bluuebunny/crossref_metadata_2025_split huggingface dataset:
The DX Center: How Complicated Can a Point Defect Be?
Authors: Theis Thomas N. 
Published: March 2011

ABSTRACTI summarize a large body of experimental and theoretical work, especially in Sidoped GaAs and AlxGal−xAs, which has led to our present understanding of the DX center. There is good evidence that the DX center is just the simple donor, but each donor atom can exist in either of two distinct lattice configurations, each with its own spectrum of bound electronic states. At present the model which appears to best explain this unexpected complexity is that of Chadi and Chang, which predicts a large bond-breaking distortion of the lattice, accompanied by capture of two electrons by the donor. I argue that the best evidence to date for the predicted distortion is provided by observations of alloyperturbations of the DX level. Furthermore, there is now very convincing evidence that the DX level is a two-electron state. I briefly summarize what is known about the bound state spectra of the substitutional and relaxed (DX) configurations, and then discuss the very interesting question of how the donor captures two electrons from the conduction band to theDX level. There is good, although indirect, evidence that an excited one-electron state acts as an intermediate in the thermal emission and capture process. A different excited state appears to 15e involved in photoemission. Although much of this complexity was unforeseen by Chadi and Chang, it nevertheless seems to be consistent with their model. However, I point out a number of issues which still require experimental or theoretical resolution.
Analysis of Anomalous Peak Heights in DlTS of MBE-Grown Aluminum Gallium Arsenide
Authors: Lim W. , Trombetta L. P. , Jamison Keith 
Published: March 2011

ABSTRACTDLTS data taken on MBE grown AlGaAs films show peak heights which increase, maximize, and then decrease with increasing sample temperature. This behavior is difficult to explain within the context of conventional DLTS analysis. We suggest that the data can be accounted for by a trap with a temperature dependent capture cross section in conjunction with a model described by Lee and Borrego in which electron and hole emission rates are comparable. Using this analysis, we obtain an effective trap depth Eeff of 0.35 eV and a capture cross section activation energy Eσ 0.25 eV.
Optical Investigations on Donor Doped CdTe
Authors: Stadler W. , Meyer B.K. , Hofmann D.M. , Sinerius D. , Benz K.W. 
Published: March 2011

ABSTRACTThe recombination luminescence involving the A-center, a Cd vacancy paired with a nearest neighbour donor, was investigated in CdTe doped with group VII and III elements. Depending on the type of donor doping, distinct differences in the A-center acceptor binding energies and electron phonon couplings are resolved. Optically detected magnetic resonance shows that the A-center behaves as a shallow effective masstype acceptor consiscent with its small binding energy.
Minority Carrier Induced Debonding of Hydrogen from Shallow Donors in Silicon
Authors: Seager Carleton H. , Anderson Robert A. 
Published: March 2011

ABSTRACTWe have investigated the dissociation of donor-hydrogen pairs in Schottky barrier capacitors fabricated from phosphorus and arsenic doped silicon, at temperatures in the range 24 to 110°C. At zero bias the release of donor trapped hydrogen does not follow first order kinetics. Introduction of minority carriers by illumination or forward bias injection enhances the rate of hydrogen release and redistribution, but otherwise leaves the functional form relatively unchanged. Numerical modeling shows that the debonding rate must be proportional to the local hole density. If the dissociation process is carried out in reverse diode bias, some of the released hydrogen rebonds deeper in the silicon, outside the depletion region. In addition, a portion of the charge density in the depleted region is seen to be metastable and disappears after several hours at room temperature. This observation suggests the existence of a positive charge state of the donor-hydrogen pair which may be the precursor to dissociation. While several groups have recently pointed out that reverse-bias annealing data suggest the existence of a negative charge state of interstitial hydrogen, our observation of an electronically controlled debonding rate. casts considerable doubt on the firmness of that conclusion.
DLTS Study of Optoelectronic Devices in the Dynamic Regime
Authors: Mil'shtein S. , Tripp D. , Karakashian A. 
Published: March 2011

