bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric Tensor Characterization for Overcoated Amorphous TbFe Alloys
Authors: Ruane M. , Jain A. , Rosenvold R. , Mansuripur M. 
Published: March 2011

AbstractAmorphous thin films of TbFe. sputter-deposited on quartz substrates with compositions supporting polar Kerr magneto-optical behavior, and overcoated with a transparent protective layer, are studied to determine their dielectric tensor elements. Refleetivity measurements over a range of angles of incidence are made in an apparatus that corrects for the overcoat layer and exploits magnetization reversal to enhance the measurement of r⊥, the complex reflectivity associated with the magneto-optical signal. Conventional Fresnel reflectivities are also found. The theoretical model for reflectivities from a thick film magneto-optical medium at oblique incidenci is developed and used within a Levenberg-Marquardt nonlinear estimation algorithm to estimate sequentially the dielectric tensor elements, considering their widely varying magnitudes and sensitivities to errors in reflectivity data. The interpretation of the dielectric elements in terms of magneto-optical performance and structural perpendicular anisotropy is discussed.
Lattice Location of Boron and Hafnium Dopants in an Aluminide by Use of Ion Channeling/Nuclear Reaactnio Analyses
Authors: Bohn H. G. , Williams J.M. , Barrett J.H. , Liu C.T. 
Published: March 2011

AbstractExperiments have made use of Rutherford backscattering (RBS), ion channeling techniques and analyses for nuclear reaction products to study lattice location of B and Hf dopantsin an ordered nickel aluminide. Studies were of an alloy single crystal of composition Ni76A123Hf1 with about 0.1 at. % of B added. Analysis for B was accomplished by detection of alpha particles resulting from the reaction 11B(p,αi)8 Be, in ion channeling experiments in which RBS from the Ni constituent was used to control channeling in the host lattice. Yield of the reaction product from proton interaction with B decreased relative to random for channeling in a <100> direction, but increased relative to random for channeling in a <110= direction. It was concluded that B occupies primarily octahedral interstitial sites. RBS/channeling half-angles for Hf in a <100> direction are somewhat smaller than those for Ni, but nevertheless considerably larger than half-angles expected for Al. It is concluded that the majority of Hf atoms are on the Ni sublattice.
Ab Initio Theory of the Ground State Properties of Ordered and Disordered Alloys and the Theory of Ordering Processes in Alloys
Authors: Stocks G. Malcolm , Nicholson D.M. , Pinski F.J. , Butler W.H. , Sterne P. , Temmerman W.M. , Gyorffy B.L. , Johnson D.D. , Gonis A. , Zhang X.-G. , Turchi P.E.A. 
Published: March 2011

AbstractWe review some of the advances in the calculation of the electronic structure and energetics of ordered and disordered alloys that hold out the possibility of obtaining, in thenot-too-distant future, an ab initio theory of ordering and phase stability in alloys. In particular, we focus on the calculation of the ground state properties of Ni3Al and discuss the competition between the Li2 and D022 ordered structures. We review the ab initio concentration functional theory of ordering developed by Gyorffy and Stocks and its application to the short-range-ordered solid-solution state in CucPd1-c alloys. Finally, we review the generalized perturbation method approach to calculation of multisite interchange potentials in Ni3Al, Pd3V, and Al3Ti and again discuss L12/D022 competition as well as antiphase boundary energies in Ni3Al.
Deformability Improvements of Li2-Type Intermetallic Compounds
Authors: Izumi Osamu , Takasugi Takayuki 
Published: March 2011

