bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deep Level Defect Studies in Mocvd-Grown InxGa1−sAs1−yNy Films Lattice-Matched to GaAs
Authors: Kwon Daewon , Kaplar R. J. , Boeckl J. J. , Ringel S. A. , Allerman A. A. , Kurtz Steven R. , Jones E. D. 
Published: April 2011

AbstractDeep level defects in MOCVD-grown, unintentionally doped p-type InGaAsN films lattice matched to GaAs were investigated using deep level transient spectroscopy (DLTS) measurements. As-grown p-InGaAsN showed broad DLTS spectra suggesting that there exists a broad distribution of defect states within the band-gap. Moreover, the trap densities exceeded 1015 cm−3. Cross sectional transmission electron microscopy (TEM) measurements showed no evidence for threading dislocations within the TEM resolution limit of 107 cm−2. A set of samples was annealed after growth for 1800 seconds at 650 °C to investigate the thermal stability of the traps. The DLTS spectra of the annealed samples simplified considerably, revealing three distinct hole trap levels with energy levels of 0.10 eV, 0.23 eV, and 0.48 eV above the valence band edge with trap concentrations of 3.5 × 1014 cm−3, 3.8 × 1014 cm−3, and 8.2 × 1014 cm−3, respectively. Comparison of as-grown and annealed DLTS spectra showed that post-growth annealing effectively reduced the total trap concentration by an order of magnitude across the bandgap. However, the concentration of a trap with an energy level of 0.48 eV was not affected by annealing indicating a higher thermal stability for this trap as compared with the overall distribution of shallow and deep traps.
Spatial Distribution of Luminescent Centers in Organometallic Vapor Phase Epitaxy Grown ZnxCdl−xSe/InP (001)
Authors: Zhang X. B. , Hark S. K. 
Published: April 2011

AbstractZincblende ZnxCdl−xSe alloys were grown on (001) InP by organometallic vapor phase epitaxy (OMVPE) using various VI / H precursor flow ratios, ranging from 0.95 to 12, at a temperature of 420°C. Spatial distribution of luminescent centers in the epilayer was characterized by cathodoluminescence (CL) spectroscopy and imaging. Both near band-gap (NBE) and deep level (DLE) emissions were observed in the spectra, with the width of the NBE peak increases with the VI / II flow ratio. Monochromatic CL images showed that the broadening of the NBE peak has its origin in the spatial inhomogeneity of the luminescent centers of the epilayer. Extended defects responsible for the DLE was only found in pyramidal hillocks seen in the CL images. The density of these defects was found to increase with the VI / I1 flow ratio.
A Peierls-Nabarro Model for Kink-Pair Generation in Screw Dislocations at Low Temperatures
Authors: Ngan A.H.W. 
Published: April 2011

AbstractKink-pair generation in three-fold screw dislocations in the bcc lattice is investigated within the framework of the generalised Peierls-Nabarro model. Using a piece-wise plane strain approximation, the apparent activation energy is predicted to vary with stress in a parabolic manner which is in good agreement with experimental findings.
From Molecular Dynamics to Kinetic Rate Theory: A Simple Example of Multiscale Modeling
Authors: Stoller Roger E. , Greenwood Lawrence R. 
Published: April 2011

AbstractRadiation damage formation in iron has been investigated using the method of molecular dynamics simulation. The MD simulations have been used to determine primary defect production parameters for cascade energies up to 50 keV at temperatures from 100 to 900K. The energy dependence of these parameters has been used to determine appropriate neutron-energy-spectrum averaged damage production cross sections for various irradiation environments. Two applications of these effective cross sections are discussed. The first is an evaluation of neutron energy spectrum effects in commercial fission reactor pressure vessels. The second example deals with the use of these cross sections in the source term of a kinetic model used to predict void swelling and microstructural evolution. The simulation of the primary damage event by MD involves times less than 100 ps and a size scale of a few tens of nm, while the kinetic simulation encompasses several years and macroscopic sizes. This use of the MD results to develop an improved source term for rate theory modeling provides a simple example of multiscale modeling.
A Study of Grain Growth and Microstructure Control in Silicon Nitride by Computer Simulation
Authors: Okamoto Y. , Hirosaki N. , Matsubara H. 
Published: April 2011

