bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling of Neutron Diffraction Patterns from Sheared Silica Gels
Authors: Butler B.D. , Hanley H.J.M. , Muzny C.D. , Straty G.C. 
Published: April 2011

ABSTRACTDense silica gels, prepared from suspensions of 24 nm colloidal silica particles, have been studied by small angle neutron scattering. Provided the volume fraction, φ, of the silica is less than about 0.18, the scattered intensity increases at low wavevector, q, as the gelation proceeds and the structure factor, S(q), of the final gel exhibits apparent power law behavior, usually interpreted as a signature of fractal growth. The power law behavior, however, was observed for all measured φ (≤0.30) when the gelation occurred in the presence of an applied shear. Furthermore, the first diffraction maximum, corresponding to the inter-particle contact distance, was more sharply peaked in the high density sheared gels, indicating that the structural arrangement of the silica particles under shear is more densely packed than in gels produced without shear under equivalent conditions. Although it is clear that shear has a marked influence on the gel structure at higher densities, a quantitative interpretation of the diffraction results is difficult because cluster-cluster interference might be present. Such difficulties encountered when trying to interpret the scattering from these dense systems are outlined, and a computer simulation that includes cluster-cluster interference is presented.
Spinodal Decomposition of the Three-Component Microemulsion System: Aot/Water/Decane
Authors: Mallamace F. , Micali N. , Trusso S. , Chen S. H. 
Published: April 2011

ABSTRACTWe have performed a series of spinodal decomposition measurements of a three-component microemulsion system made of a surfactant AOT, water, and decane. The measurements were made by a temperature jump from a one-phase droplet microemulsion to a two-phase droplet microemulsion along the critical iso-volume fraction line (10%) using the time resolved light scattering intensity technique. All three stages of the evolution were studied. The typical scattering intensity distribution is in good agreement with recent dynamic scaling theories.
Investigation of Residual Strains of the Second Kind in Plastically Deformed Metallic Materials
Authors: Vrána M. , Klimanek P. , Kschidock T. , Lukáš P. , Mikula P. 
Published: April 2011

ABSTRACTInvestigation of strongly distorted crystal structures caused by dislocations, stacking-faults etc. in both plastically deformed f.c.c. and b.c.c. metallic materials was performed by the analysis of the neutron diffraction line broadening. Measurements were realized by means of the high resolution triple-axis neutron diffractometer equipped by bent Si perfect crystals as monochromator and analyzer at the NPI Řež. The substructure parameters obtained in this manner are in good agreement with the results of X-ray diffraction analysis.
A Study of Internal Damage of Metal Matrix Composites by Neutron Diffraction
Authors: Shi N. , Bourke M. A. M. , Goldstone J. A. 
Published: April 2011

ABSTRACTUsing neutron diffraction, we have measured the elastic phase strains of Al/TiC and Al/SiC composites under uniaxial tensile loading. The phase strains were used to reconstruct the global elastic strain. It has been found that, above macroscopic yield, the global elastic strain response is not linear. A theoretical model shows that the nonlinearity is dictated by changes in the ratio of longitudinal phase stresses. Furthermore, the changes in this ratio resulting from matrix plasticity and reinforcement fracture are different which leads to distinct slope changes in the global elastic strain response that can be used to distinguish the onset of these two processes on the global elastic strain loading curve.
Observations of Cef-Split Intermultiplet Transitions in Optically Opaque EuBa2Cu3O7 Using Inelastic Neutron Scattering
Authors: Staub U. , Soderholm L. , Osborn R. , Balcar E. , Trunov V. 
Published: April 2011

ABSTRACTInelastic neutron scattering (INS) results on the intermultiplet transitions J=0 → 1 and J=1 → 2 in optically opaque EuBa2Cu3O7 are reported. Whereas these multiplets are split by the crystalline electric field (CEF), their low J values are influenced to first order only by the second-order (J=1) and additional fourth-order (J=2) CEF parameters. and the spinorbit coupling parameter were obtained by fitting the splitting of the J=l multiplet and the energy separation between the J=0 and 1 multiplets. The J=0 → 1 splitting observed here is smaller than previously seen by optical spectroscopic studies on a variety of transparent, ionic compounds, necessitating fitting of the free-ion parameter. Additional spectroscopic information on the J=2 multiplet indicates that additional fitting of free ion parameters must be included to adequately model the observed low energy separation between the two lowest J-multiplets. Preliminary calculation on the Q-dependence of the CEF split J=0 → 1 transitions and the comparison with observations are presented.
Magnetic Structure Determination for Annealed Ni80Fe20/Ag Multilayers Using Polarized-Neutron Reflectivity
Authors: Borchers J.A. , Gehring P.M. , Majkrzak C.F. , Ankner J.F. , Hylton T.L. , Coffey K.R. , Parker M.A. , Howard J.K. 
Published: April 2011

