bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of the Strain Profile in Thin Au/Ni Multilayers by X-Ray Diffraction
Authors: Chaudhuri J. , Gondhalekar V. , Jankowski A. F. 
Published: March 2011

ABSTRACTA dynamical x-ray diffraction theory has been used to obtain microscopic strain profiles in thin Au/Ni multilayers. Depth profiles of strains in these multilayers, with repeat periodicities varying from 0.82 nm to 9.0 nm, are obtained by an iterative fitting of the calculated diffraction pattern with the experimental one. Interfacial coherency is found to play an important role in understanding the origin of the supermodulus effect in metallic multilayers.
Determination of Composition and Linear Lattice Expansion Coefficient in Si1−x Gex/Si Thin Films by Simulation of X-Ray Rocking Curves
Authors: Cembali F. , Fabbri R. , Servidori M. , Zani A. , Iyer S. 
Published: March 2011

ABSTRACTBy simulation of X-ray rocking curves of Si-Ge alloys grown on Si by molecular beam epitaxy and of Ge implanted samples, the Ge composition, the linear lattice expansion coefficient, the strain depth-distribution and the static Debye-Waller factor in the MBE alloys have been determined.
Reconstructed Structure of SiO2/Si(111) Interface
Authors: Hirosawa Ichiro , Nizuki Jun'ichiro , Tatsumi Toru , Akimoto Koichi , Matsui Junji 
Published: March 2011

ABSTRACTIn order to investigate the initial oxidation process Qf the Si (111) surface, we have studied the molecular beam deposited Si0 2/Si(111)-7×7 interface structure using grazing incidence X-ray diffraction geometry. We suggest a three-fold symmetry structural model composed of stacking fault layer, dimer layer and additional ordered atoms. The three-fold symmetry structure comes from the preference for oxidation in the faulted half of the 7×7 structure.
Rheed Study of the Surface Structure of Cu(110) From 153 To 973 K
Authors: Liao Da-Zhong , Cao Y. , Montano P. A. 
Published: March 2011

ABSTRACTWe have studied the surface structure of Cu(110) from 153 to 973 K. Reflection high energy electron diffraction (RHEED) was employed to analyze the surface modifications taken place at the crystal surface. We performed careful spot profile intensity measurements as a function of temperature.The typical characteristics of forward scattering, the short wavelength at high energy, and the small grazing incidence angle in RHEED provide strong surface sensitivity and are therefore ideal to study surface structures and especially surface roughness. We observe at low temperatures strong diffraction streaks in the patterns as well as Kikuchi lines. The diffraction intensities reduce slowly when the temperature is raised from 153 K to 473 K, then fall off more rapidly after that, and from 573 K, the intensities decrease drastically. High resolution LEED measurements indicate a reduction in the coherence length at high temperatures.
Spectral Transformation of Exelfs Data and a Structural Examination of Nitrogen on Cu(100) and Cu(110) Surfaces
Authors: Dai Q. , Gellman A. J. 
Published: March 2011

ABSTRACTEXtended Electron Energy Loss Fine Structure (EXELFS) spectra have been obtained above the K-edge of nitrogen atoms adsorbed on Cu. The radial distribution functions obtained from the fine structure indicate N-Cu bond lengths of 1.84(±.03) Å and 1.81(±.03) Å for nitrogen on the Cu(100) and Cu(110) surfaces respectively. As in previous EXELFS measurements, the actual measurements made are of N"(E) rather than direct measurement of N(E), the electron energy loss distribution. The EXELFS spectra from these two surfaces are used to illustrate the influence of this collection scheme on the radial distribution function obtained by Fourier transformation of the raw data. To obtain the direct analog of the radial distribution function found from the EXAFS experiment one must either resort to spectral integration or appropriate scaling of the distribution function found in the EXELFS experiment.
Molecular Dynamics Studies of Defects in Si
Authors: Duesbery M.S. , Michel D.J. , Kaxiras Efthimios , Joos B. 
Published: March 2011

ABSTRACTThe efficacy of three modern empirical potentials in the molecular dynamic simulation of the configurations, energies and mobility of dislocation cores and their excitations is assessed in the light of recent literature. The results are found to be inconsistent both between different potentials and with experimental evidence. It is argued that the discrepancies are rooted in the limited databases which have been used in the construction of empirical potentials. The reason for the discrepancies is demonstrated by comparing empirical and density functional calculations of the generalized stacking fault energy.
On the Nature of Grain Boundary Structures in Nanophase Materials
Authors: Siegel R. W. , Thomas G. J. 
Published: March 2011

