bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Efficiency of a Natural Composite
Authors: Saliba Joseph E. , Sawaya Georges E. 
Published: March 2011

AbstractThis study was initiated to investigate the structural efficiency of the “bessbeetle” (Odontotaenius Disjunctus) as compared to typical “man-made” or synthetic composites. This synthetic laminate is configured according to standard composites design practices. In fact, an orthotropic unidirectional T300 tape with circular fibers and 60% fiber volume fraction is used. The specific ply orientation of the symmetric man-made composite is [0/+45/-45/90]2S. The natural laminate studied is unsymmetric with the individual plies made of the same orthotropic unidirectional T300 tape but with different ply orientation. Contrary to previous beliefs the natural composite did not assume a balance of inplane and bending properties which in essence mimic the behavior of isotropic behavior. The results of the efficiency of the natural composite for tension did not show any noticeable advantages while the pure bending case resulted in higher values for the principal stresses in the unsymmetric laminate.
Theoretical Study of Polar and Non-Polar Interfaces in Compound Semiconductors: A Thermodynamic Analysis Based on Electronic Structure Calculations
Authors: Kohyama M. , Kose S. , Yamamoto R. 
Published: March 2011

AbstractPolar and non-polar interfaces of grain boundaries in compound semiconductors can be defined by the stoichlometry in the interface region, and It Is possible to construct two polar and one non-polar Interfaces for a symmetrical tilt grain boundary In the zinc-blende structure of which the Interface Is polar surfaces. The atomic and electronic structures of polar and non-polar interfaces of the {122} Σ=9 grain boundary in SIC have been examined by using the SCTB method coupled with the supercell technique. By using the calculated binding energies, the relative stability of the polar and non-polar interfaces has been analyzed through calculations of the thermodynamic potentials as a function of the atomic chemical potentials. It has been shown that the wrong bonds and the stoichlometry much Influence the stability and properties of grain boundaries in SiC. The stability of polar Interfaces In heterovalent compound semiconductors has been discussed.
Density-Functional Thermodynamic Perturbation Theory of Lennard-Jones Solids
Authors: Kyrlidis Agathagelos , Brown Robert A. 
Published: March 2011

AbstractThe thermodynamics of a fcc hard spheres solid is accurately described by recent density-functional approximations. This state is used as a reference in a thermodynamic perturbation analysis for a density-functional theory of Lennard-Jones solids. The free energy functional incorporates liquid state structural information and a density dependent potential decomposition for the Lennard-Jones interatomic potential. The computed free energies of the solids compare very well with the predictions of atonlistic simulations. Solid-liquid coexistence is predicted consistently to within 15% of results of Monte Carlo simulations, over the temperature range 0.75 ≤ kT/c ε ≤ 10.
Monte Carlo Study of Reconstruction of the Au (110) Surface Using Equivalent Crystal Theory
Authors: Good Brian S. , Banerjea Amitava 
Published: March 2011

AbstractThe (110) surface of gold is known experimentally to undergo a 1 × 2 reconstruction which is believed to be of the “missing row” type. There have been a number of theoretical studies of the energetics and geometry of this reconstruction. In this work, we present new results obtained using two versions of the Equivalent Crystal Theory (ECT). The ECT has proven to be quite accurate in providing predictions of surface energies and planar relaxations. The extended version of the ECT has been modified to better describe such quantities as elastic constants and shear energies. We have computed the energetics and geometry of the missing-row reconstructed surface, in both unrelaxed and relaxed form, using a Monte Carlo energy minimization technique, allowing relaxation of the positions of atoms up to three layers deep. We compare these results with previous theoretical work and with available experimental data.
A Study of the Dependence of the Structure of Σ = 3 Tilt Boundaries in Gold on the Inclination of the Boundary Plane
Authors: Wang Gui Jin , Vitek V. 
Published: March 2011

AbstractThe atomic structure of Σ = 3 tilt boundaries with variously inclined boundary planes has been studied using the many body potentials for gold. A chain unit model, analogous to the structural unit model, describes the relationship between different boundaries. The basic units in this model are units of the (111) and (112) twin boundaries and the model corresponds to atomic level faceting into these boundaries.
Sensitivity of Microsegregation Predictions to the Description of Phase Equilibria
Authors: Rettenmayr Markus 
Published: March 2011

