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The NIST/NSF Center for High Resolution Neutron Scattering at the NIST Center for Neutron Research (NCNR) Gaithersburg, Maryland. Highlights of Research Activities - 2007 Supported by: DMR-0454672 D.A. Neumann, PI. Neutron Scattering Summer School. June 25-29, 2007.

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Highlights of Research Activities - 2007 Supported by: DMR-0454672 D.A. Neumann, PI


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    1. The NIST/NSF Center for High Resolution Neutron Scatteringat the NIST Center for Neutron Research (NCNR)Gaithersburg, Maryland Highlights of Research Activities - 2007 Supported by: DMR-0454672 D.A. Neumann, PI

    2. Neutron Scattering Summer School June 25-29, 2007 The 13th annual week-long summer school, run by the NIST/NSF Center for High Resolution Neutron Scattering (CHRNS), focused on methods and applications of neutron spectroscopy. The summer school was attended by 32 graduate students and postdocs, predominantly from U.S. physics, chemical engineering and materials science departments. Lectures, demonstrations and tours were given by NCNR/CHRNS staff members. Additional information is available at the summer school web site: http://www.ncnr.nist.gov/summerschool/ . DMR-0454672

    3. Summer Undergraduate Interns - 2007 DMR-0454672 Topics studied by the SURF students “Simulation of Small Angle Neutron Scattering on Inherently Disordered Protein Linkers” “Rheo-SANS Investigation of Fibrin Network Formation Under Flow” “Developing a Model Membrane System for Studying Gag HIV-1 Binding” “Characterization and optimization of tethered bilayer lipid membranes” “Magnetic Domain Wall Formation in Spin-Valve System” “Synthesis and Polymerization of Crosslinking Surfactant” “Using SANS to Investigate the Phase Behaviors of Mixed Lipid Systems” “Infrared Spectroscopy and Neutron Reflectometry Investigation of the Self-Assembled Monolayers of Oligo(ethylene oxide) Under Water on Au” “Fitting Polarized Neutron Reflectometry Data: Differential Evolution vs. Genetic Algorithm” CHRNS participates in NIST’s Summer Undergraduate Research Fellowship (SURF) program. Students work on individual research projects with a NIST advisor, and participate in group educational and cultural activities. The undergraduate (SURF) students who worked at the NCNR/CHRNS for 12 weeks in 2007. From left to right they are: Harry Bullen, Katherine Ku, Justin Poelma, Christopher Dosch, Junbo Park, Gina Polimeni, Ryan Hensarling, Rebecca Teague and David Tighe.

    4. NSF-supported NCNR spectrometers DMR-0454672 High Flux Backscattering Spectrometer (HFBS) @ NG-2 30 m Small Angle Neutron Scattering (SANS) Spectrometer @ NG-3 USANS Perfect Crystal Diffractometer @ BT-5 Spin-Polarized Inelastic Neutron Spectrometer (SPINS) @ NG-5 Disk Chopper Time-of-Flight Spectrometer (DCS) @ NG-4 Neutron Spin Echo (NSE) Spectrometer @ NG-5