AbstractA grain growth simulation technique is developed for microstructure design of ceramic materials by extending the Potts model. The simulation model has successfully reproduced the self-reinforced microstructure which is peculiar to silicon nitride, consists of large elongated grains and small equiaxed grains.To control the microstructure of silicon nitride further, a seeding technique is effective and often employed. Grain growth behavior of seed particles in the simulation is studied. It is found that the seed grains grow with a relatively high growth rate during the early stage of grain growth. In contrast in the later stage, the difference between microstructures with and without seed particles decreases. This behavior agrees well with that of actual silicon nitride. These results demonstrate the consistency of the simulation.
A Unified Computational Approach to Oxide Aging Processes
Authors: Hjalmarson Harold P. , Schultz Peter A. , Bowman Duane J. , Fleetwood Daniel M. 
Published: April 2011

AbstractIn this paper we describe a unified, hierarchical computational approach to aging and reliability problems caused by materials changes in the oxide layers of Si-based microelectronic devices. We apply this method to a particular low-dose-rate radiation effects problem.
Linking ab initio Energetics to Experiment: Kinetic Monte Carlo Simulation of Transient Enhanced Diffusion of B in Si
Authors: Theiss Silva K. , Caturla M.-J. , Rubia T. Diaz de la , Johnson M.C. , Uralt Ant , Griffin P.B. 
Published: April 2011

AbstractWe have developed a kinetic Monte Carlo (kMC) simulator that links atomic migration and binding energies determined primarily from first principles calculations to macroscopic phenomena and laboratory time scales. Input for the kMC simulation is obtained from a combination of ab initio planewave pseudopotential calculations, molecular dynamics simulations, and experimental data. The simulator is validated against an extensive series of experimental studies of the diffusion of B spikes in self-implanted Si. The implant energy, dose, and dose rate, as well as the detailed thermal history of the sample, are included. Good agreement is obtained with the experimental data for temperatures between 750 and 950°C and times from 15 to 255 s. At 1050°C we predict too little diffusion after 105 s compared to experiment: apparently, some mechanism which is not adequately represented by our model becomes important at this temperature. Below 1050°C, the kMC simulation produces a complete description over macroscopic time scales of the atomic level diffusion and defect reaction phenomena that operate during the anneals. This simulator provides a practical method for predicting technologically interesting phenomena, such as transient enhanced diffusion of B, over a wide range of conditions, using energetics determined from first-principles approaches.
Dislocations and Plasticity in Silicon Crystals by 3-D Mesoscopic Simulations
Authors: Kubin L.P. , Moulin A. , Pirouz P. 
Published: April 2011

AbstractSeveral problems related to the dynamics of dislocation sources and the plasticity of silicon crystals are investigated with the help of a mesoscopic simulation. The questions successively examined are the dynamics of a source of perfect dislocations and the conditions under which perfect or partial dislocations are emitted by a source. This leads to a discussion of the initial steps of the model proposed by Pirouz for mechanical twinning and, further, to the suggestion that a relation may exist between several transitions experimentally observed at low temperatures in elemental or compound semi-conductors: a change in the slope of the yield stress vs. temperature curves, a brittle-to-ductile transition and a change in the nature of the mobile dislocations. Finally, simulations are presented of the yield point phenomenon that is a well-known feature of Si and Ge crystals. The results are discussed in terms of evolutionary laws for the total dislocation density during straining.
Measurement of Planar Fault Energies in Ni3Ge-Fe3Ge Intermetallic Alloys
Authors: Kumar Mukul , Balk T. J. , Hemker K. J. 
Published: April 2011

AbstractA combination of transmission electron microscopy (TEM) and image simulations has facilitated a highly quantitative measure of superdislocation dissociations. The experimental observations have been corrected for image shifts within the framework of anisotropic elasticity by comparison with simulated images. This allows experimental quantification of planar fault energies, thus providing a benchmark for first principles and atomistic simulations and fundamental insight towards alloy modeling and design. Such measurements of superdislocation dissociations on the order of 1-15 nm have been recorded for the pseudobinary Ni3Ge-Fe3Ge alloy system. These detailed measurements of fault widths obtained by weak-beam TEM observations of deformation structures will be presented and discussed as a function of alloy composition. The transition from anomalous to normal temperature dependence of yielding behavior in these alloys will also be discussed in terms of observed dislocation structures and planar fault energies calculated using the above measurements.
A Study of Vacancies in Pure Aluminium and Their Role in the Diffusion of Lithium in a Dilute Al-Li Alloy Using the Embedded Atom Model
Authors: Derlet P. M. , Hoier R. , Holmestad R. , Marthinsen K. , Ryum N. 
Published: April 2011