AbstractIntermetallic compounds are usually so brittle that they simply cannot be efabricated into useful shape components. Recent developments of physical and metallurgical principles for the structural materials have led to the conclusion that the deformability of several intermetallic systems can be substantially improved. Among them, in this lecture, the nature of grain boundary structure in L12-type intermetallics is first discussed.Then, the possibilities and instances to overcome the brittleness are shown. Polycrystalline L12 -type Ni3Al, even prepared from high purity metals, exhibits brittle intergranular fracture. On the other hand, single crystals of Ni3Al are ductile even at room temperature. Thus, it is said that the grain boundaries of this alloy are intrinsically weak. Our recent analyses showed that there exist several configurations of atomic bonds, resulting in the heterogeneous electronic environments which can be regarded as “cavities”. The drastic ductility improvement of Ni3Al alloy by a small boron addition, which was found in 1979, can be interpreted as segregated boron atoms at grain boundaries to modify the electronic environments of boundaries and to reinforce boundary cohesion, thus suppressing intergranular fracture. From a quite similar point of view, modification of boundary structures can be achieved by substituting proper elements for the constituents of compounds or by selecting atom combinations of compounds. Thus, the ductility of Ni3Al could be improved by substituting a few percent of Mn or Fe for Al. Also, by selecting atom combination, several L12-type alloys such as Co3Ti, Cu3Pd, Ni3Mn and Ni3Fe have been found as ductile intermetallics.
An Overview of the Temperature Dependence of the Strength of the Ni3Al System
Authors: Tien John K. , Eng Sandra , Sanchez Juan M. 
Published: March 2011

AbstractMany L12ordered alloys including the Ni3Al intermetallic system are noted for their anomalous temperature dependence of strength. It is also generally accepted that this dependence is due to a thermally assisted cross-slip, work hardening based model [1,2]. An alternative antiphase boundary (APB) based model has long been dismissed by the research community because prior calculations of APB energy, and some measurements, have shown that the appropriate APB energy of Ni3Al should remain constant with temperature [3]. These aspects will be reviewed briefly and will serve as a basis for a presentation of some more recent results. These will include the strain rate insensitivity of strength versus temperature in the increasing strength temperature region, a result that is, in our view, rather contradictory to the thermally assisted cross-slip model. Some very recent calculations of equilibrium APB energies will also be reviewed in the context of the strength dependence issue. These results show that the equilibrium APB energy increases with temperature. The question of what role, if any, equilibrium APB plays in the deformation and strengthening process will be discussed.
Strengthening of Ni3Al by Ternary Additions
Authors: Heredia F. , Pope D. P. 
Published: March 2011

AbstractIt is important for a number of reasons to have a basic understanding of the mechanisms by which ternary additions strengthen Ni3Al. First of all, since the basic strength-controlling mechanisms in pure Ni3Al are different from those in pure metals and substitutional solid solutions, it is expected that the mechanisms of solid solution strengthening will also be different in Ni3Al. Secondly, such an understanding will provide valuable insights into the properties of nickel-base superalloys in which Ni3Al is a key constituent. In addition, since new alloys based on an ordered Ni3Al matrix are being developed, it is important to understand the strengthening mechanisms in such alloys. In the present study, flow stress measurements have been performed on single crystals of Ni3Al containing additions of Hf and Ta, and on binary Ni rich, Ni3A1 used as a reference alloy. The data have been collected over a wide range of temperatures, for different orientations within the unit triangle, and as a function of the sense of the applied uniaxial stress. The effect of such additions on the critical resolved shear stress (CRSS) for octahedral slip has been determined and combined with previous data. An attempt is then made to clarify whether a lattice parameter/modulus mismatch effect or a dislocation core effect is the dominant mechanism for the strength increase with compositional changes. It appears that a lattice parameter/modulus mismatch is the dominant mechanism for orientations in which the tension/compression flow stress asymmetry disappears.
Creep Cavitation in a Nickel Aluminide
Authors: Schneibel J. H. , Martinez L. 
Published: March 2011

AbstractA nickel aluminide with the composition Ni-23.5 Al-O.5 Hf-O.2 B (at. %) was creep-tested in tension at constant load (initial stress 250 MPa, temperature 1033 K). The creep rate reaches a minimum at a strain of approximately 0.3%. Its increase at larger strains is partly caused by grain boundary cavitation. Cavity size distributions corresponding to different creep times and strains were determined metallographically and evaluated in order to obtain the cavity growth rate as a function of cavity size. Contrary to a newly developed model for crack-like diffusive growth the cavity tip velocity increases with cavity size. This discrepancy is attributed to cavity coalescence. Sintering at elevated temperatures (1473 K) reduces the diameter and increases the thickness of the disc-shaped cavities. Sintering of such cavities might be exploited to measure surface diffusivities.
Effective-Pair-Interactions from Supercell Total Energy Calculations: Al-Transition Metal Alloys
Authors: Carlsson Anders E. 
Published: March 2011