    5. Bose-Einstein Condensate of Magnons in Coupled Spin Ladders V. O. Garlea1, A. Zheludev1, T. Masuda2, H. Manaka3, L.-P. Regnault4, E. Ressouche4, B. Grenier4, Y. Qiu5, J.-H. Chung5, K. Habicht6, K. Kiefer6, M. Boehm7 1ORNL, 2Yokohama Univ., 3Kagoshima Univ., 4CEA-Grenoble,5NCNR, 6BENSC, 7ILL Field-induced transitions in quantum magnets can often be interpreted as the Bose-Einstein condensation (BEC) of magnons. Such transitions are fully equivalent to the BEC of atoms in liquid 4He, laser-cooled gases in magnetic traps, or Cooper pairs in superconductors. Our neutron scattering experiments illustrate that the long-wavelength characteristics of the field-induced magnetic transition and the magnon condensate, such as critical indexes, emergence of the Goldstone mode, and behavior of gap energies, are universal. In contrast, the short-wavelength properties can be affected by the topology and one-dimensionality of the normal state. A key result of our study is the direct measurement of excitations of the magnetic BEC in the prototypical spin ladder material IPA-CuCl3. The measurements were made using the CHRNS Disk Chopper Spectrometer. Above the critical field, HC = 9.6 T, the neutron data reveal three distinct excitation branches, two of them gapped, the other one gapless (right panel). The two massive (gapped) excitations are descendants of the Sz= 0 and Sz= 1 members of the Haldane triplet at H < HC. The gapless mode, indicated by arrows, is the Goldstone mode associated with the spontaneous breaking of SO(2) symmetry. It is a collectiveexcitation of the magnon condensate and has a linear dispersion relation. It replaces the massive quadratically dispersive single-magnon excitation seen below the critical field (left panel). DMR-0454672 DE-AC05-00OR22725 V. O. Garlea et al., Phys. Rev. Lett. 98,167202 (2007) A. Zheludev et al., Phys. Rev. B 76, 054450 (2007)

    6. A B C 5 nm Measuring the Chemical and Physical Properties of the Nanoscale Building Blocks of Concrete A.J. Allen1, J.J. Thomas2 and H.M. Jennings2 CMS-0409571 W-31-109-ENG-38 DMR-0454672 DMR-9122444 1NIST, 2Northwestern University Using the CHRNS NG3 SANS spectrometer and the CHRNS USANS perfect crystal diffractometer, it has for the first time been possible, without recourse to drying, to determine the composition and density of the principal cement hydration product, calcium-silicate-hydrate (C-S-H) gel, which binds concrete together, giving it strength. Shown above is a schematic diagram of nanoscale hydration product in cement paste. It consists of layered C-S-H particles and Ca(OH)2 crystals surrounded by pore fluid. Phases containing only H are blue, while phases containing D are red. The black lines indicate the scattering interface between the solid phases and the pore fluid. A) Normal saturated paste with H2O in the pores. B) A D2O-exchanged paste. The C-S-H exchanges with OD- groups to become C-S-D, while the Ca(OH)2 is unchanged. Compared with A), the scattering between Ca(OH)2 and the pore fluid is stronger, while the scattering between C-S-D and the pore fluid is weaker. Experiments with D2O exchange allow the volume fraction of nanoscale Ca(OH)2 to be determined. C) A paste exchanged with d3-methanol (CD3OH). Since the fluid does not contain OD- groups, only the pore phase changes. Both C-S-H and Ca(OH)2 scatter strongly with CD3OH allowing the overall C-S-H/Ca(OH)2 nanoscale solid phase scattering length density to be determined. By combining results with the Ca(OH)2 volume fraction obtained in B), the scattering length density, composition, and mass density of C-S-H have been determined. A.J. Allen, J.J. Thomas and H.M. Jennings; Nature Mater., 6, 311 (2007).

    7. Guanylate Kinase Structure and Hydration Probed by SANS C.B. Stanley1,2, S. Krueger1, V.A. Parsegian2, and D.C. Rau2 1NIST, 2National Institutes of Health DMR-0454672 Interactions governing protein folding, stability, recognition, and activity are mediated by hydration. We have used the CHRNS 30m small-angle neutron scattering (SANS) instrument, coupled with osmotic stress measurements, to investigate the hydration of guanylate kinase in the presence of solutes. By taking advantage of the neutron contrast variation that occurs upon solute addition, the number of protein-associated (solute-excluded) water molecules (Nw) can be estimated. The figure shows that solutes in the series: glycerol, triethylene glycol (TEG), and poly(ethylene glycol) (PEG) of MW 400 and 1000 induce additional scattering contributions above what is obtained from protein in H2O/D2O solvent alone, which is attributed to protein-associated water. Corresponding changes in the overall radius of gyration (not shown) are consistent. Based on the size-dependence of solute exclusion, the volume of protein-associated water, and similar SANS measurements that we have made with lysozyme, it is determined that the majority of water associated with guanylate kinase for these solutes likely resides in the cavity (see models, figure inset). These results illustrate the potential use of SANS and osmotic stress for resolving structural details based on solute exclusion. C.B. Stanley, S. Krueger, V.A. Parsegian, and D.C. Rau, Biophys. J. (submitted)

