bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strain Relaxation in Heteroepitaxial Si1-xGex Films via Surface Roughening Processes
Authors: Ozkan Cengiz S. , Nix William D. , Gao Huajian 
Published: April 2011

ABSTRACTSurface roughening associated with strain relaxation of Si1-xGex films grown epitaxially on (100) Si substrates has been investigated using transmission electron microscopy, atomic force microscopy and x-ray diffraction. Epitaxial films 100 Å in thickness and containing 18% Ge, which are subcritical with respect to the formation of misfit dislocations, show strain relaxation through surface roughening on annealing at 700 °C. Enhanced surface grooves aligned along <100> directions are observed in films annealed at 850 °C. Strain relaxation as measured by x-ray diffraction is significantly greater at the higher temperature. Prolonged anneals at 850 °C also result in islanding. The surface roughening processes have also been studied in subcritical films with 15% Ge at 900 °C. These films also show enhanced grooving aligned along <100> directions. These observations are consistent with an anisotropic elastic analysis which indicates that grooving should occur preferentially along <100> directions. Intermixing effects in these samples have also been investigated through depth profiling using Auger Electron Spectroscopy. In addition to the above subcritical films, other films with 18% and 22% Ge and supercritical thicknesses have also been studied. For these films, surface grooving is observed along <110> directions, which suggests that these grooves are related to the formation of misfit dislocation networks. The role of these surface roughening processes in the nucleation of dislocations has also been explored.
Characterization of Surface Morphology in Epitaxial Growth
Authors: Amar Jacques G. , Family Fereydoon 
Published: April 2011

ABSTRACTSimulated kinematic antiphase RHEED and HRLEED profiles are calculated for a model of Fe/Fe(100) deposition in order to clarify the interpretation of diffraction profiles in recent experiments on Fe/Fe(100) growth. Similar calculations are also presented for a self-affine surface. While self-affine surfaces do not exhibit a characteristic RHEED peak, in the case of surfaces with a typical length scale, the simulated RHEED profile exhibits a peak corresponding to the typical feature size, in agreement with recent experiments. The existence of this peak appears to be due to the large amount of shadowing present in low-angle RHEED which limits the amount of destructive interference between layers. In contrast, simulated HRLEED profiles exhibit an invariant profile for both self-affine and mound-like surface morphologies. The disappearance of the peak in HRLEED for surfaces which have large mound structures is explained in terms of the antiphase condition and the range of variation of terrace sizes and provides an alternative explanation for the HRLEED results observed in the experiment of Ref. 9.
Comparative Study of Thermodynamic Properties of Metallic and Semiconducting Nanoparticles in Dielectric Matrix
Authors: Stella A. , Cheyssac P. , Kofman R. , Merli P.G. , Migliori A. 
Published: April 2011

AbstractThe mechanism of growth as well as optical and microstructural data dealing with the process of melting of metallic (Pb, Sn) and semiconducting (Ge) particles in dielectric matrix are reported and discussed. Details are given on the growth of such systems based on a self organization method that allows a rather regular shape of the particles (truncated spheres) relative low size dispersion (≤ 20%), wide range of particle size variation and negligible effects due to stress or contamination. The features of these growth techniques allow a careful study of the melting behavior vs. size that has been investigated using optical reflectivity methods and transmission electron microscopy techniques. These experimental results have made possible a careful investigation on the thermodynamics of these systems and the deduction of interesting data concerning: a) conditions for the existence of surface melting and decrease of melting temperature; b) interfacial effects related to shape and curvature of the particles; c) onset of rotations and phase fluctuations in connection with surface melting.
Solidification of Intermetallic Compounds
Authors: Assadi H. , Greer A. L. 
Published: April 2011

AbstractKinetic modelling, incorporating variation in the degree of chemical order, is developed for the solidification of intermetallic compounds, and qualitative comparisons are made with experiment. It is found that a disordered phase can be obtained other than by the process of disorder trapping, and that partitioning can increase or invert with increasing solidification velocity. Solid-state ordering and its effects on final microstructure are also considered.
Electrical Properties of Pb5Ge3O11-Based Ferroelectric Glass-ceramics
Authors: Cornejo IvÁn A. , Haun Michael J. 
Published: April 2011