ABSTRACTA significant fraction of the atoms in nanophase materials are associated with grain boundaries. Hence, the nature of the grain boundary structures in these materials is interesting in its own right as well as ultimately important to the properties of nanophase materials. Considerable uncertainty has surrounded the atomic structure of nanophase boundaries, but recent experiments have shed some light on these interesting structures. These investigations have included direct HREM observations combined with image simulations, as well as Raman spectroscopy and SANS. The emerging picture is one of nanophase boundaries that are not dissimilar in structure to those normally encountered in conventional polycrystals. The connections between this picture, of nanophase materials as ultrafine-grained polycrystals, and experimental observations on these materials are discussed.
The Free Energy Simulation Approach to Grain Boundary Segregation In Cu-Ni
Authors: Wang H. Y. , Najafabadi R. , Srolovitz D. J. , Lesar R. 
Published: March 2011

ABSTRACTA new, accurate method for determining equilibrium segregation to defects in solids is employed to examine the segregation of Cu to grain boundaries in Cu-Ni alloys. The results are in very good agreement with the ones given by Monte Carlo. This method is based upon a point approximation for the configurational entropy, an Einstein model for vibrational contributions to the free energy. To achieve the equilibrium state of a defect in an alloy the free energy is minimized with respect to atomic coordinates and composition of each site at constant chemical potential. One of the main advantages this new method enjoys over other methods such as Monte Carlo, is the efficiency with which the atomic structure of a defect, segregation and thermodynamic properties can be determined. The grain boundary free energy can either increase or decrease with increasing temperature due to the competition between energetic and configurational entropy terms. In general, the grain boundary free energy increases with temperature when the segregation is strongest.
Simulating Vacancy, Impurity And Electronic Defect States In Mgo,Lici And La2Cuo4 Using Quantum Cluster And Classical Lattice Simulation Techniques In A Consistent Manner.
Authors: Grimes Robin W. , Catlow C. R. A. , Shluger A. L. , Pandey R. , Baetzold R. , Harker A. H. 
Published: March 2011

ABSTRACTWe calculated defect energies by using a Hartree-Fock method to model an inner region that includes the defect site and oneor two shells of lattice ions. This is surrounded by an embedding region that is described by a classical Mott-Littleton calculation. Electrostatic multipole consistency between the two jegions is maintained throughout.The results of defect calculations on MgO are examined as a function of basis set. We find that a sophisticated basis set is required before a reliable defect formation energy can be guaranteed. This experience has allowed us to develop a new model for the off-center relaxation of the exciton in LiC1. These calculations have required the use of pseudo potential cores for anions and floating functions to model the diffuse electron. Lastly, we report on recent calculations concerning the stability of hole states in La2CuO4. We find considerable delocalization of the hole over both the Cu2+ ions and the 02− ions that form the Cu-O planes.
Electron Channelling Contrast Imaging (ECCI) of Dislocations in Bulk Specimens
Authors: Czernuszka J.T. , Long N.J. , Boyes E.D. , Hirsch P. B. 
Published: March 2011

ABSTRACTDislocations have been imaged in bulk specimens of Si using a FEG SEM operating at 30keV and 100keV, without using an energy filter, but by image processing of the back scattered electron signal collected by a highly efficient detector. The dislocation contrast is greater at 30 keV than at 10OkeV. Ilowever, the depth to which useful information may be obtained is greater at 1O0keV (˜210nm) than at 3OkeV (˜95nm). The final depth to which dislocations can be imaged is strongly dependent on image processing conditions.
Diffusion Mechanisms in Bcc-Zr:A Molecular Dynamics Approach
Authors: Willaime F. , Massobrio C. 
Published: March 2011

ABSTRACTBasing our calculations on a realistic N-body interatomic potential for Zr, we study the vacancy migration mechanism and determine the related diffusion coefficient in the bcc phase. The form of the potential energy along the nearest-neighborjump migration path is single-peaked. The vacancy jump rate determined by molecular dynamics simulations has a perfectly Arrhenian behavior and its activation energy is very close to the static value of the vacancy migration energy, both being very low (≈ 0.3 eV) . The diffusion coefficient is in very satisfactory agreement with experiments.
Longitudinal Relaxation of a Thermally Stressed Fiber by Prismatic Dislocation Punching
Authors: Dunand David C. , Mortensen Andreas 
Published: March 2011