AbstractEffective-pair-interactions (EPI) are computed for alloys of Al with transition metals, Li, and Zn, using a method in which concentration-independent cluster interactions are resummed to obtain the concentration-dependent EPI. The method includes alloy fluctuations in the interatomic charge transfer, enables one to transcend the muffin-tin approximation and thus treat surfaces and layered structures, and allows the inclusion of lattice strain effects. The calculated EPI have a large magnitude when d-bonding effects are important. For transition metals the EPI are strongly concentration-dependent. In Ni-Al, results for bcc and fcc lattices are similar and exhibit a quick decay of the EPI with interatomic separations. The concentration dependence of the transition metalEPI exhibits rapid oscillations with the number of valence electrons. The concentration-averaged EPI varies less dramatically. The oscillations in the concentration dependence of the EPI are interpreted in terms of the position of the Fermi level relative to peaksand valleys in the one-electron density of states.
Rolling Anisotropy of Ni3Al Single Crystals
Authors: Watanabe Katsuya , Fukuchi Masaaki 
Published: March 2011

AbstractThe rolling anisotropy of Ni3Al single crystals was studied. A single crystal sheet in the (011) plane showed remarkable anisotropy. Rolling the sheet in the [100] direction was simple but was almost impossible in the [011] direction. Substantial anisotropy was not observed in the (111) and (001) sheets. The texture of the rolled (011) and (111) sheets were {011}<011>. It is concluded that the rolling anisotropy of single crystal sheets is determined by the presence of active slip system related to compressive strain normal to the sheet plane, and tensile strain parallel to the rolling direction.
Rutherford Backscattering (RBS) and Channeling Studies of Defects in Arsenic Implanted Silicon Induced by Arsenic Clustering
Authors: Baiocchi Frank A. , Kamgar Avid 
Published: March 2011

ABSTRACTRBS/Channeling measurements have been used to characterize the Si recrystallization and As substitutionality of <100> Si wafers implanted with 100 keV As at two doses after multiple thermal anneals. It is found that low temperature thermal treatment after a high temperature rapid thermal anneal results in deactivation of the implant, presumably due to Arsenic clustering. The ion channeling results indicate the growth of a disordered layer in the silicon after the second anneal at a depth corresponding to the peak of the Arsenic implant concentration. The number of displaced Si atoms is found to be 5-10 times greater than the number of displaced As atoms. This indicates that both As clustering and growth of Si defects should be considered as possible mechanisms for the electrical deactivation of the implanted Si after post anneal.
Characterization of Structural Changes and Defects in Ion Bombarded GaAs
Authors: Johnson Stephen T. , Williams J.S. , Elliman R.G. , Pogany A.P. , Nygren E. , Olson G.L. 
Published: March 2011

ABSTRACTIn-situ time resolved reflectivity, Rutherford backscattering and channeling and transmission electron microscopy have been employed to characterise the evolution of Ar+ ion implantation damage in GaAs as a function of ion dose at various irradiation temperatures. Specific reflectivity signatures have been identified and characterised in terms of observed structural changes to the GaAs. Reflectivity provides a simple and convenient means of monitoring damage build up during ion implantation. In contrast to accepted models for amorphous phase formation in semiconductors, GaAs has been observed to undergo a sudden transformation from a crystal containing a dense network of extended defects to an amorphous phase under elevated temperature irradiation conditions.
Determination of Electrically Active Defect Profiles in Semiconductors Using a Photoelectrochemical Technique
Authors: Gealy F.D. , Tuller H.L. 
Published: March 2011

ABSTRACTElectrically active defects are common in semiconductors. Such defects include easily ionized substitutional impurities, vacancies, and interstitials which can act as shallow donors or acceptors. If one type of defect predominates, its concentration corresponds directly to the local donor or acceptor concentration. Consequently, measurement of a carrier profile in a nonhomogeneous semiconductor is effectively the same as measurement of the defect profile.The photoelectrochemical profiling technique allows for carrier profile measurement with submicrometer spatial resolution. The sample is profiled by photoetching, then carrier measurement, and iterating this procedure until the desired profile depth is obtained.Derivation of the space charge capacitance by impedance spectroscopy is discussed. An analysis of the P-doped Si-liquid electrolyte interface is presented. Phosphorous diffusivity coefficients in good agreement with literature values are derived from photoelectrochemical derived profiles.
Combined Use of Small Angle Neutron Scattering (Sans) and (Conventional and High Resolution) Electron Microscopy for the Characterization of Early Stages of Ordering and Phase Separation in Ni-Ti
Authors: Cerri A. , Schmelczer R. , Schwander P. , Kostorz G. , Wright A.F. 
Published: March 2011