AbstractSelected glass compositions in the Pb5Ge3O11-PbTiO3 (PG-PT) and Pb5Ge3O11-Pb(Zr1/2Ti1/2)O3(PG-PZT) systems were prepared by quenching from the molten state. After different heat treatments, a multiple ferroelectric composite crystallized at low temperatures, PG-PT or PG-PZT. In this paper the results obtained on the dielectric constant, dissipation factor, ferroelectric hysteresis loop, and pyroelectric coefficient of different bulk and thick-film samples of compositions in the PG-PT and PG-PZT ferroelectric glass-ceramic system are presented and discussed.
Synthesis of Nanocrystalline BaTiO3 by Electron Beam Evaporation
Authors: Li Shaoping , Eastman J. A. , Thompson L. J. , Baldo P.M. 
Published: April 2011

AbstractNanocrystalline BaTiO3 has been synthesized for the first time by a gas-condensation process using an electron beam evaporation system. BaTiO3 and Ti sources are vaporized simultaneously in either a mixed helium-oxygen or pure helium environment. Nano-BaTiO3 particles have an average particle size of approximately 18 nm. The processing parameters of the evaporation process are reported.
Properties and Perspectives of Semiconducting Transition Metal silicides
Authors: Lange H. 
Published: April 2011

AbstractThe structural, electronic, optical, and electrical properties of semiconducting silicides with transition metals from the VIth to the Vlllth Group of the Periodic Table are reviewed. Main emphasis is put on ß-FeSi2. The review includes recent results on optical measurements from the infrared up to 24 eV. Typical similarities in the phonon and interband spectra are outlined. Gap energy determinations are critically discussed. Doping impurities are characterized by EPR. Electrical investigations revealed characteristic features of transport parameters depending on temperature and magnetic field. Possible fields of application are analyzed.
MBE Growth Considerations for the Fabrication of 640×480 IR Focal Plane Arrays of SiGe Hip Detectors
Authors: Hompson P. E. , Weeks M. , Tedrow P. , Hobart K. 
Published: April 2011

AbstractEncouraging results have been reported for discrete heterojunction internal photoemission (HIP) infrared (IR) detectors composed of heavily boron doped Si1−3Gex layers on Si. We desired to build on those results and fabricate 640×480 IR focal plane arrays on 100 mm Si substrates, suitable for commercial microelectronic processing. In this paper we discuss the growth issues for growing these structures by molecular beam epitaxy. Since the wafers had already undergone processing and some had PtSi contacts, the growth temperature was constrained to be no greater than 600 °C. Precise temperature control was obtained by calibrating an optical pyrometer with a thermocouple embedded in the substrate heater assembly, which was calibrated using the eutectic emperatures of Au/Si and Al/Si. The final step of the cleaning process was a 1% HF dip/ spin dry, which resulted in a H-terminated surface. The H was removed at 550 °C in vacuum prior to rowth. The growth of the B-doped SiGe layer was done at 350 °C to minimize segregation and diffusion of the Ge and B. Doping levels of 2×1020/cm3 were obtained with near 100% activation. Using Si0.35, doped with 2×1020 B/cm3, a cut-off wavelength of 11.1 μm and an emission coefficient of 19.8 %/eV were obtained for discrete detectors. Preliminary results from the detector arrays show full functionality in the spectral range of 6.1 to 12.8 μm.
Electrical Resistivity of Three Polymorphs of Basi2 and P-T Phase Diagram
Authors: Imai M. , Hirano T. 
Published: April 2011

AbstractThis paper reports a pressure-temperature phase diagram for BaSi2 and evaluates the electrical resistivity of orthorhombic, cubic and trigonal BaSi2. In-situ X-ray diffraction measurements revealed the transition sequence of cubic and trigonal BaSi2 from orthorhombic BaSi2 at high pressures and high temperatures. The electrical resistivity measurements of three polymorphs show that the electrical properties depend on the crystal structure: orthorhombic BaSi2is an n-type semiconductor as previously reported; cubic BaSi2is an n-type semiconductor; trigonal BaSi2is a hole metal that shows superconductivity with an onset temperature of 6.8K.
Ti-Salicide Improvement by Preamorphization for ULSI Applications
Authors: Chenl Chun-Cho , Wang Q. F. , Jonckx Franky , Jenq Jyh-Shyang , Maex Karen 
Published: April 2011