AbstractConstant temperature and pressure molecular dynamics are employed to study bulk Al and the substitutional Al-Li alloy using the embedded atom model. The appropriate embedding energy functionals and pair potentials have been determined using known experimental data of bulk Al and Li, together with the results of density functional theory studies of small Aln-Lim clusters and the ordered Al3Li crystallographic phase. The primary goal is to study the role vacancies play in the early stages of the nucleation and growth of the Al3Li crystallographic phase. To this end we present the preliminary results of a study of vacancy diffusion in Al, and Li diffusion through the Al matrix via a vacancy mechanism. In the present work the results of vacancy diffusion are analysed using a modified inverse Laplace transform, producing a continuous distribution of vacancy hopping times which reproduces the characteristic times for both the single and double vacancy hopping events.
Substitution Behavior in NiAl-A First Principle Prediction Considering Lattice Relaxation
Authors: Xu D. S. , Li D. , Hu Z. Q. 
Published: April 2011

AbstractThe substitution behavior of alloying elements in NiAl is investigated on the basis of electronic structure calculation using the discrete variational Xα cluster method. The method proposed by the authors to predict the substitution behavior is extended to considering lattice relaxation around an alloying atom. A diagram is drawn using the binding energy of clusters when each alloying element occupies either Ni or Al sites as parameters. Two straight lines on the diagram with slope of unity and passing the point of Ni or Al separate the alloying elements into three groups. The elements above the upper line will take Al sites and those below the lower line will take Ni sites regardless of the composition. The substitution behavior of elements in between the two lines will be affected by the alloy composition. The driving force for an element to order on one sublattice is related to its position on the diagram. The effects of temperature, composition and multi-element alloying are discussed. The concepts of site competition and stepped ordering are put forward.
The Influence of Heat Excitations, Vacancies and Impurities on the Energy Electronic Band-Structure of Metallic Lithium
Authors: Popov V. A. 
Published: April 2011

AbstractThe Korringa-Kohn-Rostoker method with Green's function averaged over the atomic configurations in a complex Ising lattice and a muffin-tin potential was used to calculate the electronic-band structure in lithium containing vacancies and s, p, and d impurities. It is shown that substantial changes in the profile of the Fermi surface do not lead to necking, as was postulated previously, but cause splitting of the electronic states at the face of the Brillouin zone. This is attributed to the reduced symmetry of the crystal lattice with impurity excitation of the electronic-subsystem.
Microscopic Description of Plasticity in Computer Generated Metallic Nanophase Samples
Authors: Spaczér M. , Swygenhoven H. Van , Caro A. 
Published: April 2011

AbstractWe report simulations on the plastic behaviour of nanocrystalline Ni and Cu with grain sizes in the range of 3-12 nm. We observe a change in deformation mechanism in both materials: at the smallest grain sizes all deformation is accommodated in the grain boundaries, while at higher grain sizes we observe intragrain deformation. Analysis of the atomic configurations shows that stacking faults are produced by the passage of partial dislocations generated and absorbed in opposite grain boundaries. In Cu, we observe the stacking faults at smaller grain sizes than in Ni (8 and 12nm, respectively), which is attributed to the lower stacking fault energy of copper. Dislocations appear on slip systems that are not necessarily those favoured by the Schmid factor. Atomic displacement analysis shows deformation starts at triple points, with grain boundary sliding followed by the creation of intragrain partial dislocations.
Atomistic Aspects of Fracture Modelling in the Framework of Continuum Mechanics
Authors: Cleri F. 
Published: April 2011

