170 2 2 85 015 7ti T Schmitte and R. Bruschia (M = Ba and Sr) High T Membranes Temperature-Dependent Crystallogra- 102 102 SANS Study of the DNA/Flap Endonu- Superconductors S. T. Krueger , C. F. Majkrzak phy and Zero-Field Magnetic Order of , 102 188 63 102 104 clease Complex J. A. Dura , A. L. Plant and , Marezio Q. Z. Huang M. , 80 80 Mn[N(CN) ] (pyrazine-d ) 63 102 2 2 4 104 J. Trewhella , C. Kim and F. Licci and A. Santoro C. Meuse 211 102 80 J. L. Manson , J. W. Lynn and S. Gallagher Structure Change of BaRuO, Under 211 Lysozyme Adsorption at the Air/Water J. S. Miller SANS Study of Protein Folding High Pressure Interface Temperature Evolution of the Spin 71 71 Mechanisms 102 - 188 102 8 - J. Erickson and K. J. Stebe Q. Z. Huang , S. F. Trevino Excitation Spectrum in a Reentrant 188 188 and 102 136 R. M. Briber , R. Perez-Salaz A. Santoro , R. J. Cava Field Alignment of Mixed Spin Glass Fe AI Magnetic 102 07 03 S. T. Krueger Structure and Magnetic Ordering of 80 18 Lipid Discotic Micelles W. Bao , S. Shapiro and 27 74 SANS Study of the Ferredoxin TOL = 188102 M"[N(CN) (M Co, Ni, Mn) J. Katsaras , R. Prosser ] S.-H. Lee , 2 2 Component of Toluence Dioxygenase 211 102 102 J. L. Manson S. T. Krueger and C. J. Glinka , Three-Dimensional Spin Structure of from Pseudomonas Putida F1 125 C. R. Kmety-Stevenson , Membrane Active Peptides: Phase 93 186 Sr CuO CI : Field Dependent Neutron T. 102 188 102 S.-L. Huang , D. Gibson , Q. Z. Huang , J. W. Lynn Supramolecular , Scattering Study Transitions and 93 102 150 150 W.-H. Li and J. W. Lynn G. Bendele , Pagola Membranes S. , 102 Assemblies of Peptides in T Yildirim , S. Skanthakumai^and 150 138 Self Assembly of Peptide Amphiphiles P. W. Stephens 138 , 102 H. W. Huang , W. Heller , J. W. Lynn 191 191 191 18 H. , T. Gore , Y. Dori and L. M. Kiable-Sands 138 138 Bianco , T Harroun and L. Yang 191 18 Ultra-High Energy Resolution Studies Tirrell A. L. Rheingold M. , 125 211 of the Second Length Scale in Single A. J. Epstein and J. S. Miller Structural Investigation of the High Terbium Crystal Temperature Protonic Conductors 65 65

, Farago 102 - 188 J. E. Lorenzo B. , 206 , Q. Z. Huang C. Karmonik , 65 102 B. F. Frick , P. M. Gehring , 102 102 T J. Udovic and J. J. Rush 102 18 C. F. Majkrzak and G. Shirane

NIST CENTER FOR NEUTRON RESEARCH ?-: Structure of Hybrid Bilayer The Dynamics of Potassium Crytand Inelastic Neutron Scattering Study of Neutron Scattering Study of the Membranes by Direct Inversion of Complexes Al Charged with Hydrogen Dynamics of Hydrogen and Deuterium Neutron Reflectivity Data 102 102 102 Solved in Crystalline Pd Si N. C. Maliszewskyj I J. Udovic , J. J. Rush , , g 2 102 102 102 90 184 184 206 102 F. D. A. Gilbert C. Majkrzak , N. Berk Neumann , D. J. and C. Buckley and H. K. Birnbaum C. Karmonik , T. J. , Udovic , 104 104 90 102188 102 C. , V. Silin J. L. Dye W. Meuse , Q.Z.Huang , J.J. Inelastic Scattering in Ce- and Rush , 104 102 212 212 A. L. Plant and S. T. Krueger Dynamics of Selenium-Arsenic- U-Based Non-Fermi Liquid Systems Y. Andersson and T. B. Flanagan Structure of Intact Influenza Hemag- Bromine Glasses 172 172 Neutron Scattering W. Beyermann , T. Kelly Study of the Role , 102 80 173 glutinin Protein Containing the Viral R. L. Cappelletti and R. Robinson and B. Maple of Diffusion in the Hydration Reaction Region 169 of Tricalcium Silicate Membrane Spanning B. E. Schwickert In Situ Neutron Reflectometry Study 95 143 124 120 R. , D. A. Remeta FitzGerald , Blumenthal , S. J. J. The Effects of Confinement on of Self-Assembled Poly(Dimethyl Thomas , 95 102 102 S. Durell and S. T. Krueger Tunneling in Methyl Iodide Siloxane) Film D. A. Neumann and 41 Structure of Microtubule-Based 102 179 179 R. A. Livingston R. M. Dimeo Tsao , J. Rabolt M.-W. , 179 102 188 Cellular Motors Investigated by SANS - Neutron Scattering Study of the Evolution of the Structure of the A. Kalambur , L. Sung and 174 174 102 F. Vibrational Modes of Cubane R. Mendelson , D. Stone and K NiF Phases of La^S^NiO^ with C. Majkrzak 2 4 80 102 102 R. Hjelm T. Yildirim , P. M. Gehring Oxidation State: Octahedral Distortion Investigation of Slow Motion , 102 176 D. A. P. Vectorially-Oriented Protein and Phase Separation (0.2 < x < 1.0) Dynamics in Selective Adsorption Neumann , E. Eaton and 176 Monolayers: Neutron Reflectivity 130 130 192 192 T. E. Emrick J. E. Millburn , M. A. Green H. Taub , D. Fuhrmann , , Studies 130 192 5 Neutron Spectroscopy of Single- M. J. Rosseinsky and L. Criswell , K. Herwig and R. M. 197 197 102 102 Walled Nanotubes J. K. Blasie , L. Kneller D. A. Dimeo , Neumann 197 197 102 197 E. , J. Strzalka Nordgren and First-Principles Calculations and Isotopic Ordering in La(D H, R Papanek , J. Fischer and x ,) 3 197 197 A. Edwards Neutron Scattering 102 102 188 A. Clay T J. Udovic , Q. Z. Huang and 102 197 102 T Yildirim and 0. Gulseren J. J. Rush Neutron Vibrational Spectroscopy of

First-Principles Calculations of Location of K and/or D Dissolved in Poy^HtD), 102 102 188 Q. - CHEMICAL PHYSICS OF Structural, Vibrational, and Electronic Crystalline Pd P T J. Udovic , Z. Huang and 3 08 212 102 102 188 MATERIALS Properties of Solid Cubane - Y Andersson T J. Udovic , Q. Z. Huang and 102 15 15 209 Yildirim Kilic Ciraci Y. Neutron Vibrational Spectroscopy of A Quasi-Elastic and Inelastic Neutron T , C. and S. Andersson Sr lrH Scattering Study of Hydrogen in First-Principles Investigation of The Microscopic Glass Transition in 2 5 102 162 Zeolite Structure and Dynamics of Negative- Viscous Metallic Liquids T J. Udovic and R. 0. Moyer 133 102 Thermal-Expansion Materials 102188 20 Layer Shearing Modes in Li-Graphite R Sokol and R. M. Dimeo A. Meyer , R. Busch , 102 153 65 Bond Lengths and Ground State T Yildirim J. Neuhaus and H. Schober Compounds 102 197 Structure of the Fulleride Polymer Fulleride Superconductors Neutron and X-Ray Reflectometry W. A. Kamitakahara C. Bindra 191 102 Fischer I Yildirim Studies of Rough Interfaces in a and J. E. 80 150 Langmuir Blodgett Film Low Energy Dynamics of Alkali G. M. Bendele , A. Huq and High Resolution Powder Diffraction of 150 128 158 Silicate Glasses R W. Stephens H. Kepa , L. J. Kleinwalks CeRh Si , 2 2 102 102 79 102

