bluuebunny/crossref_metadata_2025_split huggingface dataset:
Semiempirical Angular-Force Method for BCC Transition Metals
Authors: Carlsson A. E. 
Published: March 2011

ABSTRACTAn angular-force method for bcc transition-metals is obtained by generating a functional form via a quantum-mechanical analysis, and subsequently fitting the parameters in this form to experimental and ab-initio theoretical inputs. The quantummechanical analysis uses a four-moment treatment of the electronic density of states (DOS) in a d-band tight-binding model. Calibration of the method gives excellent results for the bcc-fcc energy difference and the vacancy-formation energy in W. The method is used to treat relaxation and c(2 × 2) reconstruction on the W (100) surface. The relaxation energy is primarily due to two-body terms, while the reconstruction requires the angular terms. Agreement with ab-initio results is obtained for reasonable values of the parameters in the model. However, the energy difference between the reconstructed surface and the optimally relaxed surface is quite sensitive to the details of the implementation of the method.
Calculation of Defect Properties of NiTi and FeTi
Authors: Lutton Russell T. , Sabochick Michael J. , Lam Nghi Q. 
Published: March 2011

ABSTRACTThe energies and configurations of interstitials and vacancies in the B2 ordered compounds NiTi and FeTi were calculated using atomistic simulation. The stable configuration of a vacancy after the removal of an Ni atom was a vacant Ni site; similarly, the removal of an Fe atom in FeTi resulted in a vacant Fe site. Removal of a Ti atom in both compounds, however, resulted in a vacant Ni or Fe site and an adjacent antisite defect. The effective vacancy formation energies in NiTi and FeTi were calculated to be 1.48 and 1.07 eV, respectively. Interstitials in NiTi formed split <111> configurations consisting of a Ni-Ni dumbbell oriented in the <111> direction with one or two adjacent antisite defects. The Fe interstitial in FeTi had a similar configuration, except the dumbbell contained Fe atoms. The Ti interstitial in FeTi formed an <110> Fe-Fe dumbbell.
Calculation of Diffraction Patterns Associated with Electron Irradiation Induced Amorphization of CuTi.
Authors: Devanathan R. , Lam N. Q. , Sabochick M. J. , Okamoto P. , Meshii M. 
Published: March 2011

ABSTRACTA new approach that uses the multislice method in conjunction with molecular dynamics simulations to study electron irradiation induced amorphisation is presented. Diffraction patterns were calculated for CuTi and found to be more sensitive than the pair correlation function to the structural changes preceding amorphisation. The results from this approach and from a study of long range order are presented.
First-Principles Study of Soliton Hyperfine Interactions in Polyacetylene
Authors: White C. T. , Kutzler F. W. , Mintmire J. W. , Cook M. R. 
Published: March 2011

ABSTRACTAll-trans-polyacetylene is considered the prototypical broad band gap quasi onedimensional organic semiconductor. Intrinsicsoliton defects have long been known to be important to the understanding of the observed properties of this system at low doping levels. Magnetic resonance techniques provide powerful experimental probes into the nature and environment of these neutral-radical defects. In an earlier work we showed that firstprinciples spin-polarized local density functional (LDF) methods reliably predict proton Fermi-contact coupling constants for planar, neutral, organic π-radicals. We have also used these methods to calculate the Fermi-contact proton coupling constants associated with the soliton defect in polyacetylene.Herein we compare the results of these earlier soliton calculations to results from recent electron-nuclear double-resonance (ENDOR) experiments. Our predicted ratio of the negative to positive spin densities is in good agreement with these ENDORstudies. The negative spin densities arise from spin-polarization effects which are found to cause the soliton level at midgap to be split by several tenths of an eV.
Alternative Length Scales for Polycrystalline Materials
Authors: Nichols C.S. , Cook R.F. , Clarke D.R. , Smith D.A. 
Published: March 2011