ABSTRACTEvery semiconductor device contains as grown and process induced defects even though the techniques to minimize the density of defects are known. Conventional DLTS methods are used to identify the trapping defects in the device. However, the activity of the traps could be suppressed or enhanced by the operating conditions of the device such as temperature, current through the device or light directed onto the device. We studied the DLTS spectra of silicon polycrystaline solar cells, as well as silicon and GaAs photodetectors in the dynamic regime, namely under light and at elevated temperature. Significant change in the resulting spectra were observed when compared to the spectra obtained by conventional DLTS methods.
Ferroelastic Domain Switching In Tetragonal Zirconia
Authors: Chan C. J. , Lange F. F. , Rühle M. , Jue J. F. , Virkar A. V. 
Published: March 2011

ABSTRACTFerroelastic domain switching is one of the possible toughening mechanisms in ceramic materials. Microstructural evidence of domain reorientation (switching) in polydomain tetragonal zirconia single crystals is observed upon the application of a unidirectional compressive stress. Dark field imaging of the three {112} tetragonal twin variants in a {111} zone indicates that two sets of twin variants grow at the expense of the third set upon application of uniaxial compression. The diminishing variant is the one with its c axis parallel to the compression axis. Indentation experiments on uniaxially compressed samples show an anisotropy in crack length. Crack propogates more easily along the loading direction. A construction for the orientation relationship of domains and their twin boundaries is presented.
New Concepts in Modelling Interfacial Defects in Yba2Cu307−X
Authors: Darab John G. , Maccrone R.K. , Rajan K. 
Published: March 2011

ABSTRACTThe {110} twin planes and the dislocations at orthogonal domain interfaces which form in YBa2Cu3O7−x during cooling from =950°C have been modelled using a simple geometric approach. A summary of the stereochemistries of the distorted copper(II)-oxygen complexes associated with these interfacial defects has been compiled. The localization of holes at these distorted copper(II) complexes and the effect they have on thesuperconducting properties of YBa2Cu307−x materials arediscussed.
Microstructural Analysis of Hexagonal Close-Packed Metals Using X-Ray Diffraction and Transmission Electron Microscopy
Authors: Griffiths M. , Winegar J.E. 
Published: March 2011

ABSTRACTThe techniques employed for X-ray diffraction analysis of dislocation substructures in hexagonal close-packed metals are descibed and assessed by comparison with direct observations using transmission electron microscopy.
Electron Channeling Pattern: A Tool for Studying YBaCuO-HTSC Thin Films
Authors: Young K. H. , Sun J. Z. , James T. W. , Nilsson B. J. L. 
Published: March 2011

ABSTRACTHigh Tc superconducting (HTSC) films synthesis for demanding applications requires epitaxial c-axis growth without high angle grain boundaries. Electron channeling pattern (ECP) analysis using a scanning electron microscope is a non-destructive, fast, direct,and economical tool to determine the orientation and crystallinity of epitaxial films. We have successfully employed this technique to examine our in-situ laser ablated YBa2Cu307−δ superconducting thin films grown on LaAI03 (100) substrates. By changing the energy of the incident electron beam, we can also monitor the film quality vs. depth. The surface bending of YBa2Cu3O7−δ thin films due to the cubic-rhombohedral transition of LaAI03 substrates is also visiblewhen sharp ECPs are present. For films with rough surfaces, the ECP contrast is obscured by unwanted contrast arising from surface features. This unwanted contrast can be minimized by defocusing the electron beam.
Preparation and Characterization of La1Sr2Nb5O10−x Specimens
Authors: Galvàn Donald H. , Avalos-Borja M. , Cota-Araiza L. , Cruz-Reyes J. , Early E. A. 
Published: March 2011

ABSTRACTRecently Ogushi et al reported a La-Sr-Nb-O compound with a superconducting temperature of about 225 K. The possibility of having superconductors with such a high temperature is certainly technologically relevant. We prepared specimens with the same nominal stoichiometry and performed characterization by SEM, high resolution TEM, Scanning Auger and X-rays.
Positron Lifetime Studies of Defect Structures in Bal-xKxBiO3
Authors: O'Brien J.C. , Howell R.H. , Radousky H.B. , Sterne P.A. , Hinks D.G. , Folkerts T.J. , Shelton R.N. 
Published: March 2011