AbstractA numerical model has been developed to predict the element distribution and some microstructural features in dendritically solidified binary and ternary alloys. Phase diagrams calculated on the basis of thermodynamic functions are taken into account. Thus, a minimum of assumptions is needed to describe the equilibrium at the solid/liquid interface, the partition coefficient of an alloying element is allowed to change as a function of temperature and concentration of other alloying elements.The description of the equilibrium at the interface appears to be highly significant. Assuming a constant partition coefficient may be justified for some binary alloys, but the assumption has to be verified for each system. Small additions, like dopants or impurities, influence the position of equilibria in phase diagrams, thus requiring the treatment of basically binary alloys as multicomponent systems. In ternary or higher order alloys the assumption of constant partition coefficients leads to erroneous results. For microsegregation predictions in technical alloys realistic phase diagrams have to be taken into account.
New Semi-Empirical Method for Alloys
Authors: Bozzolo Guillermo , Ferrante John 
Published: March 2011

AbstractWe introduce a new semi-empirical method for calculating alloy properties. The method Is based on the concepts of equivalent crystal theory of defect formation energies in elemental solids. With this new method we predict heats of formation, lattice parameters, surface energies, segregation senergies and other properties of several binary alloys of fcc (Cu, NI, Ag, Au, Al, Fe, Pd and Pt) and bcc (Cr, Mo, Fe, V) elements. The method is characterized for its extreme computational simplicity and good agreement with experimental results. Several applications of the method are discussed.
Continuous Displacement of “Lattice” Atoms
Authors: Kikuchi Ryoichi , Beldjenna Arezki 
Published: March 2011

AbstractIn the existing CVM (Cluster Variation Method) formulations, atoms are placed on lattice points. A modification is proposed in which an atom can be displaced from a lattice point. The displaced position is written by a vector r, which varies continuously. This model is treated in the CVM framework by regarding an atom at r as a species r. The probability of finding an atom displaced at r in dr is written as f(r)dr, and the corresponding pair probability is written as g(r1, r2)dr1dr2. We formulate using the pair approximation of the CVM in the present paper. The interatomic potential is assumed given, for example as the Lennard-Jones form. The entropy is written in terms of f(r) and g(r1, r2) using the CVM formula. The special feature of the present formulation which is different from the prevailing no-displacement cases of the CVM is that rotational symmetry of the lattice is to be satisfied by the f(r) and g(r1, r2) functions. After the general equations are written in the continuum vector form and in the integral equation formulation, an example of a single-component system is solved by changing integrals into summations over finite intervals. Further we construct simulations of displacement patters in such a way that the pattern satisfies the pair probability distribution which has been calculated as the output of the CVM analysis. The simulated pattern shows the wavy behavior of phonons. Future directions are discussed.
Molecular Dynamics Simulations of Hot Electrons and Lattice Relaxation in Realistic Cascade Volumes
Authors: Mazzone A.M. 
Published: March 2011

AbstractThis work presents a molecular dynamics simulation method designed to describe the processes of electron and lattice relaxation taking place in typical cascade volumes formed by high-energy implants. The simulation method is based on classical mechanics and includes the motions of electrons and nuclei. The results are in agreement with experiments.
Monte Carlo Modeling of Atomic Oxygen Interaction with Protected Polymers for Projection of Materials Durability in Low Earth Orbit
Authors: Banks Bruce A. , Auer Bruce M. , Rutledge Sharon K. , Gebauer Linda , Sechkar Edward A. 
Published: March 2011

AbstractAtomic oxygen in low Earth orbit (LEO) readily attacks and oxidizes exposed spacecraft polymeric materials such as polyimide Kapton photovoltaic array blankets. The application of thin film silicon dioxide protective coatings can greatly extend the useful life of such materials in LEO. A Monte Carlo computational model has been developed which simulates atomic oxygen interaction with polymeric and protective coating materials for both ground laboratory and in-space experiments, allowing the determination of the geometrical shape of atomic oxygen attack of protected polymeric materials at defect sites in protective coatings. Modeling of attack of unprotected carbon-carbon composite materials predicts textured surfaces suitable for high emittance radiators. Results for fiberglass composites indicate loss of the matrix polymer leading to friable fibers. The computational modeling to project in-space performance based on ground laboratory testing predicts mass loss per fluence in space to be approximately one third that observed in plasma ashers.
Thermodynamic and Elastic Properties of Polyethylene at Elevated Temperatures
Authors: Cagin Tahir , Karasawa Naoki , Dasgupta Siddhart , Goddard William A. 
Published: March 2011

