bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural Relaxation and De-Relaxation Phenomena in Amorphous Ge Films upon Irradiation with Short and Ultrashort Laser Pulses
Authors: Solis J. , Siegel J. , Afonso C.N. 
Published: April 2011

ABSTRACTThe state of relaxation of amorphous Ge films has been modified upon melting and rapid solification induced by irradiation with ps laser pulses. The material obtained upon irradiation with fluences sligthly above the melting threshold is less relaxed than the as-deposited one (de-relaxation process). For larger fluences the results obtained suggest that the degree of relaxation is related to the supercooling achieved prior solidification.
Laser Assisted Deposition of Amorphous Hydrogen Containing Carbon at Room Temperature
Authors: Stenberg G. , Piglmayer K. , Boman M. , Carlsson J.-O. 
Published: April 2011

ABSTRACTHydrogen-containing amorphous carbon films were produced from CH,I, by photolytical laser assisted chemical vapour deposition at room temperture. An Ar+ laser operated in the ultraviolet spectral region (351 and 364 nm) was used as the excitation source. The beam was focused in parallel to the Si(lOO) substrate. The deposition process was studied for different partial pressures of CH,I2 and for different heights of the laser beam above the substate surface. The mass thickness of the film was determined by energy dispersive X-ray spectrometry. The hydrogen content of the carbon films was determined by nuclear reaction analysis and the iodine content in the films was obtained by Auger electron spectroscopy and energy dispersive X-ray spectrometry. Carbon hybridization was investigated by Raman and infrared spectroscopy while morphology was examined by atomic force microscopy.
Open Air Fabrication Process of Cu Thin Films on Teflon Surface Using Arf Excimer Laser Irradiation
Authors: Okoshi M. , Toyoda K. , Murahara M. 
Published: April 2011

ABSTRACTCopper thin films were selectively fabricated on a Teflon surface by using an ArF excimer laser and a Cu electroless plating solution in open air. Photo-excited C-F bonds of the surface were effectively defluorinated with hydrogen atoms which were photodissociated from the Cu solution. The dangling bonds of the defluorinated carbon atoms were combined with the oxgen and the copper atoms which were also photodissociated. Thus, C-O-Cu bonds were formed on the surface and functioned as Cu nuclei for an electroless plating. The Cu thin films were successfully deposited in electroless plating solution only on the Cu nuclei.
Orientation and Velocity Dependence of the Nonequilibrium Partition Coefficient
Authors: Beatty K.M. , Jackson K.A. 
Published: April 2011

ABSTRACTMonte Carlo simulations based on a Spin-1 Ising Model for binary alloys have been used to investigate the non-equilibrium partition coefficient (kneq ) as a function of solid-liquid interface velocity and orientation. In simulations of Si with a second component kneq is greater in the [111] direction than the [100] direction in agreement with experimental results reported by Aziz et al. The simulated partition coefficient scales with the square of the step velocity divided by the diffusion coefficient of the secondary component in the liquid.
Bubble Formation in Zr Alloys Under Heavy Ion Implantation
Authors: Pagano Luciano , Motta Arthur T. , Birtcher Robert C. 
Published: April 2011

ABSTRACTWe report here the results of a study conducted to examine the effect of Kr ion irradiation on bubble formation in Zr alloys. We used the HVEM/Tandem facility at Argonne National Laboratory to irradiate several Zr alloys, including Zircaloy-2 and Zircaloy-4, at temperatures from 300 to 800 C and to doses up to 2 × 1016ion.cm−2. Both in-situ irradiation of thin foils as well as irradiation of bulk samples with an ion implanter were used in this study. For the thin foil irradiations, a distribution of small bubbles in the range of 30-100 Å was found, at all temperatures with the exception of the Cr-rich Valloy where bubbles of 130 Å were found. The irradiation of bulk samples at high temperature (700–800 C) produced large faceted bubbles (up to 300 Å) after irradiation to 2 × 1016ion.cm−2. The results are examined in the context of existing models for bubble formation and growth in other metals.
On the Roles of Temperature and Interfaces in Irradiation and Thermally Induced Solid State Amorphization
Authors: Wang L.M. , Gong W.L. , Ewing R.C. , Webert W.J. 
Published: April 2011

