bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin and Behavior of Main Electron Traps in Si-Implanted GaAs
Authors: Fang Z-Q. , Yamamoto H. , Look D. C. 
Published: March 2011

ABSTRACTThe electron traps in Si-implanted active layers(n∼1017 cm−3) have been studied by capacitance and conductance DLTS techniques in conjunction with different anneal conditions, which include rapid thermal anneals at different temperatures and furnace anneals with a Si3N4 cap or capless in an AsH3 atmosphere. As compared to the electron traps in as-grown bulk n-GaAs (n∼4×1016 cm−3), nearly the same electron traps, i.e. EL2, EL3, ELM, EL5, EL6 and EL9 can be observed in the Si-implanted layers. Through a comparison with the annealing behavior of the main elect ron traps in bulk n-GaAs, the processing associated origins of some of the traps(EL2, EL3, EL4, EL5 and EL9) observed in Si-implanted GaAs layers have been determined. For some Si-implanted GaAs capped with Si3N4 and furnace annealed, traps EL3 and EMA dominate the trap EL2. In such layers it is found that emission due to EL3 is reduced while emission from EL12 is augmented by increasing the filling pulse width from 10 μs to 5×103 μs. This phenomenon can be explained in terms of a defect reaction enhanced by electron capture, showing a metastability or bistability.
Order-Disorder Phenomena in Complex Alloys: The Case of A15-Based Substitutional Alloys
Authors: Turchi P.E.A. , Finel A. 
Published: March 2011

AbstractWe first discuss the applicability of the Generalized Perturbation Method to the study of ordering phenomena in complex alloys for which stability properties are electronically driven. In particular, according to previous work, it is recalled that a 3D-generalized Ising model is appropriate to address the problem of configurational order in A 15-based substitutional alloys. A ground state analysis of this model, including 1st, 2nd and weak 3rd and 7th pair interactions, generates two new ordered states at the composition A5B3 and A7B, apart from the well known A3B configuration. The stability of these predicted configurations is examined as a function of temperature and concentration by means of standard statistical techniques. The results are discussed in relation with the experimental situation.
Phase Equilibria and Solidification of Al-Rich Ai-Ui-Cu Alloys
Authors: Chen Sinn-Wen , Chang Y. Austin 
Published: March 2011

AbstractA liquidus projection of the Al-rich Al-Li-Cu system is proposed. The proposed liquidus projection was based on DTA, X-ray diffraction, metallography, EPMA, SEM, and chemical analysis of 50 ternary alloys. Using these data and those reported in the literature, and thermodynamic models of Al-Li, AI-Cu and Cu-Li, a thermodynamic description of the Al-rich AI-Li-Cu system was developed. The calculated isothermal sections at several temperatures and the liquidus projection are in agreement with the experimental determinations. Combining the thermodynamic models and a Scheil-type equation, quantitative solidification paths were described. The calculated amount of primary solidification phase was compared to the experimental determination.
Nanoscale Phase Separation Induced by Mechanical Alloying in the Iron-Erbium-Nitrogen System
Authors: Fu Z. , Fecht H. J. , Johnson W. L. 
Published: March 2011

AbstractMetastable phases, including nanocrystalline and amorphous structures, can be prepared by high energy cyclic deformation processes. In the present study, we compare the behavior of a stable congruent melting compound (Fe2Er Laves phase) with a mixture of pure elemental Fe and Er powders subjected to high energy ball milling. X-ray diffraction and transmission electron microscopy reveal similar results in both cases. In the early stages, a nanocrystalline fcc phase with lattice parameter a = 0.484 nm and a grain size of 6 nm is formed together with a bcc Fe-rich phase. Extended milling results in a nanoscale phase separation into Fe-rich and Er-rich crystallites with average grain sizes of 1.8-4 nm. Based on a lattice parameter analysis, the fcc phase was initially thought to be a metastable FeEr3 phase. Further studies revealed nitrogen gas in the milling vial had reacted with the powder during ball milling to produce the cubic ErN phase (“NaCl” structure with a lattice parameter of 0.4836 nm). Our experiments demonstrate that the steel vials for ball milling do not remain hermetically sealed during the milling process and a nitride phase can be formed easily if a catalyst for the dissociation of nitrogen molecules (such as Fe) exists in the system.
Grain Boundary Intermetallic Phases in Alloy 718
Authors: Burke M. G. , Miller M. K. 
Published: March 2011

