bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Situ X-Ray Diffraction and Resistivity Analysis of CoSi2 Phase Formation with and without a Ti Interlayer at Rapid Thermal Annealing Rates
Authors: Cabral C. , Clevenger L. A. , Stephenson G. B. , Brauer S. , Morales G. , Ludwig K. F. 
Published: April 2011

AbstractIt has been demonstrated, using synchrotron radiation, that at rapid thermal annealing rates (3°C/s) the formation of CoSi2 shifts to higher temperatures when a thin Ti interlayer is placed between Co and polycrystalline Si. It has also been shown that the Ti interlayer reduces the temperature range between the start of CoSi formation and CoSi2 formation (i.e. the range over which CoSi is present). 13 nm of Co deposited by physical vapor deposition on polycrystalline Si with and without either a 2 nm or 3.4 nm interlayer of Ti was analyzed in-situ by monitoring x-ray diffraction (XRD) peak intensity as a function of temperature using monochromatic radiation from a synchrotron beam line and by monitoring resistivity as a function of temperature in a rapid thermal annealing (RTA) system. The XRD analysis indicates that the phase formation proceeds from CoSi to CoSi2 in a temperature range that decreases from about 200°C to 140°C to 115°C with pure Co, Co/2 nm Ti and Co/3.4 nm Ti films respectively. The onset of the CoSi formation increases by about 135°C and 160° for Co/ 2 nm Ti and Co/3.4 nm Ti compared to pure Co. The CoSi temperature range decreases from about 75°C in pure Co to less than 50°C in Co/Ti. In-situ RTA resistance along with in-situ XRD analysis indicates that the onset formation temperatures for CoSi are about 440°C, 575°C and 600°C and the temperatures for the completion of CoSi2 formation are about 640°C, 715°C and 715°C for Co, Co / 2 nm Ti and Co / 3.4 nm Ti films respectively. The results are consistent with the Ti interlayer acting as a diffusion barrier during the initial stages of the Co-Si reaction.
Studies of Calcium-Nickel-Potassium Oxide Films by Synchrotron X-Ray Fluorescence Microscopy
Authors: Perry D. L. , Thompson A. C. , Russo R. E. , Mao X. L. 
Published: April 2011

AbstractThe use of synchrotron x-ray fluorescence microscopy to study the composition and homogeneity of laser deposited films of calcium-nickel-potassium oxides is described. Experimental conditions for preparing the films are given, and the results are discussed with respect to the x-ray fluorescence data concerning the distribution of the three metals in the films.
Electron Transport and Photoemission Studies of Amorphous CaAl Thin Films
Authors: Morton Simon A. , Greig D. , Walker C. G. H. , Mayeya F. , Howson M. A. , Mat-Hew J. A. D. , Norman D. 
Published: April 2011

AbstractAmorphous alloys of the binary system CaAl are known to have highly unusual electron transport properties with resistivities up to 450μΣcm and a Hall coefficient that deviates from free electron values at Ca concentrations higher than 45 atomic percent. For amorphous CaMg alloys, on the other hand, the resistivity is very much less and this great difference between the two sets of alloys is not fully understood.We report on the correlation of photoemission and transport measurements made on two sets of amorphous CaAl and CaMg alloys prepared by magnetron sputtering in such a way that we could carry out both sets of measurements within the same UHV system. A special feature of the measurements was that the electrical resistivity was also measured in-situ using a specially designed 4-point probe to check for amorphicity and to compare with transport experiments carried out elsewhere.Photoemission studies were carried out in the energy range 15–50 eV with tuneable synchrotron radiation enabling us to examine the Ca 3p-3d photoemission resonance in detail. The main result from the present series of experiments was that whereas in the CaAl alloys the Fermi edge developed a shoulder at high concentrations of Al, this feature was completely absent in CaMg. At the same time the intensity of the Ca 3p-3d photoemission resonance revealed the presence of d-states in both sets of alloys, indicating that the presence of these dstates cannot, by itself, explain the high resistivity of CaAl.
Magnetic Structure of Multilayers from Soft-X-Ray Magnetic Circular Dichroism
Authors: Chen C. T. , Idzerda Y. U. , Kao C.-C. , Tjeng L. H. , Lin H.-J. , Meigs G. 
Published: April 2011