ABSTRACTThe roles of irradiation temperature and interfaces (free surfaces and grain boundaries) in irradiation- and thermally- induced amorphization of ceramics (coesite, apatite, olivines and spinels) have been studied by transmission electron microscopy (TEM). The irradiations were performed with 1.5 MeV Kr+, 200 keV and 1 MeV electrons over a wide temperature range (20-700 K). The critical amorphization dose at which amorphization is complete, Dc, increased with increasing irradiation temperature for most materials except coesite (a high pressure polymorph of Si02) which showed a decreasing Dc with increasing temperature under 1 MeV electron irradiation. Although amorphization may occur directly within a displacement cascade or by cascade overlap, this study shows that free surfaces and grain boundaries are favorable sites for nucleation of amorphous volumes. Once the amorphous volume is formed at interfaces, it may grow rapidly under continued irradiation. Coesite which has a glass transition temperature higher than its melting temperature underwent spontaneous amorphization during thermal annealing at 1200 K. This thermally-induced amorphization also started at free surface and grain boundaries and propagated into the interior of the crystal. The interface-mediated amorphization is analogous to the process of thermodynamic melting.
A Tem Study of Inverse Melting in Nb45Cr55
Authors: Sinkler W. , Michaelsen C. , Bormann R. 
Published: April 2011

ABSTRACTInverse melting of bcc Nb4sCr55 is investigated using transmission electron microscopy, high-resolution TEM and electron diffraction. It is shown that the transformation to the amorphous phase initiates at the bcc grain boundaries. The transformation results in an increase in incoherence, evidenced by a loss of bend contours. Some anisotropy is found in the amorphous phase produced by inverse melting, which is associated in HRTEM with preferentially oriented but discontinuous and distorted fringes. The results are consistent with the production of an amorphous phase by inverse melting.
Thermodynamic Properties of Coherent Interphase Boundaries in Substitutional Fcc Alloys
Authors: Asta Mark 
Published: April 2011

ABSTRACTThermodynamic and structural properties of coherent interphase boundaries (IPBs) in the Al-Li and Ag-Al alloy systems are studied using the cluster variation method (CVM) and low-temperature expansion (LTE) techniques. The energy parameters required as input for the CVM and LTE calculations were obtained by fitting to phase diagram data in the case of Al-Li alloys and from a fit to the results of first-principles total energy calculations for Ag-Al. Interphase energies are calculated as a function of temperature and composition profiles across coherent IPBs are computed for high-symmetry crystallographic orientations. It is demonstrated that the calculated temperature dependence of interphase energies and the “widths” associated with compositionally diffuse IPBs can be appreciable even at temperatures well away from critical points.
Kinetic Competition in Undercooled Liquid Alloys
Authors: Perepezko J. H. , Allen D. R. 
Published: April 2011

ABSTRACTMost alloy systems can develop more than one solid phase for a given composition during solidification. For metastable undercooled liquids a thermodynamic analysis can provide insight into the range of structural and compositional options that are possible. The numerous examples of metastable phase formation during solidification of undercooled melts demonstrates that the actual phase selection is dominated by kinetics. Indeed, the observation of undercooling is linked to kinetic control. Different forms of kinetic control can be identified and include suppression of heterogeneous nucleation during slow cooling and constrained growth during rapid quenching. In both cases the kinetic competition involved in phase selection is mediated by the thermal history. Nucleation controlled kinetics can be examined in fine powders of undercooled liquids where crystallization rates and metastable phase diagrams provide a basis for analysis. Similarly, constrained growth can be examined during controlled cooling where microstructures and kinetic models can be used for analysis. The existing kinetics models appear to be adequate but the processing conditions are often dynamic and in nonsteady state conditions so that critical tests are difficult unless specific kinetic transitions are available.
Kinetics of Structural Relaxation in Metal Glasses
Authors: Nakonechna O.I. , Zakharenko N.I. , Kopan V.S. , Dashevsky N.N. , Babich N.G. 
Published: April 2011

ABSTRACTRelaxation processes in different amorphous transition metal-metalloid (TM-M)-type alloys have been studied using thermopower measurements. The migration of two types of atomic complexes has been considered. For Ti-based amorphous alloys the migration of TM atoms and TM-M complexes diffusion are at least two processes that define the structural relaxation. For Ni and Fe-based alloys the relaxation processes are determined first of all by isolated TM atom migration.
Phase transition in non-crystalline solids viewed from heating
Authors: Nakayama K. , Kojima K. , Takahashi N. , Masaki Y. , Kitagawa A. , Suzuki M. 
Published: April 2011

ABSTRACTThe heating-rate dependence of crystallization temperature, Tc, and the glass transition temperature, Tg, is studied from the view points of nucleation and fragmentation processes in disordered structures. Tc and Tg are expected to increase monotonically with heating rate. Such behaviors of Tc and Tg are classified into four characteristic regions with respect to the heating rate. Results are summarized in the Transient Phase Diagram where Tc and Tg are given as a function of heating rate. The scaling rule in the Transient Phase Diagram is given.
Thermodynamics of the System Ag2se-Ag2s: A Molecular Dynamics Study
Authors: Smith A. , Ravelo R. , Pingitore N. 
Published: April 2011