ABSTRACTThe decomposition of Ni ∼ 11.5 at.% Ti single crystals was studied for an ageing temperature of 540°C. In this alloy, coherent ordered zones of γ′-Ni3Ti (Cu3Au structure) are formed prior to the stable n precipitates. The early stages of zone formation were investigated by in-beam SANS and transmission electron microscopy (TEM). Electron diffraction, high resolution electron microscopy, TEM analysis of dislocation arrangements in samples deformed after ageing and X-ray measurements of the integrated intensity at L12 superstructure positions show that ordered regions already appear in quenched samples, whereas compositional changes, as determined by SANS measurements, occur only upon ageing.
Accurate Interatomic Potentials for Ni, Al and Ni3Al
Authors: Voter Arthur F. , Chen Shao Ping 
Published: March 2011

ABSTRACTTo obtain meaningful results from atomistic simulations of materials, the interatomic potentials must be capable of reproducing the thermodynamic properties of the system of interest. Pairwise potentials have known deficiencies that make them unsuitable for quantitative investigations of defective regions such as crack tips and free surfaces. Daw and Baskes [Phys. Rev. B 29, 6443 (1984)] have shown that including a local “volume” term for each atom gives the necessary many-body character without the severe computational dependence of explicit n-body potential terms. Using a similar approach, we have fit an interatomic potential to the Ni3Al alloy system. This potential can treat diatomic Ni2, diatomic Al2, fcc Ni, fcc Al and L12 Ni3Al on an equal footing. Details of the fitting procedure are presented, along with the calculation of some properties not included in the fit.
Synchrotron X-Ray Topography of Dislocation Arrays
Authors: Bilello J. C. 
Published: March 2011

ABSTRACTThe application of relatively low resolution x-ray topography methods, typically ∿ 1 micrometer, is limited in studies which involve large scale dislocation networks. However, the ability to non-destructively image wide areas for “thick” specimens at high intensity with a tunable x-ray source makes the synchrotron an ideal probe for a range of problems previously inaccessible by other methods. Some examples will be discussed such as: (a) crack initiation and propagation in fatigued bicrystals, (b) real-time in situ plastic deformation studies in strain-annealed Mo crystals, and (c) strain distributions in vapor deposited and LPE thin films on Si and GaAs substrates.
X-Ray Double Crystal Topography of Processed Silicon Wafers
Authors: Loxley Neil , Tanner Brian K. 
Published: March 2011

ABSTRACTDouble crystal topographs of a processed silicon device wafer, taken in highly asymmetric reflection conditions using synchrotron radiation are presented. By using a variety of wavelengths and reflections the depth and distribution of defects generated by the fabrication process are explored. Examples of several reflections are given, with a spatial resolution of better than 5 microns and extremely high device and defect visibility. Results suggest that a high mismatch of lattice parameter at device edges leads to the formation of dislocation loops penetrating junctions.
Atomic Structure of Dislocations and Dipoles in Silicon
Authors: Nandedkar A. S. , Narayan J. 
Published: March 2011

ABSTRACTDislocations of a/2<110> Burgers vectors lying in {001} and {111} planes in the form of cross-grids are often observed in ion implanted and thermally annealed specimens. In order to asses the mechanism of formation of these dislocations, we have calculated energies and determined atomic core structuresof a/2<110>{001} edge dislocations and their dipoles,and of a/2<110>{111} dislocations in silicon by minimizing the total configurational energy.
Positron Annihilation Spectroscopy of Defects in Solid
Authors: Hautojärvi P. 
Published: March 2011

