bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of Single Crystal Gallium Nitride Films on Sapphire by Pulsed Laser Deposition
Authors: Sharma A.K. , Oktyabrsky S. , Dovidenko K. , Narayan J. 
Published: April 2011

AbstractPulsed laser deposition has been explored to synthesize gallium nitride films on c-plane sapphire by ablating a pressed GaN target in vacuum. The films were characterized by X-ray diffraction, and high resolution transmission electron microscopy to study the nature of epitaxy, growth, and defect content. Single crystal films with narrow o0-rocking curve width were deposited in the substrate temperature range 700-780°C. High resolution microscopy revealed uniform film surface at lower substrate temperature for films as thin as 150 nm. The predominant extended defects were found to be threading edge dislocations (Burgers vector 1/3<1120>) with the density ~1010 cm-2. The thickness of all these films were in the range 100-150 nm. The coexistence of zincblende phase of GaN alongwith wurtzite phase was found in the film deposited at 780°C. The stabilization of metastable zincblende phase at higher temperature point towards the noneqilibrium nature of laser ablation. These preliminary results indicate the potential of PLD to synthesize high quality GaN films free of hydrogen.
Microstructure and IR Range Optical Properties of Pure DLC and DLC Containing Dopants Prepared by Pulsed Laser Deposition
Authors: Wei Q. , Sharma A.K. , Narayan R.J. , Ravindra N.M. , Oktyabrsky S. , Sankar J. , Muth J.F. , Kolbas R.M. , Narayan J. 
Published: April 2011

AbstractWe have investigated the microstructure and the IR range optical properties(emittance, transmittance and reflectance) of diamond-like carbon (DLC) films with the incorporation of dopants. The DLC films were deposited by pulsed laser deposition with a novel target configuration allowing incorporation of dopants, such as silicon, titanium and copper, into the films. Raman spectroscopy, radial distribution function (RDF) and coordination defect analysis of the electron diffraction pattern of the films showed typical features of DLC with a structure dictated by sp3 bonded carbon, indicating that the overall DLC characteristics did not change upon doping. The IR range optical measurements showed that in addition to the general band-toband transitions, free carriers and phonon contributions, localized states also contribute to the emissivity in DLC and they smooth out the sharp features of the emissivity spectra. The effect of dopants is to enhance the contribution from the free carriers and localized states. The results were discussed on the basis of the effect of dopants on the electronic structure of DLC films.
Vacuum Ultraviolet and Visible Optical Emission Spectra from Laser Ablation of Graphite at 193 NM: Application to Carbon Nitride Thin Films Deposition
Authors: Henck R. , Fuchs C. , Fogarassy E. , Hommet J. , Le Normand F. 
Published: April 2011

AbstractOptical emission spectra in the ultraviolet and visible range (110-600 nm) were recorded during pulsed ArF laser ablation of graphite targets in vacuum and in low pressure N2 atmospheres. During graphite ablation in vacuo, the recorded spectrum consists only of several atomic lines lying below 300 nm. They are due to radiative transitions from upper carbon excited states down to the fundamental one. The most intense atomic lines are observed at 247.85 nm and near 165.5 and 156 nm. During ablation in increasing nitrogen pressure, the spectra are quickly dominated by the bands of the CN violet system whereas the intensity of the atomic lines only slightly increases. We have observed the bands corresponding to the vibrational sequences Δv = +1 (358.4-369.7 nm), Δv = 0 (384.7-394.4 nm) and Δv = -1 (414.3-421.6 nm). They already appear at nitrogen pressure as low as 0.05 mbar. Their intensity reaches a broad maximum between 0.5 and 0.8 mbar and slowly decreases.Taking into account the results of this optical study, the deposition of carbon nitride thin films has been undertaken. The surface analysis by X-ray photoelectron spectroscopy (XPS) of the obtained C1-xNx deposits shows a correlation law between the nitrogen incorporation (x) and the pressure of nitrogen.
Diamondlike Carbon, Carbon Nitride, and Titanium Nitride Coatings on Metal and Polymer Substrates
Authors: Narayan R.J. , Wei Q. , Sharma A.K. , Cuomo J.J. , Narayan J. 
Published: April 2011