80 80 N. F. Berk , C. F. Majkrzak J. Toulouse and D. A. Neumann Deposition Interdiffusion at Room , G. M. Bendele , W. Bao , 154 80 80 I S. Berzina, V. I. Troitsky Temperature and the Kinetics of , Orientational Dynamics of P R. A. Robinson and J. L. Sarrao 4 208 66 Interlayer Diffusion in Barium R. Antolini and L. A. Feigin Molecules in White Phosphorus Hydrogen Dynamics in K MnH 3 5 Stearate Langmuir-Blodgett Films at Neutron Investigation of Molecular 102 102 165 102 W. A. Kamitakahara , T. Yildirim , G. Auffermann , T. J. Udovic , 102 73 the Temperature Just Below the 102 102 Reorientations in Solid Cubane D. A. Neumann and F. Gompf J. J. Rush and T. Yildirim Melting Point 102 102 T Yildirim , P. M. Gehring , Preferential Isotopic Site Occupation Hydrogen Dynamics in ZrBeH, 66 66 5 102 176 L. A. Feigin and I. I. Samoilenko D. A. Neumann , P. E. Eaton and 102 61 in Rare-Earth Hydrides I J. Udovic and B. Hauback 176 102 Dynamics of Arsenic-Selenium T. E. Emrick 102 - 188 T. J. Udovic , Q. Z. Huang and Lipid Incoherent Scattering from 102 Glasses Neutron Scattering Studies of J. J. Rush Bilayers and Bilayers with Channel 126 126 Hydration Reaction of Tricalcium B. Effey , R. L Cappelletti and Phonon Density of States in Sc (W0 Proteins Imbedded 2 4 ) 3 102 W. A. Kamitakahara Silicate and Portland Cement 71 71 83 83 C. Broholm , C. Urich and H. H. Chen , C. Liao and 124 120 S. A. FitzGerald , J. J. Thomas 71 The Dynamics of Hydrogen Bonded 138 , G. Gasparovic T Weiss 102 41 Materials D. A. Neumann , R. A. Livingston Guanidinium Based Pressure Dependence of Phonon Inelastic Neutron Scattering Study of 120 191 102 and J. McLanghlin A. Pivovar D. A. Neumann , Density of States in Zr,W,0, the Dynamics of Crown Ethers in 102 Neutron Scattering Studies of the M. Ward and J. J. Rush 71 Ulrich 71 Potassium Electrides C. Broholm , C. and Dynamics of Hydrofluorocarbons Dynamics of Hydrogen in Laves Phase 82 Maliszewskyj 102 A. P. Ramirez N. C. , Hydrides Encaged in NaX and NaY Zeolites 102 47 Proton Dynamics in Hydrated Nations D. A. Neumann , M. Wagner and 206 88 188102 C. Karmonik , 102 8 A. V. Skripov , J. C. Cook 90 102 - , F. J. L. Dye 102 102 T J. Udovic , S. Trevino and 102 102 N. C. Maliszewskyj , T. J. Udovic T J. Udovic and D. A. Neumann , 35 Inelastic Neutron Scattering Study of 102 35 M. K. Crawford J. J. Rush , M. K. Crawford , The Dynamics of Hydrogen in Single- of 3 115 Proton Dynamics in Strontium Cerate the Dynamics Guanidinium-Based D. R. Corbin and R. R. Cavanagh Walled Nanotubes Clathrate Materials and Zirconate Ceramics 188102 102 Neutron Scattering Studies on the W. M. Brown , T. Yildirim and 191 191 206 102 A. Pivovar , M. C. Karmonik , T. Yildirim Ward , , 102 Vibrational Excitations and the D. A. Neumann 102 102 102 102 D. A. Neumann , T. Yildirim and T J. Udovic , J. J. Rush and Structure of Ordered Niobium Dynamics of Hydrogen Trapped by 102 103 J. J. Rush Hydrides R. L. Paul Defects in Pd Inelastic Neutron Scattering Study of 59 59 Quasielastic Scattering Study of the B. Hauer , E. Jansen 201 102 , T. J. R. Kirchheim , Udovic and the Hydration of Tricalcium Silicate 59 59 Liquid-Glass Transition W. Kockelmann , W. Schafer 102 , J. J. Rush 124 120 59 200 Intertramethyl-Heptane S. A. FitzGerald , J. J. Thomas , D. Richter , R. Hempelmann , 79 28 Dynamics of Layered Silicates: Inter- 120 102 102 J. C. McLaughlin J. Toulouse , H. Cummins and , T J. Udovic and J. J. Rush 102 28 calated Water D. A. Neumann and S. Goiqing Neutron Scattering Study of the N. Wada 160 and R. A. Livingston 41 Structure of Na C as a Function of Relaxational Dynamics in GeO, 102 2 60 188 153 W. A. Kamitakahara Inelastic Neutron Scattering Study 102 - Pressure and Temperature A. Meyer , J. Neuhaus and 65 Dynamics of Li-Doped Carbon of Rare Earth Trihydrides and 102 102 H. Schober I Yildirim , D. A. Neumann , Electrode Materials Trideuterides 102 8 197 S. F. Trevino and J. E. Fischer Rotational Dynamics of C in 60 102 197 191197 102 102 -

Fischer , J. R Papanek , J. E. T J. Udovic J. Rush and (ND )K C 3 3 60

102 102 - 188 and W. A. Kamitakahara Q. Z. Huang 203 203 , Prassides S. Margadonna K. , 102 2

D. A. Neumann , H. Shimoda and 2 Y. Iwasa

G 2 RESEARCH TITILES '

Rotational Excitations of Methane Data Acquisition and Analysis Dy/SPP Neutron Detector Neutron Scattering Properties and for 101 102 102 Confined to Porous Glass Software the Backscattering Spec- Y.-T. Cheng and J. K. Stalick Materials Properties Testing of the , 75 102 trometer 102 to B. Asmussen , R. M. Dimeo and and B. H. Toby Null Scattering Titanium Alloy be 102 102 D. A. Neumann N. C. Maliszewskyj and R. The Disk Chopper Time-of-Flight used for High Pressure Cells 102 102 102 M. Dimeo - 8 Search for Bragg Peaks in Se-As-Br Spectrometer(DCS) S. F. Trevino , K. T. Forstner and 110 Glasses Data Analysis Software for the Fermi 102 188102 R. Fields J. R. D. Copley , J. C. Cook 102 169 102132 R. Cappelletti and B. Schwickert Chopper Spectrometer and F. B. Altofer The NIST Neutron Spin Echo Spec- 102 188 T. trometer (NSE) Search for Su b lattice Ordering in Yildirim and C. M. Brown Evaluation of New Neutron Area- N. 102 188 102 PrD Design of a Cable and Hose Detectors Rosov , S. Rathgeber and 2+1 59 102 102 188 103 ' 101 M. Monkenbusch T. J. Udovic and Q. Z. Huang Management System for the NSE Y. T. Cheng Spectrometer Supermirror Tests Slow Motion in Bulk-Glass Forming Evaluation of a Beryllium Single Osmic and Mica 102 102 102 Zr Ti CU Ni Be D. B. Fulford Crystal as a Monochromator K. T. Forstner and C. F. Majkrzak 46 8 82 7 5 10 27. 5 102 18S 153 Design of the Disk Chopper for'DARTS" The Perfect Crystal SANS Diffractome- A. Meyer , J. Wuttke , 153 65 102 W. Petry and H. Schober Spectrometer P. C. Brand and eter

1 102 ' 188 188102 102 C. Brocker T. " Structural Ordering in LaD W. Gnaupel-Herold J. G. Barker , M. Agamalian and 3i 102 102 102 188 Design of the Filter Analyzer The Filter Analyzer Spectrometer C. J. Glinka T. J. Udovic , Q. Z. Huang and 102 Spectrometer 102 197 Performance Tests of the Phase Space J. J. Rush D. A. Neumann , P. Papanek , 102 102 197 102 Transform Chopper on NG-2 D. J. Pierce , R. Christman and J. E. Fischer , J. J. Rush Structure and Dynamics of Amorphous , 102 197 175 102 102 J. T. L. Klein P. Carbon Kenney M. and A. C. Cheetham M. Gehring , D. A. Neumann 206 102 102 ' 197 and C. Karmonik P. Papanek Design and Performance Testing of The High Flux Backscattering , 102 W. A. Kamitakahara and the DCS Data Acquisition System Spectrometer (HFBS) SANS Polarization Analysis with 197 Electronics 102 102 Nuclear-Spin-Polarized 3 He J. E. Fischer R. M. Dimeo , D. A. Neumann , 102 59 206 188 102 107 107 J. B. Ziegler . J. Raebiger C. Karmonik , A. Meyer and T. R. Gentile , G. L. Jones Structure and Dynamics of Hydrogen , , 102 102 102 107 102 P. Klosowski N. P. A. K. C. Maliszewskyj M. Gehring , J. G. Barker Thompson , 102 102 102 124 102 and H. Layer Hydrogen Cold Source Development C. J. Glinka , B. Hammouda and S. A. FitzGerald . T. Yildirim , 102 102 Design and Testing of Vertically 102 102 J. W. Lynn L. J. Santodonato R. E. Williams , P. A. Kopetka , 102 102 Polarized Heusler Alloy Monochrometer/ 102 Search for Effects on Neutron Trans- D. A. Neumann , J. R. D. Copley , and J. M. Rowe 102 5 Analyzer mission to Multiple Reflection by J.J. Rush andF. Trouw In-Situ Real-Time Neutron Beam due 102 102 J. Glass Capillary Walls Structure and Dynamics of Hydrogen W. Lynn , J. A. Borchers and Imaging