AbstractIt is well established from studies of bicrystals that the properties of a grain boundary depend on the atomic structure of the boundary. However, constitutive relations for the properties of polycrystalline materials do not currently take into account this boundary-toboundary variability. Instead, such relations depend on a single length scale, typically the average grain diameter. We extend the traditional viewpoint by proposing that boundaries may be divided into two distinct categories, depending on their misorientation angle. The relevant length scale in constitutive relations for polycrystals is then the average cluster size, where clusters consist of grains connected by boundaries in the same misorientation category. A brief discussion of this additional length scale and how it may be reflected in various constitutive relations for physical and mechanical properties of polycrystals is given.
Raman Studies of Fluorine-Intercalated Carbon Fibers
Authors: Rao A. M. , Fung A. W. P. , Dresselhaus M. S. , Dresselhaus G. , Endo M. , Nakajimat T. 
Published: March 2011

ABSTRACTWe report Raman scattering measurements on fluorine-intercalated graphite fibers (CxF) for stoichiometries x =7.8, 4.5 and 2.9. Lorentzian fits to our Raman lineshapes indicate the presence of two lines around 1600 cm−1 and a broad line around 1355 cm−1 . The 1355 cm−1 line is the disorder-induced graphite line and the ratio of the integrated intensity of this line to that of the 1600 cm−1 doublet (R) provides a measure of the intercalationinduced disorder in the CjF fibers. Both TEM and Raman studies indicate the presence of unintercalated graphitic regions in the CxF fiber. The inverse relation between the average crystal planar domain size La, and the Raman intensity ratio R yields La. ,˜52Å for C7.8F fibers and La. , ˜40Å for C4.5,F and C2.9F fibers.
Vacancy Properties in Ordered NiGa And NiAl
Authors: Kim S.M. 
Published: March 2011

ABSTRACTThe recently formulated theory of vacancy formation in CsCl-type ordered alloys has been applied to β-NiGa and β-NiAl. The observed Nisublattice vacancy concentrations in these compounds could be well described by the theory. For the first time it is also shown that structural vacancies most likely exist in Ga-rich NiGa and Al-rich NiAl at absolute zero temperature.
Hrem Investigation of the Structure of the σ5(310)/[001] Symmetric Tilt Grain Boundary In Nb.*
Authors: King Wayne E. , Campbell G. H. , Coombs A. , Mills M. J. , RüHle M. 
Published: March 2011

ABSTRACTRecent atomistic simulations using interatomic potentials for Nb developed employing the embedded atom method (EAM) and the model generalized pseudopotential theory (MGPT) have indicated a possible cusp at the Σ5(310) orientation in the energy vs tilt angle curves for<001> symmetric tilt grain boundaries. In addition, the most stable structure predicted using EAM exhibits shifts of one crystal relative to the other along the tilt axis and along the direction perpendicular to the tilt axis lying in the boundary plane. The structure predicted using the MGPT was mirror symmetric across the plane of the grain boundary. This boundary has been prepared for experimental study using the ultra high vacuum diffusion bonding method. A segment of this boundary has been studied using high resolution electron microscopy.
Impurity-Defect Complexes in Hydrogenated Amorphous Silicon
Authors: Yang Lin H. , Fong C. Y. , Nichols Carol S. 
Published: March 2011

ABSTRACTThe two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H) - a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping - have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using firstprinciples self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results, we have studied the electronic and structural properties of substitutional fourfoldcoordinated phosphorus and boron at the second neighbor position to a dangling bond defect. We demonstrate that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H.
Spectroscopic Study of Hydrogen Induced Defect in a-Ge:H
Authors: Jin Shu , Ley Lothar 
Published: March 2011

ABSTRACTTotal yield photoelectron spectroscopy has been used to study the electronic structure change of UHV evaporated a-Ge subjected to posthydrogenation and various annealing cycles. We identify in R.T. hydrogenated a-Ge:H a new hydrogen induced defect at about Ev + 0.45eV, which can be healed upon 300°C annealing. This new defect accounts for the defect density gradient of hydrogenated amorphous semiconductors, spanning the range from ∼ 1018 cm−3 at the growing surface to 1018−1015 cm−3 in the bulk, depending on growth condition and time. The origin of this new defect is discussed.
Diffraction Effects from [111] Twist Boundaries in Gold
Authors: Majid I. , Wang D. , Bristowe P. D 
Published: March 2011