AbstractTo improve Ti SALICIDE process, Si preamorphization by arsenic before Ti sputtering has been studied in two parts: process characterization and fundamental studies. Sheet resistance (Rs) reduction by the preamorphization is more pronounced on thinner and narrower-line silicide formation. At 60keV implantation energy, there is an optimum arsenic dose for the improvement. Through the treatment, more uniform silicide layer can be formed, indicated by the improved Rs uniformity. In the fundamental study, preamorphization appears to have little effect on promoting C49-to-C54 phase transformation. It is suggested that the treatment is able to enhance the reaction rate between Ti and amorphous Si, and results in C54-TiSi2 with larger grains and consequently slightly lower resistivity.
Reduction of the C54-TiSi2Phase Formation Temperature Using Metallic Impurities
Authors: Mann R. W. , Clevenger L. A. , Miles G. L. , Harper J. M. E. , Cabral C. , D'Heurle F. M. , Knotts T. A. , Rakowski D. W. 
Published: April 2011

AbstractThe effects of small concentrations of metallic impurities have been studied in conjunction with the formation of titanium disilicide. We report that, by introducing small quantities of a refractory metal such as molybdenum or tungsten at or near the titanium/silicon interface, the temperature required to form the C54 phase TiSi2can be reduced by as much as 100°C. Furthermore, the resulting C54-TiSi2film exhibits small (∼ 0.2μm) grain size and improved thermal stability. This discovery has the potential to reduce the complexity and cost associated with forming low resistivity TiSi2on submicron structures and to significantly improve the titanium silicide process window for future sub-half-micron VLSI applications.
Depth Dependence of Residual Strains in Textured Mo Thin Films Using High-Resolution X-Ray Diffraction
Authors: Malhotra S. G. , Rek Z. U. , Yalisove S. M. , Bilello J. C. 
Published: April 2011

AbstractThe magnitude of the average stress in a thin film can be obtained by measuring the curvature of the film-substrate couple. However, the details of the strain distribution, as a function of depth through the thickness of the film, can have important consequences in governing film quality and ultimate morphology. A high-resolution x-ray diffraction method was used to determine the depth dependence of strain in a textured Mo film, with a nominal thickness of 260 nm, which was deposited by planar magnetron sputtering onto Si (100) substrates. The principal strains, resolved onto a laboratory reference frame, displayed a negligible gradient in the azimuthal directions (x and y), but displayed a large gradient in the direction normal to the film (z). A similar trend was previously observed for a 100 nm polycrystalline film, but the magnitude of the normal strain very near the free surface was about a factor of 2 less. The increase in the normal strain may be due to the development of a preferred growth direction and grain facetting. A linear elastic model was also used to determine the strains in successive slabs of the film, where strain variations between slabs were indicated.
Tensile Tests of Low Density Multilayer Thin Films
Authors: Heerden D. van , Josell D. , Shechtman D. 
Published: April 2011

AbstractAlthough mechanical studies of multilayer thin films are increasingly more abundant, the majority of studies merely determine film hardness using micro- or nanoindentation techniques. Actual tensile tests are still quite rare. We have therefore conducted tensile tests of free standing aluminum-titanium multilayer thin films. This system was selected for its potential use as a low density (3.3 g/cm3) structural material with potential aerospace applications. The strongest multilayers produced, with bilayer thicknesses 7nm Ti/16 nm Al, fractured at tensile stresses (UTS) of 900 MPa - well beyond the UTS of either of the constituent materials. Specimen characterization by xray diffraction as well as transmission electron microscopy (TEM) revealed near perfect texturing and an intriguing hcp to fec transformation of the titanium layers during preparation of samples for TEM viewing.
Measurement of the Interfacial Shear Strength of thin Copper Films on Sapphire by Microindentation Experiments
Authors: Dehm G. , Raj R. , Rühle M. 
Published: April 2011

AbstractMicroindentation experiments were carried out on 500 nm thick films of copper grown on sapphire substrates, containing titanium interlayers of different thicknesses. The films were near single crystal and were grown by molecular beam epitaxy. The width of the titanium interlayers was varied from 0.7nm to I 10nm. The load-displacement data obtained from the indentation experiments was analyzed in terms of a new model. Just 0.7nm of titanium produced a 40% increase in the interfacial shear strength. Further increase in the thickness of the titanium interlayers produced only a slightly larger increase in the interfacial strength, suggesting that the measurement reflected the influence of the atomic bonding at the interface. The technique and the model present a simple way to estimate the relative change in the interfacial strength of metal-ceramic interfaces.
X-Ray Residual Stress Measurement in Films with Crystallographic Texture and Grain Shape
Authors: Yu L. G. , Hendrix B. C. , Xu K. W. , He J. W. , Gu H. C. 
Published: April 2011