ABSTRACTA model predicting the number of prismatic loops dislocation punched at the ends of a cylindrical fiber by thermal mismatch stresses is presented and compared to another based on a mismatching ellipsoid. The longitudinal stress in the fiber and the interfacial shear stress are derived by adapting a shear-lag model to the plastic portion of the interface. In certain cases, the central part of the fiber is strained by plastic and elastic interfacial shear until it exhibits no mismatch with the matrix. This leads to a critical fiber length above which the number of punched loops is constant.
Effect of Particle Size on the Plastic Zone Formation in Front of Mode I Crack in ABS Polymers
Authors: Ni Beta Y. , Li J. C. M. 
Published: March 2011

AbstractTwo different sizes (0.4 and 0.1 μm) of rubber particles (polybutadiene) are usually used to toughen the glassy SAN (styrene acrylonitrile) matrix in ABS copolymers. Experiments on a batch of specimens without the large particles confirmedour previous contention that cavitation of large particles within a zone of cardioid shape is an important part of crack tip plasticity which protects the crack tip from the applied stress field. Large rubber particles require a less strong applied stress field than small rubber particles to initiate crazes so that the large rubber particles help avoid brittlefracture which occurs without crazes.
Theory of Hydrogen Complexes in Si
Authors: Zhang S. B. , Jackson W. B. 
Published: March 2011

ABSTRACTThe predominance of Si-H bonding and the origin of {111} platelets in hydrogenated Si remain important unsolvedproblems in the study of H in Si.Recent theoretical and experimental results indicate that H predominately enters the Si network in pairs. A promising diatomic H configuration consists of a bond centered H closely associated with an antibonding centered H. In this work, we show that adjacent diatomic H pairs have a binding energy of 0.2 eV/2H. The binding originates from relaxation of strained Si-Si backbonds. Further clustering of the H pairs eliminates all strained bonds, forming a hydrogenated platelet oriented along the {111} plane. The binding energy of 3.95 eV/2H for the platelet is 0.15 eV lower than that for interstitial H2 molecules in c-Si. Lattice expansion makes the platelets energetically more competitivewith the lowest energy Si-H bonding confi gration at hydrogenated Si (111) surfaces. These higher level complexes explainthe formation of platelets, Raman spectra, and absence of gap states in hydrogenated c- Si as well as the clustered phaseseen in NMR and of H evolution and diffusion in hydrogenated amorphous Si.
The Precipitation of Nickel and Copper at Grain Boundaries in Silicon
Authors: Möller H. J. , Jendrich U. , Huang L. , Foitzik A. 
Published: March 2011

ABSTRACTThe precipitation of copper and nickel at grain boundaries in cast polycrystalline silicon is investigated. The metals are diffused into the specimens from a surface source between 800 – 1000 °C and the precipitation after cooling is studied by TEM. Copper precipitates in form of colonies containing hundreds of particles with a size between 5–6 nm. In the grain boundary they nucleate preferentially at dislocations and steps. The distribution and size of the precipitates depend on the cooling rate after the diffusion. Nickel forms only few large (micrometer size) plate-like or three dimensional precipitates at and near grain boundaries. The main features of the results and the differences between the two elements are explained under the assumption that the precipitation requires the transport of native point defects.
On the Distribution Mechanism of Voids in Si-Implanted GaAs
Authors: Chen Samuel , Lee S.-Tong , Braunstein G. , Ko K. Y. , Tan T. Y. 
Published: March 2011

ABSTRACTVoids, formed by the condensation of an excess of implantation-induced vacancies, have been recently identified as the defect directly responsible for dopant diffusion and electrical activation anomalies in Si-implanted and annealed GaAs and GaAs/AlGaAs superlattice materials. Depending on the implanted dose, voids can be distributed either throughout the implanted region or in two bands. We have examined the origin of this void distribution difference. In the asimplanted sample associated with the latter case, a buried continuous band of amorphous GaAs has formed. GaAs formed by the recrystallization of amorphous GaAs does not contain excess vacancies, and therefore cannot form voids. However, on either side of the amorphous layer, the excess vacancies can condense to form the observed banded distribution of voids. In the as-implanted sample associated with the former case, a continuous amorphous GaAs layer did not form and therefore, upon annealing, voids are seen throughout the implanted region.
Frequency Dependence of Hopping Conductance in Crystalline Electron Irradiated Semiconductors
Authors: Kouimtzi S.D. 
Published: March 2011