102 22 - 24 K. T. Forstner 102 R. E. Beneson in Na C K. T. Fortner and , x M 22 102 124 102 Design of the Perfect Crystal SANS 102 H. H. Chen-Mayer and J. W. Lynn . T. Maliszewskyj S. A. FitzGerald Yildirim , N. C. 102 Diffractometer Spin Echo Supermirror Development L. J. Santodonato and Installation and Testing of the New 102 102 102 102 102 D. A. Neumann J. J. Mover and J. T. Kenney Thermal Beam Tube Shutter Design N. Rosov and C. F. Majkrzak Structure and Dynamics of an Development and Design of the Next- Using a Remote Actuated Cast System Supermirror Reflectivity Measure- Ultrahard Carbon Generation Triple-Axis Spectrometer 102 188102 ments J. J. Moyer , C. W. Wrenn , 102 188 102 188102 102 102 102 , P. , F. Majkrzak W. A. Kamitakahara C. W. Wrenn M. Murbach C. Brand A. W. Clarkson , C. , , 102 3 64 102 102 102 102

S. F. Trevino and S. G. Buga P. C. Brand and J. W. Lynn G. M. Baltic , D. L. Clem , TANQENS-A New Utility for the 102 102 Structure of the Ruddlesdon-Popper, Development and Installation of a M. J. Rinehart and S. Slifer Analysis of Quasiolate Neutron (Ln,Ca) Mn 0 Series Leak-Tight, Top-Loading, Horizontal Installation of a New Heusler Alloy Scattering Data n+1 n 3n+1 102 (Ln = Lanthanide) Field Superconducting Magnet Polarizing Analyzer for BT-2 T. Yildirim

140 140 102 ' 88 102 102 102 M. Green and J. Waldron D. C. Dender and R. W. Erwin K. T. Forstner , J. A. Borchers 102 Vibrational Densitites of States for Development and Installation of a and J. W. Lynn Cubic and Hexagonal Boron Nitride Radial Collimator and Horizontally Installation of Dedicated Crystal NEUTRON PHYSICS W. A. Kamitakahara 102 Focussed Pb Analyzer for BT-2 Alignment Spectrometer at BT-7 , Accurate Determination of Neutron 102 46 102 102 Beamline for Construction of FANS D. A. , G. Doll J. G. LaRock and A. W. Carkson Neumann , Capture Flux 46 1 Double Focusing Copper B Sweeting and A. W. Moore Development and Testing of Fe/Si 107 107 M. S. Dewey , M. Arif Monochromator , The Vibrational Isocoordinate Rule in Supermirror Plates for the NSE 107 80 D. Gilliam , G. L. M. Greene , 102 Se-As-Ge Glasses Analyzer K. T. Forstner and 56 62 W. M. , J. Pauwels and 102 Snow 126 126 102 188102 A. W. Clarkson 85 B. Effey , R. L Cappelletti and N. Rosov , S. Rathgeber , R. Scott 102 102 129 Installation of the Sample Chamber, W. A. Kamitakahara C. F. Majkrzak and J. L. Wood Benchmark Measurements and Flight Chamber, and Detector Development of a Radially-Focussed Calculations of Neutron Transport for Assembly the DCS 107 107 Polarizing Supermirror Analyzer Array D. Gilliam M. , M. S. Dewey ,

102 - 188 188 102 102 C. W. Brocker , 107 107 INSTRUMENTATION M. Murbach , P. C. Brand and J. S. Nico , C. M. Eisenhauer 102 102 , 102 M. J. Rinehart , G. M. Baltic and 107 6 N. Rosov J. A. Grundl and H. Gerstenberg Assembly and Testing of the Filter 102 S. Slifer Analyzer Spectrometer Development of a Robust Static Certified Neutron Fluence Standards Laue Focussing and its Applications A. 102 102 Thermal Switch for Fixed Sample from the Cavity Fission Source W. Clarkson , D. J. Pierce 76 76 , V. A. 102 102 V. K. Kvardakov Somenkov , 107 107 Environment Temperatures from A. and J. A. Grundl J. Reardon , S. Slifer and J. Adams 76 102

, J. Lynn S. S. Shilstein W. , G. M. Baltic 102 15 Kto 650 K 103 Defined-Geometry Alpha Counting 102 D. F. R. Mildner and L. Santodonato 107 107 Characterization of Fe/Si Reference 103 D. M. Gilliam and J. S. Nico H. H. Chen-Meyer Development of the HFBS Doppler Layers for Reflectivity Data Inversion Determination of the Neutron Lifetime MBE Chamber for in-situ Neutron 102 Drive C. F. Majkrzak 107 107 M. S. Dewey , J. S. Nico 102 188102 Scattering: Instrument Development , R. , A. Meyer 107 56 "DARTS": A M. Dimeo , New Neutron D. , M. 102 M. Gilliam W. Snow , 102 102 J. A. Dura R. Christman and P. C. Brand 80 56 Diffractometer for Residual Stress G. L. Greene and X. Fei Mica and Ge Reflectivity Measurement, Texture Determination, Development of Synthetic Mica 102 102 Highly Accurate Neutron Wavelength K. T. Forstner and C. F Majkrzak and Single Crystal Diffraction Monochromators Measurements 102 102 102 18 Monte Carlo Methods for Nuclear P. K. T. Forstner and L. Passell 107 114 C. Brand , H.J. Prask and , K. J. Coakley M. S. Dewey , 188102 Applications 107 T. Gnaupel-Herold Development of a Vacuum Rated W. M. Snow56 and M. Arif 102 Preamplifier/Amplifier/-Discriminator R. E. Williams Intercomparison of NIST and PNL for 3 Neutron Detectors Monte Carlo Simulation of the NIST He Calibration Facilities 102 J. B. Ziegler Cold Neutron Beamlines 107 107 , B.Schwartz A. K. Thompson R. ,

188 - 102 J. C. Cook 12 12 J. McDonald and M. Murphy

NIST CENTER FOR NEUTRON RESEARCH 33 LASER Polarization of 3 He for Neutron MATERIALS ANALYSIS High Sensitivity Gamma-Ray Spec- Neutron Transmission Through Spin Filters and Medical MRI trometry Tapered Capillaries A Bender-Focuser for Prompt Gamma 107 107 103 103 A. K. , T. R. Gentile R. M. Lindstrom H. Thompson , H. Chen-Mayer Activation Analysis , 107 07 56 103 S. , G. L. Jones' D. F. R. M. Dewey , 103 103 Homogeneity and Composition of Mildner and E. A. Mackey , H. H. Chen-Mayer 10749 56 , 220 E. E Wietfeldt , W. M. Snow 103 Small Solid Samples V. A. Sharov R. M. Lindstrom , D. F. R. 197 R. Rizi 103 and 103 103 213 R. Zeisler New Developments in Monitor Mildner , R. L. Paul , Q.-F Xiao Neutron Calorimetry 220 Activation and V. A. Sharov Hydrogen Detection in Industrial Analysis 56 56 103 103 , Z. Chowdhuri P. W. M. Snow , G. Lamaze , R. M. Lindstrom Analytical Applications of Cold Materials by Incoherent Neutron , 56 107 103 103 X. Fei and M. S. Dewey Neutrons Scattering E. A. Mackey and R. L, Paul Neutron Fluence Rate Measurements 103 103 103 New Developments in NDP H. H. Chen-Mayer , V. V. H. H. Chen-Mayer , R. Demiralp , 107 107 103 103 76 103 103 103 , J. S. Nico and Kvardakov D. F. R. Mildner P. D. M. Gilliam H. H. Chen-Mayer , G. Lamaze , R. R. Greenberg , G. P. Lamaze , 107 76 72 103 J. A. Adams 103 103 V. A. Somenkov and D. Kozlenko and J. K. Langland J. K. Langland , R. M. Lindstrom , 103 103 F. Neutron Interferometry and Optics E. A. Mackey , D. R. Mildner Improvements to INAA Methodology Quality Assurance for , Improvements 107 107 103 220 103 103 Arif L. R. L. Paul and V. A. Sharov D. A. NAA , D. Jacobson Becker , R. Demiralp M. , , 14 107 103 103 103 Clothier , A. K. R. R. Greenberg , R. M. A. R. Thompson , Application of Radioisotope-lnduced D. Becker , R. Demiralp , 192 192107 103 103 103 S. A. , A. loffe Lindstrom , E. A. R. R. Werner Mackey and Greenberg , , X-Ray Emission to the Identification of R. M. 185 194 103 103 103 A. , K. R. Zeisler Zeilinger Raum in Lindstrom , E. A. , Lead and Other Elements Ceramic Mackey and 194 194 103 B. Schillinger , C. Rausch and Glazes and Housewares Improvements to PGAA Methodology R. Zeisler 85 43 W. Richards D. L. Anderson and 43 103 Quality Assurance Programs D. L. Anderson , R. M. Lindstrom , 43 103 103 43 Neutron Radiography/Tomography W. C. Cunningham E. A. Mackey and R. L. Paul D. L. Anderson and 107 107 43 T. R. Gentile , M. Arif and Archeological Applications of NAA Lithium Migration in Electrochromic W. C. Cunningham 107 147 103 D. L. Jacobson R. Bishop and M. J. Blackman Thin Films Reactor Characterization for NAA Parity Non-Conserving Neutron Spin 103 103 103 Bromation in Breadmaking G. P. Lamaze , H. H. Chen-Mayer D. A. Becker , Rotation 43 144 163 W. C. Cunningham and M. Badding , A. Gerouk and Radionuclides in Foods 214 214 43 163 B. Heckel , D. Markoff R. Goldner 43 , C. R. Warner D. L. Anderson and 214 214 E. Adelberger , S. Penn and 43 Bio-Analytical and Specimen Bank Multielement Analysis of Foods and W. C. Cunningham 107 49 F E. Wietfeldi ' Related Materials by NAA Research Revalidation of Food SRMs 43 Quality Assurance Checks on Masses 103 113 D. L. Anderson and 43 R. R. Greenberg , G. V, Iyengar , D. L. Anderson and 43 and Impurities in Neutron Dosimeters 103 103 W. C. Cunningham 43 J. K. Langland , E, A, Mackey , W. C. Cunningham for NRC Reactor Pressure Vessel 103 103 B. J. Porter and R. Zeisler Neutron Absorption Measurements Size Distribution and Deposition of Embrittlement Surveillance Using Converging Certification of Standard Reference Beams to 107 107 Toxic Elements Lake Michigan, by J. A. Adams , D. M. Gilliam and 103 103 H. H. Chen-Mayer , E. A. Mackey Materials by Neutron Activation , 107 Size and by Source J. A. Grundl 103 103 Analysis D. F, R. Mildner and R. L. Paul 188 188 P. F. Caffrey and J, M. Ondov Response of Albedo Dosimeters 103 103 D. A, Becker , R. Demiralp Neutron Autoradiography of Paintings , Studies in Elemental Speciation Versus Distance from a Neutron R. R. 103 101 103 127 Greenberg , R. M. Y.-T Cheng and J. Olin 103 103 D, A. Becker , E. A. Mackey and Source 103 103 Lindstrom , E. A. Mackey and Neutron Spatial Distributions 103 107 Beam R. Zeisler R. B. Schwartz and 103 R. Zeisler Using Imaging Plate Technology 107 Test of a Novel High Sensitivity A. K. Thompson Characterization of Sources and 44 103 H. J. Bahre , H. H. Chen-Mayer , Neutron Detector Response of Albedo Neutron Fluxes of Particulate Pollutants 101103 103 Y.-T Cheng , D. F. R. Mildner 121 103 B. Feller , H. H. Chen-Mayer and Dosimeters as a Function of Angle Depositing to Great 220 Waters and V. A. Sharov 103 107 G. Lamaze R. B. Schwartz 188 188 P. F. Caffrey , A. E. Suarez and Neutron Depth Profiling of AIN Thin 188 Trace Elemental Characterization of Study of Time Reversal Invariance in J. M, Ondov Films Silicon Semiconductor Materials Neutron Beta Decay Characterization of Submicrometer 103 103 H. H. Chen-Mayer , G. P. Lamaze 103 217 169 D. A. Becker and R. M. J. Wilkerson , E. Wasserman 31 , Aerosol Particles and S. McGuire Lindstrom 103 107 169 188 188 J. S. Nico , R. G. H. Robertson , F. Heller-Zeisler J. M. , S. Ondov Neutron Depth Profiling of c-BN 169 195 103 S. Freedman , A. Garcia , and R. Zeisler 103 103 H. H. P. 23 23 Chen-Mayer , G. Lamaze T Chupp , K. Coulter , Determination of Hydrogen by PGAA 12 107 80 and L. Pilione M. S. Dewey , G. L. Greene , 103 R. R. Greenberg 107 169 , Nitrogen Profiling of Thin Titanium A. K. Thompson , B, Fujikawa , 103 103