ABSTRACTTemperature-dependent positron lifetime experiments have been performed from room temperature to cryogenic temperatures on Ba1−xKxBiO3. for x=0.4 and 0.5. From the temperature dependence of the positron lifetime in the normal state, we observe a clear signature of competition between separate defect populations to trap the positron. Theoretical calculations of lifetimes of free or trapped positrons have been performed on Ba1−xKxBiO3, to help identify these defects. Lifetime measurements separated by long times have been performed and evidence of aging effects in the sample defect populations is seen in these materials.
Phonons, Oxygen Isotope Effect and Superconductivity in Ba1−xKxBiO3
Authors: Jin W. , Loong C.K. , Hinks D.G. , Vashishta P. , Kalia R.K. , Degani M. H. , Price D.L. , Jorgensen J.D. , Dabrowski B. 
Published: March 2011

ABSTRACTThe phonon densities-of-states (DOS) of superconducting Ba1−xKxBi16O3 and Ba1−xKxBi18O3 (x=0.4) are determined using molecular dynamics (MD) simulations and inelastic neutron scattering measurements. The reference isotope-effect exponent is obtained from the mass variation of the first frequency moment of the phonon DOS. The energy gap, oxygen isotope-effect exponent and electron tunneling characteristics are calculated within the framework of Eliashberg theory of electron-phonon coupling.
Defects, Microstructure and Properties of the Industrial 35 CrMoV Steel
Authors: Wu Wangzi Wu Wangzi , Qiao Guiwen Qiao Guiwen 
Published: March 2011

ABSTRACT35 CrMoV steel is widely used in industries. To select the best technology for improving the mechanical properties, a series of heat treatments were tested. Metallographic examination indicates that the microstructure is a kind of non-typical bainite and, to a certain extent, similar to tempered troostites. TEM observation shows that rod-like alloying cementite distributed in ferrite grains laid parallel to each other and ultra-fine alloying carbides also dispersed in the lath-like ferrite grains. Moreover, there exists high density of dislocation tangles and microtwins. Detailed discussions are made on the solid solution strengthening, the work hardening process and the crack propagation by view of microstructure, defects and stress concentration.
Modulated Atomic Displacement Description and Easy Structural Factor Computing
Authors: Wolfers P. 
Published: March 2011

ABSTRACTThe displacement of a particular atom in a modulated crystallographic structure can be described in terms of a Fourier Series. In the harmonic single wave vector approximation, the structure factor can be written as a function of the atomic displacement vectors. Such expressions are however not valid in the multi-wave-vector case. We propose a general description for the modulation of displacement where each scattering center (atom) is distributed on several sites whose population is modulated. In the paper, we will show that approach is well suited for computing. We have developed a general least squares program which has been applied to the modulated phase of αU(T < 43 K) [2].
Stationary States in Inhomogeneous Ordered Binary Alloys : Long-Period Superlattices
Authors: Avignon M. , Chakraverty B.K. 
Published: March 2011

ABSTRACTWe examine the nature of all possible stationary states in an inhomogeneous ordered binary alloy. For this purpose, we use a development of the free energy in terms of the gradient of the non linear Euler equations is determined from the nature of its singular points. This method allows us to study these solutions for arbitrary expressions of the free energy of the homogeneous system as well as of the gradient coefficients. In general, periodic solutions which can be identified with long period superlattices are found. In specific cases, analytic solutions can be obtained. Fourier components are calculated and compared with experimental values determined for CuAu II.
Ordering With Phase Separation in an Fe-Al-Si Alloy
Authors: Matsumura S. , Sonobe A. , Oki K. , Eguchi T. 
Published: March 2011

ABSTRACTTwo kinds of process of ordering with phase separation, B2 or DO3 → (A2 + DO3), on annealing at a temperature of 873 K in an alloy of Fe-6 at%Al-9 at%Si were investigated by means of transmission electron microscopy and X-ray diffraction. The decomposition of DO3 phase proceeds by the development of periodic fluctuations along <100> directions in both B2 and DO3 types of degree of order. Newly born DO3 domains take the form of rectangular prism and align along <100> directions. In the transition from B2, on the contrary, there is a marked difference between the morphologies of the fluctuations in the two types of degree of order at the early stage of annealing. The degree of B2 type order fluctuates along <100> directions, while the fluctuation in the degree of DO3 type order does not form the <100> modulated structure sat the early stage of annealing. The morphology after a prolonged annealing is similar to that in the case of DO3 → (A2 + DO3).
On The Phase Structure of the Asymmetric Three-State Potts Model
Authors: Gehlen G. v. 
Published: March 2011