AbstractThe validity and predictive capability of continuum models of fracture rests on basic informations whose origin lies at the atomic scale. Examples of such crucial informations are, e.g., the explicit form of the cohesive law in the Barenblatt model and the shear-displacement relation in the Rice-Peierls-Nabarro model. Modem approaches to incorporate atomic-level information into fracture modelling require to increase the size of atomic-scale models up to millions of atoms and more; or to connect directly atomistic and macroscopic, e.g. finite-elements, models; or to pass information from atomistic to continuum models in the form of constitutive relations. A main drawback of the atomistic methods is the complexity of the simulation results, which can be rather difficult to rationalize in the framework of classical, continuum fracture mechanics. We critically discuss the main issues in the atomistic simulation of fracture problems (and dislocations, to some extent); our objective is to indicate how to set up atomistic simulations which represent well-posed problems also from the point of view of continuum mechanics, so as to ease the connection between atomistic information and macroscopic models of fracture.
Self Consistent-Charge Density-Functional Tight-Binding Method for Simulations of Biological Molecules
Authors: Elstner M. , Porezag D. , Seifert G. , Frauenheim Th. , Suhai S. 
Published: April 2011

AbstractWe apply a self-consistent charge tight-binding scheme to biomolecules. This method has been shown to give a reliable description of reaction energies, geometries and vibrational frequencies of small organic molecules. We discuss the performance of this method for model peptides and non-bonding interactions in biologically relevant molecular complexes. A comparison with semi-empirical methods and ab initio calculations will be given for DNA base pair H-bonding and stacking interactions.
Structural Characteristics and Quantum Chemistry Calculation of Si-Doped Boron Carbides
Authors: Xinmin Min , Cewen Nan , Kefeng Cai 
Published: April 2011

AbstractStructural characteristics, chemical bonds and thermoelectric properties of Si-doped boron carbides are studied through calculations of various structural unit models by using a self-consistent-field discrete variation Xα method. The calculations show that Si atom doped in boron carbide is in preference to substituting B or C atoms on the end of boron carbide chain, and then may occupy interstitial sites, but it is difficult for Si to substitute B or C atom in the centers of chain or in the icosahedra. A representative structural unit containing a Si atom is [C-B-Si]ε+ [B11C]ε-, while the structural unit without Si is [C-B-B(C)]δ--[B11C]δ+, and the coexistence of these two different structural units makes the electrical conductivity increases. As the covalent bond of Si-B or Si-C is weaker than that of B-B or B-C, the thermal conductivity decreases when Si is added into boron carbides. With the electrical conductivity increases and the thermal conductivity decreases, Si doping has significant effect on thermoelectric properties of boron carbides.
Atomistic Simulations of Cross-Slip Processes in Model FCC Structures and L10 TiAl
Authors: Rao S. 
Published: April 2011

AbstractThree dimensional (3D) cross-slipped core structures of a/2[110] screw dislocations in model FCC structures are simulated using lattice statics within the Embedded Atom Method (EAM) formalism using potentials fitted to the elastic and structural properties of FCC Ni as well as L10TiAl. 2 and 3-D Green's function (GF) techniques are used to relax the boundary forces in the simulations. The core structure of the constrictions are diffuse. At large separation distances between Shockley partials in the unconstricted configuration, the two constrictions formed by cross-slip onto a cross {111} plane have significantly different energy profiles suggesting that self-stress forces dominate the energetics of the cross-slip process. The variation in cross-slip energy with stacking-fault energy is in reasonable agreement with continuum predictions, excepting at high fault energy values as in L10TiAl. Cross-slip energies estimated for Cu, Ni and γ-TiAl from these calculations show reasonable agreement with experimental data. The cross-slip energy shows a significantly weaker dependence on Escaig stress as compared to elasticity calculations, with the activation volume for the cross-slip process being approximately 20b3 at an applied Escaig stress of 10-3μ in Cu.
Temperature Effects and Fast-Moving Screw Dislocations at High Strain Rate Deformations
Authors: Roos A. , Metselaar E.D. , Hosson J.TH.M. De , Cleveringa H.H.M. , Giessen E. Van Der 
Published: April 2011

AbstractIn this paper, shear deformation at high strain rates is modeled within the framework of discrete dislocation plasticity. The method of discrete dislocation plasticity is extended to incorporate the temperature rise induced by moving dislocations. Also, the stress and displacement fields of a screw dislocation on inclined planes in a periodic structure are developed. The influence on the temperature rise on various micro-mechanical processes is discussed.
A Dlts Investigation of The Effect of Ion Mass, Fluence and Energy on the Introduction of a Higher-Order Vacancy Cluster in Noble Gas Ion Bombarded n-Si
Authors: Deenapanray P.N.K. , Williams J.S. 
Published: April 2011