R. M. Lindstrom , E, A. Mackey 107 56 107 Nitride Films L. , J. A. G. Jones Adams , 103 and R. L. Paul 10749 169 103 103 G. P. Lamaze , H. H, Chen-Mayer , E E. Wietfeldt , L. Using , 23 214 Determination of Phosphorus via 68 115 S. Hwang and T. Steiger N. Cox and E. B. Steel RNAA with Beta Counting Trapping of Ultra Cold Neutrons Neutron Focusing for Analytical 103 R. L. Paul 49 80 Chemistry J. Doyle , S. K. Lamoreaux M. , 48 80 Development of Radiochemical 103 103 H. Chen-Mayer , G. P. Lamaze , R. Golub , L. Greene G. , 107 49 Separation for NAA 103 103 J. K. Langland , R. M. Lindstrom , M. S. Dewey , P. R. Huffman , 103 103 103 103 49 49 D. A. Becker , R. R. Greenberg E. A. Mackey , D. F. R. Mildner , C. R. Brome , C. E. H. Mattoni , 103 49 and E. A. Mackey 220 115 J. Butterworth and V. A. Sharov and J. R, Swider D. N. McKinsey 49 Evaluation of Accuracy and Precision Neutron Distribution Measurements in INAA of Botanical Materials Utilization of the Materials Dosimetry by Neutron Induced Autoradiography D. A. Becker103 213 213 Reference Facility-Tests of New IRMM Z. En , J. S. Brenizer and 237 238 103 Np and U Fast Neutron Evaluation of Errors and Interferences D. A. Becker Dosimeters in NAA Neutron Dosimetry for Instrument 107 107 103 147

J. A. , J. A. Grundl D. A. Becker , M. J. Blackman Development Adams , , 107 107 103 103 Eisenhauer , D. Gilliam R. C. M. M. R. Greenberg , R. M. Lindstrom 23 103 103 P. R. M. Lindstrom R. Zeisler and Simpson and Neutron Scattering Effects on PGAA Focusing Methods for Radiography 103 R. R. Greenberg , R. M. and Topography 103 103 Lindstrom , E. A. Mackey , H. H. 103 103 213 Chen-Mayer , R. L. Paul and M. Blaauw 103 76 D. F. R, Mildner , K. M. Podurets 220 76 V. A. Sharov and S. S. Shilstein

