bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combined Tem and X-Ray Topographic Characterization of InxGa1−xAs/GaAs Strained Layer Systems.
Authors: Dudley Michael , Yao Gong-Da , Paine David , Howard David , Sacks Robert N. 
Published: March 2011

ABSTRACTNovel application of a combination of TEM and non-destructive synchrotron X-ray topography in both Bragg and grazing Bragg-Laue geometries to the characterization of InxGa1−xAs/GaAs strained layer films is reported. Specialized epilayer lift-off procedures enabled TEM characterization of the defect distributions in macroscopic area films, effectively increasing the field of view of the technique by several orders of magnitude. These lateral distributions correlated well with those observed on both Bragg and grazing Bragg- Laue topographs. Grazing Bragg-Laue images also afforded depth sensitivity. Excellent correlations exist between results obtained with all these techniques for systems with a wide range of In concentrations, corresponding to a broad range of interfacial dislocation densities, although only results for x=;0.085 are presented. This work demonstrates that it is possible to bridge the gap that has traditionally existed between the areas of application of these two generic techniques, in terms of both tolerable defect densities and fields of view. This gap also spans the range of defect densities which is of interest in this and other systems.
Wrong Bonds at Compound Semiconductor Grain Boundaries
Authors: Lambrecht W. R. L. , Lee C. H. , Methfessel M. , Van Schilfgaarde M. , Amador C. , Segall B. 
Published: March 2011

ABSTRACTThe role of cation-cation and anion-anion “wrong” bonds at compound semiconductor grain boundaries is investigated. Results are presented for the {110} and {001} inversion domain boundaries in SiC and GaAs. The role of electrostatic effects, compensation of over- and undersaturated bonds, “chemical” reconstructions andbond length relaxations are discussed.
Interface Structure of Epitaxial Nb Films on Sapphire: Grazing Incidence X-Ray Diffraction and X-Ray Reflectivity Studies
Authors: Lee C. H. , Liang K. S. , Shieu F. S. , Sass S.L. , Flynn C. P. 
Published: March 2011

ABSTRACTThe interface structure of MBE grown Nb films on sapphire substrates was studied using grazing incidence x-ray diffraction and x-ray reflectivity measurements. Specifically, the use of these x-ray techniques in probing the buried interfaces was demonstrated. Diffraction effects were observed which are consistent with the presence of misfit dislocations in the interface.
Deep Level Defect Characterization of MBE Grown Ingaas/Gaas Heterostructures.
Authors: Buchwald W.R. , Zhao J.H. , Rong F.C. 
Published: March 2011

ABSTRACTDeep level transient spectroscopy (DLTS) measurements have been performed on Schottky diodes fabricated on MBE grown InGaAs/GaAs heterostructures. The dominant electron trap in this material is found at a depth of 0.30eV below the GaAs conduction band and is believed to be the previously observed M3 defect. Two other defects, at depths of 0.50eV and 0.58eV below the GaAs conduction band, were also observed. Defect depth profiling shows the 0.50eV defect to be spatially locatednear the heterointerface. The 0.58eV defect is not observed near the heterointerface but is observed in large concentrations deep in the GaAs epilayer. Optical DLTS measurements reveal deep defects at 0.54eV and 0.31eV above the InGaAs valence band as well as a large, broad peak, most likely consisting of several energy levels with varying capture cross sections,located at the heterointerface. Two carrier accumulation peaks were also seen in the CV carrier profiling measurements and are suggested to be due to two heterointerface defects located at 0.68eV and 0.87eV below the GaAs conduction band.Thermally stimulated capacitance measurements also indicate minority hole emission in this n-InGaAs/N-GaAs heterostructure.
High Quality GaAs Mis Diodes With Very Low Surface State Density
Authors: Fujisaki Yoshihisa , Sakai Sumiko , Ataka Saburo , Shibata Kenji 
Published: March 2011

ABSTRACTHigh quality GaAs/SiO2 MIS( Metal Insulator Semiconductor ) diodes were fabricated using (NH4)2S treatment and photo-assisted CVD( Chemical Vapor Deposition ). The density of states at the GaAs and SiO2 interface is the order of 1011 cm-2eV-1 throughout the forbidden energy range, which is smaller by the order of two than that of the MIS devices made by the conventional CVD process. The mechanism attributable to the interface improvement was investigated through XPS( X-ray Photoelectron Spectroscopy ) analyses.
Influence of Surface Relaxation on X-Ray Topographic Imaging of Interfacial Dislocations in Heterosystems.
Authors: Yao Gong-Da , Wu Jun , Dudley Michael , Shastry Vijay , Anderson Peter 
Published: March 2011