ABSTRACTWe report on Molecular Dynamics (MD) studies of free energy and vibrational entropy differences of the binary system Ag2Se-Ag2S as function of temperature. We have employed the methods of adiabatic switching and temperature integration over a reversible path to obtain the phase diagram. We discuss the nature of the entropy difference in terms of ion mobility and previous MD calculations of diffusion rates in these systems.
An Investigation of Grain Refinement in Deeply Undercooled Alloy Droplets Using Texture Analysis
Authors: Norman A.F. , Gärtner F. , Eckler K. , Zambon A. , Greer A.L. , Ramous E. , Herlach D.M. 
Published: April 2011

ABSTRACTFor Cu - 30 at.% Ni droplets processed by containerless solidification under lévitation, the crystallographic texture correlates strongly with the microstructure seen in optical metallography and with the undercooling at which solidification started. The variation in texture is useful in understanding the development of the microstructure, in particular at the extremes of the undercooling range where grain-refined microstructures are observed.
Morphological Evolution and Properties of LPE Grown GaSb, AlGaSb and AlGaAsSb
Authors: Dutta P.S. , Bhat H.L. , Kumar Vikram , Dieguez E. 
Published: April 2011

ABSTRACTThe nucleation morphologies of LPE grown GaSb, AlGaSb and AlGaAsSb layers on GaSb substrates are presented. The morphology of the GaSb layers grown from Sb-rich melts showed facets on highly terraced surface, whereas those grown from Ga-rich melts exhibited fine terraces without facets. An optimum temperature in the range of 500 – 550°C was found to be suitable for the growth of mirror smooth layers from Ga-melts. The surface morphology of the AlxGa1-xSb layers degrades drastically with increase in Al content beyond x = 0.5. The surface morphology of AlGaAsSb epilayers has been found to depend strongly on the pre-growth melt dissolution sequence.
Self-Limiting Growth Kinetics of 3D Coherent Islands
Authors: Chen K. M. , Jesson D. E. , Pennycook S. J. , Thundat T. , Warmack R. J. 
Published: April 2011

ABSTRACTLarge 3D coherent islands are found to kinetically resist their further growth during post-deposition annealing of metastable 2D strained films. We reveal that a kinetic energy barrier exists to successive facet-layer growth of a 3D strained island at the expense of its surrounding 2D structure. The barrier increases with further growth of the island, which defines a self-limiting behavior of island growth. This self-limiting effect naturally explains a number of relevant features which have been observed experimentally including narrow island size distributions.
Equilibrium Shapes of Small Strained Islands
Authors: Spencer Brian J. , Tersoff J. 
Published: April 2011

ABSTRACTWe calculate the equilibrium morphology of a strained layer, for the case where it wets the substrate (Stranski-Krastonow growth). Assuming isotropic surface energy and equal elastic constants in the film and substrate, we are able to calculate two-dimensional equilibrium shapes as a function of the island size and spacing. We present asymptotic results for the equilibrium shape of a thin island where the island height is much smaller than the island width. We also present numerical results of the full equations to describe the island shape when the islands are widely separated. From these solutions we are able to determine the chemical potential of the island as a function of island volume and the strain energy density along the surface of the island for small to medium-sized islands.
X-Ray Scattering and Absorption Studies of MnAs Thin Films Grown by MBE on GaAs (001) Substrates
Authors: Huang S. , Ming Z. H. , Soo Y. L. , Kao Y H. , Tanaka M. , Munekata H. 
Published: April 2011

ABSTRACTMnAs thin films grown on GaAs (001) substrates by molecular beam epitaxy have been studied by grazing incidence x-ray scattering (GIXS), x-ray diffraction (XRD) and extended x-ray absorption fine structure (EXAFS). Microstructures in films prepared with different first-layer growth conditions (template effects) are compared in terms of the interfacial roughness, lattice constants, epilayer thickness, local environment surrounding the Mn atoms, coordination number, and local disorder. The template effects are found to cause significant differences in the local structures and crystallinity of MnAs epitaxial layers.
Void and Dislocation Microstructure Development in Heteroepitaxial Film Growth
Authors: Smith Richard W. , Srolovitz David J. 
Published: April 2011

ABSTRACTTwo dimensional, non-equilibrium molecular dynamics simulations have been performed to examine the microstructures of both homoepitaxial and heteroepitaxial thin films grown on single crystal substrates. The principal microstructural features to develop within these films are small voids and edge dislocations. Voids form near the surface of the growing film as surface depressions between microcolumns pinch off to become closed volumes. These voids often form in such a way as to introduce dislocations into the crystal with their cores positioned within the voids. Dislocations are also formed during heteroepitaxy at the interface between the substrate and film. These dislocations tend to be mobile. When voids are present in the film and when the lattice misfit is low, dislocations tend to be trapped in the voids or pulled toward them due to dislocation image interactions. Once attached to voids, dislocations are effectively pinned there. When voids are absent or when the misfit is high, dislocations are restricted to the film-substrate interface. In the case of heteroepitaxy, dislocations are found to relieve either tensile or compressive misfit stresses. Misfit stresses may also be accommodated, to some extent, merely by the free volume of the voids themselves.
Deformation Behavior of Strained Layer Heterostructures
Authors: Fischer A. , KüHNE H. 
Published: April 2011