AbstractWe have deposited diamondlike carbon, carbon nitride, and titanium nitride biocompatible coatings using pulsed laser deposition and magnetron sputtering on metallic (cobalt-chromium and titanium- 6% aluminum- 4% vanadium) and polymeric (high-density polyethylene) substrates commonly used in human prosthetic devices. A major advantage of the magnetron sputtering deposition technique is that it provides conformal coverage of large-area films. The coatings were characterized by electron diffraction and imaging, Raman spectroscopy, X- ray photoelectron spectroscopy, and electron- energy loss spectroscopy, and nanoindenter hardness measurements. The physical properties (especially hardness) of the diamondlike carbon films were controlled using carbide and noncarbide forming elements. By varying the doping concentration as a function of thickness, functionally gradient materials with superior tribological and mechanical properties can be created. The implications of these results are discussed in the context of biomedical applications.
Excimer Laser Ablation of Silicon at High Temperature
Authors: Zhang Y.F. , Tang Y.H. , Lee C. S. , Wang N. , Bello I. , Lee S.T. 
Published: April 2011

AbstractPulsed laser ablation of granulated Si target was carried out at 1200 °C in an Ar atmosphere. Multishot ablated target surface forms intensity dependent features, including porous, skeleton, and columnar structures. Very long columnar structures were observed when the angle of the target surface with respect to the direction of the laser beam was small. Evidence on preferable remove of smaller particles has been observed. Formation of the columnar structures started from the biggest particles at the surface and grew deeper, straight in the laser beam direction, by consuming the removed Si species from the deep channel between columns. The Si species ablated off the granulated Si target deposited as Si nanowires or nanoparticles down stream of the Ar flow. Significant decrease in the deposition rate of Si nanostructures has been observed upon the formation of the columnar structures at the target surface.
Real-Time Monitoring of Indium Tin Oxide Laser Ablation in Liquid Crystal Display Patterning
Authors: Hong M.H. , Lu Y.F. , Meng M. , Low T.S. 
Published: April 2011

AbstractAudible acoustic wave detection is applied to investigate KrF excimer laser ablation of Indium Tin Oxide (ITO) thin film layer for Liquid Crystal Display (LCD) patterning. It is found that there is no acoustic wave generation if laser fluence is lower than ITO ablation threshold. For laser fluence higher than the threshold, audible acoustic wave will be detected due to shock wave generation during ITO laser ablation. The amplitude of the acoustic wave is closely related to the laser ablation rate. With more laser pulse applied, the amplitude is dropped to zero because the ITO layer is completely removed. However, if laser fluence is increased higher than ablation threshold for glass substrate, the amplitude is also dropped with pulse number but not to zero. It is due to laser ablation of ITO layer and glass substrate at the same time. Since the thickness of ITO layer is in a scale of 100 nm, laser interaction with glass substrate will happen even at the first pulse of high laser fluence irradiation. Laser ablation induced ITO plasma emission spectrum in visible light region is analyzed by an Optical Multi-channel Analyzer (OMA). Specific spectral lines are In I (325.8, 410.2 and 451.1 nm) and In II 591.1 nm. Spectral intensities of 410.2 and 451.1 nm lines are selected to characterize the evolution of ITO plasma intensity with laser fluence and pulse number. It is found that the spectral intensities are reduced to zero with laser pulse number. It is also found that spectral lines other than ITO plasma will appear for laser fluence higher than ablation threshold for glass substrate. Threshold fluences for glass and ITO ablation are estimated for setting up a parameter window to control LCD patterning in real-time.
Atomic Defects in Intermetallic Compounds and Diffusion Processes
Authors: Schaefer H.-E. , Frenner K. , Würschum R. 
Published: April 2011

ABSTRACTFor the understanding of the properties of the technically important intermetallic compounds as transition metal aluminides and silicides the understanding of atomic defect properties is pivotal. From recent positron lifetime studies high or low values for the effective vacancy formation enthalpy were found for close-packed or for more open-structured bcc type compounds, respectively, which can be well understood theoretically. In B2-FeAl the vacancy migration enthalpy could be additionally derived at high temperatures from vacancy equilibration processes. It is shown here by a study on B2-FeAl in comparison to the positron annihilation experiments that the thermal formation and migration of defects can be specifically investigated by time-dependent length-change experiments at high temperatures by the defect equilibration behavior after temperature changes. With the present data on vacancy formation and migration the wide variation of the transition-metal self-diffusivities in intermetallic compounds can be understood.
Theory and Simulation of Diffusion Kinetics in Intermetallic Compounds
Authors: Murch G.E. , Belova I.V. 
Published: April 2011