ABSTRACTExtensive irradiations were carried on crystalline semiconductors InSb, GaAs and InAs. At low temperatures the frequency dependence of the conductivity is observed to be sublinear (σαωs). where s<1. The dependence of s on both the degree of the induced damage and on temperature is studied and discussed in terms of the quatum mechanical tunnelling and of correlated barrier hopping mechanisms.At fairly low doses of irradiation activated conductance is observed with s having a weak temperature dependence. As the degree of damage is further increased conduction at helium temperatures takes place by variable range hopping, σαexp(-b/T1/4). The constant b is observed to depend on the effective mass for different semiconductors.At higher temperatures activated conduction is observed again. The observed activation energies E are Eg 1/4 <E<Eg 1/2 and we believe they could represent hopping of single and double carriers.
Phonons in Mixed II-VI Compound Semiconductors
Authors: Talwar D. N. , Coleman Alan C. , Amirtharaj P. M. , Perkowitz S. , Feng Z. C. , Becla P. 
Published: March 2011

ABSTRACTWe have analysed the far infrared reflectivity and Raman scattering spectra of phonons in Cd1−xMnxTe, Zn1−xMnxTe, Hg1−xMnxTe, and Hg1−xZnxTe for low composition of x. Unlike CdMnTe and ZnMnTe, weak impurity induced peaks are observed in HgZnTe and HgMnTe, near ˜ 96 and 98 cm−1, well above the LA-phonon band of HgTe. Comprehensive calculation of lattice dynamics based on a semi-empirical Green's function theory has provided convincing arguments to support the above features as gap modes of Zn and Mn in HgTe. The theory also predicts the possibility of resonance modes, above the TA cutoff of HgTe, in HgMnTe and HgZnTe to be observed by IR spectroscopy.
Effect of the Extinction Distance in X-Ray Rocking Curve Analyses of II-VI Compounds
Authors: Moran P.D. , Matyi R.J. 
Published: March 2011

ABSTRACTDouble crystal x-ray rocking curves from single crystal CdTe and CdZnTe of various degrees of crystalline perfection were recorded under diffraction conditions in which the extinction distance varied from under 10 microns to more than 100 microns. In crystals of intermediate quality the rocking curves recorded under conditions of long extinction length showed structure not evident in those recorded under conditions of short extinction length. Integrated reflectivity measurements were performed at both long and short extinction lengths. The results have been interpreted within the framework of a transition from kinematic to dynamical diffraction.
PAC Studies of Defects in AgCI and II-VI Compounds
Authors: Austin J.C. , Swanson M.L. , Hughes W.C. , Choi S.S. 
Published: March 2011

ABSTRACTThe Perturbed Angular Correlation (PAC) method has been used to study In -vacancy complexes in AgCl and II - VI compounds. Although these materials are quite different in structure and properties, they are related by photoconductive properties which make them interesting intrinsically and for application to photography (silver halides) and to the design of photodetectors and photovoltaic cells (II - VI compounds). We have obtained the first PAC results for silver halides and ternary II-VI compounds.For AgCl, measurement at 77 K clearly reveals two different 111In - vacancy complexes characterized by quadrupole interaction frequencies Vq1 = 21.5 MHz and Vq2=43 MHz, both having axially symmetric electric field gradient (EFG) tensors with principle axes along <100> directions. Temperature dependence of the PAC signal allows a determination of the activation energy and attempt frequency for vacancy motion by measurement of the damping arising from dynamic effects.For 4% Zn - doped bulk CdTe samples, vacuum annealed in the range 400°C to 550°C, PAC shows that a large fraction of the 111 In probe atoms occupy non-cubic lattice sites having an EFG characterized by vQ = 60 MHz, η = 0.2. The concentration of this complex was decreased by annealing between 400°C and 600°C in a Cd overpressure, suggesting tha the observed EFG is caused by a 111In - cadmium vacancy complex. Similar measurements of Cd0.8Mn0.2Te showed an identical EFG which, however, appeared at a lower annealing temperature.
Point Defect Injection and Enhanced Sb Diffusion in Si During Co-Si and Ti-Si Reactions
Authors: Honeycutr J.W. , Rozgonyi G.A. 
Published: March 2011