ABSTRACTThe influence of surface relaxation on the imaging of dislocations in thin single crystal films, using white beam synchrotron radiation topography in grazing Bragg-Laue geometry, has been assessed. The predicted visibility of dislocation images on grazing Bragg- Laue topographs, for the particular case of interfacial edge dislocations in a GaAs/Si heterostructure, is shown to be strongly influenced. Agreement between predicted and observed visibility could only be obtained by incorporating the surface relaxation effects, which thus strongly influence the depth sensitivity of the technique, i.e. the ability to pinpoint the depth of a dislocation. Dislocation image widths are also influenced by these effects.
Antiphase Boundary Calculations for the L12 Structure Using an Embedded Atom Method Model
Authors: Brown Jeanne R. , Johnson Robert A. 
Published: March 2011

ABSTRACTA model based on the embedded atom method [1] has been used to calculate antiphase boundary (APB) energies of three low-index planes for alloys having the L12 structure. The lattice constant, cohesive energy, unrelaxed vacancy formation energy, bulk modulus, and average shear modulus for each element are used as inputs into the model. Effects of the APB orientation and of the range of interaction in the model are examined. Both unrelaxed and relaxed APB energies are compared with available experimental values and earlier theoretical results. A strong anisotropy was found in six of the seven alloys studied. The {111} APB energy was consistently smaller than that for the {110} APB, while the {100} APB energy was found to be very close to zero with very little difference between the unrelaxed and relaxed values. For both energy and relaxation amounts, the results did not vary much with the range of interaction, so that 3rd nearest-neighbor calculations were found to be satisfactory approximations.
Comparison Between Homo-And Hetero-Epitaxial Layers by Photoreflectance Spectroscopy
Authors: Jiao K.L. , Shi Z.Q. , Anderson Wa. 
Published: March 2011

ABSTRACTMOCVD grown GaAs and InP epitaxial layers have been studied using photoreflectance spectroscopy. Homogeneous and heterogeneous structures were employed to investigate the influence of the mismatch induced strain and dislocations. All the tested spectra contained a sharp peak related to the fundamental absorption edge and a pronounced Franz-Keldysh oscillation. The data analysis revealed a consistent difference in bandgap, temperature coefficients of the bandgap, and surface electric
field, in the order of the degree of mismatch. For GaAs/GaAs and GaAs/Si samples, the bandgaps derived from the three point method were 1.436 and 1.324eV, respectively. Values of 1.334, 1.325, and 1.294 eV for the bandgap were found for InP/InP, InP/GaAs, and InP/GaAs/Si, respectively. For GaAs epitaxial layers, the intensity of the surface
field bore a ratio of 1.18:1 between GaAs and Si substrates. For InP epitaxial layers, the ratio was 1.23:1.12:1 in the sequence of InP, GaAs, and GaAs/Si substrates. Such a measure must be related to the mismatch in the heteroepitaxy structures. A shoulderlike peak, 18-23 meV below the gap-energy peak (Eo), was found for GaAs samples, which could be impurity related. A broad shoulder-like peak 30 meV below the fundamental absorption edge was also observed only for InP/GaAs/Si and hence attributed to some shallow defect levels induced by antiphase disorder.
Defect Network in Superconducting Ceramic Oxides Studied by Neutron and Proton Irradiation
Authors: Mezzetti E. , Andreone D. , Castagno G. , Cherubini R. , Colombo S. , Gerbaldo R. , Minetti B. 
Published: March 2011

ABSTRACTThis paper investigates both transport properties and nature of superconductivity breakdown or, conversely, enhancement in oxide ceramics, due to radiation-induced defects.Low-fluence neutrons (≈107 n cm-2 at 3 MeV) can sensitively damage the samples, giving experimental evidence that the breakdown of coherent percolating paths produces decoupled domains. A set of preliminary measurements shows that high-fluence proton implantation can either damage or enhance critical current density in a currently non controllable way. In both cases strongly damaged or enhanced superconducting paths short-circuit the unaffected bulk network.
X-Ray Scattering from Highly Distorted Lattices Undergoing Phase Separation
Authors: Rao Satish I. , Wu C.H. , Houska C.R. 
Published: March 2011