ABSTRACTIn this paper we provide an overview of the progress that has been made in the understanding of diffusion kinetics in intermetallic compounds. Both analytical theories and computer simulation are dealt with and the following ordered structures are covered: B2 (and B1), L12, A15 and DO3.
Point Defects and Diffusion in Ni3Ga
Authors: IKEDA T. , Almazouzi A. , Funao A. , Numakura H. , Koiwa M. , Shirai Y. , Nonaka K. , Sprengel W. , Nakajima H. 
Published: April 2011

ABSTRACTThe properties of intrinsic point defects and the self-diffusion behaviour of the constituent elements in Ni3Ga have been studied by positron annihilation, tracer diffusion and interdiffusion experiments. Thermal vacancies have been detected by positron lifetime measurements for specimens quenched from high temperatures. The vacancy formation energy is in the range between 1.7 and 1.8 eV, and is not dependent strongly on the composition. The tracer diffusion coefficients of Ni and Ga are of the same order of magnitude, and the interdiffusion coefficient is about 10 times larger than the diffusion coefficient of Ni. The diffusion in Ni3Ga has been found to satisfy the Darken-Manning equation, as expected from the model of the self-diffusion in this type of materials, where both the species of atoms are assumed to migrate primarily in the sub-lattice of the major element via the ordinary vacancy mechanism.
Mechanism of “Order-Order” Kinetics in Ll2 Superstructure Studied by Computer Simulation
Authors: Oramus P. , Kozubski R. , Cadeville M.C. , Pierron-Bohnes V. , Pfeiler W. 
Published: April 2011

ABSTRACTMonte Carlo simulations of the isothermal long-range order (LRO) relaxation in A3B system with Ll2 superstructure have been performed within a model based on a vacancy jump mechanism between nearest neighbour lattice sites. The studies aimed at the explanation of the origin of two simultaneous LRO relaxation processes experimentally observed in Ni3Al. An effect of pair interaction energies and saddle-point energies (assigned to jumping atoms) was studied. The preference of vacancies for the A-sublattice (face centres), commonly postulated for Ni3Al, occurred only for a narrow range of pair-interaction energies within the domain corresponding to Ll2 ordering. It was found that the appearance of the fast relaxation process is definitely correlated with the efficiency of B-atom jumps, as well as with the values of the saddle-point energies. The results lead to a microscopic model of the “order-order” relaxation in Ll2 superstructure and yield new indications for the choice of pair-interaction energy parameters applied in Monte Carlo simulations of atomic migration in Ll2 intermetallic compounds.
Grain Boundary Diffusion and Segregation in the Solid State Phase Transformations
Authors: Rabkin E. , Gust W. 
Published: April 2011

ABSTRACTWe consider the problem of solute diffusion and segregation in the grain boundaries moving during a phase transformation in the framework of Cahn's impurity drag model. The concept of a dynamic segregation factor for the diffusion along moving grain boundaries is introduced. The difference between static and dynamic segregation factors may cause the apparent difference of the triple product of the segregation factor, grain boundary width and grain boundary diffusion coefficient for stationary and moving grain boundaries. The difference between static and dynamic segregation is experimentally verified for the Cu(In)-Bi system, for which the parameters of static segregation are well-known. It is shown that the complications associated with the dynamic segregation may be avoided during the study of the discontinuous ordering reaction. From the kinetics of this reaction, the activation energy of the grain boundary self-diffusion can be determined.
Respective Roles of Surface, Grain Boundary and Volume Diffusions in Driving Structural, Microstructural and Magnetic Properties of MBE Alloy Thin Films
Authors: Pierron-Bohnes V. , Maret M. , Bouzidi L. , Cadeville M.C. 
Published: April 2011