AbstractX-ray diffraction provides an easy and powerful method for measuring residual stress in thin films. However, nonlinearity of the d vs. sin2ψ relation can lead to the misinterpretation of results, especially when one of the measurements is made at low values of ψ relation for different combinations of ideal crystallographic textures and grain shapes are given. In all cases, a high ψ angle range exists where the d vs. sin2ψ relation in the low ψ angle range.
Annealing Effects of Indium-Tin Oxide Films Produced by Atmospheric RF Plasma Deposition Technique
Authors: Moss R. W. , Lee D. H. , Vuong K. D. , Ryan J. , Fagan J. , Condrate R. A. , Wang X. W. 
Published: April 2011

AbstractThin-films of indium-tin oxide (ITO) on soda-lime-silicate (SLS) glass were fabricated using an atmospheric RF plasma mist deposition process. Some of the films were deposited at substrate temperatures between 400 C and 500 C, and were subsequently annealed at 400 C and 530 C for 1 hour. Conductivity was improved due to post-annealing. Film thickness, particle size, film morphology and crystallite size were characterized. The structural changes on the glass and the ITO film were investigated by DRIFT spectroscopy.
Thermodynamics and Microstructure Development in the Thin Film Reaction of Aluminum on Silicon Carbide
Authors: Hayes T. S. , Ray F. T. , Trumble K. P. , Kvam E. P. 
Published: April 2011

AbstractA refined thernodynamic analysis of the reaction between molen Al and SiC is presented. The calculations indicate much higher Si concentrations for saturation with respect to AkC 3 formation than previously reported. Preliminary microstructural studies confirm the formation of interfacial A14C3 for pure Al thin films on SiC reacted at 9000C. The implications of the calculations and experimental observations for the production of ohmic contacts to p-type SiC are discussed.
Massively Parallel Molecular Dynamics and Simulations for Many-Body Potentials
Authors: Wille L. T. , Cornwell C. F. , Morrey W. C. 
Published: April 2011

AbstractWe discuss the implementation of classical molecular dynamics simulations on Single- Instruction Multiple-Data computers with two-dimensional mesh connectivity. Specific timing results are given for the MasPar MP-1, complemented by a general time complexity analysis. Our main interest is in simulations with a number of particles N that is comparable to the number of processors P. In particular, we discuss results for large Si-clusters with up to 2000 particles, using a Stillinger-Weber potential. Particular attention is paid to the problem of handling in an efficient way the calculation of the three-body potential and force.
Early Stages of Sintering of Si3N4 Nanoclusters Via Parallel Molecular Dynamics
Authors: Tsuruta Kenji , Omeltchenko Andrey , Kalia Rajiv K. , Vashishta Priya 
Published: April 2011

AbstractWe investigate early stages of sintering of silicon nitride (Si3N4) nanoclusters by molecular-dynamics (MD) simulations on parallel computers. Within 100 pico seconds, an asymmetric neck is formed between nanocrystals at 2,000K. In the neck region, there are more four-fold than three-fold coordinated Si atoms. In contrast, amorphous nanoclusters develop a symmetric neck, which has nearly the same number of three-fold and four-fold coordinated Si atoms. In the case of sintering among three nanoclusters, a chain-like structure forms in 200 pico seconds. The present study shows that sintering is driven by rapid diffusion of surface atoms and cluster rearrangement.
Lattice Instabilities, Anharmonicity and Phase Transitions in PbTiO3 and PbZrO3
Authors: Rabe K. M. , Waghmare U. V. 
Published: April 2011

AbstractMost perovskite structure oxides exhibit structural phase transitions from a hightemperature cubic phase to a distorted low-temperature phase which can be described by the freezing-in of one or more phonon modes of the cubic structure [1]. The first-order cubic-tetragonal ferroelectric transition in PbTiO3 at Tc = 763 K involves the freezing-in of a single F15 polar mode. In PbZrO3 , the structure of the antiferroelectric low-temperature orthorhombic phase is far more complicated, with forty atoms per unit cell and the freezing-in of R25 and Σ3 modes, perhaps accompanied by other modes as well [2][3].
Molecular Dynamics Study of Structural Transitions and Melting in Two Dimensions
Authors: Boyer L. L. 
Published: April 2011