AbstractA nickel base superalloy, Alloy 718, has been studied by analytical electron microscopy in order to trace the development of the complex microstructure which is produced during a typical multistage thermal treatment. The distribution of δ γ″, γ′ and Laves phases was found to be strongly dependent on aging treatment.
Atomistic Modeling of Extended Defects in Metalic Alloys: Dislocations and Grain Boundaries in Ll2 Compounds
Authors: Vitek V. , Ackland G. J. , Cserti J. 
Published: March 2011

AbstractExtended defects, such as dislocations and grain boundaries, control a wide variety of material properties and their atomic structure is often a governing factor. A necessary precursor for modeling of these structures is a suitable description of atomic interactions. We present here empirical many-body potentials for alloys which represent a very simple scheme for the evaluation of total energies and yet reflect correctly the basic physical features of the alloy systems modeled. As examples of atomistic studies we show results of calculations of the core structures of screw dislocations in Ll2 compounds. The same potentials have also been used to calculate structures of grain boundaries in these compounds. The deformation and fracture behavior of Ll2 alloys is then discussed in the light of grain boundary and dislocation core studies.
Deformation and Fracture Behavior of Tial
Authors: Fu C. L. , Yoo M. H. 
Published: March 2011

AbstractFirst-principles total-energy calculations of the elastic constants, shear fault energies, and cleavage energies of TiAl are presented. We find a large elastic shear anisotropy along the [011] direction, and high APB energies due to the strong cohesion between Ti and Al layers. Shear faults of SISF, SESF, and twin boundary are predicted to be prevalent due to their low energies. The anomalous temperature dependence of flow stress is explained by the cross-slip pinning and fault dragging mechanisms. The intrinsic brittleness of TiAl is discussed in terms of the low mobility of 1/2[110] dislocations.
Ground State Properties And Magnetism In Substitutionally Disordered Fe1-xCrx Alloys
Authors: Shelton W. A. , Pinski F. J. , Johnson D. D. , Nicholson D. M. , Stocks G. M. 
Published: March 2011

AbstractWe have performed calculations of the electronic structure of the random substitutional bcc Fe1-xCrx alloys, using the spin-polarized, self-consistent Korringa, Kohn and Rostoker coherent potential approximation (KKR-CPA) method. This is a first principles method based on a local spin density approximation for electron exchange and correlation energy. For the iron-rich alloys, we find that the average moment decreases linearly with Cr concentration, although the individual moments show a different concentration dependence and the Cr moment is anti-parallel to the Fe moment. This system is similar to Fe1-xVx system, although some details are different.
Design of High Elastic Modulus Alloy Using First Principles Electronic Theory
Authors: Masuda-Jindo K. , Terakura K. 
Published: March 2011

AbstractThe first principles ASW (augmented spherical wave) method is used to predict the elastic properties of Al-base and Ni-base fcc alloys. It is shown that the elastic modulus increase or decrease of the fcc alloys is closely correlated with the change in the lattice constants and that the results for various solute atoms can be summarized in the simple curves, depending on the species of the solute atoms. We demonstrate that the theoretical calculations for the binary alloys can be used for the design of the (multi-component) fcc alloys with desired elastic properties and lattice constants.
Microstructures of Ni3 Al Rapidly Solidified by Hammer-Anvil Technique
Authors: Mishima Yoshinao , Sasaki Shirou , Suzuki Tomoo 
Published: March 2011

AbstractThe Hammer-Anvil technique is employed for the rapid solidification of Ni3Al in the present work. The effect of off-stoichiometry on the change in the microstructure in the quenched alloy is examined for compositions within the L12 phase field at equilibrium. It is shown that non-equilibrium phases of various morphologies appear with fine grains of Ll2 phase, which have never been reported for the compound rapidly solidified by the roll techniques. With increasing aluminum concentration and with increase in cooling rate, the latter being judged by the difference in the thickness of the quenched foil, the fraction of the non-equilibrium phases appearing is found to increase giving more complex microstructure.
Designing Precipitation-Strengthened Iron-Aluminides for High-Temperature Applications
Authors: Maziasz P.J. , Mckamey C.G. , Hubbard C.R. 
Published: March 2011