64 RESEARCH TITILES AFFILIATIONS: 55 Imperial College, United Kingdom 11 NIST, Polymers Division 72 University of California at Riverside 56 Indiana University 12 NIST, Semiconductor Electronicis 73 University of California at San Diego I Advanced Ceramics Corporation 57 Insitute of Physics, Peoples Division 74 University of California at San : Advanced Institute of Science and Republic of China 13 NIST, Standard Reference Materials Francisco Technology, Japan 58 Institut fur Physikalische Chemie, Program 75 University of California at Santa 3 AEA Technology, United Kingdom 14 Germany NIST, Statistical Engineering Division Barbara 4 American Manufacturing Technology 59 15 76 Institut fur Festkorperforschung, NIST, Surface and Microanalysis University of Chicago 5 Argonne National Laboratory Germany Science Division 77 University of Connecticut 6 Armed Forces Radiobiology 60 16 Institute for Chemical Research, NIST, Thermophysics Division 78 University of Cincinnati Research Institute 17 Japan North Carolina State University 79 University of Delaware 7 Medical Research Institute Army 61 18 Institute for Energiteknikk, Norway Northeastern University 80 University of Florida 8 Research Laboratory Army 62 19 Institute for Reference Materials and Northern Illinois University 81 University of Grenoble, France 9 Army Research Office Measurements, Belgium 20 Northwestern University 82 10 University of Guelph, Canada Australian Geological Survey, 63 Institute for Special Materials, Italy 21 83 Nova Scientific University of Houston Australia 64 Institute for Superhard and Novel 22 84 Oak Ridge Institute for Science and University of Illinois II Australian Nuclear Science and Carbon Materials, Russia Education 85 University of Innsbruck, Austria Technology Organization, Australia 65 Institut Laue-Langevin, France 23 86 12 Oak Ridge National Laboratory University of Iowa Battelle Pacific Northwest 66 Institute of Crystallography, Russia 24 87 Laboratory Oberlin College University of Manitoba 67 Institute of Physical and Chemical 25 13 Ohio State University 88 Belarus Academy of Sciences, University of Maryland at College Research, Japan 26 Belarus Ohio University Park 68 Intel Corporation 27 89 14 Bethany College Olin Conservation Incorporated University of Massachusetts 69 Iowa State University 28 15 Bilkent University, Turkey Oregon State University University of Michigan 70 John Deere Corporation 29 16 Birbeck College, United Kingdom OSMIC, Incorporated University of Minnesota 71 Johns Hopkins University 30 17 Boeing Helicopter Group Oxford University, United Kingdom University of Missouri at Columbia 72 Joint Institute of Nuclear Research, 31 18 Brookhaven National Laboratory Pacific Lutheran University University of Missouri-Rolla Russia 32 19 Paul Scherrer Institute, Switzerland University of Munich, Germany Brown University 73 Karlsruhe Nuclear Research Center, 33 20 California Institute of Technology Pennsylvania State University University of Notre Dame Germany 34 21 Cambridge University, United Philips Research Laboratories, The University of Oklahoma 74 Kent State University Netherlands of Kingdom 75 University Pennsylvania Kiel University, Germany 35 22 Polytechnic University la Republica Carnegie Mellon University 76 Universidad de Kurchatov Institute, Russia 36 23 Princeton University Argentina Center for Advanced Research in 77 Kyunghee University 37 Biotechnology Queen's University, Canada 199 University of Rhode Island 78 Kyoto University, Japan 38 24 d'Etudes Nucleaires de Rice University 200 Universtat des Saarlandes, Germany Centre 79 Lehigh University 39 Grenoble, France Royal Institute of Technology, 201 University of Stuttgart, Germany 80 25 Los Alamos National Laboratory 202 Centre National de la Recherche Sweden University of Surrey, United 81 Los Alamos Neutron Science Center 40 Scientifique, France Royal Institution, United Kingdom Kingdom 82 26 Lucent Technologies, Bell 41 Centra Brasileiro de Pesquisas Ruhr University, Germany 203 University of Sussex, United Laboratories Fisicas, Brazil 42 Russian Academy of Sciences, Kingdom 83 Massachusetts Institute of Chalk River Laboratories, Canada Russia 204 University of Sydney, Australia Technology 43 City College of New York Rutgers University 205 University of Tennessee 84 Max-Planck Institut, Germany 44 College of William and Mary SAGE Electrochromics 206 University of Texas 85 McClellan Nuclear Radiation Center 45 Commissariat d'Energie Atomique, Seoul National University 207 University of Tokyo, Japan 86 McGill University, Canada 46 208 France Sid Richardson Carbon Company University of Trento, Italy 87 McMaster University, Canada 47 Cornell University Smithsonian Institute 209 Unversity of Uppsala 88 Metal Physics Institute, Russia 48 Cracow University of Technology, Stanford Linear Accelerator 210 University of Uruguay 89 Michigan Molecular Institute 49 Poland Stanford University 211 University of Utah 90 Sciences, Czech Michigan State University 50 212 Czech Academy of State University of New York, Stony University of Vermont Republic 91 Moscow Steel and Alloys Institute, Brook 213 University of Virginia Davidson Chemical Company Russia 51 Tata Institute of Fundamental 214 University of Washington Dupont Company 92 National Aeronautics and Space Research, India 215 University of Waterloo, Canada Johnson Space Dupont Experimental Station Administration, 52 TEC 216 Walter Reed Army Institute of Center Dupont Marshall Laboratory "Technical University Munchen, Research 93 National Central University, Taiwan Eastman Kodak Germany 217 94 Washington University National Institute for Research in 54 Eidgenossische Technische Technobiochip 218 West Virginia University Inorganic Materials, Japan Hochschule, Switzerland 55 Tel Aviv University, Israel 219 Worcester Polytechnic Institute 95 Institute of Health National 56 ExxonMobil Research and Texaco Research and Development 220 96 X-Ray Optical Systems National Sun Yat-Sen University, Engineering Company Center Taiwan Federal Highway Administration "Texas Materials Institute 97 National Taiwan University, Taiwan Florida State University 58 Thomas Jefferson High School 98 National Tsing Hua University, Food and Drug Administration 59 Tohoku University, Japan Taiwan Fuji Medical Systems USA, 60 Toyo University, Japan 99 Naval Research Laboratory Incorporated 61 Tokyo University, Japan 100 NEC Research Institute Incorporated General Electric Corporate Research 62 Trinity College 101 Neutek Incorporated General Motors Research and 63 Tufts University 102 NIST Center for Neutron Research Development Center 64 U. S. Department of Transporation 103 Chemistry Division George University NIST, Analytical Washington 65 University of Aachen, Germany 104 NIST, Biotechnology Division Hahn-Meitner Institute, Germany 66 University of Akron 105 NIST, Ceramics Division Harvard University 67 Universitat Autonoma de Barcelona, 106 NIST, Electron and Optical Physics Hongik University, South Korea Spain Division Howard University 68 Universita di Brescia, Italy 107 NIST, Ionizing Radiation Division IBM, Almaden 69 University of California at Berkeley 108 NIST, Materials Reliability Division Idaho National Engineering and 70 University of California at Davis 109 NIST, Materials Reliability Division Environment Laboratory 71 University of California at Irvine 110 Imaging and Sensing Technology NIST, Metallurgy Division NIST CENTER FOR NEUTRON RESEARCH 65 PUBLICATIONS

Abdurashitov, J. N., Gavrin, V N., Girin, S. V, Gorbachev, V V, Ibragimova, Balsara, N. P., "Multicomponent Polyolefin Blends with Ordered and Disordered

T. V, Kalikhov, A.V., Khairnasov, N. G., Knodel, V N., Kornoukhov, Microstructures," Curr. Opin. Sid. St. Mtls. Sci. 3, 589 (1998).

V N., Mirmov, I. N., Shikhin, A. A., Verentenkin, E. P., Vermul, V. M., Yants, Balsara, N. P., Lefebvre. A. A., Lee, J. H., Lin, C. C, Hammouda, B., "The J., V E., Zatsepin, G. T. , Khomyakov, Y S., Zvonarev, A. V , Bowles, T. Search for a Model Polymer Blend," AIChE J. 44, 2515 (1998). Nico, J. S., Teasdale, W. A., Wark, D. L„ Cherry, M. L., Karaulov, V. N., Bandyopadhyay, S., Klein, M. L., Martyna, G. L, Tarek, M., "Molecular Levitin, V. L., Maev, P. I., Nazarenko, P. I., Shkol'nik, V S., Skorikov, N.V., Dynamics Studies of the Hexagonal Mesophase of Sodium Dodecylsulfate in Cleveland, B. T., Daily, T., Davis, R., Lande, K., Lee, C. K., Wildenhain, Aqueous Solution," Mol. Phys. 95, 377 (1998). 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 Bandyopadhyay, S., Tarek, M., Klein, M. L., "Nature of Lipid-DNA Interactions:

Source," Phys. Rev. C 59, 2246 (1999). A Molecular Dynamics Study of DNA Intercalated into a Lipid Bilayer," J. Phys. Chem., in press.

Abdurashitov, J. N., Gavrin, V N., Girin, S. V , Gorbachev, V V , Ibragimova,

T. Kalikhov, A.V., Khairnasov, N. Knodel, N., I. N., Bandyopadhyay, S., Tarek, M., Lynch, M. L., Klein, M. L., "C EO,/Water V, G, V Mirmov, 12 Shikhin, A. A., Verentenkin, E. P., Vermul, V. M., Yants, V. E., Zatsepin, System: A Molecular Dynamics Study," Langmuir, in press.

L., L., G. T., Bowles, T. J., Teasdale, W. A., Wark, D. Cherry, M. Nico, Balizer, E., DeReggi, A. S., Neumann, D. A., Bateman, F, "Polarization J. S., Cleveland, B. T., Davis, R., Lande, K., Wildenhain, P. S., Elliott, and Structural Transitions of Irradiated Vinylidene Fluoride-Trifluorethylene

S. R., Wilkerson, J. E, "Measurement of the Solar Neutrino Capture Rate Copolymer," in 1999 Conference on Electrical Insulation and Dielectric with Gallium Metal," Phys. Rev. 60, 55801 (1999). C Phenomena, Vol. 1, (IEEE Publ. No 99CH36319, 1999), p. 104.

Abdurashitov, J. N., Gavrin, N., Girin, S. Gorbachev, Ibragimova, V V , V V , Bao, W, Broholm, C, Aeppli, G, Carter, S. A., Dai, P., Rosenbaum, T.

T. Khairnasov, I. V, Kalikhov, A.V., N. G„ Knodel, V N„ Mirmov, N„ F, Honig, J. M., Metcalf, P., Trevino, S. F, "Magnetic Correlations and Shikhin, A. A., Verentenkin, E. P., Vermul, V. M., Yants, V. E., Zatsepin, Quantum Criticality in the Insulating Antiferromagnetic, Insulating Spin G. T„ Bowles, T. J., Teasdale, W. A., Wark, D. L., Cherry, M. L., Nico, Liquid, Renormalized Fermi Liquid, and Metallic Antiferromagnetic Phases J. S., Cleveland, B. T, Davis, R., Lande, K„ Wildenhain, P. S., Elliott, of the Mott System V 0,," Phys. Rev. B 58, 12727 (1999). 2 S. R., Wilkerson, J. E, "Measurement of the Solar Neutrino Capture Rate Barilo, S. N., Bychkov, G. L., Kurnevich, L. A., by SAGE and Implications for Neutrino Oscillations in Vacuum," Phys. Rev. J. L., Shiryaev, S. V, Lynn, W , Vasiliu-Doloc, "Seeded Growth from Flux Lett., in press. and Neutron Study of La, Ba MnO, (0.2 < x < 0.5) Single Crystals," J. x x Adams, J. M., "Results from the NIST Round Robin Test of Fissionable Cryst. Growth, in press. Dosimeters in a Reactor Leakage Spectrum," in Reactor Dosimetry, edited Barilo, S. N., Shiryaev, S. V, Gatalskaya, V. I., Lynn, J. W, Baran, M., by J. G. Williams, D. W. Vehar, F H. Ruddy, and D. M. Gilliam, in press. Szymczak, H., Szymczak, R., Dew-Hughes, D., "Scaling of Magnetization Aeppli, G, Bishop, D. J., Broholm, C, Bucher, E„ Cheong, S. W, Dai, P., Fisk, and Some Basic Parameters of Ba, K BiO, Superconductors near T," Xx x +y+ Z., Haysedn, S. M., Kleiman, R., Mason, T. E., Mook, H. A., Perring, T. Phys. Rev. B 58, 12355 (1998). ' * G, Schoeder, A., "Neutron Scattering and the Search for Mechanisms of Barilo, S. N., Shiryaev, S.V., Gatalskaya, V I., Zhigunov, D. I., Pushkarev, A. Superconductivity," Physica C 318, 9 (1999). V, Fedotova, V. V, Szymczak, H., Szymczak, R., Baran, M., Lynn, J. W,