AbstractSimple pair potentials are constructed which give hexagonal- or squarelattice ground states in two dimensions, depending on the value of a single parameter controlling the width of the potential well. Molecular dynamics calculations for free clusters of a few hundred particles are used to examine a structural transition from the square lattice, at low temperatures, to the hexagonal lattice at high temperatures. Another structural transition (melting) is identified by the onset of diffusion. The melting temperature is found to be a minimum near the point where the barrier between the two structures, as a function of lattice strain, is also a minimum.
Molecular-Dynamics Simulations of Hydrogenated Amorphous Silicon Thin-Film Growth
Authors: Ohira T. , Ukai O. , Noda M. , Takeuchi Y. , Murata M. , Yoshida H. 
Published: April 2011

AbstractWe have performed molecular-dynamics (MD) simulations of hydrogenated amorphous silicon (a-Si:H) thin-film growth using realistic many-body semiclassical potentials developed to describe Si-H interactions. In our MD model, it was assumed that SiH3, SiH2 and the H radicals are main precursors for the thin-film growth. In MD simulations of a-Si:H thin-film growth by many significant precursor SiH3 radicals, we have evaluated average radical migration distances, defect ratios, hydrogen contents, and film growth rates as a function of different incident radical energies to know the effect of the radical energization on the properties. As a result of the comparison between the numerical and experimental results, it was observed that the agreement is fairly good, and that an increase of radical migration distance due to the radical energization is effective on a- Si:H thin-film growth with a low defect.
Full-Potential LMTO Calculation of Ni/Ni3Al Interface Energies
Authors: Price D. L. , Cooper B. R. 
Published: April 2011

AbstractSolid solution precipitates, including Ni3Al in Ni, play an important role in modifying and improving properties of structural and high temperature alloys. The nature of the interface between the host alloy and the precipitate has a large influence on the nature of the precipitate properties, and upon the energetics of their formation. We present here a brief summary of initial ab-initio electronic structure calculations of the Ni/Ni3Al interface, and present results for the interfacial energy. Our results indicate that that the spin-moment transition from high moment Ni to low moment Ni3Al accounts for much of the (zero temperature) interface energy. Corresponding paramagnetic calculations give a significantly lower interfacial energy, and one that is more consistent with high temperature (above the Curie temperature) experimental results.
Simulations of the Structure and Properties of the Polyethylene Crystal Surface
Authors: Wilhelmi J. L. , Rutledge G. C. 
Published: April 2011

AbstractThe structures and thermodynamic properties of the (100), (010), and (110) lateral surfaces of extended-chain polyethylene crystals between 0 K and 300 K were determined by free energy minimization using consistent quasi-harmonic lattice dynamics. Slight rotations of the outermost chains from their corresponding orientations in the bulk were observed. These deviations from bulk structure were confined to the first three molecular layers (approximately 10 Å) at the surface. Surface free energy calculations found the (110) surface to be the most stable over the entire temperature range modeled, with free energies ranging from 95.4 erg/cm2 to 103.5 erg/cm2, at temperatures of 0 K and 300 K, respectively. Surface free energies of the (100) and (010) surfaces were found to be at least 15% higher than the (110) surface, with the (100) surface slightly more stable than the (010) surface, over all temperatures considered. Surface free energy increases as the density of chains at the surface decreases. The surface free energy at low temperatures was determined predominantly by intermolecular potential energy; at higher temperatures, excess entropy accounted for nearly half the surface free energy. Surface entropy was almost entirely due to lattice mode motions.
Ab Initio Core-Level Shifts in Metallic Alloys
Authors: Fiorentini Vincenzo , Methfessel Michael , Oppo Sabrina 
Published: April 2011

AbstractCore-level shifts and core-hole screening effects in alloy formation are studied ab initio by constrainedl-density-functional total-energy calculations. For our case study, the ordered intermetallic alloy MgAu, final-state effects are essential to account for the experimental Mg 1s shift, while they are negligible for Au 4f. We explain the differences in the screening by analyzing the calculated charge density response to the core hole perturbation.