ABSTRACTCalculations by Krivogtaz [1] dealing with quasiline formation in highly distorted lattices undergoing phase separation have been extended for randomly arranged particles. Qualitative experimental evidence from powder patterns, already in the literature for Cu-Be,Ni-Be,Cu-Ti and Nimonic alloys[2-5], have demonstrated the existence of quasilines. This extended calculation deals with ellipsoids of revolution and allows one to examine different shapes and transformation strains in an anisotropic medium. it is shown that the precipitate transformation strains play a very important role in shaping the Bragg-like profiles. This is most obvious in the intermediate stage which includes Bragg scattering from the lattice, regular static diffuse scattering and the quasiline. For precipitate sizes associated with maximum age hardening, all three normally become scrambled into a broad assymetrically shaped Bragg-like peak. However, a comparison of the theoretical calculations with experimental data from an age hardened Cu-Be alloy shows qualitative agreement, which we believe is due to the non-random nature of precipitation in this system.
Effect of 120 MeV Oxygen Ion Irradiation on Current-Voltage Characteristics in YBaCuO
Authors: Iwase A. , Masaki N. , Iwata T. , Nihira T. 
Published: March 2011

ABSTRACTThe effect of 120 MeV oxygen ion irradiation on the current-voltage(I-V) characteristics has been studied at 77.3 K in YBaCuO superconductors. In the small current region, the voltage V against the current I and the ion-fluence Φ can be described by the following simple form; ln(V/VO)=αln(I/IO)×ln(Φ/ΦO), where α, VO, IO and ΦO are constants. The experimental results have been discussed in terms of current-induced unbinding of thermally excited vortex pairs.
Unstable Plane in Bi-Sr-Ca-Cu-O System by TGA
Authors: Zhang H. , Feng Q.R. , Feng S. Q. , Zhu X. , Gan Z. Z. 
Published: March 2011

ABSTRACTBy thermogravimetry analysis (TGA), x-ray diffraction and R(T) relationship determination, the BiSrCaCuO system superconductors with composition of 2201, 2212 and 2223 were studied systematically. The experiments discovered that there is an unstable plane in 2223 sample, but not in 2201 and 2212. Comparing this result with the structure and property of 123 phase in YBCO-system, analyzing carefully, we found that only those superconductors which have the unstable plane are of higher Tc value. The role of the unstable plane in a superconductor is discussed. It is possible that 110K superconductivity in Bi-system has a close relationship with the existence of this unstable plane.
Quantitative Analysis of Diffuse Scattering from Concentrated Alloys: The Last Two Decades
Authors: Cohen J. B. , Georgopoulos P. 
Published: March 2011

ABSTRACTThe techniques for measurement and analysis of the absolute intensity from concentrated alloys have now improved to the point where reliable analysis for local order and displacements can be performed in reasonable times, for both clustering and ordering. Coupling the results with computer simulation provides information on the details of chemical fluctuations and, as well, tests of modern theories of transformations. In some cases, the results have been confirmed via direct imaging (FIM, HRTEM). The role of this information in our understanding of phase transformations is reviewed, and suggestions for future studies are given.
Phase Transitions in and Ferroelasticity of 9-Hydroxyphenalenone
Authors: Svensson Christer , Abrahams S. C. 
Published: March 2011

ABSTRACTCrystalline 9-hydroxyphenalenone is monoclinic between 145 K and the melting point at 475 K. The space group is P21 below 255 K, P21/c between 255 K and 380 K, and I2/c above 385 K. A model for the 255 K transition involves inplane rotations of about 40° for one quarter of the molecules. Further rotation and translation takes place at the 380–385 K phase transitions. All three phases are expected to be ferroelastic, but at present only the unit cell of the room temperature phase has been reversibly reoriented. The spontaneous strain decreases from 0.24 at 145 K through 0.18 at room temperature to 0.14 at 430 K, assuming a tetragonal prototype. Domain walls are temperature dependent with orientation (1.86, 0, 1) and (1, 0, −1.86) at 298 K. Ferroelastic transformation proceeds by a slip process, approximately in the molecular planes. A prototype common to all three phases can be derived with space group P41. Macroscopically, the transformation is accompanied by a remarkable change of shape; if unfractured, the crystals exhibit shape memory.
The Role of Phonon Dispersion in Controlling Atomic Rearrangement in Solid Solutions
Authors: Wu T.B. 
Published: March 2011