AbstractSoft-x-ray magnetic circular dichroism (MCD) is the difference between the absorptivity or reflectivity of left and right circularly polarized soft-x-rays at the magnetically interesting L2,3- edges of 3d transition metals or the M4,5-edges of the 4f rare earth elements. Thanks to its large absorption cross-section and strong MCD effect, this technique has become a powerful new means for probing, in an element- and site-specific manner, the magnetic properties of ultra-thin films and multilayers. Soft-x-ray MCD experiments, recently conducted at the Dragon beamline, are utilized to demonstrate the recent progress in this technique and its applications in the research of magnetic thin films.
What Can we Learn from off-Specular Neutron Reflection?
Authors: Pynn Roger 
Published: April 2011

ABSTRACTThis paper provides a brief introduction to the subject of off-specular neutron scattering by rough interfaces. Such scattering can be calculated using the distorted-wave Born approximation (DWBA) in which the neutron wavefunctions for a system with smooth interfaces are used as the basis for perturbation theory. Although it has been applied successfully to model the scattering from rough surfaces, the DWBA has several quantitative and qualitative limitations, some of which are described in this paper. When it is applied to multilayer systems, the DWBA correctly predicts a number of qualitative features of the diffuse scattering, including fringes of scattering that result from correlations between the roughnesses of neighbouring interfaces. A remarkable feature of diffuse neutron reflection is the range of length scales within a surface or interface that is probed. This is illustrated here by data obtained with a self-assembled multilayer of organic molecules where distances between 500 Å and 3 μm parallel to the layers are probed.
Reflection of Neutrons from an Optical Grating
Authors: Munter Alan E. , Adenwalla S. , Felcher G.P. , Zhou X.L. 
Published: April 2011

ABSTRACTSpecular and off-specular neutron intensities were measured at grazing incidence from an optical grating. The periodicity of the grating was determined from the locations of the intensity peaks in the off-specular data. An analysis of the widths of the off-specular intensity peaks showed that the effect of the coherence length of the neutron beam on the determination of a surface length scale of approximately 30 μm was negligible when compared to that of the instrument resolution.
Bulk and Surface Structure of a Ternary Microemulsion
Authors: Lee D. D. , Chen S. H. , Satija S. K. , Majkrzak C. F. 
Published: April 2011

ABSTRACTMicroemulsions are isotropic mixtures of water, oil, and surfactant which self-assemble to form interfacial monolayers with a characteristic length scale on the order of hundreds of Angstroms. Small angle neutron scattering was used to determine the bulk structure of a wateroctane-C10E4 bicontinuous microemulsion. The mean curvature of the surfactant film was verified to be near zero by independently measuring the scattering contributions from the water-surfactant and oil-surfactant interfaces through hydrogen-deuterium contrast variation. The exponentially damped, oscillatory scattering length density profile of the microemulsion near a hydrophobic silicon surface was also observed with neutron reflectivity. The surface reflectivity results as well as the bulk small angle scattering measurements are explained using a simple Ginzburg-Landau theory.
Instrumentation for Neutron Scattering at the National Institute of Standards and Technology
Authors: Kamitakahara W.A. , Rush Jj. , Rowe J.M. , Prask Hj. 
Published: April 2011

ABSTRACTThe National Institute of Standards and Technology (NIST) offers a wide range of neutron beam instruments to the U.S. community. Many of these are of recent construction, and are located in the Cold Neutron Research Facility, a large guide hall with fifteen experimental stations on seven neutron guides. A new liquid hydrogen cold source is being installed. Thermal neutron instruments in the reactor confinement are to be upgraded over the next few years.
Radius of Gyration Scaling in the Semidilute Regime
Authors: Barker J.G. , Mayes A.M. , Briber R.M. , Orts W.J. 
Published: April 2011

ABSTRACTSmall-angle neutron scattering is used to investigate swelling effects of polystyrene in carbon tetrachloride and cis-decalin in the semidilute regime. The observed scaling exponent m where Rg2 ~ ф-m was m=0.15±0.01 both in carbon tetrachloride and in cis-decalin at T=180 C, which is much weaker than the theoretical prediction m=0.25. A review of the literature has found the scaling exponent to vary from 0.1 to 0.25. Possible causes for this variation in the observed scaling exponent are discussed.
Intercalation of Organic Compounds in Lipid Bilayers
Authors: Hamacher K.A. , Kaiser H. , Kulasekere R. , Worcester D.L. 
Published: April 2011