ABSTRACTFinite-size scaling is applied to the Hamiltonian version of the asymmetric Z3-Potts model. Results for the phase boundary of the commensurate region and for the corresponding critical index ν are presented. It is argued that there is no Lifshitz point, the incommensurate phase extending down to small values of the asymmetry parameter.
Simulation of Atomic Configurations in Short Range Ordered Ni3Fe
Authors: Bley F. , Cenedese P. , Lefevbre S. 
Published: March 2011

ABSTRACTA procedure similar to that of Gehlen and Cohen and Williams is used to simulate atomic configurations of short range ordered Ni3Fe. The short range order parameters were previously measured after different heat treatments. Probabilities of different clusters are computed from those models : triangles, tetrahedrons, clusters as defined by Clapp.These probabilities vary with the enhancement of short range order. It is shown that most of the clusters the probabilities of which increase with short range order, are directly related with the L12 ordered structure: either they have the L12 structure, or the L12 structure modified by one or two antiphase boundaries. Such clusters are identified in the model in order to display perfectly ordered domains.
Computer Models of Rapid Solidification
Authors: Gilmer G. H. , Broughton J. Q. 
Published: March 2011

ABSTRACTWe discuss some recent simulations of crystal growth from the melt at large values of the undercooling. Molecular dynamics studies of the crystallization of a Lennard-Jones liquid and Monte Carlo simulations of the Ising model have together provided information on several aspects, including maximum growth rates, generation of vacancies and other defects, and impurity trapping.
Precipitation Reactions in Ai-Zr-Alloys
Authors: Haugan T. , Nes E. , Ryum N. 
Published: March 2011

ABSTRACTA new mode of precipitation of the metastable Al3 Zr in Al-Zr-alloys has been investigated. The salient aspects of this precipitation reaction are: (i) The formation of precipitate configurations of a well defined macroscopic morphology, (ii) Each individual precipitate within the colonies grows in crystallographic directions, and (iii) The absence of a high angle grain boundary as a reaction front.
Mechanical Behavior of Cu-10ni-6Sn Spinodal Alloy
Authors: Lee T. C. , Shekhar S. , Vilassakdanont A. , Subramanian K. N. 
Published: March 2011

ABSTRACTExperimental studies on deformation behavior of Cu-10Ni-6Sn spinodal alloy specimens subjected to different aging treatments were carried out at various temperatures ranging from 77°K to 353°K, using a micro-tensile device. It was found that the total elongation was independent of aging time as long as the modulated structure was coherent. Observed slip distribution and activation energy obtained in these investigations are presented. Transmission electron microscopy of deformed specimens showed straight dislocations in as-quenched samples; they were curved and wavy in aged samples. Burgers vector analysis of the dislocations present in the deformed aged samples indicated that they were of mixed character. Preliminary theoretical results on the role of wave-squaring of the internal stress field on CRSS are also presented.
Multilayer Solid Adsorption and The Roughening Transition
Authors: Weeks John D. 
Published: March 2011

ABSTRACTWe discuss some the physical issues involved with the adsorption of several layers of a solid adsorbate on a strongly attractive substrate. The experimental observation at low temperature of vertical risers (the “layering transitions”) in the plot of coverage versus pressure can be understood using a one-layer 2D lattice-gas model. The behavior at higher temperature is described in terms of a coarse-grained interface hamiltonian which emphasizes the role of long-wavelength interface fluctuations. A simple variational theory predicts that the coverage in the nth layer is a continuous function of pressure above a critical temperature Tc,n which depends weakly on n and has as its large n limit the bulk roughening temperature TR.
Equilibrium Shapes for Grain Boundaries and Surfaces with Anisotropic Surface Tension Functions
Authors: Taylor J.E. 
Published: March 2011

ABSTRACTThe geometric configuration of grain boundaries and surfaces seems to play a significant role in phase transformations and surface phenomena. Determining the equilibrium configurations of such boundaries for a given surface tension function γ is additionally an interesting mathematical problem; it reduces in the case of isotropic surface tension to the minimal surface problem. A framework is given here for determining such configurations in the other extreme case, where the equilibrium shape of a crystal of fixed volume (the Wulff shape) is a polyhedron. Some results obtained within this framework are outlined.
Phase Transitions in Graphite Intercalation Compounds
Authors: Clarke R. 
Published: March 2011