ABSTRACTThe elastic energy of a solid solution of atoms of different sizes can be written as a Fourier sum with coefficients as a function of position in reciprocal space. Each coefficient is made up of three components. The first one is an energy associated with taking atoms of the pure elements and placing them randomly on the average lattice o f the alloy. The second one is an elastic gradient energy associated with composition fluctuations and which is proportional to the second derivative of the dispersion curve. The third is the relaxation energy concerned with the motion of atoms away from the average lattice to more comfortable positions. Because of the contribution of the elastic gradient energy, it is shown that the shape of the phonon dispersion curve can affect precipitation or ordering in a solid solution.
A Tem Study of the Metakaolin-to-Mullite Transformation in Kaolinite
Authors: Horner J.A. , Martinez W.A. , Greenhut V.A. 
Published: March 2011

ABSTRACTTwo different kaolinites were heated in the range 850–1000°C and subsequently analyzed using TEM to study the metakaolinite-to-mullite reaction sequence. Metakaolinite was found to exist as amorphous relics of the original kaolinites. Small particles of a spinel composition appeared and grew to a maximum size of ∼50Å at temperatures below the 980°C exothermic reaction. Mullite was detected at and above 980°C which accounts for the 980°C exothermic reaction of these kaolinites.
Phase Transitions in Hoalga
Authors: Doukoure M. , Gignoux D. , Sayetat F. 
Published: March 2011

ABSTRACTHoAlGa is hexagonal at room temperature. It undergoes two magnetic transitions succesively at TN = 32 K from a paramagnetic to a triangular antiferromagnetic state where the Ho moments lie in the basal plane and at Tt = 18 K in the course of which the moments rotate toward c giving rise to a colinear antiferromagnetic arrangement. X-ray experiments performed between 5 and 300 K allow to determine the crystal evolution through the two transitions. The hexagonal symmetry is not lowered through the transitions; this result is compatible with the observed magnetic groups. The thermal expansion curves show a very anisotropic behaviour of the lattice parameters. The “c” parameter shrinks below TN and this anomaly is to be related to the magnetic order. Along a, a positive thermal anomaly appears below 70 K and this can be interpreted by crystal field effects. Stability of magnetic structures is discussed with regard to exchange interactions and magnetocrystalline anisotropy.
Anisotropic Effects in Antiferromagnetic MnSb2O4 and NiSb2O4 : Structural and Vibrational Evolution Studies
Authors: Gavarri J.R. , Chater R. , Genet F. 
Published: March 2011

ABSTRACTPowdered samples and crystals of the antimony isomorphous MnSb2O4 and NiSb2O4 have been prepared using hydrothermal synthesis. The anisotropic elastic and magnetic properties of these tetragonal structures are compared, using low temperature diffraction techniques (X-ray and neutron) and Raman scattering experiments. Magnetostrictive effects in MnSb2O4 are interpreted. An anomalous frequency shift is observed below 70 K and the change of the Grüuneisen constant is interpreted.
Effects of the Tahir-Kheli,Intermediate-Temperature Teriis on the Clapp and Moss, High–Temperature Formulation of Short Range Order (Sro) in Li-Mg Alloys
Authors: Gilder H.M. , Vignesoult S. 
Published: March 2011

ABSTRACTPresent calculations of the Cowley-Warren SRO parameters, using the Rasolt-Taylor-Dagens, first principles pair potential for Li-Mg alloys show that the higher order terms of Tahir-Keli's intermediate-temperature solution of the Ising, spin-1/2 ferromagnet modify the Clapp and Moss, hightemperature solution in a very significant way. The present results are compared to previous calculations and measurements on Li-10 at.% Mg and Li-50 at.%Mg alloys.
A New Ordered Structure of the off-Stoichiometric Laves Phase Having C15- Type Structure in Mg-Cu-Si System
Authors: Komura Y. , Matsunaga T. 
Published: March 2011