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Ivkov, R., Gehring, P. M., Maliszewskyj, N. C, Krishnamoorti, R., "Structure Hawaii, A. I., Adams, J. M., "A Method for the Minimization of the HPGe and Dynamics of Polymers in Confined Geometries: Neutron Studies Detector Efficiency Bias in the Measurement of the Spectral Index," in of Intercalated Clay-Polymer Nanocomposites," in Proceedings of Society Reactor Dosimetry, edited by J. G. Williams, D. W. Vehar, F. H. Ruddy and Plastics Engineers—ANTEC '99, in press. D. M. Gilliam, in press. Izumi, F, Ikeda, T, "A Rietveld-Analysis Program RIETAN-98 and its Hedrick, J. L„ Carter, K. R., Labadie, J. W., Miller, R. D., Volksen, W, Hawker, Applications to Zeolites," Proceedings of the Sixth European Conference on C. J., Yoon. D. Y, Russell, T. P, McGrath, J. E., Briber, R. M., "Nanoporous Powder Diffraction, Materials Science Forum, in press. Polyimides," Progr. Polyimide Chem. II 141, 1 (1999). Jacobson, D. L., Arif, M., Bergmann, L., Ioffe, A., "Development of the Neutron Heller, W. T, Waring, A. J., Lehrer, R. I., Huang, H. W, "Multiple States of Phase Contrast Imaging Technique and its Application in Materials Science Beta-Sheet Peptide Protegrin in Lipid Bilayers," Biochem. 37, 17331 (1998). Research," in Proceedings, SPIE Conference, Denver, July 17-23, 1999, in Heller-Zeisler, S., Ondov, J., Zeisler, R., "Collection and Characterization of a press. Bulk PM, Air Particulate Matter Material for Use in Reference Materials," 5 J. Bio. Trace Ele. Res. 71, 195 (1999).

NIST CENTER FOR NEUTRON RESEARCH 69 Jeon, H. S., Lee, J. H., Balsara, N. P., Newstein, M. C, "An Experimental Kilic, C, Yildirim, T, Mehrez, H., Ciraci, S., "A First-Principles Study of the

Study of the Thermodynamics of Multi-Component Polyolefin Blends with Structure and Dynamics of C H Si H and Ge H Molecules," J. Phys. g 8 , 8 g g 8 Ordered and Disordered Phases," Macromol. 31, 3340 (1998). Chem., in press.

Jeon, H. S., Lee, J. H., Balsara, N. P., "Predicting the Thermodynamics of Kim, Y. J., Aharony, A., Birgeneau, R. J., Chou, F. C, Entin-Wohlman, O.,

Multi-Component Polymer Blends from Measurements on Two-Component Erwin, R. W., Greven, M., Harris, A. B., Kastner, M. A., Korenblit, I.,

Systems," Macromol. 31, 3328 (1998). Ya, Lee, Y. S., Shirane, G., "Ordering due to Quantum Fluctuations in Phys. Rev. Lett. 83, 852 (1999). Johnson, G. M., Reisner, B. A., Tripaathi, A., Corbin, D. R.. Toby, B. H., Parise, Sr^CUjOPj,"

J. B., "Flexibility and Cation Distribution upon Lithium Exchange of AlSi- Kimura, H., Hirota, K., Matsushita, H., Yamada, K., Endoh, Y, Lee, S. -H.,

and AlGe-RHO Framework Materials," Chem. Mat. 11, 2780 (1999). Majkrzak, C. F, Erwin, R. W., Shirane, G., Greven, M., Lee, Y. S.,

Kastner, M. A., Birgeneau, R. J., "Neutron Scattering Study of Static Jones, G. L., Adams, J. M., Anaya, J. M„ Bowles, T. J., Chupp, T. E., Coulter, Antiferromagnetic Correlations in La, Sr Cu Zn 0 ," Phys. Rev. B 59, 6517 K. P., Dewey, M. S., Freedman, S. J., Fujikawa, B. K., Garcia, A., Greene, G. { 4 (1999). L., Hwang, S. -R., Lising, L. J., Nico, J. S., Robertson, R. G. H., Steiger, T.

D., Teasdale, W. A., Thompson, A. K., Wietfeldt, F. E., and Wilkerson, J. F, Kitade, S., Ochiai, N., Takahashi, Y, Noda, I., Matsushita, Y, Karim, A.,

"Time Reversal in Polarized Neutron Decay - The EMIT Experiment," Nucl. Nakatani, A. I., Kim, H., Han, C. C, "Lamellar Orientation of Diblock Instram. Meth. A, in press. Copolymer Solutions Under Steady Shear Flow," Macromol. 31, 8083 (1998). Jones, G. L., Gentile, T. R., Thompson, A. K., Chowdhuri, Z., Dewey, M. S.,

Snow, W. M.. Wietfeldt, F. E., "Test of 'He -based Neutron Polarizers at Kline, S. R., "Polymerization of Rod-Like Micelles," Langmuir 15, 2726 (1999). N1ST," Nucl. Instrum. Meth. A, in press. Kline, S. R., "Structural Evolution During Micelle Polymerization," J. Appl.

Jones, R. L., Kumar, S. K., Ho, D. L., Briber, R. M., Russell, T. P., "Chain Crystallogr, in press.

Conformation in Ultrathin Polymer Films," Nature 400, 146 (1999). Kmety, C. R., Manson, J. L., Huang, Q., Lynn, J. W„ Erwin, R. W., "Collinear

Jolly, M., Bender, J., Carlson, J. D., "Properties and Applications of Commercial Ferromagnetism and Spin Orientation in the Molecule-Based Magnets Magnetorheological Fluids," Proc. SPIE 3327, 262 (1998). M[N(CN) (M = Co,Ni)," Phys. Rev. B 60, 60 (1999). 2 ] 2

Kaduk, J. A., Wong-Ng, W., Greenwood, W., Dillingham, J., Toby, B. H., Kmety, C. R., Manson, J. L., Huang, Q., Lynn, J. W., Erwin, R. W., Miller,

"Crystal Structures and Reference Powder Patterns of BaR,ZnO (R = La, J. S., Epstein, A. J., "Magnetic Phase Transitions in M"[N(CN),L," J. Mol.

Nd, Sm, Eu, Gd, Dy, Ho, Y, ER and Tm)," J. Res. Natl. Inst. Stand. 140, Liq. Cryst., in press. 147 (1999). Kossuth, M. B., Morse, D. C, Bates, F. S., "Viscoelastic Behavior of Cubic

Kamitakahara, W. A., Wada, N., "Dynamics of Intercalated Water Molecules in Phases in Block Copolymer Melts," J. Rheology 43, 167 (1999). Synthetic Layered Silicates," Mol. Cryst. Liq. Cryst., in press. Koubi, L., Tarek, M., Klein, M. L., Scharf, D., "Distribution of Volatile General

Karen, P., Kjekshus, A., Huang, Q., Karen, V. L., "The Crystal Structure of Anesthetics in a Model Membrane from Molecular Dynamics Simulation,"

Magnesium Dicarbide," J. Alloys Compnds. 282, 72 (1999). Biophy. J., in press.

Karim, A., "Interactions of Polymers with Fillers and Nanocomposites, NIST Krishnamoorti, R., Silva, A. S., Modi, M. A., Hammouda, B., "Small Angle June 18-19, 1998," NISTIR 6312. Neutron Scattering Study of a Cylinder to Sphere Order-Order Transition in Block Copolymers," Macromol, in press. Kasper, N. V., Troyanchuk, I. O., Khalyavin, D. D., Hamad, N., Haupt,

L., Frobel, P., Barner, K., Gmelin, E., Huang, Q., Lynn, J. W., "Effect Krone, C. A., Robisch, P. A„ Tilbury, K. L., Stein, J. E„ Mackey, E. A., Becker, of Oxygen Content and Oxygen Vacancy Ordering on Properties of P R., O'Hara, T. M., Philo, L. M., "Elements in Liver Tissues of Bowhead TbBaCo 0 (x 0.5) Perovskites," Phys. Status Solidi B 215, 697 (1999). Whales (Balaena mysticetus)," Marine Mammal Sci. 15, 123 (1999). 2 x 6 6

Kent, M. S., Majewski, J„ Smith, G. S., Lee, L. T, Satija, S. K., "Tethered Lamaze, G. P., Chen-Mayer, H. H., "Nitrogen Analysis in Thin Films Using Chains in Poor Solvent Conditions: An Experimental Study Involving Cold Neutron Depth Profiling," in Proceedings of the 9* International

Angmuir Diblock Copolymer Monolayers," J. Chem. Phys. 110, 3553 Conference on Modern Materials and Technologies, edited by P. Vincenzini,

(1999). (TECHNA, Faenza, Italy), in press.