ABSTRACTGraphite intercalation compounds offer a unique laboratory in which to study many kinds of phase transitions. These include melting, reorientations, staging, commensurate-incommensurate effects, and certain types of lattice gas transitions. Molecular and alkali-metal intercalates are discussed with reference to results of X-ray diffuse scattering studies as a function of temperature and pressure.
18R to 2H Martensite Transformation in A Cu-Zn-Al Alloy
Authors: Rios Jara D. , Morin M. , Guénin G. 
Published: March 2011

ABSTRACTAn unexpected 18R martensite to martensite transformation was obtained in Cu-Zn-Al alloy during the training process for 18R single crystal preparation: this later was induced from a β1 single crystal by application of a constant tensile force at room temperature and by lowering the temperature until β1 -->18R transformation occurs. At this condition, and after several cycles, some plates of a new phase were observed to appear in a sudden way inside the 18R single crystal region. By studying the transformation characteristics as given by elongation temperature curves and trace analysis we conclude that this new phase plates are 2H martensite.
Precursor States in the Phase Transformation Accompanying a Solid-Solid Reaction
Authors: Chaix-Pluchery O. , Bouillot J. , Freund F. , Niepce J.C. , Peyrard M. 
Published: March 2011

ABSTRACTThe studied transformation is associated with the decomposition reaction of brucite-type hydroxides into the corresponding oxide. It is shown, by various techniques (X-ray and neutron diffraction, Raman Spectroscopy, proton conductivity) that some modifications take place in the hydroxide structure before its transformation into the oxide structure,i.e., at a temperature lower than the transformation temperature. A mechanism is proposed to account for the experimental data.
Quench Sensitivity of Almgsi-Alloys Containing Mn or Cr
Authors: Dons A.L. , Lohne O. 
Published: March 2011

ABSTRACTIn AlMgSi-alloys cooled from about 773K (500°C) the strength after ageing depends on the rate of cooling. By addition of Mn or Cr dispersoids are formed which may control grain structure. The dispersoids also act as nucleation sites for coarse β′-Mg2Si particles. This makes the alloys more quench sensitive, in this paper the influence of 0.56%Mn on quench sensitivity is compared to that of 0.23%Cr in Al–O.6%Mg-1.0%Si industrial alloys.The alloys were homogenized at 793K (520°C) and 853K (580°C), extruded, quenched in water or cooled in air, and aged to maximum hardness. The density of dispersoids varied with homogenizing heat treatment. Quench sensitivity increased with increasing density of dispersoids.The two alloys had about equal densities of dispersoids after homogenizing at 793K (520°C), but the alloy containing Cr was found to be more quench sensitive than the alloy containing Mn. This is discussed and compared with other findings.
Solid State Ionics in Solid Oxide Fuel Cells
Authors: Schoonman J. , Dekker J.P. , Broers J.W. , Kiwiet N.J. 
Published: March 2011

AbstractDue to the high operating temperatures (900-1000 °C) the material demands upon Solid Oxide Fuel Cell (SOFC) components are quite stringent. Preferably lower operating temperatures (700-800 °C) are desired so that gas feed lines, heat exchangers, and structure components can be fabricated from relatively cheap stainless steel components.Typically, the materials used in a SOFC are yttria stabilized zirconia (YSZ) as the solid electrolyte, nickel-zirconia cermet as the anode, strontium doped lanthanum manganite as the cathode, and magnesium doped lanthanum chromite as the interconnection material. The electrolyte and interconnect are difficult to fabricate, because they need to be gas tight, yet thin (30-50 microns) and mechanically stable. Due to the high volatility of CrO3the densification of LaCrO3into thin layers is a more demanding challenge than the fabrication of the electrolyte.Electr°Chemical Vapor Deposition is the key technology for making thin layers of the solid electrolyte as well as the interconnection material LaCrO3. In the simplest case the oxide growth can be modeled with the Wagner oxidation theory for metals. In this paper theory and experiment of the growth of ionically conducting YSZ and electronically conducting LaCrO3will be discussed.
Influence of Macrocyclic Ligands on Ion Transport in Solid Polyelectrolytes
Authors: Chen K. , Doan K. , Ganapathiappan S. , Ratner M. , Shriver D. F. 
Published: March 2011

AbstractCryptands and crown ethers increase the cation transport in phosphazene and alkoxyaluminate polyelectrolytes. Vibrational spectroscopy indicates that the increased conductivity originates from reduced ion pairing.