    8. Glass Transition Behavior of Thin Film Miscible Binary Polymer/Polymer BlendsPeter F. Green1, Brian M. Besancon2, Christopher L. Soles31University of Michigan at Ann Arbor, 2University of Texas at Austin, 3NIST DMR-0454672 DMR-0601890 The glass transition temperatures, Tg, of thin polymer films are thickness (h) dependent. While much is known about the h dependence of Tg for homopolymer films, little is understood about factors that influence the Tg of thin film homopolymer/homopolymer mixtures. Elastic incoherent neutron scattering (EINS) measurements (fig. 1) on a completely miscible blend of dPS* and TMPC#, using the CHRNS High Flux Backscattering Spectrometer, reveal evidence of a separate Tg distinct from that of the film as measured by spectroscopic ellipsometry (SE); see fig. 2. The deviations are h-dependent, and due to the fact that the local concentration of a blend, in the miscible range of the phase diagram, deviates significantly from the average concentration, largely due to a so-called self-concentration effect associated with monomer connectivity. The Tg measured by EINS probes the local TMPC environment whereas SE measures the average Tg. The effective Tg of the mixture is dictated by an effective local concentration. The situation is compounded by effects associated with confinement and by interfacial interactions in thin films. Fig. 1 (above): results for a 50:50 mass fraction blend. Fig. 2 (right): TMPC effective Tg values for films and mixtures, using various techniques. *dPS: deuterated polystyrene #TMPC: tetramethyl bisphenol-A polycarbonate B.M. Besancon, C.S. Soles, and P.F. Green, Phys. Rev. Lett. 97, 057801 (2006).

    9. active site (a) UV visible (b) Revealing Light-enhanced Protein Activity with Neutrons C. Ted Lee, Jr.1, A.C. Hamill1, S.-C. Wang1, and A. Faraone21USC, 2NCNR DMR-0454672 CBET-0554115 We are interested in understanding how photo-reversible control of protein structure with light-responsive surfactants might be used to control enzyme activity. We have used the CHRNS 30m small-angle neutron scattering (SANS) spectrometer to determine in vitro conformations in lysozyme-azoTAB solutions. The results provide unique insights into catalytic processes. Enzyme dynamics can also have considerable influence on activity. Native and partially-folded lysozyme display similar active sites, but measurements using the CHRNS neutron spin echo spectrometer detect ns/nm domain motions in the partially-folded form whereas the native form appears rigid. The increased molecular flexibility leads to a 7-fold increase in activity relative to the native state. Panel (a) shows the structure of the molecule in its native state, as revealed by x-ray crystallography (in grey) and by SANS (in blue). There are no detectable motions on the ns/nm scale. The partially folded state, panel (b), is flexible, exhibiting ns/nm domain motions.