AbstractOver the years molecular modeling techniques, such as Molecular Mechanics, Monte Carlo and Molecular Dynamics have been applied to study the equilibrium thermodynamic and mechanical properties of materials. The accuracy of the predictions made by these techniques strongly depend on the force fields employed to represent the interactions in the studied system. Recently developed force field parameters for crystalline polyethylene are shown to reproduce the mechanical properties of polyethylene accurately through molecular mechanics. Here, we will present the statistical fluctuation formulae for the elevated temperature equilibrium thermodynamic and elastic properties in terms of microscopic variables such as energy, enthalpy, pressure, volume, microscopic strain or stress tensors and present preliminary results of our calculations.
Computersimulations of the Dielectric Breakdown in Ceramics Based on Laplace'S Equation
Authors: Köller Ralf J. 
Published: March 2011

AbstractIn this work, the benefits of a modern personal computer are used to get a deeper insight into the processes occurring in a ceramic material just before and during a dielectric breakdown. Especially, a model to simulate the thermal breakdown behavior in a two-phase material is presented, which is based on a random resistor network. To study the influence of different parameters on the thermal breakdown, simulations were done changing the values of a set of six variables, e.g. external voltage, resistivity, etc. The resulting plots time vs. maximum temperature are shown.
ESR Study of Fluorine Implanted a-Si:H and a-C:H Thin Films
Authors: Wong S. P. , Peng Shaoqi , Ke Ning , Li Pengxu 
Published: March 2011

ABSTRACTThe study of ESR splitting effects induced by fluorine implantation into a-Si:H and a-C:H films has been performed. The implanted fluorine concentration Cp ranges from 1 × 1017 to 6 × 1021 cm−3. It is found that for both a-Si:H and a-C:H after fluorine implantation, in addition to the g1 resonances due to dangling bonds in the respective materials, there is a g2 resonance of g value close to 2.003 in both materials. This g2 resonance is further observed to be closely related to some doping effect of the implanted fluorine atoms in both materials. For a-C:H, it is also found that there is anisotropie hyperflne splitting (HFS) induced by the implanted fluorine atoms. These HFS signals exhibit unexpected peculiar CF dependence and do not show up at some intermediate CF values. A model based on the spin polarization effect has been proposed to attribute the HFS signals to be arisen from interaction between the π electrons of the carbon atoms and the 2p orbitals of the fluorine atoms.
Reduction of Secondary Defects in High Energy O-Implanted Si by High Energy Si Irradiation
Authors: Ellingboe S. L. , Ridgway M. C. 
Published: March 2011

ABSTRACTThe effect of 4.2 MeV, low dose Si irradiation before annealing of 1 MeV, high dose O-implanted Si has been studied. Si irradiation results in differences in the defect structure both before and after high temperature annealing. With no Si irradiation, annealing results in polycrystalline Si (polySi) formation and microtwinning at the front SiO2/Si interface. With Si irradiation, the polySi volume fraction is greatly reduced after annealing, twinned Si having grown in its place. Si irradiation has no effect on Si inclusions within the SiO2 layer. The dependence of secondary defect formation on Si dose and implant temperature is presented. In particular, Si irradiation at low implant temperatures (150°C) and moderate doses (5×1016 cm−2) is shown to be most effective in the reduction of the polySi volume fraction at the front SiO2/Si interface.
Electronic Stopping of Channeled Ions in Silicon
Authors: Hobler Gerhard , Pötzl Hans W. 
Published: March 2011

ABSTRACTConcentration profiles of channeling and random implants of boron, phosphorus, and arsenic in silicon are compiled from the literature and are analyzed using Monte Carlo simulations. An empirical 3-parameter model of the electronic stopping power is found which yields excellent results for all channeling directions in the energy range of about 20 keV to 1 MeV. The model contains a local impact parameter dependent part and a nonlocal part, the latter increasing with ion energy. In addition, local electron density dependent stopping power models are investigated, using a realistic electron density distribution obtained by first principles band structure calculations. These models fail to describe the slowing down of ions channeled along the <110> axis.
Structural Phase Transition in Buried CoSi2 Layers
Authors: Spanninga W. G. , Sandy A. R. , Niesen L. 
Published: March 2011