ABSTRACTUsing neutron diffraction we studied the incorporation of small hydrophobic compounds into bilayers consisting of phosphatidylcholine (PC) and cholesterol. They were found to be localized in a narrow band at the center of the hydrocarbon region, between the two halves of the bilayer. The structures formed by introduction of the compounds are therefore intercalated structures with the long axis of the intercalated molecules lying in the plane of the bilayer. We worked with several bilayers which differed by the length of the hydrocarbon chain of the PC. The quality of the localization depended on the presence of cholesterol, the water content and the PC chain length.
Novel Kinetic Effects in Vkcoelasttc Surfactant Solutions Under Shear
Authors: Butler P.D. , Magid L.J. , Kreke P.J. , Hayter J.B. , Hamilton W.A. , Hammouda B. 
Published: April 2011

ABSTRACTUsing small-angle neutron scattering (SANS), we have investigated the transient alignment and relaxation under Couette shear of viscoelastic aqueous micellar solutions of cetyltrimethylarmmonium 3,5-dichlorobenzoate (CTA3,5C1) and CTA3,5C1/CTAB mixtures at concentrations well above ф* (but below 1.0 wt. %). Time constants of the order of ten's of minutes are reported for alignment and relaxation, orders of magnitude slower than any previously observed in similar micellar systems. The collective properties of the network of entangled, threadlike micelles, rather than the individual micellar segments, dominate the alignment and relaxation behavior. At low micellar surface charge density (σ) (e.g., in pure CTA3,5C1), the first observation of alignment proceeding in two stages has been made. Increasing a decreases by an order of magnitude the shear rate required to reach full alignment and provides a comparable decrease in the rate constant for relaxation after cessation of shear.
A Study of Tio2 Aerogels Pore and Ramified Structure by Small-Angle Neutron Scattering
Authors: Zhu Zhu , Lin Min , Dagan Geula , Tomkiewicz Micha 
Published: April 2011

ABSTRACTThe microstructral characteristics of titanium dioxide aerogels were studied by Small Angle Neutron Scattering (SANS). A variety of models were used to extract the morphological parameters from the SANS data. The evaluation of scattering data was found to be consistent with nitrogen gas adsorption and TEM measurements of a model of aerogel consisting of a light density matrix in which meso- and macro-pores are embedded.
Small-Angle Scattering Methods for Studying the Sintering of Nanophase Ceramic Compacts
Authors: Krueger Susan , Allen Andrew J. , Skandan Ganesh , Long Gabrielle G. , Hahn Horst , Kerch Helen M. 
Published: April 2011

ABSTRACTStudies of microstructure evolution as a function of sintering parameters are necessary to better control the microstructure of nanophase ceramic compacts during processing. Small-angle scattering provides a comprehensive probe of the statistically-representative microstructures present in nanophase ceramics. A complete characterization includes complementary density, electron microscopy, nitrogen desorption and x-ray diffraction measurements. Small-angleneutron and ultra-small-angle x-ray scattering have been used to determine the effects of different sintering temperatures, pressures and additives during sintering of nanophase zirconia compacts. The samples were of sufficient size and uniformity to permit absolute calibration of the scattering data, making it possible to confirm that scattering from the pore/grain interface dominates the total scattering cross-section. A quantitative microstructural model was developed for this system, resulting in the determination of specific pore surface area, total pore volume fraction, pore number size distribution and grain size as a function of sintering parameters.
Determination of The Local Atomic Structure of LA2-x(SR,BA)xCUO4 Materials From Neutron Powder Diffraction Data
Authors: Billinge S. J. L. , Kwei G. H. 
Published: April 2011

ABSTRACTWe describe the use of neutron powder diffraction for studying the local structure of high-temperature superconductors. This is accomplished by carrying out a pair distribution function (PDF) analysis. This approach does not presume a periodic structure and allows short range deviations from perfect crystalline order to be observed. Data from a sample of La2CuO4 collected on two different diffractometers are compared to determine the degree of reproducibility of the results. It is found that the data reproduce very well; however, a model-PDF, fit to the data assuming the average crystal structure in the low-temperature-orthorhombic (LTO) phase, differs from the data in a number of significant ways. This is related to earlier observations that the local structure of the La1.875Ba0.125CuO4 compound differs from the average crystal structure.
Magnetic Structures in RNi2B2C (R = Ho, Er) Superconductors
Authors: Stassis C. , Goldman A. I. , Dervenagas P. , Zarestky J. , Canfield P. C. , Cho B. K. , Johnston D. C. , Sternlieb B. 
Published: April 2011