ABSTRACTThe co-deposition of two metals using a molecular beam epitaxy (MBE) technique at various growth temperatures (TG) yields single-crystal alloy thin films with a columnar microstructure whose structural and magnetic properties can be different from those of the corresponding equilibrium bulk alloys. A general overview of results obtained in hcp Co-Ru and hcp or fcc Co-Pt thin films grown on a hcp (0002) substrate will be presented. Around the A 3B composition (A = Co, B = Ru or Pt) the films display a composition modulation along the growth direction whose amplitude is strongly dependent of TG passing through a maximum at respectively 600 and 650 K. This long range order (LRO) that does not exist in equilibrium phases is explained as resulting from the competition between two phenomena occurring simultaneously during the growth process: a surface effect driven by surface interactions and surface diffusion that tends to enrich the surface layer in one element (Co, Ru or Pt segregation) and a bulk effect driven by bulk interactions and bulk diffusion that tends to restore the bulk equilibrium phase when the bulk diffusion becomes efficient during the growth time. A thermally activated model that takes into account both surface and bulk diffusion during the growth time reproduces quite satisfactorily the TG dependencies of the LRO in Co3Ru and Co3Pt as well as that of the uniaxial magnetic anisotropy in CoPt3.At high TG ( > 800 K) or after ex situ anneals, the diffusion of the Ru buffer through the grain boundaries of the columnar microstructure, that occurs before the inside grain diffusion, isolates the columns magnetically and is thought to be responsible of the large observed coercive field and of a substantial modification of the magnetic domain shapes.
Effect of Surface Segregation on the Temperature Dependence of Ion-Bombardment Induced Surface Morphology
Authors: Aufray B. , Giordano H. , Petrova V. , Seidman D. N. 
Published: April 2011

ABSTRACTWe present a scanning tunneling microscopy (STM) study, performed at different elevated temperatures, on the influence of Sb surface segregation on the morphology of the (111) surface of a Cu-0.45 at.% Sb solid-solution single-crystal; the surface was initially cleaned at room temperature by Ar+ ion sputtering. Unexpectedly, when the temperature is increased from room temperature to 380°C, the typical (111) surface morphology, obtained after sputtering, evolves in two very different manners that depend on the heating rate. If the heating rate is rapid (approximately a few minutes), it evolves to a structure with large terraces, whereas if it is slow (about 10 hours) the morphology does not evolve -- i.e., it is frozen. These unexpected results are interpreted in terms of excess subsurface point defects (vacancies and self-interstitials) created during ion bombardment, which are mobile and can mediate Sb diffusion at low temperatures. This is mainly on step edges, but the point defects can precipitate out of solution, for a rapid heating rate, thereby forming small secondary clusters in the near-surface region, in which Sb atoms are trapped.
Kinetic Monte Carlo Simulation of Diamond Film Growth with the Inclusion of Surface Migration
Authors: Netto Armando , Frenklach Michael 
Published: April 2011

ABSTRACTDiamond films are of interest in many practical applications but the technology of producing high-quality, low-cost diamond is still lacking. To reach this goal, it is necessary to understand the mechanism underlying diamond deposition. Most reaction models advanced thus far do not consider surface diffusion, but recent theoretical results, founded on quantum-mechanical calculations and localized kinetic analysis, highlight the critical role that surface migration may play in growth of diamond films. In this paper we report a three-dimensional time-dependent Monte Carlo simulations of diamond growth which consider adsorption, desorption, lattice incorporation, and surface migration. The reaction mechanism includes seven gas-surface, four surface migration, and two surface-only reaction steps. The reaction probabilities are founded on the results of quantum-chemical and transition-state-theory calculations. The kinetic Monte Carlo simulations show that, starting with an ideal {100}-(2×1) reconstructed diamond surface, the model is able to produce a continuous film growth. The smoothness of the growing film and the developing morphology are shown to be influenced by rate parameter values and by deposition conditions such as temperature and gaseous species concentrations.
Evidence for Non-Equilibrium Vacancy Concentrations Controlling Interdiffusion in III-V Materials
Authors: Gillin W.P. , Khreis O.M. , Homewood K.P. 
Published: April 2011

ABSTRACTInterdiffusion and self-diffusion in III-V semiconductors has usually been assumed to operate through the diffusion of point defects, the concentrations of which are at thermal equilibrium values. We have studied the interdiffusion of multiple quantum well samples, grown under a range of growth conditions, each containing a thin source of vacancies. This has enabled simultaneous measurements of the interdiffusion coefficient, diffusion coefficient for vacancies and the concentration of those vacancies in a single experiment. We have shown that independent of growth conditions, within a wide window of III-V flux ratio and temperature, the diffusion at all temperatures is governed by a constant background concentration of vacancies.
Molecular Simulations of Pore Diffusion in Zeolites
Authors: Pohl P.I. , Fisler D.K. , Nenoff T.M. 
Published: April 2011