ABSTRACTHeteroepitaxial Si/CoSi2/Si<111> structures were made by high dose implantation of Co in a Si wafer. These single crystaline layers were investigated with 57Co source Mössbauer spectroscopy, 4He ion channeling and X-ray scattering. All results show there is a structural phase transition in the buried CoSi2 layer at a temperature around 200 K.
Lattice Location of Supersaturated Arsenic Atoms in Silicon Studied by Channeled Ion Beam
Authors: Xu Li , Tsien Peihsin , Li Zhijian 
Published: March 2011

ABSTRACTBy using rapid thermal annealing (RTA) we can obtain a me testable carrier concentration which well exceeds the solid solubility of arsenic dopant in silicon. The deactivation of such the supersaturated dopant, however, may result in relaxation of the metastable concentration. This paper describes lattice location of the deactivated arsenic atoms determined by channeling angular distribution. On the basis of the results for lattice site location the deactivation mechanism of supersaturated As in Si is discussed.
Thin Ni Silicide Formation by Low Temperature-Induced Metal Atom Reaction with Ion Implanted Amorphous Silicon
Authors: Erokhin Yu.N. , Patnaik B. K. , Pramanick S. , Hong F. , White C. W. , Rozgonyi G. A. 
Published: March 2011

ABSTRACTWe have extended our recent work [1,2] on buried suicide formation by Ni diffusion into a buried amorphous silicon layer to the case where silicide formation is at lower temperatures on silicon substrates which have been preamorphized. The reaction of metal atoms from a 12 nm Ni film evaporated on top of a 65 nm thick surface amorphous layer formed by 35 keV Si+ ion implantation has been investigated at temperature ≤400 °C. Rutherford Backscattering Spectrometry (RBS) with channeling, cross-sectional transmission electron microscopy (XTEM), X-ray diffraction and four-point-probe measurements were used to determine the structure, interfacial morphology, composition and resistivity of the silicide films. It has been found that an increased rate of silicidation occurs for amorphous silicon with respect to crystalline areas permitting a selective control of the silicon area to be contacted during silicide growth. Vacuum furnace annealing at 360 °C for 8 hours followed by an additional step at 400 °C for one hour produces a continuos NiSi2 layer with a resistivity 44 μΩ cm.
Defect-Minimized SiGe Layer Using Ion Beam Synthesis
Authors: Im Seongil , Washbum Jack , Gronsky Ronald , Cheung Nathan W. , Yu Kin Man 
Published: March 2011

ABSTRACTIon Beam Synthesis for SiGe layers was performed to study the end-of-range(EOR) defects and strain-induced dislocations. High Ge doses of 5×1016/cm2, 3×1016/cm2 and 2×1016/cm2 at 120 keV were implanted to obtain 12 at%, 7 at% and 5 at% of Ge peak concentrations respectively. RBS spectra show a projected range(Rp) at a depth of 65nm and an amorphous thickness of 170nm on a wafer with 12 at% of Ge peak concentration. Ge ion implantation was performed both at room temperature(RT) and at liquid nitrogen temperature(LNT), in order to investigate the effect of implantation temperature on reducing EOR defect density. Solid phase epitaxial(SPE) annealing for all SiGe layers was done in nitrogen ambient at 800°C. The EOR defect density is considerably reduced by LNT implantation and the strain-induced dislocations have a threshold Ge peak concentration(about 6 at%) for their abrupt generation. For SiGe layer with 12 at% Ge peak concentration, the amorphous-crystalline(a/c) interfacial morphology changes from a planar interface into a faceted interface during SPE growth at 550°C.
Evaluation of Subsurface Ion Implant Damage by Photothermal Displacement Measurement
Authors: Takamatsu Hiroyuki , Sumie Singo , Nishimoto Yoshiro , Tsunaki Hidetoshi , Nishine Koichi , Hara Tohru 
Published: March 2011

ABSTRACTSubsurface damage in silicon formed by ion implantation and the residual damage after annealing have been successfully evaluated by measuring the photo-acoustic displacement (PAD) induced by an intensity modulated pump beam. The PAD was detected by a laser interferometrie probe with a sensitivity of 0.1 picometers in a noncontact manner. A temperature rise within the subsurface damage due to a decrease in the thermal conductivity leads to significant thermal expansion and causes a displacement on the sample surface. Therefore, subsurface damage can be monitored by measuring the PAD. Experimental results for As+ and B+ implanted samples indicate that recrystallization of ion implant damage by annealing can be monitored by this technique. Samples of higher doses (>1014/cm2) have residual damage even after annealing at 800'C for 30 minutes. The results for high-energy (2MeV) implanted samples also show that the secondary defects after annealing, which are formed in a deep region a few microns under the surface, can be detected with high sensitivity.
MeV Ion Implantation of Er into LiNbO3
Authors: Fleuster M. , Buchal Ch. , Holzbrecher H. , Breuer U. , Dinand M. , Suche H. , Brinkmann R. , Sohler W. 
Published: March 2011