ABSTRACTSputtered Ni80Fe20/Ag multilayers, annealed post-growth, show giant magnetoresistive (GMR) effects at unusually low magnetic fields (≈ 5 Oe)[l]. Structural characterization by cross-sectional TEM[2] and x-ray diffraction indicates that the Ag preferentially diffuses into the Ni80Fe20 layers at the interfaces. Using polarized-neutron specular reflectivity, we have obtained magnetization depth profiles for a series of annealed [Ni8oFe2o(20Å)/Ag(40Å)]4 multilayers. Though GMR in related materials is associated with coherent antiferromagnetic alignment of the ferromagnetic layers, specular neutron data for the Ni80Fe20/Ag multilayers show no trace of half-order spin-flip intensity characteristic of this simple structure. In small applied fields, transverse scans at the half-order position show a broad feature which disappears upon saturation. These data suggest that while the Ni80Fe20 moments are antiferromagnetically correlated along the growth axis, the in-plane magnetic domains are only of micron-order size and are thus not apparent in a specular measurement.
Neutron Studies of Disordered Alloys: a Brief Review/Update
Authors: Moss Simon C. 
Published: April 2011

ABSTRACTBoth neutron and X-ray scattering are used to determine the pair correlation functions (short-range order), the atomic displacements arising from atom size disparity, and the (derived) effective pair interactions in binary alloy solid solutions. This enterprise has taken on a new vitality through concomitant advances in both electronic theory and computer modeling of the atomic arrangements in alloys. An overview of the diffuse scattering formalism will be presented with an emphasis on the ways in which neutron scattering is particularly effective in sorting out the separate contributions to the total scattering pattern. Aspects of contrast variation and enhancement, and the utilization of both elastic and inelastic scattering will be discussed and examples of both past and recent work will be covered, including some future directions. We will also note briefly the relation between local order studies and details of the electronic and the elastic response functions of alloys.
Neutron Scattering Facilities at Chalk River
Authors: Holden T.M. , Powell B.M , Dolling G 
Published: April 2011

ABSTRACTThe Chalk River Laboratories of AECL Research provides neutron beams for research with the NRU reactor. The NRU reactor has eight reactor loops for engineering test experiments, 30 isotope irradiation sites and beam tubes, six of which feed the neutron scattering instruments. The peak thermal flux is 3 x 1014n cm−2s−1. The neutron spectrometers are operated as national facilities for Canadian neutron scattering research. Since the research requirements for the Canadian nuclear industry are changing, and since the NRU reactor is unlikely to operate much beyond the year 2000, a new Irradiation Research Facility (IRF) is being considered for start-up in the first decade of the next century. An outline is given of this proposed new neutron source.
Precursor Phenomenon of Martensitic Transformation in Au-49.5at%Cd Alloy
Authors: Ohba Takuya , Shapiro S.M. , Aoki Shingo , Otsuka Kazuhiro 
Published: April 2011

ABSTRACTPhonon softening was observed in the parent phase of a AuCd alloy which transforms from the β2(B2) parent to ζ2¹(trigonal) martensite. Since Cd strongly absorbs neutrons, the isotope 114Cd was used in preparing the single crystal for the measurements. The [ζζ0]TA2 phonon branch was measured and found to be anomalously low. A minimum is present at ζ=0.35 which softens with decreasing temperature towards Ms. The results are consistent with the model proposed by Ohba et al. based upon a crystallographic study of the ζ2¹ phase.
Neutron Spectroscopy of Phonon and Bound Multiphonon States in γ-ZrH
Authors: Kolesnikov A.I. , Bashkin I.O. , Ponyatovsky E.G. , Prager M. , Belushkin A.V. 
Published: April 2011

ABSTRACTLattice dynamics of γ-ZrH(D) ordered phases with essentially one-dimensional H-H (D-D) interaction was studied by inelastic neutron scattering. The experimental optic peaks were described within the Born-von Kármán model. The bound multiphonon states were observed in the spectra. Their binding energies were derived from the experimental data.
Phonon Spectra of Ordered Pdcuh and Pdagh Produced Under a High Hydrogen Pressure
Authors: Kolesnikov A.I. , Antonov V.E. , Prager M. , Bennington S. , Tomkinson J. 
Published: April 2011