ABSTRACTA combination of molecular dynamics and energy barrier mapping has been used to study diffusion of xylene gas molecules in silica zeolites. Rigid ion models were created for silicalite phases and the energy barriers to xylene permeation by pore diffusion were mapped using constrained steps and energy minimization. Zeolite ZSM-5 proved to exhibit the desirable properties of a high degree of selectivity while retaining a high permeability to p-xylene. The model zeolite was then minimized with various cation dopants using a shell model to mimic ionic polarization, and changes in cell size and energy surface were examined. Long term molecular dynamics simulations showed an increased diffusion rate for the structures doped with cations of larger ionic size.
DC Conductivity of Potassium Titanyl Phosphate Crystal along ITS Z-AXIS
Authors: Guan Qingcai , Wang Jiyang , Cui Weihong , Wei Jingqian , Liu Yaogang , Yin Xin 
Published: April 2011

ABSTRACTThe J-U relation of the KTP crystal along its z-axis under low DC field deviates from linearity, which is different from that of the crystal along the other two principle axis. The resistance of the crystal along its z-axis increases with the time under high DC stress and the crystal becomes dark. The dark color can be removed by annealing. Electrode reactions were also observed. The phenomena are related to the easy movement of ions along the z-axis of the KTP crystal.
Simulation of Intrinsic Diffusion in Multicomponent Multiphase Systems
Authors: Hunkel M. , Bergner D. 
Published: April 2011

ABSTRACTA simulation model for intrinsic diffusion of multicomponent multiphase systems is presented. The model is not restricted onto a certain number of components or phases. For simplicity, Manning's random alloy model with vanishing vacancy wind effect is used. Then the cross terms of the diffusion flux can be neglected. The simulation routine uses equations for the fluxes, the equation of continuity and an equation for the change of the thickness of volume elements due to the vacancy flux. With this model diffusions paths, concentration profiles, fluxes of the components as well as marker positions can be calculated. The shift of interfaces and the growth of new phases can also be determined. The simulation results were compared with experimental data of the Cu-Fe-Ni system. Diffusion was studied in single-phase areas and across interfaces.
A Model for Oxygen Transport in Microencapsulated Islets
Authors: Iwata H. , Park Y. G. , Ikada Y. 
Published: April 2011

AbstractOxygen supply is expected to be one of major limiting factors that determine survival of islets in microcapsules after transplantation. Fick's law is applied to derive equations describing the oxygen pressure (PO2) profiles. The PO2 profiles calculated demonstrate that the thickness of the microcapsule membrane does not significantly affect oxygen supply to the islet. On the other hand, it drastically decreases as the fibrous tissue surrounding the microcapsule becomes thicker. The islet will be destroyed non-immunologically by limiting oxygen supply, when the microencapsulated islets are surrounded by the thick fibrous tissue.
Construction of Biomimetic Environments with A Synthetic Peptide Analogue of Collagen.
Authors: Bhatnagar Rajendra S. , Qian Jing Jing , Wedrychowska Anna , Smith Nancy 
Published: April 2011

AbstractThe flow of chemical and mechanical signals among cells, and between cells and their environment plays a crucial role in cell differentiation and morphogenesis. In tissues, type I collagen serves as the template for cell anchorage and migration, and it mediates the flux of regulatory signals via highly specific receptors. Cells respond to mechanical cues by secreting growth factors and remodeling their surrounding matrix in an exquisitely orchestrated spatial and temporal program of matrix turnover and organization. Cellular tractional forces contribute to the organization and orientation of the newly synthesized matrix, establishing the template for subsequent morphogenesis. The junction between cells and collagen plays a key role in cell differentiation, morphogenesis and tissue remodeling. An optimal biomimetic environment would emulate this pathway for the exchange of stimuli. To achieve this goal, we have constructed templates which place cells in apposition to P-15, a synthetic peptide ligand for collagen receptors. These environments prompted 3-D colony formation, induced increased osteogenic differentiation, and the deposition of highly oriented and organized matrix by human dermal and gingival fibroblasts and by osteoblast like HOS cells. These observations support our concept for biomimetic environments for tissue engineering.