AbstractA combination of minor solutes was added to an Fe3AI-type base alloy (Fe-28%AI6%Cr-0.05%B) to produce carbide precipitates. These solutes reacted to produce coarse Ti-rich MC and Cr- and Mo-rich M6C precipitates during fabrication at 650–1000°C. X-ray diffraction of hot-worked material revealed a significant amount of the higher temperature B2 phase is retained at room temperature, indicating that the D0s.↔,B2 phase transformation was retarded. During subsequent heat-treatments, the coarse carbides partially dissolved during annealing at 1100–1200°C, and no grain coarsening was observed at temperatures up to 1200°C. Specimens annealed for lh at 1250°C and quenched exhibited fine carbide precipitates both along some of the dislocations and at grain boundaries. The annealed and quenched specimens also contained many fine dislocation loops which coarsened and evolved into networks during further aging at 750°C for 1-10h. Tensile testing at 600°C showed improvements in strength and ductility of annealed and aged material relative to the hot-worked condition. Correlation of microstructural behavior with tensile properties changes supports the idea that microstructural control can be used to develop better high-temperature strength in the B2 phase. However, more data is needed on the combinations of alloying and heattreating which produce fine, stable matrix carbide dispersions in iron-aluminides.
The Stability of the T2 (AL6CuLi3) Phase During Examination in the Tem
Authors: Ramani A. S. , Tosten M. H. , Bartges C. W. , Michel D. J. , Reed J. R. , Ryba E. R. , Howell P. R. 
Published: March 2011

AbstractTransmission electron microscopy (TEM) has been employed to examine the stability of the (presumed) icosahedral T2 (A16 Cu Li3) phase. The T2 phase was found to be unstable either when irradiated by the electron beam or during in-situ heating. In addition, certain specimen preparation techniques (e.g., ion-beam thinning) also led to the decomposition of the T2 phase. When the T2 particles were formed during conventional aging of aluminum-rich Al-Li-Cu based alloys, the transformation products were invariably microcrystalline. Individual microcrystals have been identified as the aluminum rich ∝-solid solution which, in certain instances, contained the δʹ (Al3Li) phase. TB (A17.5 Cu4Li) and T1 (Al2CuLi) particles were also found. When the T2 phase was prepared by casting alloys of the proposed stoichiometry of T2, then the transformation products were more complex, although certain reaction products have been identified as the a solid solution, TB and T1.
A Comparative First Principles Study of Phase Stability in Ni-Ti and Ni-Al Alloys Around Equiatomic Composition
Authors: Turchi P.E.A. , Sluiter M. , Pinski F.J. , Johnson D.D. 
Published: March 2011

AbstractElectronic structure and phase stability properties of Ni-Ti and Ni-Al around equiatomic composition are investigated with a first principles approach. The study is based upon the generalized purturbation method applied to the Korringa-Kohn-Rostoker multiple scattering formulation of the coherent potential approximation. Within this framework, effective cluster interactions which build up the configuration-dependent part of the internal energy are calculated. The strength of ordering tendencies in both bcc-based substitutional alloys is compared and contrasted in terms of hybridisation effects, in relation with experimental evidences.
Theoretical Investigation of Phase Stability in Ti-V and Ti-Cr Substitutional Alloys
Authors: Sluiter M. , Turchi P.E.A. 
Published: March 2011

AbstractThe phase stability of Ti-V and Ti-Cr alloys is examined within the context of an electronic structure description. Energies of mixing, effective pair interactions, and phase diagrams are computed and compared to available experimental data. A metastable distorted B2 type of structure is predicted in near equiatomic Ti-Cr.
Percolation Structure Observed in Evaporated Nd-Fe-B Films
Authors: Shang C.H. , Liu B.X. , Li H.D. 
Published: March 2011

AbstractThin alloy films were prepared by evaporating a standard magnetic Nd2Fe14B ingot in a high vacuum e-gun system at roam temperature. The as-deposited films of 50 nm thick were characterized by transmission electron microscopy (TEM) and in situ energy dispersive spectroscopy (EDS). Bright field examination showed that a novel morphology with holes of varied sizes emerged in the films. The hole-like white areas enriched with Nd, and the dark network with Fe. The electron micrograph was digitized by an VAX image processor. An infinite cluster was proved to be a two-dimensional percolating structure at the percolation threshold. The fractal dimension and the percolation threshold were calculated to be 1.90±0.04 and 0.60±0.04, respectively, which are in good consonance with the theoretical predictions. The as-deposited samples were aged at roam temperature for about two months. Enhanced diffusion and solid state reaction induced another percolating networks camposed essentially by Fe7Nd and Nd-riched solid solution.
Microstructure and Stabiulty of TiB2 and Cu Multilayers
Authors: Basu S. N. , Hubbard K. M. , Hirvonen J-P. , Mitchell T. E. , Nastasi M. 
Published: March 2011