Kent, M. S„ McNamara, W. F, Baca, P. M., Wright, W., Domeier, L. A., Wong, Lamaze, G. P., Chen-Mayer, H. H, Badding, M., Laby, L., "In Situ

A. P. Y., Wu, W. L., "Water Adsorption in Interfacial Silane Layers by Measurements of Lithium Movement in Thin Film Electrochromic Coatings

Neutron Reflection: II. Epoxy + Silane on Silicon Wafers," J. Adhesion 69, Using Cold Neutron Depth Profiling," J. Surf. Interface Anal. 27, 644 (1999). 139(1999). Lamaze, G. P., Chen-Mayer, H. H., Langland, J. K., "Recent Developments in

Kerch, H. M., Long, G. G., Krueger, S., Allen, A. J., Gerhardt, R., Cosandey, Neutron Depth Profiling at NIST," in Proceedings of the 1998 International F, "Characterization of Porosity Over Many Length Scales: Application of Conference on Characterization and Metrology for Ultra Large Scale

Colloidal Gels," J. Mater. Res. 14, 1444 (1999). 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, Kernick III, W. A„ Wagner, N. J., "The Role of LCP Pheology on the Evolving 1998), p. 883. Microstructure of Immiscible Blends Containning LCPs," J. Rheol. 43, 521 (1999). Lee, S.-H., Broholm, C, Aeppli, G., Cheong, S.-W., "Short-Range Spin Correlations in a Geometrically Frustrated Magnet, SrCr Ga 0 ," in . Kesler, O., Matejicek, J., Sampath, S., Suresh, S., T, Brand, P. C, Prask, H. J., 9p ]2 9f 19 Proceedings the International Workshop on Cold Neutron Utdization "Measurement of Residual Stress in Plasma-Sprayed Metallic, Ceramic, and of (Korean Atomic Energy Institute, Taejon, South Korea), in press. Composite Coatings," J. Mater. Sci. Eng. 257, 215 (1998).

Lee, S.-H., Broholm, C, Cheong, S.-W, Kim, T. H., Ratcliff II, W, "Local Kessler, E. G., Dewey, M. S., Deslattes, R. D., Henins, A., Borner, H. G., Spin Resonance and Spin-Peirls Like Phase Transition in the Geometrically Jentschel, M., Doll, C, Lehmann, H., "The Deuteron Binding Energy and Frustrated Antiferromagnet ZnCr 0 ," Phys. Rev. Lett., in press. the Neutron Mass," Phys. Rev. Lett. 255, 221 (1999). 2 4 Lee, S.-H., Majkrzak, C. F, "A New Technique for Polarized Neutron Kholifah, P., Erwin, R. W., Lynn, J. W., Huang, Q., Batlogg, B., Cava, R. J., Diffraction," Physica B 268, 341 (1999). "The Magnetic and Electronic Characterization of Quasi-One-Dimensional

La RuO ," Phys. Rev. B 60, 9573 (1999). Lee, S.-H., Majkrzak, C. F, "Polarized Neutron Diffraction with an Area- 3 ? Sensitive Detector," J. Neutron Res. 7, 131 (1999).

7 D PUBLICATIONS A

Lee, S.-H., Majkrzak, C. E, Sinha, S. K., Stassis, C, Kawano, H., Lander, G. Lynn, J. W. "Magnetic in in Research, , Neutron Scattering," Methods Materials

H., Brown. P. J., Fong, H. F. Cheong, S. W. . Matsushita, H., Yamada, K., edited by Kaufman (lohn Wiley & Sons), in press. Endoh, Y., "Search for Orbital Moments in Underdoped Cuprate Metals— J. Lynn, W , "Spin Dynamics of Magnetoresistive Oxides," in The Physics of Sisyphian Task," Phys. Rev. B 60, 10405 (1999). Manganites, edited by Kaplan and Mahanti (Plenum Publishing, 1999), p.

S., Birgeneau, R. I, Kastner, M. A., Endoh, Wakimoto, S., Lee, Y. Y , Yamada, 149. K., Erwin, R. W., Lee, S. H.. Shirane, G., "Neutron Scattering Study of Spin J. Lynn, W , "Spin Dynamics of the Magnetoresistive Oxides," Int. J. Mod. Phys. Density Wave Order in the Superconducting State of Excess-Oxygen-Doped 12, 3355 (1998). LajCuO^," Phys. Rev. B 60, 3643 ( 1 999). Lynn, I. W, Rosov, N., Barilo, S. N, Kurnevitch, L., Zhokhov, A., "Pr Magnetic Lefebrve, A. A., Balsara, N. P., Hammouda, B., Jeon, H. S., La, R. J., Lee, J. Order and Spin Dynamics in the Cuprates," Chin. J. Phys., in press. H., "Initial Stages of Nucleation During Liquid-Liquid Phase Separation in

Lynn, J. W. , Skanthakumar, S., "Neutron Scattering Studies of Rare Earth Polymer Blends," J. Chem. Phys. Ill , 6082 (1999). Magnetic Ordering," Handbook on the Physics and Chemistry of Rare Lefebrve, A. A., Lee, J. H., Balsara, N. P., Hammouda, B.. Krishnamoorti, R., Earths, edited by K. A. Gschneider, Jr., L. Eyring, M. B. Maple (Elsevier "Relationship Between Internal Energy and Volume Change on Mixing in Science), in press. Pressurized Polymer Blends," Macromol. 32, 5460 (1999). Mackey, E. A., Demiralp, R., Fitzpatrick, K. A., Porter, B. J., Wise, S. A., Lefebvre, K. K., Lee, J. H., Balsara, N. P., Hammouda, B., Krishnamoorti, R., Greenberg, R. R., "Quality Assurance in Analysis of Cryogenically Stored Kumar, S., "Relationship Between Internal Energy and Volume Change of Specimens from the NIST National Biomonitoring Specimen Bank," Sci. Mixing in Pressurized Polymer Blends," Macromol. 32, 5460 (1999). Total Environ. 226, 165 (1999).

Leheny, R.L., Christianson, R. J., Birgeneau, R. J., Erwin, R. W, "Spin Magid, L. J., "The Surfactant-Polyelectrolyte Analogy," J. Phys. Chem. B. 102, Correlations in an Isotropic Spin - 5/2 Two-Dimensional Antiferromagnetic," 4064 (1998). Phys. Rev. Lett. 82,418 (1999). Magid. L. J., Han, Z., Li, Z., Butler, P.D., "Tuning Microstructure of Cationic Leheny, R. L., Nagel, S. R., "Dielectric Susecptibility Studies of the High- Micelles on Multiple Length Scales: The Role of Electrostatics and Specific Frequency Shape of the Primary Relaxation in Supercooled Liquids," J. Non- Ion Binding," Langmuir, in press. Cryst. Solids 235, 278 (1998). Majkrzak, C. F, "Neutron Applications in Materials Science and Engineering,"

Li, W.-H., Wu, S. Y , Lee, K. C, Lynn, J. W. , "Magnetic Ordering of Mn in J. Neut. Res., in press. Ca-Doped NdMnO,," Physica B, in press. Majkrzak, C. F, "Neutron Reflectometry Studies of Thin Films and Multilayered Li, W.-H.. Wu, S. Y, Lee, K. C, Lynn, J. W, Liu, R. S., Wu, J. B., Huang, C. Materials," Acta Physica Polonica A 96, 8 1 ( 1 999). Y, "Magnetic Order and Spin Reorientation in Nd Ca MnO ," J. Appl. 045 055 3 Majkrzak, C. F, Berk., N. F, "Exact Determination of the Phase in Neutron Phys. 85, 5588 (1999). Reflectometry by Variation of the Surrounding Media," Phys. Rev. B 58, Li, W.-H, Wu, S. Y, Lin, Y. C, Lee, K. C, Lynn, J. W, Weng, S. S„ Hong, I. P., R15416 (1998). ," Lin, J. -Y, Yang, H. D., "Magnetic Ordering in Double-Chain PrBa,Cu O 4 g Majkrzak, C. F, Berk, N. F, "Experimental Demonstration of Phase Phys. Rev. B 60, 4212 (1999). Determination in Neutron Reflectometry by Variation of the Surrounding Li, Z. G., Harlow, R. L., Foris, C. M., Li, H., Ma, P., Vickery, R. D., Maunn, Media," Physica B, in press. M. B., Toby, B. H., "Polymorph Determination for the GPIIb/IIIa Antagonist, Majkrzak, C. F, Berk, N. F, "Inverting Neutron Reflectivity from Layered Film Roxifiban, Using a Combination of Electron Diffraction and Synchrotron Structures Using Polarized Beams," Physica B 268, 168 (1999). X-Ray Powder Diffraction Techniques," J. Pharmctl. Sci. 88, 297 (1999).