ABSTRACTThe use of positron annihilation to study vacancy defects and some recent results are reviewed. For metals, theoretical calculations have reached the leyel where they can reliably predict lifetime values of positrons trapped at vacancy defects of various size, geometry and impurity environment. Experimental results are shown on vacancy recovery and vacancysolute interaction in electron irradiated Fe, Nb, and Ta. During last years the technique has been applied also to semiconductors. Positron trapping in Si is discussed and some results are given on native and irradiation induced vacancies in GaAs. A beam of slow positrons is a new tool to probe nearsurface regions and thin films. Examples are shown on Mo(111) surface sputtered with Ar+ ions and on Si(100) implanted with 35 keV H+ ions.
Imaging of Dislocations and SUB–Grain Boundaries in Alumina Through Chromia – Vacancy and Molybdenum Solute Atmospheres
Authors: Raman S.V. 
Published: March 2011

ABSTRACTThe phenomenon of plastic flow in alumina was previously [1 and 2] characterized using sintering models and transmission electron microscopy. Some of the findingsof the work were (a) near equality in the activation energy for volume diffusion and surface area reduction (82 kJ/mol), (b) a higher activation energy (440 kJ/mol) for Coble creep mechanism in the absence of gamma/alpha phase transformation and a lower activation energy (250 kJ/mol) when phase transformation was a part ofthe sintering process and, (c) presence of extended dislocations and deformed electron diffraction spots.In view of these results it was of interest to follow the effect of solute addition on plastic flow [ 3 ]. The solutes were incorporated in alumina through gel synthesis route and formed solid—solution systems of Cr203— A1203 and MoO3 — A12O3 at 1000°C. In the course of sintering there is partiai vaporization of caromiaand reduction of MoO3. The chromiavacancy and Mo metal thus impart an impurity decoration to the lattice. The scanning electron micrographs seem to show that they are segregated along grain boundaries, sub—grain boundaries and dislocations. With increase in temperature the linear vacancy segregations and the scattered vacancy clusters annihilate to form pores. These pores transform to creep cavities that extend from grain boundary to volume. The clustered occurrence of Mo at grain boundaries and its extended spacing in the subgrain boundary is perhaps indicative of a dislocation pipe model for its segregation. On the basis of these modeling and microstructural results a heuristic argument is presented in favor of kinetic equality among self diffusion, dislocation pipe diffusion and dislocation climb, and in favor of the commencement of Coble and Nabarros—Herring creep with severance of these equalities.
Characterization of Defect Structures by Perturbed Angular Correlation Technique
Authors: Wichert Thomas 
Published: March 2011

ABSTRACTIn applications of the perturbed angular correlation (PAC) technique to the characterization of defect structures in materials conclusions are drawn from the local electric field gradient measured at the site of a radioactive probe atom. In metals, PAC has been very successful in labeling and identifying simple probe atom-defect pairs. Based on these results, new experiments were performed on defect structures in cold-worked samples, on the dynamics of He-defect interactions and on the growth of vacancy clusters. Recent results on interactions between the acceptor atom In and different donor atoms or intrinsic defects in Si indicate that PAC may provide atomistic information also in the case of semiconductor materials.
The Behavior of Oxidation Stacking Faults During O2/NF3 Oxidation of Silicon
Authors: Kim U. S. , Jaccodine R. J. 
Published: March 2011

ABSTRACTThe behavior of oxidation—induced stacking faults(OSFs) during the O2 /NF3 oxidation of silicon has been investigated in the temperature range of 850–1100°C with varying concentration of NF 3 (0.011—0.044 vol%). In this study, we report the rapid and non-linear shrinkage of pregrown OSFs with time by a new oxidation process including small(ppm) additions of fluorine compound to the oxidant. It is also found that the shrinkage rate of OSF decreases as the oxidation time is increased. It is proposed that the fast OSF shrinkage is due to excessive vacancy flux as a result of the reaction of fluorine at the Si/SiO2 interface during the initial transient state, and subsequently the shrinkage rate is reduced as the steady—state condition of vacancy—interstitial recombination is approached.
Characterization of Sub-Surface Structures by Double Crystal X-Ray Diffraction
Authors: Bowen D.K. , Hill M.J. , Tanner B.K. 
Published: March 2011

ABSTRACTThe application of double crystal X-ray diffractometry and computer simulation to the characterization of lattice parameter variations through the thickness of heteroepitaxial layers is reviewed. The sensitivity is demonstrated in studies of graded layers grown by vapour phase epitaxy. Capping layers significantly affect rocking curves from superlattice structures. The use of glancing angle diffraction to characterize thin, low period multilayers is examined.