AbstractWe have recently reported the annealing and electrical properties of three new families (N1, N2 and N3) of vacancy complexes introduced in 1 keV He-, Ne- and Ar-ion bombarded nSi. In this paper we have employed deep level transient spectroscopy to investigate the ion mass, fluence and energy dependence of the introduction of N1 -defects. We observed an increase in the intensity of Ni -defects with increasing mass of bombarding ions for a fluence of 1×1012cm−2and flux of 1×1011cm−2s−1, which we have correlated with the mass dependence of nuclear energy deposition. The ratio of the intensities of Ni-defects to VO-center, [N1]/[VO], increased by ∼5 when bombarding with Ar- compared to He-ions. Increasing the Ar-ion fluence from 1×1012cm−2to l×1014cm−2for a flux of 5×1010 cm−2s−;1increased the intensity of N1-defects by ∼20 times, while [N1]/[VO] increased by a factor ∼2.3. N1-defects were not created by 5.4 MeV alpha-particle irradiation, but were present in varying relative concentrations in 1 to 150 keV He-ion bombarded n-Si.
Radiation Effects in Nonmetals: Amorphization, Phase Decomposition, and Nanoparticles
Authors: Meldrum A. , Boatner L.A. , White C.W. , Henderson D.O. 
Published: April 2011

AbstractRadiation effects in nonmetals have been studied for well over a century by geologists, mineralogists, physicists, and materials scientists. The present work focuses on recent results of investigations of the ion-beam-induced amorphization of the ABO4 compounds – including the orthophosphates (LnPO4; Ln = lanthanides) and the orthosilicates: zircon (ZrSiO4), hafnon (HfSiO4), and thorite (ThSiO4). In the case of the orthosilicates, heavy-ion irradiation at elevated temperatures causes the precipitation of a nanocrystalline metal oxide. Electron irradiation effects in these amorphized insulating ceramics can produce localized recrystallization on a nanometer scale. Similar electron irradiation techniques were used to nucleate monodispersed compound semiconductor nanocrystals formed by ion implantation of the elemental components into fused silica. Methods for the formation of novel structural relationships between embedded nanocrystals and their hosts have been developed and the results presented here demonstrate the general flexibility of ion implantation and irradiation techniques for producing unique near-surface microstructures in ion-implanted host materials.
Interaction of Deuterium with Cavities In Crystalline Si and Mgo
Authors: Fedorov A. V. , Veen A. Van , Schut H. 
Published: April 2011

AbstractTo create cavities a Si (100) single crystal and a MgO (100) single crystal were subjected to 30 keV 3 He implantation and a subsequent annealing at 1100 K. In both materials the formation of cavities takes place during the annealing stage when the implanted gas is released. The presence of cavities was detected by positron beam analysis. After the creation of cavities was established the samples were re-filled with deuterium by means of 15 keV D+ implantation with a dose of 1015 cm−2. During the subsequent annealing at 1000 K D escaped from the cavities. In the case of MgO further growth of cavities was observed.
The Structure of Ion-Implanted Amorphous Silicon
Authors: Gibson J. M. , Cheng J-Y. , Voyles P. , TREACY M.M.J. , Jacobson D.C. 
Published: April 2011

AbstractUsing fluctuation microscopy, we show that ion-implanted amorphous silicon has more medium-range order than is expected from the continuous random network model. From our previous work on evaporated and sputtered amorphous silicon, we conclude that the structure is paracrystalline, i.e. it possesses crystalline-like order which decays with distance from any point. The observation might pose an explanation for the large heat of relaxation that is evolved by ion-implanted amorphous semiconductors.
Irradiated Microstructures of Magnesium Aluminate Spinel and their Controlling Factors
Authors: Kinoshita C. , Matsumura S. , Yasuda K. , Soeda T. , Noujima M. 
Published: April 2011

AbstractThis paper reviews our recent progress in study on the strong resistance of magnesium aluminate spinel to void swelling during irradiation, along with the related characteristic features of its radiation damage. Comparative experimental results on irradiated microstructures and mechanical properties in magnesium aluminate spinel and alpha-alumina are shown in terms of controlling factors of radiation resistance of the former crystal. It is experimentally shown that structural vacancies due to non-stoichiometry provide effective recombination sites for displaced cations to suppress the formation of interstitial loops. Decreased formation of interstitial loops enhances the further recombination of interstitials and vacancies and thereby the formation of voids.