AbstractThe Interfacial stability of a high strength TiB2/Cu multilayer structure was examined by subjecting the layers to ion irradiation by 400 keV Ne++ ions up to a maximum dose of 12×1015 ions/cm2. Even at the highest dose, with a maximum dpa value of 4.92, the TiB2/Cu interface did not show any mixing. This stability of the multilayers has been explained by examining the maximum thermodynamic driving force for Interfacial reactions in this system.
MBE Growth of Artificially-Layered Magnetic Metal Structures on Semiconductors
Authors: Farrow R.F.C. , Lee C.H. 
Published: March 2011

AbstractIn this review, recent developments in MBE growth of artificially-layered magnetic metal structures on semiconductor substrates are considered. It is seen that the ability to seed specific orientations of such structures and to probe their structural and chemical properties with a variety of in situ probes are key advantages of MBE over more conventional deposition techniques.
Tracer Diffusion in Amorphous NI-ZR Alloys
Authors: Wu H.-M. , Hahn H. , Averback R.S. 
Published: March 2011

AbstractTracer impurity diffusion coefficients for Co and Hf were measured in a series of amorphous NixZr(1−x) alloys in the range 0.30 < × < 0.70 and at temperatures between 250°C and 350° C. The diffusion coefficients for the Co atoms are between 2 and 4 orders of magnitude greater than those for Hf depending on alloy composition and temperature. Diffusion coefficients for Hf are independent of alloy composition, whereas those for Co decrease strongly with increasing Ni content. The activation enthalpies of diffusion and the pre-exponential factors were both found to be significantly smaller for the Hf than the Co tracer impurity atoms. These results are discussed in terms of possible diffusion mechanisms in amorphous metallic alloys.
Atomistic Structure and Composition of a Ag/Ni Interphase Boundary
Authors: Gumbsch P. , Daw M. S. , Foiles S. M. , Fischmeister H. F. 
Published: March 2011

AbstractUsing the embedded atom method we atomistically model the compensation of the misfit induced stresses in a “cube on cube” oriented Ag/Ni bicrystal with (011) interface plane, in which zones of maximum misfit (misfit dislocations) run along the [100] and the [011] directions.The ideal interface corresponds to an abrupt transition between Ag and Ni. The interfacial enthalpy is found to be lowered by the introduction of vacancies on the Ni side (equivalently, vacancies are trapped on the Ni side of the boundary). Pursuing this perspective, we find that the interfacial enthalpy is lowered considerably by the removal of a complete line of Ni atoms along the [011] direction from the Ni side of the boundary. The minimum energy configuration consists of a Ni layer whose atomic density is reduced by 16% sandwiched between the ordinary Ni and Ag lattices.
Diffusional Asymmetry in Amorphous Alloys:Implications for Interfacial Reactions
Authors: Greer A.L. , Dyrbye K. , Andersen L.-U. Aaen , Somekh R. E. , Bøtiger J. , Janting J. 
Published: March 2011

AbstractEarlyllate transition metal systems such as Ni-Zr and Co-Zr exhibit solid state amorphization (SSA) in which the amorphous phase is formed by reaction between the crystalline elements. The rate of the amorphization is governed by the diffusion of the faster species, Ni or Co. Here results are presented on the homogenization of compositionally modulated thin films which show that the Zr diffusion is up to 106 times slower. The difference in diffusivities is correlated with atomic size. The consequences of the marked diffusional asymmetry are considered, particularly for the interpretation of results on the indiffusion of Co into amorphous Co-Zr. It is proposed that for amorphous alloys such as Ni-Zr and Co-Zr, changes in composition by rapid diffusion of Ni or Co can yield structures which are not in internal equilibrium. This would affect, for example, the validity of the common tangent construction as applied to predict the limiting compositions of the amorphous phase in contact with the elemental layers during SSA.
Interfacial Composition and Structure in Pt/Ni and Pt/Nb Multilayer Films
Authors: Bain J.A. , Clemens B.M. , Brennan S. 
Published: March 2011