ABSTRACTThe effects of Co and Ti silicide film formation on diffusion of buried Sb-doped layers in Si have been investigated. Sb profile analysis by secondary ion mass spectrometry shows that greatly enhanced, non-uniform Sb diffusion occurs during reactions of various thicknesses (30- 300 nm) of Co and Ti by rapid thermal annealing. A simple non-equilibrium intrinsic diffusion model is invoked to estimate time-averaged excess vacancy concentrations. Vacancy concentrations of about 107 times equilibrium values are shown to exist during CoSi2 formation by reaction of a 30 nm Co film at 700°C for 5 min in Ar.Diffusion enhancements at large distances from silicide stripe edges are observed by bevel and etch techniques. These effects tend to decrease with increasing annealing time, indicating that film stresses may play an important role in the interfacial point defect injection process.
Investigation of Deep Level Defects in Mercuric Iodide by Thermally Stimulated Current Spectroscopy
Authors: Bao X.J. , Schlesinger T.E. , James R.B. , Cheng A.Y. , Olrtale C. , Van Den Berg L. 
Published: March 2011

ABSTRACTMercuric iodide (HgI2) single crystals deposited with semitransparent Pd, Al and Ag contacts were studied by thermally stimulated current spectroscopy (TSC). Distinct differences were found among spectra obtained friom samples withdifferentmetal contacts, indicating that interactions between the metal contacts and mercuric iodide substrates have strong effects on the deep defect levels in mercuric iodide. The activation energies of some of these defect levels were estimated bytaking TSC spectra with different heating rates. In addition, a pyroelectric effect was observed in Ag-contactedsamplesbythermally stimulated depolarization current technique (TSDC). The implications of these results in device applicationsof mercuric iodide are discussed.
Hydrogen Diffusion in N-Type Silicon.Comparison With P-Type Silicon
Authors: Rizk R. , De Mierry P. , Ballutaud D. , Aucouturier M. , Mathiot D. 
Published: March 2011

ABSTRACTDeuterium diffusion profiles in medium phosphorus doped silicon (1016 and 1017 cm−3) at two different deuteration temperatures (120 and 150°C) are simulated with an improved version of a previously reported model. The new approach which excludes the H2 molecule formation, as applied recently to ptype silicon, allows the determination of kinetic and thermodynamic parameters such as diffusion coefficients, activation and dissociation energies. These parameters 6re compared with those found for p-type silicon and discussed in the light ofavailable data for n-type material.
The Accommodation of Lattice Mismatch on the (111) Interphase Boundary Plane in FCC Metals
Authors: Gumbsch P. , Fischmeister H.F. 
Published: March 2011

ABSTRACTUsing the embedded atom method we atomistically model the accommodation of the lattice nismatch and study the propertiesof the misfit dislocations in parallel oriented bicrystals. We calculate and analyze in detail the excess interfacial energies on the (100) and (111) boundary planes. The Ag/Ni system is chosen as a model system for metal/metal interfaces with a large lattice mismatch.Among the possible boundary planes in parallel oriented fcc bicrystals, the ones with terminating {111} planes arc energetically most favourable and are most often observed in experiments. This can be explained by a detailed analysis of the elastic strain fields in the interfaces, which correspond to networks of misfit dislocations. While the misfit dislocations on the (100) and (011) planes have a ½[01ī] Burgers vector, those on (111) can dissociate into misfit partials. The elastic strains connected with the misfit partials are, of course, much smaller than those for other types of misfit dislocations. The misfit partials form a triangular network within the boundary plane.
Imaging of Cracks in Semiconductor Surfaces Using Scanning Tunneling Microscopy
Authors: Foecke T. , King R. , Dale A. , Gerberich W.W. 
Published: March 2011

ABSTRACTScanning Tunneling Microscopy (STM) has developed into a useful tool for atomic-scale characterization of material surfaces. It is proving especially useful in the field of fracture, as the vast majority of high-resolution images of fracture processes are made in the transmission electron microscope, where thin film effects and sample preparation may greatly modify crack tip stresses and dislocation structures. This investigation involved imaging of cracks introduced in Si at room temperature and single crystals of galena (PbS) by rapid indentation at 77K. Images were obtained at the arrested cracktip, around the indentation, and along the flanks of the crack in the dynamic growth region. Measurements were made of both crack-tip morphology and upsets observed along the flanks of the cracks in PbS. Interesting results concerning crack tip geometry in Si, the effect of STM tip geometry and scan conditions on the resulting image of the cleavage crack, as well as work in progress on other material systems, will be discussed.