ABSTRACTA new ordered structure has been found in a ternary Mg-Cu-Si Laves phase whose composition is around Mg(Cu0.80Si0.20)2.50. The ordering between Cu and Si of Cl5-type Mg(Cu0.81Si0.19)2.53 specimen was analysed by a single crystal X-ray diffraction method. It belongs to a space group P41 32(or P4 332) having a=6.9598Å contrary to the disordered structure of Fd3m. The ordered structure is characterized by the ordered 4-fold screw arrangements of Cu and Si atoms located on four tetrahedra in the unit cell leaving Mg atoms on 8c sites. The order parameter S= αl−α2 was found to be 0.74 in this specimen, where αland α2 are occupancy factors of Cu for 12d and 4a sitesof the space group P4 132, respectively. The order parameters were measured as a function of annealing temperature by using Warren's method for quenched powder specimens of Mg(Cu 0.80 Si 0.20)2.40. The maximum value of S reached to 0.75 at 200°C, which is a little lower than the expected value of perfect order, S=0.85. The order parameter then decreases continuously with increasing annealed temperature and become zero at about 600°C, indicating order-disorder transformation temperature.
Determination of Short Range Order Parameters in 62Ni0.765Fe0.235 At 600°C Effect of a Quench
Authors: Lefebvre S. , Bley F. , Cenedese P. 
Published: March 2011

ABSTRACTDifferent states of local order have been previously measured at room temperature on water quenched crystal of Ni0.76562 Fe0.235 [1−2]. The Cowley' parameters and the interaction pair potentials in a Clapp and floss approximation have been determined at : 385° C, 470°C, 507°C, 535°C, 685°C that is under and above Tc which is equal to 500°C for this composition.The kinetic of long range order establishment is, in this alloy, very sluggish even near Tc [3]; the kinetic of short range order (SRO) is completely different and may be more complex [4]. In the previous experiments it has been supposed that the state of high temperature was retained during the quench. The following experiments check this hypothesis.
Ordered Structures in Ti Al Alloys in the Composition Range from Ab To Ab3
Authors: Loiseau A. , Lasalmonie A. , Van Tendeloo G. , Van Landuyt J. 
Published: March 2011

ABSTRACTThis paper describes crystal structures of Ti1−x, Alx alloys containing from 40 to 75 % at. Aluminum observed by electron microscopy. Two new phases are in particular discussed : Ti2 Al and a phase denoted X, which is a non stoichiometric Ti3Al5.
Order-Disorder Transition at High Temperature and Microdomain Formation in Oxidized Ferrites
Authors: Grenier J.C. , Pouchard M. , Hagenmuller P. , Henche M.J.R. , Vallet M. , Calbet J.M.G. , Alario-Franco M. A. 
Published: March 2011

ABSTRACTAt high temperature, nonstoichiometric perovskite-type related ferrites can be oxidized in air. At first sight, this phenomenon appears rather surprising since it corresponds to a partial formation of iron +IV. Moreover a structural transition occurs from a vacancy ordering state to a pseudodisordering one characterized by a cubic perovskite-type X-ray diffraction pattern. A TEM study has shown in fact a more complex situation attributed to a microdomain texture. This is explained from a crystallographic point of view and correlated to the existence of mixed valencies of iron.
Evidence of a Coupling Between Magnetic and Chemical Interactions in Iron-based Alloys
Authors: Pierron-Bohnes V. , Cadeville M.C. , Gautier F. 
Published: March 2011

ABSTRACTThe simultaneous occurrence of chemical and magnetic interactions in transition metal alloys greatly influences their thermodynamic properties. However the experimental evidence of the Coupling between both interactions has not been demonstrated so far. The present study shows that such a coupling exists in iron-based alloys (FeCo, FeMn, FeV) and that it modifies qualitatively the chemical short range order. This is evidenced from its temperature dependence in both ferromagnetic and paramagnetic phases which displays a marked change of behaviour at the Curie temperature (Tcm). Theoretical models which account qualitatively for the whole of the observed behaviours are briefly discussed.
Towards a True Fe-Ni Phase Diagram
Authors: Rossiter P L. , Jago R. A 
Published: March 2011

ABSTRACTA modification to the existing Fe-Ni phase equilibrium diagram is proposed that takes account of the low-temperature ordering reaction to FeNi. It is shown that true equilibrium is never attained during slow cooling of Fe-Ni alloys, even for iron meteorites (which cool extremely slowly). In all real cases, a metastable phase diagram applies, in which the depressed γ/α+γ solvus produces a more extensive γ+ FeNi phase field than for the equilibrium case. This enlarged phase field is used to explain the decomposition of supersaturated Fe-Ni to γ+ FeNi, which is observed only in iron meteorites.