ABSTRACTAtomically ordered PdAgH and PdCuH hydrides synthesized in an atmosphere of gaseous hydrogen at P = 3 GPa were studied by inelastic neutron scattering. The results showed a large difference between the Pd-H, Ag-H and Cu-H interactions. Values of 93 and 116 meV were predicted for the local H vibrations in dilute Ag-H and Cu-H solid solutions.
Similarity of Vibrational Spectra of High Density Amorphous Ice and High Pressure Phase Ice Vi
Authors: KOLESNIKOV A.I. 
Published: April 2011

ABSTRACTInelastic incoherent neutron scattering measurements on the hdaice, ice Ih and high-pressure phases ice VI and ice VIII revealed similarity between the amorphous phase and crystalline ice VI and led to the new proposition that hda ice consists of two interpenetrating hydrogen-bonded networks with no hydrogen bonds between “sublattices”.
Temperature Dependence of Cathodoluminescence From InxGa1-xAs/GaAs Multiple Quantum Wells
Authors: Rammohan K. , Rich D.H. , Larsson A. 
Published: April 2011

ABSTRACTThe temperature dependence of the cathodoluminescence (CL) originating from In0.21Ga0.79As/GaAs multiple quantum wells has been studied between 86 and 250 K. The CL intensity exhibits an Arrenhius-type dependence on temperature (T), characterized by two different activation energies. The spatial variations in activation energy caused by the presence of interfacial misfit dislocations is examined. The CL intensity dependence on temperature for T ≲ 150 K is controlled by thermally activated nonradiative recombination. For T ≳ 150 K the decrease in CL intensity is largely influenced by thermal re-emission of carriers out of the quantum wells.
Microstructure of Oxidized Ge0.78SiO.12 annealed in a Reducing Ambient
Authors: Theodore N.D. , Liu W.S. , Lie D.Y.C. , Cams T.K. , Wang K.L. 
Published: April 2011

ABSTRACTTransmission electron microscopy, conventional and high-resolution, is used to characterize the microstructural behavior of oxidized Ge0.78Si0.12 layers annealed in a reducing 95% N2+ 5% H2 ambient. An epitaxial Ge layer grows by solid-phase epitaxy on an underlying Ge0.78Si0.12 seeding layer with a Ge-Sio2 matrix positioned between them. Defect densities in the epitaxial Ge are significantly lower than in the underlying Ge0.78Si0.12. Microstructural details of this behavior are investigated.
On The Origin of The Coarse and Fine Contrast Modulation in Epitaxial InGaAs Strained Layers Grown On InP Substrates.
Authors: PeirÓ F. , Cornet A. , Roura P. , Morante J.R. 
Published: April 2011

ABSTRACTIn this paper we summarise the TEM observations carried out on InxGa1-xAs strained layers grown by Molecular Beam Epitaxy on (100) InP substrates (xIn in the range 54.3%-62.5%). The evolution of the modulation wavelength with the epilayer thickness, growth temperature (Tg) and layer-substrate strain is reported. The quantification of the amplitude of the composition variation linked to the coarse contrast modulation from the theoretical fitting of the Optical Absorption spectra is also presented. In view of these results we suggest a model for the appearance of the contrast modulations in ternary and quaternary III-V alloys according to the different structural configurations driven by the alloy stabilisation inside the miscibility gap due to the minimization of the free Gibbs energy as Tg increases.
InAs Island Quantum Box Formation and Vertical Self-Organization on GaAs (100) Via Molecular Beam Epitaxy
Authors: Xie Qianghua , Kobayashi N. P. , Ramachandran T. R. , Kalburge A. , Chen P. , Madhukar A. 
Published: April 2011

ABSTRACTIn-situ, ultra high vacuum combined scanning tunneling microscope/atomic force microscope (STM/AFM) studies were undertaken to examine the initiation of 3D InAs islands on GaAs (100) and their density and size distribution as a function of growth conditions. A decreasing island density with increasing As4 pressure is observed and points to the significance of strain in affecting In migration and As4 incorporation. A stack of InAs islands separated by GaAs spacer layers exhibit a vertically self-organized growth. Through analysis of a phenomenological model, this is shown to be a consequence of a directional In adatom migration caused by the islandinduced nonuniform strain fields.
Phase Stability and Electronic Structure of GaAs1–xNx Alloys
Authors: Neugebauer JÖrg , Van De Walle Chris G. 
Published: April 2011