    10. Melting in Dehydrated Lipid Bilayers 395 K 310 K DMR-0454672 DMR-0134910 J.J. de Pablo1, M. Doxastakis1, S. Ohtake1, J.K. Maranas2, V. García Sakai2,31The University of Wisconsin, 2The Pennsylvania State University, 3NIST Lipid bilayers occur in nature as cell membranes, and synthetic equivalents are used as drug delivery agents. Storing real or artificial cell membranes often requires dehydration, yet the dehydrated state of lipid bilayers is not well understood. We have used the CHRNS high flux backscattering spectrometer (HFBS) and the CHRNS disk chopper spectrometer (DCS), in combination with molecular simulations, to understand the dynamic nature of a phase transition in lipid bilayers with impact on cell viability. Below the transition, mobility in lipid headgroups is severely limited, as indicated by the simulation images at 310K, presented as a time progression (upper figure). Above the transition (images at 395 K), headgroup mobility is enabled. The lipid tails present significant mobility even below the melting temperature (~350 K). The scattering decay curves, for wave vectors 0.82 Å-1(circles) and 1.58 Å-1 (squares), combine HFBS and DCS data for a sample where tail motion is isolated. The curves above the melting transition, covering different spatial scales, decay faster than those below; tail mobility increases at the melting transition, in agreement with the simulations. Treatment of the data with theoretical models, together with insights from the simulations, reveals significant variation of mobility as a function of position along the lipid tail (lower figure). The average extent of spatial exploration at the tails (position 16) is as much as six times greater than at the headgroups (position 2). M. Doxastakis, V. García Sakai, S. Ohtake, J.K. Maranas and J.J. de Pablo, Biophysical J. 92, 147 (2007).

    11. Finding missing entropy with neutrons in the “hidden order” state of the heavy-fermion superconductor URu2Si2 DMR-0454672 DMR-0084173 C.R. Wiebe1, J.A. Janik1, G.J. MacDougall2, G.M. Luke2, J.D. Garrett2, H.D. Zhou1, Y.-J. Jo1, L. Balicas1, Y. Qiu3,4, J.R.D. Copley3, Z. Yamani5, and W.J.L. Buyers5 1Florida State University, 2McMaster University, 3NIST, 4University of Maryland, 5Chalk River Labs For nearly two decades, little progress has been made to identify the “hidden order” state in URu2Si2 (a precursor to the superconducting state) – until now. Combining work at the National High Magnetic Field Laboratory and at the NCNR at NIST, we have used the CHRNS disk chopper spectrometer (DCS) to study the interactions among electrons in the “hidden order” state. The change in the specific heat at the phase transition is predominantly due to the gapping of magnetic excitations. This discovery rules out many current theories of how the electrons org- anize themselves at the transition, and provides further clues with regard to the enigmatic “hidden order.” Above: Spin excitations in the hidden order state of URu2Si2. The inset shows how the gap develops at low temperatures. At right: the sample, comprising four single crystals. C.R. Wiebe et al,Nature Physics 3, 96 (2007)

    12. Quantum Phase Coherence in a Spin Chain Guangyong Xu1,2, C. Broholm1,3, Yeong-Ah Soh4, G. Aeppli5, J. F. DiTusa6, Ying Chen1,3, M. Kenzelmann1,3, C. D. Frost7, T. Ito8, K. Oka8, H. Takagi8,9 1Johns Hopkins Univ., 2BNL, 3NIST, 4Dartmouth College, 5LCN/UCL (U.K.), 6Louisiana State Univ., 7ISIS (U.K.), 8AIST (Japan), 9Univ. Of Tokyo (Japan) Quantum weirdness is generally associated with atomic physics and is washed out at technological length scales. But in the present work we report quantum coherence at lithographic length scales among the magnetic dipole moments of nickel atoms in crystalline Y2BaNiO5. Using the CHRNS spectrometer SPINS, we have discovered that although the system itself is considered a quantum spin liquid which lacks classical magnetic order, the quantum phasecoherence length exceeds 20 nm in the cleanest samples. We have also shown that the coherence length can be easily modified by static and thermally activated defects in a quantitatively predictable manner. The observation of quantum coherence beyond the nano-scale in a solid state magnet without classical order is a surprising first, which improves prospects for applications in quantum computing. Temperature and doping dependence of the coherence length. Gapped magnetic excitations from the quantum spin liquid Y2BaNiO5 (MAPS, ISIS). DMR-0454672, DMR-0306940, DMR-0074571, DMR-9453362, DE-AC02-98CH10886 Guangyong Xu, C. Broholm, Yeong-Ah Soh, G. Aeppli, J. F. DiTusa, Ying Chen, M. Kenzelmann, C. D. Frost, T. Ito, K. Oka, H. Takagi, Science 317, 1049 (2007).