AbstractThe interfacial structure of Pt/Nb and Pt/Ni sputtered multilayer films was studied using x-ray diffraction in symmetric, asymmetric, and grazing incidence modes. The grazing incidence and asymmetric diffraction were used to distinguish alloying effects on the lattice spacing from strain in the films. This strain was shown to be consistent with semi-coherent interfaces in the Pt/Ni but not in the Pt/Nb in which another strain generating mechanism dominates.
Determination of the Strain Source in Mo/Ni Multilayers
Authors: Chyung L.J. , Clemens B.M. , Brennan S. 
Published: March 2011

AbstractStructural characterization and strain measurements were conducted on Mo/Ni multilayers, with bilayer periods between 10 Å and 200 Å, utilizing symmetric, asymmetrin, and grazing incidence x-ray diffraction techniques. The structural difference between the 15 Å and 20 Å modulation wavelength samples, evident in the symmetric high angle diffraction spectra, is attributed to the absence of crystalline registry in the early stages of sputter deposition, yielding crystalline order only when the bilayer deposition thickness exceeded 15 Å. The dominant mechanism for the observed modulation wavelength dependent strain behavior, both in the growth direction and in the plane of the film, is consistent with a coherency strain model. The orientation relationship predicted for the Mo/Ni system, based on their atomic radii ratio is the Nishiyama-Wasserman relationship, (110)BCC//(111)FCCand[001]BCC//[101]FCC. This relationship would provide the source for the observed coherency strain.
Al-Ge Phase Separation During Vapor Deposition
Authors: Adams C. D. , Atzmon M. , Cheng Y.-T. , Srolovitz D. J. 
Published: March 2011

AbstractThe phase- and grain microstructure and surface morphology of Al-Ge films formed by electron beam co-deposition have been studied as a function of the deposition temperature. X-ray diffraction, scanning- and transmission electron microscopy with x-ray fluorescence analysis were used to characterize the films. At room temperature and above, crystalline, phase separated films are obtained. The phase dimensions and surface roughness were observed to increase with the deposition temperature and the dependence yields activation energies for atomic migration consistent with a surface diffusion mechanism. The surface roughness is observed to reflect the microstructure under the surface.
Formation of Amorphous Interlayers by Solid-State Diffusion in Refractory Metal/Silicon Systems
Authors: Cheng J.Y. , Wang M.H. , Chen L.J. 
Published: March 2011

AbstractFormation and growth of amorphous interlayers (a-interlayers) in nine refractroy metal and silicon systems by solid-state diffusion have been investigated by conventional and high resolution transmission electron microscopy. The amorphous interlayers were found to form in samples annealed at 350–650 °C. The growth was found to follow a linear growth law initially then slow down until a critical thicknees was reached. The interface structures were examined. The correlations among difference in atomic size between metal and Si atoms, growth rate and activation energy of the linear growth, critical and maximum a-interlayer thickness, the largest heat of formation energy for crystalline silicides, the calculated free energy difference in forming amorphous phase as well as atomic mobility in refractroy metal/silicon systems are discussed.
Laser Assisted Deposition of Thin BiSrCaCuO Films
Authors: Cheenne A. , Perriere J. , Kerherve F. , Hauchecorne G. , Fogarassy E. , Fuchs C. 
Published: March 2011

ABSTRACTA study of the pulsed laser evaporation process of thin superconducting films using both Nd:YAG and ArF eximer lasers is presented. Nuclear reaction analysis, Rutherford backscattering spectrometry (RBS) and scanning electron microscopy were used to characterize composition, thickness and surface morphology of the deposited films. The influence on the properties of the films, of the various parameters of the method such as photon wavelength, laser power density and geometrical conditions are presented and discussed.
Spectroscopic Evidence for Cluster Emission from Laser Ablated Surface in Group IV Elements
Authors: Kasuya A. , Nishina Y. 
Published: March 2011

ABSTRACTTransient process of laser ablation has been investigated by space/ time-resolved optical spectrometry. An excimer laser excitation on crystal surfaces of group IV elements produces highly excited microclusters of atoms which continue to absorb laser energy and begin to decompose in time scale of nanosecond. The spectral characteristics indicate that they are highly charged and decompose dominantly through ejections of neutral or singly charged monomers of constituent element rather than fragmentation into smaller clusters like a fission process.