ABSTRACTWe investigate the electronic structure and stability of GaAs1–xNx alloys for several compositions, using state-of-the-art first-principles total-energy calculations. We consider several ordered structures, and in addition we address the case of low-dimensional structures, such as zero-dimensional point defects (NAs in GaAs). Our results reveal two rem ark-able features of this alloy system: (i) a very large bowing of the band gap (the system may even become metallic for compositions around x = 0.5) and (ii) a very limited miscibility. Both properties are related to a distinctive property of this alloy system: a more than 20% lattice mismatch between GaAs and GaN.
Asymmetric Mosaic Spread During Relaxation in SiGe/ Si Strained Layer Superlattices Grown on Miscut Substrates
Authors: Nam S. , Goorsky M. S. 
Published: April 2011

ABSTRACTThe evolution of defects in SiGe/Si strained layer superlattices (SLS)-with thickness and composition near the critical thickness -was investigated. The structures were grown on 2° miscut (001) substrates by ultrahigh vacuum chemical vapor deposition. The samples were then annealed between 700 °C and 900 °C. After annealing, the satellite peak intensity from double axis diffraction decreased and triple axis diffraction showed that this decreased intensity was due to increased mosaic structure. Interestingly, for some of the annealed samples, the (004) reciprocal space maps showed an asymmetric mosaic spread, indicating a preferential tilt. This result stems from a preferential propagation of certain types of misfit dislocations due to the substrate miscut.
Deep Photoluminescence Bands in Mbe Grown Si and Sige.
Authors: Buyanova I.A. , Henry A. , Chen W.M , Ni W.X. , Hansson G.V. , Monemar B. 
Published: April 2011

ABSTRACTBroad photoluminescence (PL) bands with energy position ranging from 0.70 to 1.03 eV, are shown to appear in Si epilayers and Sil−xGex/Si heterostructures grown by molecular beam epitaxy under non-optimized conditions. The presence of a particular broad band (BB) is found to be determined by the growth conditions, in particular by the bias applied to the substrate during the growth. Ion bombardment during the growth is shown to be a main factor enhancing the formation of BB-related defects. To clarify their origin, the effects of post-growth hydrogen treatments and of an external magnetic field are investigated. The BBs are shown to be related to various types of radiative centres, either point or extended defects. A correlation between X-ray diffraction and PL measurements is also observed. The spatial location of the BB-related defects is inferred by results from optically detected cyclotron resonance (ODCR) and PL excitation studies.
Effects of Lateral Limited Area and Substrate Compliance on Strain Distribution and Critical Thickness of Sige Film on Si Mesa Substrates
Authors: Rong Zhang , Hongbin Huang , Yi Shi , Kai Yang , Shulin Gu , Ronghua Wang , Shunming Zhu , Youdou Zheng 
Published: April 2011

ABSTRACTIn this paper, we calculated theoretically the strain distribution and the critical thickness of the SiGe epilayers on Si(100) mesa structural substrates by considering the effect of the compliance of substrates, along with the effect of the limited area, and found that the compliance of substrates was relevant not only to its thickness, but also to their lateral size. The introduction of substrate compliance significantly reduced the total strain energy in the epilayers, and increased the critical thickness. That approach was realized by growth on the mesa substrates. The TEM observations confirmed the results of calculations.
Sil−xGex/Si Multiple Quantum Well Wires Fabricated Using Selective Etching
Authors: Yi Shi , Feng Wang , Jianlin Liu , Rong Zhang , Shulin Gu , Shunming Zhu , Lique Hu , Youdou Zheng 
Published: April 2011

ABSTRACTUsing lithography, and selective etching the Si1-xGex/Si multiple quantum well wires are fabricated. The characteristics of the selective chemical etching of Si1-xGex and Si are investigated, and high-performance etchants are developed. The etchant composed of HF:NH4F:H202:NH4OH is used for the etching of the epitaxial Si1-xGex films, the selectivity is better than 250 for Si0.76Ge0.24, and increases with the increase of the mole fraction x of Ge. Another etchant composed of NH4NO3:NH4OH is used for the etching of Si, the selectivity is higher than 1000 ( x ≥ 0.1 ). A preliminary photoluminescence (PL) result obtained from the Si0.76Ge0.24 multiple quantum well wires is presented. As the linewidth of the wires is reduced down to 50 nm, an intense complicated PL spectrum in the wavelength range of 500∼800 nm is observed at liquid nitrogen temperature. The origin of such spectrum is unclear.
Ion-Enhanced Chemical Reaction of XeF2 with Silicon by Modulated Molecular Beam Mass Spectrometry
Authors: Balooch M. , Olander D. R. , Siekhaus W. J. 
Published: April 2011