ABSTRACTSingle crystal neutron diffraction techniques have been employed to study the evolution of magnetic structures in RNi2B2C compounds in an attempt to understand the relationship between magnetic ordering and superconductivity in several members of this series. For HoNi2B2C, below the superconducting transition (Tc = 8 K), an incommensurate magnetic structure characterized by two wave vectors (0.585 a* and 0.915 c*) is found in a narrow temperature range between 4.7 K and 6 K. This is the same temperature range where bulk measurements find a deep minimum in the upper critical field, Hc2. Below 4.7 K, HoNi2B2C is a simple collinear antiferromagnet. ErNi2B2C (Tc = 11 K) orders in an incommensurate modulated antiferromagnetic state characterized by an ordering wave vector 0.553 ā * below 7 K, which coexists with superconductivity.
Neutron Diffraction Studies on Recrystallization of Solution Derived Lead Zirconate Titanates
Authors: Morosin B. , Lawson A. C. , Kwei G.H. , Voigt J. A. , Tuttle B. A. 
Published: April 2011

ABSTRACTWe performed neutron powder diffraction on solution-derived lead zirconate titanates (PZT). Three compositions, PZT 45/55, PZT 20/80 and PbTiO3, were investigated. The materials were annealed so that the perovskite phase had just begun to grow from the precursor phase. In our materials this precursor phase is the pyrochlore rather than fluorite phase. The results show that in the pyrochlore phase, the (Ti,Zr) and the Pb are ordered in their crystallographic sites while the O are essentially disordered in both of the two usual pyrochlore anion sites.
Neutron Scattering Studies of Network Glasses
Authors: Wright Adrian C. , Vessal Behnam , Bachra Bilber , Hulme Robert A. , Sinclairc Roger N. , Clare Alexis G. , Grimley David I. 
Published: April 2011

ABSTRACTA review is presented of recent neutron diffraction studies of silicate and borate glasses, using a combination of steady-state reactor and pulsed neutron sources. The samples studied include both single component glasses and binary systems, consisting of a network modifier plus a network former, and the data have been extended to high magnitudes of the scattering vector, Q, to achieve high real-space resolution. Peak fitting techniques are employed to extract the detailed geometry of the basic structural units and to investigate the distortions caused by the introduction of network modifiers. The data are compared to various structural models and conclusions are drawn not only with regard to the validity of the structural models themselves but also concerning the environment of the network modifying cations.
The Structure of Lead-Indium Phosphate Glass
Authors: Suzuya K. , Price D. L. , Loong C.-K. , Sales B. C. , Boatner L. A. 
Published: April 2011

ABSTRACTLead-indium phosphate glasses exhibit a number of useful properties such as a high index-of-refraction, low preparation temperature and melt viscosity, and good chemical durability. The structure of such a glass (composition in wt. %: 65 PbO, 29 P2O5, 6 In2O3) has been investigated by total neutron scattering using the GLAD diffractometer at Argonne's spallation neutron source IPNS. Peaks corresponding to the P-O, Pb-O/In-O, and 0-0 pairs were observed in the radial distribution function. The short-range structure in the glass, in terms of average coordination numbers and bond distances, is compared with those of a pure P2O5 glass and with the crystal structure of lead pyrophosphate, Pb2P2O7. Unlike silicate glasses in which the SiO4 tetrahedra form a 3-dimensional network, the PO4 tetrahedra in phosphate glasses form a chain-like structure. The structural modification by the lead cations in phosphate glasses appears to occur mainly in the medium range affecting the lengths and connectivity of the chain-like structure.
Crystal Field and Exchange Interactions in DyT4Al8 (T = Fe and Mn)
Authors: Loewenhaupt M. , Loong C.-K. , Tils P. , Hahn W. 
Published: April 2011

ABSTRACTWe investigated the magnetic excitations in polycrystalline samples of hard magnet related compounds DyFe4Al8 and DyMn4Al8 by neutron spectroscopy. For both compounds the magnetic spectra at energies below 40 meV are dominated by the response of the Dy3+ ions. In DyMn4Al8 we observed pure crystal-field transitions within the Dy3+ J=15/2 ground multiplet which is split into 8 doublets under the low point-group symmetry of 4/mmm. In DyFe4Al8 the Dy crystal-field-split states are perturbed by the molecular fields of the ordered Fe sublattice.
One-Dimensional Sans Employing Bent-Single Crystal Optics: Theory and Demonstration
Authors: Heuser B. J. , Popovici M. , Berliner R. 
Published: April 2011