ABSTRACTThe structural characteristics of [111] twist boundaries in gold are investigated using a combination of x-ray diffraction and computer modeling techniques. Comparison of the measured scattering effects with those generated from EAM computer models reveals that the [111] boundary displacement field is weak, rotational in form and centered on ‘O’ lattice sites. Furthermore, the measured intensities of the strong ‘O’ lattice reflections decrease smoothly with increasing boundary angle up to 30°, as calculated from the model. The effect of double positioning on the diffraction pattern and the structural analysis is discussed.
Damage Freeze-In Phenomena as a Function of Dopant Implant Type In Germanium-Rich Regions in Silicon
Authors: Aronowitz Sheldon , Hart Courtney , Myers Sharon 
Published: March 2011

ABSTRACTEnd-of-range damage produced by n-type dopants is frozen-in if that damage is produced in germanium-rich regions in crystalline silicon. This is not the case with p-type dopants. High germanium doses were implanted into silicon; the wafers were annealed at 1000 C for 30 minutes under nitrogen. Phosphorus or boron then were implanted into the crystalline siliconfollowed by a 900 C, 30 minute neutral ambient anneal.Explanation of the freeze-in phenomenon relies on results of semiempirical quantum chemical calculations that showed that group V dopants, whether interstitial or substitutional, as well as interstitial silicon, would be attracted to the vicinity of substitutional germanium sites in germaniumrich regions ofthe crystalline silicon. This general preferential diffusion behavior is not calculated to occur with the p-type dopants from group III. When substitutional, in fact, the group III impurities are predicted to be repelled from the germanium-rich regions.TEM studies show that any residual damage with boron as the implant and germanium present is low in density and within 20 nm of the silicon interface. This is contrary to studies involving phosphorus where damage is exclusively associated with the end-of-range of the phosphorus implant. Both sets of results are in accord with the theoretical considerations.
Electrical Properties Of S+Implantation in Si GaAs
Authors: Xia Guanqun , Guan Anmin , Geng Haiyang , Wang Weiyuan 
Published: March 2011

ABSTRACTThe electrical properties of S+implanted in SI GaAs have been studied. The rapid diffusion and redistribution of S+implanted in GaAs after conventional thermal annealing (CTA) depends not on conventional diffusion of S+or VAs, but on the enhanced diffusion by ion implantation. By employing rapid thermal annealing (RTA) techniques enhanced diffusion can be restrained, redistribution of S+implantation can be decreased greatly and a thin active layer suitable for fabricating GaAs MESFET devices can be obtained.
Long Range Coulomb Effects on Hydrogen Debonding from Boron Acceptors in Silicon
Authors: Anderson R. A. , Seager C. H. 
Published: March 2011

ABSTRACTPrevious work has demonstrated that B-H pairs in silicon thermally dissociate obeying simple first order kinetics if theyare located in a region depleted of majority carriers. B.H debonding in equilibrium, however, is a slower, more complex process. We have investigated the dissociation of B.H pairs under a variety of equilibrium and non-equilibrium conditionsand have demonstrated that the dissociation process is strongly influenced by the local concentration of majority and minority carriers. In particular, we show that injection of minority carriers can markedly accelerate the dissociation process. A model is proposed which suggests that hydrogen released from an acceptor, while initially positive, must always beneutralized before escape is possible. This picture correctly describes the time dependence of debonding in equilibrium, and it predicts the enhanced debonding in forward biassed diodes provided the characteristic time for H charge conversionislong.
Structural Properties of a-Ge1−xnx:H Alloys
Authors: Marques F. C. , Chambouleyron I. 
Published: March 2011

ABSTRACTAmorphous hydrogenated and unhydrogenated germanium-nitrogen alloys were prepared by rf glow discharge using a GeH4+NH3atmosphere and by rf sputtering using a Ge target with different gases (Ar, N2, NH3 , and mixtures). A difficulty in obtaining nonstoichiometric films was encountered for both methods. Films prepared by rf glow discharge tend to be either Gerich or close to stoichiometric composition, and films prepared by sputtering tend to have low nitrogen concentration. Thesamples prepared by glow discharge at 220°C do not contain the NH2 absorption band, which is usually present in filmsprepared by sputtering. The Urbach energy (determined by PDS), Tauc's gap, refractive index, dark conductivity and activation energy are also reported.
Temperature Dependent Recombination Lifetime in Silicon: Influence of Trap Level
Authors: Buczkowski Andrzej , Radzimski Zbigniew J. , Kirino Yoshi , Shimura Fumio , Rozgonyi George A. 
Published: March 2011