AbstractThe reaction of XeF2 with the Si(100) surface was studied by modulated (10–1000 Hz) molecular beam-mass spectrometry in the temperature range 300–1300K and equivalent XeF2 pressure of 5×10−6 to 10−4 Torr. Simultaneous bombardment of the reacting surface by Ar+ was used to determine the extent of ion-enhancement of the reaction.In the absence of the ion beam, the main reaction product was SiF4, which was formed with a reaction probability of ˜5×10−2 at room temperature. In the presence of the ion beam three products, SiF4, SiF2 and F2 (or F), were detected with formation probabilities of ˜1×10−1, 6×10−2 and 7×10−2 respectively. Increasing surface temperature reduced the ion-enhanced reactivity.
New Devices for the Production of Intense Pulsed Jets of CF2: Laser Spectroscopic Characterization
Authors: Knickelbein Mark B. , Webb Douglas A. , Grant Edward R. 
Published: April 2011

AbstractWe report the development of two new sources for the production of intense pulsed jets of atomic and molecular free radicals. The present work applies these sources to the generation of the widely used semiconductor etchant, CF2, in each case characterizing the yield and internal energy distribution of this diradical by laser induced fluorescence. The methods employed modify a commercial high-vacuum compatible pulsed molecular beam valve to accept either a glow discharge or pyrolysis nozzle. The source compound for both systems is hexafluoropropylene oxide (HFPO). In each case measured yields of CF2 are high: For pyrolysis we find intensities as great as 5×1017 sr−1sec−1 representing nearly complete conversion of HFPO to CF2 + CF3CFO. The discharge source yields about an order of magnitude less CF2 intensity in a shorter beam-pulse which also contains ions and other atomic and molecular radicals. The vibrational energy distribution of the CF2 varies with source conditions, with the hottest CF2 produced by the pyrolysis source at high temperature.
X-Ray Photoelectron Spectroscopy Analysis of Silicon Oxide Deposited by a Nitrous Oxide/Silane Glow Discharge
Authors: Thomas J. H. , Kaganowicz G. 
Published: April 2011

AbstractThin layers (100Å) of SiO were deposited at room temperature in a RF glow discharge in a nitrous oxige – silane ambient. Surface properties of the deposit were studied using quantitative and qualitative XPS and AES. Abrupt changes in the energy difference between the O 1s and Si 2p photoelectron peaks, the O/Si stoichiometric ratio, and nitrogen incorporation are observed with varying amounts of silane in the gas ambient (for a fixed nitrous oxide flow). The abrupt change in binding energy difference correlates with the presence of free oxygen in the glow discharge as measured by in-situ mass spectrometry. At silane flows below the abrupt change, nitrogen is excluded from the deposit and the surfaces appear to be chemically silicon dioxide with a O/Si ratio of 2.1 as determined from quantitative XPS analysis. Above the abrupt change, the films exhibit a surface composition of less than 2.0.
Temperature, Velocity, and Species Mapping in an Induction Plasma
Authors: Donaldson A. D. , Batdorf J. A. , Fincke J. R. , Varacalle D. J. , Richardson L. S. 
Published: April 2011

AbstractAs part of an effort to determine the feasibility of carbothermic reduction of alumina in plasmas, spatial distributions of temperature, velocity and species in the plume of an argon radio-frequency plasma with alumina and carbon additions were estimated using a two dimensional theoretical model of the flow field and a thermochemical model based on equilibrium conditions. Experimentally determined boundary conditions were input to the models. Using a 30 kW inductively coupled plasma, experimental measurements were made to allow comparison with predictions. A practical process for carbothermic reduction will require prevention of back reactions, either by separation of the aluminum species or by some kind of quenching of the process. The significance of the experimental results and comparisons with predictions are discussed.
Crystallization, Doping, Orientation and Grain-Size of Microcrystalline Silicon and Germanium
Authors: Tsu Raphael , Brazil S. P. 
Published: April 2011

AbstractPreparation and characterization of microcrystalline silicon are discussed. In addition to the usual characterization techniques using TEM,X-ray, Auger, etc., Raman scattering and electro-reflectance measurements have been extensively incorporated into routine analyses. In particular, conductivity percolation, detection of trace crystallites in an amorphous matrix, measurements of grain-size, doping as well as preferred orientation are fully discussed. The single most important effect on the properties of microcrystalline Si and Ge is the presence of impurities. Thus better technical performances must be preceded by an improvement in vacuum and purer gases used in deposition systems.