ABSTRACTA recent small-angle neutron scattering (SANS) instrumentation development at the University of Missouri Research Reactor Center (MURR) using bent, double Si crystal diffraction is presented. Neutron rocking curves of flat single crystals are only a few seconds of arc with correspondingly low integrated intensities. The rocking curve can be significantly broadened if the crystals are bent. However, the phase-space acceptance and emergence windows of two bent crystals in parallel can be matched only if the reflecting planes have different d-spacing. We have used a combination of the Si (111) and (220) reflections in the work presented here. The peak intensity of the rocking curve with this configuration was approximately 2.5 x 105 neutrons per second over a 5 cm2 area of sample at 1.5 Å. The rocking curve wings fell sharply (approximately as Q"11), permitting accurate scattered intensity measurements down to a minimum Q value of 0.005 1/Å at a Q resolution of 0.003 1/Å. The technique also offers the possibility of variable resolution without too much difficulty; changes up to a factor of 2 can be made by adjusting the sample-to-analyzer crystal distance, while changes of a factor of 10 can be made by using different Si reflections. Since the incident neutron wavelength can be tuned to the peak of the leakage spectrum, this technique is ideal for low-flux reactors, which otherwise cannot be used for SANS research. The usefulness of one-dimensional SANS is demonstrated by measurements of Portland cement.
The Electronic Contribution to The Elastic Constants of Strained III-V Materials Under High Magnetic Fields
Authors: Ghatak Kamakhya P , Nag B. , Mazumder G. 
Published: April 2011

ABSTRACTIn this paper an attempt is made to study the electronic contribution to the elastic constants of strained III-V materials under high magnetic fields on the basis of k.p theory. It is found taking strained Hgi - x CdxTe and Ini - xGaxAsyPi-y lattice matched InP as examples that they increase with increasing doping and oscillate with inverse magnetic field respectively. The strain enhances the numerical values of the elastic constants. The theoretical formulation is in quantitative agreement with the suggested experimental method of determining the above contributions for degenerate materials having arbitrary dispersion laws. In addition, the well-known results for strain free wide gap materials in the absence of magnetic field have been obtained from our generalized analysis under certain limiting conditions.
Spectroscopic Ellipsometry and Band Structure of Si1–yCy Alloys Grown Pseudomorphically on Si (001)
Authors: Zollner Stefan , Herzinger Craig M. , Woollam John A. , Lyer Subramanian S. , Powell Adrian P. , Eberl Karl 
Published: April 2011

ABSTRACTWe have measured the dielectric functions of three Si1−yCy, alloys layers (y ≤1.4%) grown pseudomorphically on Si (001) substrates using molecular beam epitaxy at low temperatures. From the numerical derivatives of the measured spectra, we determine the critical point energies E′0 and E1 as a function of y (y ≤ 1.4%) using a comparison with analytical line shapes and analyze these energies in terms of the expected shifts and splittings due to negative hydrostatic pressure, shear stress, and alloying. Our data agree well with the calculated shifts for El, but the E′0 energies are lower than expected. We discuss our results in comparison with recent tight-binding molecular dynamics simulations by Demkov and Sankey (Phys. Rev. B 48, 2207, 1993) prediciting a total breakdown of the virtual-crystal approximation for such alloys.
Effects of Substrate Misorientation Direction on Strain Relaxation at InGaAs/GaAs(001) Interfaces
Authors: Goldman R.S. , Wieder H.H. , Kavanagh K.L. 
Published: April 2011

ABSTRACTWe have investigated the effects of substrate misorientation direction on strain relaxation at InGaAs/GaAs(001) interfaces. Calculations of the shear stresses due to the misfit strain, resolved on the glide plane in the glide direction, suggest that the dislocation glide force and the activation energy for dislocation nucleation are essentially identical for the α and β slip systems. However, experimental results indicate that asymmetries in strain relaxation are sensitive to A-type misorientation and/or step-edge densities. Thus, a dislocation nucleation source or glide velocities sensitive to step densities or local roughness may explain these results.
Schottky Barrier Heights of A1/p-Sil-xGex
Authors: Jiang R. L. , Li J. , Zhou X. C. , Liu J. N. , Zheng Y. D. 
Published: April 2011

ABSTRACTElectrical properties of Al/p-Sil-xGex Schottky contacts were investigated. The Sil-xGexstrained layers were grown by using Rapid Thermal Process/Very Low Pressure-Chemical Vapor Deposition. It was found that Schottky barrier height decreased with increasing Ge fraction. The decrement is in accordance with the decrement of the bandgap of the strained Sil-xGex. The Fermi level at the interface is pinned at about 0. 43eV below the conduction band. The influence of strain relaxation for SiGe alloy layers and the Si cap layers on the properties of Schottky contacts were also investigated.