ABSTRACTThis paper discusses the temperature dependence of recombination lifetime in a variety of silicon materials using energy level as a parameter. A theoretical approach based on the Shockley-Read-Hall theory for energy level calculations has been used. Various types of defects created by introducing impurities, dislocations and grain boundaries into silicon waferswere studied. Results are presented for Czochralski grown Si wafers intentionally contaminated with gold and chromium, EFG ribbon with varying concentration of oxygen, web ribbons with extended defects and contaminants, large grain polycrystalline material, and Si/Si-Ge/Si heterostructures with varying misfit and threading dislocation density.
Analysis of Oxygen Gettering and Dislocation Locking in Silicon
Authors: Maroudas Dimitrios , Brown Robert A. 
Published: March 2011

ABSTRACTThe motion under an applied stress of dislocations in silicon crystals is slowed and stopped by the presence of oxygen inthe material. A model is presented that quantitatively describes the inhibition of dislocation motion by accounting for the oxygen gettering to dislocations caused by diffusion and stress-enhanced migration. Drag on the dislocation motion ismodelled using the elastic interactions between the interstitial oxygen and the dislocation and the energy needed to breakbonds formed between silicon and aggregated oxygen atoms within the dislocation core. The predictions of the model agree quantitatively with the experimental data of Imai and Sumino.
Electron Microscopy Study Of Mocvd-Grown Tio2Thin Films and Tio2/Al203 Interfaces
Authors: Gao Y. , Merkle K. L. , Chang H. L. M. , Zhang T. J. , Lam D. J. 
Published: March 2011

ABSTRACTTiO2 thin films grown on (1120) sapphire at 800°C by the MOCVD technique have been characterized by transmission electron microscopy. The TiO2 thin films are single crystalline and have the rutile structure. The epitaxial orientation relationship between the TiO2 thin films (R) and the substrate (S) has been foundto be: (101)[010]R║(1l20)[0001]s. Growth twins in the films are commonly observed with the twin plane{101} and twinning direction <011>. Detailed atomic structures of the twin boundaries and TiO2/α-Al203 interfaces have been investigated by highresolution electron microscopy (HREM).When the interfaces are viewed in the direction of [010]R/[000l]S, the interfaces are found to be structurally coherent in the direction of [1Ol]R/[1100]s,in which the lattice mismatch at the interfaces is about 0.5%.
Observation of Hexagonal AiGaAs Grown by OMCVD
Authors: Hwang D. M. , Ravi T. S. , Bhat R. , Simhony S. , Chen C. Y. , Kapon E. 
Published: March 2011

ABSTRACTExtended regions of hexagonal zinc sulfide (wurtzite) structure are found to exist in AlGaAs grown by low-pressure OMCVD at 750°C. The specimen was prepared on a (001) GaAs substrate patterned with [110]-orientedV-grooves, intended for a quantum wire laser structure. A high density of planar faults was observed to originate in theAl0.66Ga0.34As cladding layers near the inner corners of the V-grooves and propagate towards the surface along the {111} planes. Many of these faults are stacking faults and microtwins. However, there also exhibit extended regions of hexagonal structure, revealed in electron diffraction patterns and high resolution lattice images. The hexagonal phase shares the same close-packed layers with the cubic phase, i.e., (0001)hexagonal // {111}cubic. The mechanism for the formation of hexagonal structure in this specimen is not yet fully understood.
Interpretation of Alumina/Yttrium-Aluminum Garnet Orientation Relationships by Geometric Criteria
Authors: Hay R.S. , Matson L.E. 
Published: March 2011

ABSTRACTGeometric criteria for low interface energy and interface structure were tested for the cubic-rhombohedral system YAG/alumina. Orientation relationships near (111){110}a // (112){110}y and facets on (111)a(112)y were observed in both sol-gel derived composites and directionally solidified eutectic composites. The ΣYAG=12 near-CSL of 2{111}, {110}, {112} was inferred to be the preferred structural unit. Dislocations with b=1/3{111}a and b=1/2{110}a were observed and inferred to accomodate deviation from the structural unit, respectively. The {110}a,y direction met some of the criteria for an invariant line. Although the OR was explained by geometric criteria it would have been difficult to predict it with such criteria
Defect Dependence of Positron Lifetimes in Oxide Superconductors
Authors: Sterne P.A. , O'Brien J.C. , Howell R.H. , Kaisert J.H. 
Published: March 2011