    13. Discovery of Zone Boundary Soft Modes in the Relaxor Ferroelectric PMNI.P. Swainson1, C.K.D. Stock2,3, P.M. Gehring4, G. Xu5, H. Luo61NRC (Canada), 2JHU, 3ISIS (UK) 4NCNR, 5BNL, 6Shanghai Inst. Ceramics (China) The lead oxide perovskite Pb(Mg1/3Nb2/3)O3 (PMN) belongs to a class of materials known as "relaxors" that possess ultrahigh piezoelectric coefficients far exceeding those of PbZrxTi1-xO3 (PZT) ceramics, the current material of choice for use in transducer and actuator devices. When PMN is combined with small amounts of PbTiO3 (PT), a well-studied, conventional ferroelectric, the piezoelectric coefficients are enhanced to record-setting levels, making these materials enormously attractive for industrial, medical, and military uses. Anomalous dynamics in the lattice are known to occur near the zone centre of this class of materials, e.g. the famous “waterfall” effect. We have studied the zone boundary using the CHRNS disk chopper spectrometer, with a crystal mounted in the HHL zone, and scans taken along the Brillouin Zone edge (see inset top left). A strong "column" of inelastic scattering at the M-point zone boundary at (1.5,1.5,-1) extends from 5 meV to the elastic line. Weaker columns are visible at the R-point zone boundary locations e.g., (1.5,1.5,-0.5). These excitations are well defined in Q, but broad in energy, indicating a highly periodic form of disorder. The columns at M and R in PMN are not observed either in PT or in PMN-60%PT, both of which I.P. Swainson et al, to be submitted to Science. undergo transitions to long-range ferroelectric ground states. Hence, these unusual soft zone boundary modes could be associated with the exceptional piezoelectric character of PMN and other relaxor materials. This suggests a picture in which PMN lies energetically close to states with competing polar order such that the application of a small external voltage could produce the novel, ultrahigh piezoelectric reponse. DMR-0454672, DMR-0306940, DE-AC02-98CH10886

    14. Nanostructured liquids from disordered surfactant melts blended with functional homopolymers Commercially available Pluronic triblock copolymer surfactants do not form ordered microphases at reasonable temperatures due to their low molar mass (< 15,000 g/mol). Thermodynamics dictates n that phase segregation of low molar mass block copolymers can only be achieved when the segment-segment interactions are strongly repulsive. Pluronic copolymer segments, however, are weakly repulsive and thus miscible in the melt state. Measurements using the CHRNS 30m n Small Angle Scattering Spectrometer, on a partially deuterated Pluronic-like copolymer, reveal that the addition of any homopolymer with selective specific interactions significantly enhances phase segregation. The effective segregation strength between polyoxy-ethylene and polyoxypropylene is so strong that the blend morphology remains highly ordered even at 175º C whereas the neat copolymer is disordered at 25º C. These results suggest that homopolymers with specific interactions are thermodynamically similar to small-molecule solvents. + V.R. Tirumala1,2, E.K. Lin2, J. J. Watkins1 DMR-0454672 CMMI-0531171, CBET-0304159 1UMass-Amherst 2NIST 2D SANS data from poly (oxyethylene-deuterated oxy-propylene-oxyethylene) (left) and its blend with poly (acrylic acid) at 30% by mass (right), measured in the melt state at 80ºC. The neat copolymer is fairly disordered whereas its blend is very well ordered at the same temperature. V.R. Tirumala, A.R. Omang, E.K. Lin, J.J. Watkins, Adv. Mater., submitted (2007).