Mang, J. T, Hjelm, R. P., "Small Angle Neutron Scattering Studies of Vesicle Liang, J. K., Huang, Q., Santoro, A., Liu, Q. L., Chen, X. L., "A Neutron Stability," Intl. J. Thermophys. 19, 461 (1998). Powder Diffraction Study of the System La^COj Fe ) Ti for x = 0.0, 0.2, x s 16 and 0.4," J. Appl. Phys. 86, 1226 (1999). Margadonna, S., Brown, C. M., Lappas, A., Prassides, K., Tanigaki, K., Knudsen, K. D., le Bihan, T, Mezouar, M., "Pressure and Temperature Liang, J. K„ Huang. Q., Santoro, A., Wang, J. L., Yang, F. M., "Magnetic Evolution of the Structure of the Superconducting Na CsC Fulleride," J. Structure, and Site Occupancies in YFe CoTi (x = 1, 3, 7, 9)," J. Appl. 2 M| n Solid State Chem. 145, 47 1 ( 1 999). Phys. 86, 2155 (1999). Margadonna, S., Prassides, K., Neumann, D. A., Shimoda, H., Iwasa, Y, Licci. F, Marezio, M., Huang, Q., Santoro, A., Bougerol-Chaillout, C, Masini, "Rotational Dynamics of C in (ND )Kf " Phys. Rev. B 59, 943 (1999). R, "Synthesis, Structure, and Superconductivity of Hg Mo Ba,CuO ," 6(l } m 075 f)15 4+6 Physica C, in press. Matejicek, J., Sampath, S., Brand, P. C, Prask, H. J., "Quenching, Thermal, and Residual Stress in Plasma Sprayed Deposits: NiCrAlY and YSZ Coatings," Lin. E. K., Kolb, R., Satija, S. K., Wu, L. U., "Reduced Polymer Mobility Acta Mater. 47, 67 (1999). Near the Polymer/Solid Interface as Measured by Neutron Reflectivity," Macromol. 32, 3753 (1999). Maurer, R. H., Roth, D. R., Fainchtein, R., Goldsten, J. O., Kinnison, J. D., Thompson, A. K., "Portable Real Time Neutron Spectrometry," in Lin, E. K, Kolb, R, Wu, W. L., Satija, S. K., "Enhanced Polymer Segment Proceedings of the Space Technology and Applications International Forum Exchange Kinetics due to an Applied Shear Field," Macromol. 32, 4741 (STAJF-99), Conference on International Space Station Utilization, in press. (1999). McKinsey, D. N, Brome, C. R„ Butterworth, J. S., Dzhosyuk, S. N, Golub, R., Lin, E. K., Pochan, D. J.. Kolb, R., Wu, W. L., Satija, S. K., "Neutron Habicht, K., Huffman, P. R., Lamoreaux, S. K., Mattoni, C. E. H., Doyle, Reflectivity for Interfacial Materials Characterization," in Characterization 3 + J. M., "Radiative Decay of the Metastable Molecule He (a 2 ) Molecule in and Metrology for VLSI Technology, edited by D. G. Seiler, A. C, Diebold, 2 u Liquid Helium," Phys. Rev. A 59, 200 (1999). W. M. Bullis, T. J. Shaffner, R. McDonlad, E. I. Watters, AIP Conference A., Majumdar, B., Satija, S. K., Paul, D. R., "Interfacial Series 449 (American Institute of Physics, Woodbury, NY 1998), p. 879. Merfeld, G. D., Karim, Thickness Between Immiscible Bilayers of Poly(phenylene oxide) and Liu, Y, Chen, S.-H., Huang, J. S., "Small-Angle Neutron Scattering Analysis of Styrenic Copolymers," J. Poly. Sci. Part B, in press. the Structure and Interaction of Tri-Block Copolymer Micelles in Aqueous

J. Rolison, D. R., "The Solution," Macromol. 31, 2236 (1998). Merzbacher, C. I., Barker, J. G., Long, W , Morphology of Nanoscale Deposits of Ruthenium Oxide in Silica Aerogels," Long, G. G., Krueger, S., Allen, A. J., "Multiple Small-Angle Neutron Nanostructured Mater., in press. Scattering," J. Neutron Res. 7, 195 (1999).

NIST CENTER FOR NEUTRON RESEARCH 71 ,

Meyer, A., Busch, R., Schober, H., "Time-Temperature Superposition of Papanek, P., Fischer, I. E., Sauvajol, I. L., Dianoux, A. J., McNeillis, P. M., Structural Relaxation in a Viscous Metallic Liquid," Phys. Rev. Lett., in Mathis, C, Francois, B., "Low-Frequency Phonons in Pristine and Doped

press. Phases of Poly acetylene: An Inelastic Neutron Scattering Study," J. Chem. Phys., in press. Meyer, A., Wuttke, J., Petry, W., "Two-Step Relaxation in a Viscous Metallic

Liquid," J. Non-Cryst. Solids, in press. Pardo, H., Ortiz, W. A., Araujo-Moreira, F. M., Suescun, L., Toby, B. H.,

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NIST CENTER FOR NEUTRON RESEARCH 75 INSTRUMENTS AND CONTACTS

High resolution powder diffractometer (BT-1) Fermi-chopper time-of-flight spectrometer (NG-6)

J. K. Stalick, (301) 975-6223, [email protected] C. M. Brown, (301) 975-5134, [email protected]

B. H. Toby, (301) 975-4297, [email protected] T. J. Udovic, (301) 975-6241, [email protected]

Residual stress and texture diffractometer (BT-8) Disk-chopper time-of-flight spectrometer (NG-4)

H. J. Prask, (301) 975-6226, [email protected] J. R. D. Copley, (301) 975-5133, [email protected]

P. C. Brand, (301) 975-5072, [email protected] J. C. Cook, (301) 975-6403, [email protected]

30 m SANS instrument (NG-7) High-flux backscattering spectrometer (NG-2)

C. J. Glinka, (301) 975-6242, [email protected] R. M. Dimeo, (301) 975-8135, [email protected] J. B. Barker, (301) 975-6732, [email protected] D. A. Neumann, (301) 975-5252, [email protected] S.-M. Choi, (301) 975-4863, [email protected] Neutron spin echo spectrometer (NG-5)

30 m SANS instrument (NG-3) (NIST/NSF-CHRNS) N. S. Rosov, (301) 975-5254, [email protected] B. Hammouda, (301) 975-3961, [email protected] Prompt-gamma neutron activation analysis (NG-7) S. R. Kline, (301) 975-6243, [email protected] R. M. Lindstrom, 975-6281, [email protected] S. Krueger, (301) 975-6734, [email protected] (301) R. L. Paul, (301) 975-6287, [email protected] 8 m SANS instrument (NG-1) Other activation analysis facilities A. Karim, (301) 975-6588, [email protected] R. R. Greenberg, (301) 975-6285, [email protected] Perfect crystal SANS (BT-5) (NIST/NSF-CHRNS) Cold neutron depth profiling (NG-O) J. B. Barker, (301) 975-6732, [email protected] G. Lamaze, (301) 975-6202, [email protected] Cold neutron reflectometer - vertical sample-polarized beam option (NG- Instrument development station (NG-O) C. F. Majkrzak, (301) 975-5251, [email protected] D. F. R. Mildner, 975-6366, [email protected] J. A. Dura, (301) 975-6251, [email protected] (301) H. H. Chen, (301) 975-3782, [email protected] Cold neutron reflectometer - horizontal sample (NG-7) Neutron interferometer (NG-7) S. K. Satija, (301) 975-5250, [email protected] Arif, 975-6303, [email protected] R. Ivkov, (301) 975-6737, [email protected] M. (301)

Triple-axis polarized-beam spectrometer (BT-2) Fundamental neutron physics station (NG-6) M. S. Dewey, 975-4843, [email protected] J. W. Lynn, (301) 975-6246, [email protected] (301)

Triple-axis spectrometer (BT-9) Theory and modelling

F. 975-6224, [email protected] R. W. Erwin, (301) 975-6245, [email protected] N. Berk, (301) I Yildirim, 975-6228, [email protected] P. M. Gehring, (301) 975-3946, [email protected] (301)

Spin-polarized triple-axis spectrometer (NG-5) (NIST/NSF-CHRNS) Sample environment D. C. Dender, 975-6225, [email protected] P. M. Gehring, (301) 975-3946, [email protected] (301) L. J. Santodonato, 975-6657, [email protected] S. -H. Lee, (301) 975-4257, [email protected] (301)

Filter-analyzer neutron spectrometer (BT-4)

T J. Udovic, (301) 975-6241, [email protected]

P. Papanek, (301) 975-5049, [email protected] D. A. Neumann, (301) 975-5252, [email protected]

76 NIST CENTER FOR NEUTRON RESEARCH

For additional information on the facility, contact:

J. Michael Rowe (301) 975-6210 [email protected]

John J. Rush (301) 975-6231 [email protected]

To obtain guidelines for preparing proposals to conduct research at the facility, contact:

William Kamitakahara (301) 975-6878 [email protected]

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/