ABSTRACTThe incorporation of Er into LiNbO3 is of great interest for fabricating waveguide lasers and amplifiers. We compare Er diffusion data with the results of Er implantation, performed at 3.6 MeV energy. Even after annealing for 4h at 1060°C, the resulting Er profiles display very good matching to the optical modes. The results of a theoretical gain estimate are presented.
Colloid Formation in Implanted Glasses
Authors: Arnold G. W. , Mazzoldi P. , Tramontin L. , Boscolo-Boscoletto A. , Battaglin G. 
Published: March 2011

ABSTRACTMetal colloids in glasses can yield an enhanced (χ((3)) susceptibility which leads to an intensity dependent refractive index. Ion implantation is a convenient means of introducing the metal species. The host glass plays an important role in colloid formation. We have characterized Ag-colloid formation in various silicate glasses and, in addition, have studied the formation of colloids in Ag-doped phosphate glass as a function of N and H implantation. Some preliminary results for Cu-implanted glasses are presented.
Plasma Immersion ion Implantation of Semiconductors
Authors: Cheung N. W. , En W. , Jones E. , Yu C. 
Published: March 2011

ABSTRACTThis paper reviews recent developments of plasma immersion ion implantation (PHI) for semiconductor applications: ultra-shallow junction formation, microscopic conformai doping, metallization, and impurities gettering. We also discuss semiconductor processing issues with PHI: reactor design, wafer charging, surface deposition/etching., and secondary electron emission.
Raman Spectroscopy of C-Irradiated Graphite
Authors: Hembree D. M. , Pedraza D. F. , Romanoski G. R. , Withrow S. P. , Annis B. K. 
Published: March 2011

ABSTRACTHighly oriented pyrolytic graphite samples were irradiated with C+ ions at 35 keV in a direction normal to the basal plane and subsequently annealed up to 1373 K. Substantial surface topography changes were observed at fluences of 5×1018 ions/m2 and higher using scanning electron and atomic force microscopies. Intricate networks of surface cracks and ridges developed after high dose implantation. A systematic study of the irradiation effects was conducted using Raman spectroscopy. Microstructural changes in irradiated regions were first detected at a dose of 1×1017 ions/m2 through the appearance of the Raman D-line at ∼1360 cm−1. The intensity of this line increases while that of the Raman G-line at 1580 cm−1 decreases as the irradiation dose is increased or the irradiation temperature is decreased. After irradiation at 280K to a fluence of 5×1019 ions/m2 or higher the first order spectrum exhibits one single line at a wavelength intermediate between the D- and G-lines. Damage recovery upon thermal annealing depends not only on the initial damage state but also on the annealing temperature sequence. Samples irradiated to a damage level where two distinct Raman peaks are no longer resolvable exhibited upon direct annealing at a high temperature two distinct Raman lines. By contrast, pre-annealing these highly irradiated specimens at lower temperatures produced less pronounced changes in the Raman spectra. Pre-annealing appears to stabilize damage structures that are more resistant to high-temperature annealing than those induced by irradiation.
The Effect of High Energy Electron Beam on the Interaction Between CH4/CF4 and the Diamond (100) Surface
Authors: Lin B. Y. , Beetz C. P. , Brown D. W. , Lincoln B. A. 
Published: March 2011

ABSTRACTThe interaction of the diamond (100) surface with pure CH4 and CF4 gases was investigated as a function of temperature and total gas exposure. We found that sp2 carbon does not form on the diamond (100) surface after exposures of up to lO9L of CH4 or 106 L of CF4 in a UHV system over the range of temperatures from room temperature to 900°C. When a high energy electron beam (5keV) intersected the path of the impinging gas or the diamond surface was exposed to a high energy electron beam before gas exposures, sp2 carbon was not produced at levels detectable by Auger spectroscopy. However, sp2 carbon was formed when the gas exposure was coincident with the electron beam on the diamond surface. The mechanisms responsible for these observations are discussed.