ABSTRACTFirst principles calculations of the positron lifetimes are used to interpret experimental lifetime data for Ba1-xKxBiO3. The observed lifetimes are found to be very sensitive to the presence of defects in the sample. The temperature dependence of the lifetime and the change in lifetime with sample aging are both attributed to defects. The qualitative differences between metal vacancy defects and oxygen vacancy defects in metal oxides are also discussed.
Defect Chemistry of High Tc Superconductors
Authors: Fueki Kazuo , Idemoto Yasushi 
Published: March 2011

ABSTRACTThe oxygen deficiency δ in YBa2Cu3O7−δ was determined as a function of oxygen partial pressure and temperature. It was found that all the δ−log Po2 data points fall on a single smooth curve (master curve) when the points for each temperature were shifted in parallel with each other in the direction of abscissa by a certain distance. A theoretical equation describing the δ−logP02 relation was derived on the basis of electroneutrality, mass action law and site conservation.The theoretical curve agreed well with the experimental hL.Lster curve.
Defects in Decomposed Yba2Cu4Ox(124) Superconductor after Rapid Annealing
Authors: Li Y. , Gao Y. , Merkle K. L. , Shi H. , Balachandran U. 
Published: March 2011

ABSTRACTDecomposition of 124 into 123 has been studied after rapid annealing at temperatures from 800°C to 1000°C. It was foundthat the superconducting transition temperature (Tc) depended on the annealing temperature and atmosphere. For decomposedsamples, fine-scale defects with strong strain contrast are observed in the 123 matrix. High-resolution electron microscopy studies show that the defects are parallel to the (001) planes of the 123 matrix. The length of the defects varies andranges from 5 nm to 50 nm in the direction parallel to the (001) planes. The defects have been interpreted to be copper oxides, which could be flux pinning centers in these materials.
Thermal Desorption Studies of Isotopically-Labeled Oxygen from La2Cuo4+δ
Authors: Shinn N. D. , Bartram M. E. , Schirber J. E. , Overmyer D. L. , Rogers J. W. , Fisk Z. , Cheong S.-W. 
Published: March 2011

ABSTRACTIsotopically-labeled oxygen enrichment and thermal desorption mass spectroscopy (TDMS) have been combined to study interstitial oxygen desorption from superconducting La2CuO4+δ(δ≤5 0.032). Single crystal samples of magnetic, insulating La2CuO4+δ were annealed at 860K under 1-3 kbar oxygen pressure for 12-100 hours to yield hole-doped, superconducting La2CuO4+δ samples with 35K <Tc <40K. Whereas no TDMS signals were observed for the insulator, rapid bursts (FWHM <0.5 sec) of molecular oxygen were observed above 350K while heating the superconductor at less than I K sec−1 in high vacuum. A kinetic model is proposed in which the interstitial oxygen diffuses to internal grain boundaries and defects during heating, thereby inducing stress in the lattice as it attempts to revert to the LaCuO4.00 crystal structure. This stress is relieved by lattice fracture at grain boundaries during the TDMS experiment, releasing the trapped oxygen from the sample as micro-cracks are formed. In addition, the facile oxygen exchange between interstitial and latticeoxygen sites has been discovered by TDMS and weight gain measurements from isotopically-enriched crystals, supporting thestructural model of Chaillout, et al. in which the interstitial oxygen atom dimerizes with a lattice oxygen ion.
High Resolution Double Crystal Diffractometry of High TcSuperconducting Epitaxial Gd-Ba-Cu-O Films
Authors: Dai D Y , Green G S , Tanner B K , Li H C , Yi H R , Wang R L 
Published: March 2011

ABSTRACTHigh-Tc superconducting epitaxial thin films of gadolinium barium copper oxide,grown in situ by dc-magnetron sputtering onto substrates of single crystal (001) orientated LaAIO3 , SrTiO3 and yttrium stabilisedZrO2 have been studied by high resolution double axis difffactometry, X-ray white beam-Laue topography and double crystal topography. Rocking curve halfwidths were found to vary from about 1000 to 3000 arc seconds, very good in thecontext of these complex materials. The topographs showed that the orientations of the small crystallites was randomly distributed across the sample.