ABSTRACTWe present a new Volterra dislocation approach in equilibrium theory for strain relaxation in heteroepi-taxial semiconductor structures, one which includes surface relaxation effects and elastic interactions between straight misfit dislocations. The free-surface boundary conditions are satisfied by placing an image dislocation outside the crystal in such a manner that its stress field cancels that of the real interface misfit dislocation at the surface. The effect of the Airy stress function that removes the fictitious shear and normal stresses at the surface are discussed. This image method provides an equilibrium theory which correctly predicts critical strained layer thicknesses and completely describes the elastic and plastic strain relief as well as the phenomenon of work hardening in lattice mismatched epilayers.
Equilibrium Configuration of Epitaxially Strained Thin Film Surfaces
Authors: Jagannadham K. , Narayan J. , Hirth J.P. 
Published: April 2011

ABSTRACTThe formation of convex and concave regions on the surface of a strained thin epitaxial film on a thick substrate is analyzed by minimization of energy associated with the configuration. The strain energy change resulting from the formation of undulations is modelled with the strain in the film represented by a continuous distribution of dislocations along the perturbed surface and the interface. A discrete dislocation model is also used when periodic undulations are formed. Results of energy minimization for germanium or germanium-silicon alloy films on silicon substrate illustrate that convex regions tend to grow. On the other hand, convex regions formed to conserve mass in shape changes associated with concave regions become stable with minimum energy under quasi-equilibrium when the mobility of adatoms is low. We have determined the size and radius of curvature of the undulations at minimum energy and conclude that it is favorable to form atomic steps on the surfaces from which dislocation generation and strain relaxation takes place.
Growth of GaAS and InAlAs on High Quality, Epitaxial, NiAl Metal Film
Authors: Hung C.-Y. , Weckwerth M.V. , Visokay M.R. , Pao Y.C. , Harris J.S. 
Published: April 2011

ABSTRACTSuccess in incorporating single crystal, epitaxial metal layers into semiconductors will have a significant impact on electronic and optical devices. The growth of GaAs on (001) pseudomorphic NiAl/GaAs by molecular beam epitaxy has been studied using transmission electron microscopy. The island growth of GaAs on pseudomorphic (lattice matched) NiAl is the origin of the formation of stacking faults and microtwins in the GaAs overlayer. The GaAs islands are considered to be due to heterogeneous nucleation, which occurs more easily at the corner of a step on a strained metal film. Growth of almost twin free In0.25Al0.75As on thick, lattice relaxed, epitaxial NiAl films has been achieved, which supplying useful information for the investigation of the possible factors causing poor quality of GaAs overlayers.
A New Method for Fast Simulation of Adsorbate Dynamics
Authors: Kumar P.V. , Warakomski Steven J. , Fichthorn Kristen A. 
Published: April 2011

ABSTRACTWe present a dynamical version of the Smart Monte Carlo method to model the diffusion dynamics of a metal atom on a metal surface. This method, in conjunction with umbrella sampling, can be used to simulate the dynamics of metal thin film growth, including all relevant atomic-scale phenomenon, over long time scales, characteristic of experimental studies. To demonstrate the accuracy of this method we simulate the dynamics of Rh on Rh(111) and Cu on Cu(100). Interatomic forces are modeled with Lennard-Jones and Corrective-Effective-Medium potentials for the Rh and Cu systems, respectively. We show that this new simulation method correctly reproduces the diffusion dynamics and, with some modification, allows us to reach experimental time scales.
Fabrication of Fine Grain Size Shape Memory Alloys Through Crystallization of Amorphous Ribbon
Authors: Shi J. D. , Ma J. L. , Gao Y. , Pu Z. J. , Wu K. H. 
Published: April 2011

AbstractThe objective of this work is to fabricate fine grain size NiTi-based shape memory alloys through crystallization of amorphous materials. An amorphous material with a composition of Ti50Ni25Cu25 was used as a sample for this study. First, a systematic investigation was conducted to understand the kinetics of the crystallization process of amorphous materials under an isothermal mode and under a continuous heating mode, respectively. The characteristic parameters associated with the crystallization process, such as the starting and finishing times for the isothermal crystallization process, the peak temperature for the continuous heating crystallization process, and the activation energy of the material were determined. Based on the results of the kinetic study, a series of isothermal annealing experiments were conducted to characterize the microstructure of the fully crystallized materials. The TEM micrographs indicate that the mean grain size of the fully crystallized Ti50Ni25Cu25 alloy is independ of isothermal temperature. The mean grain size is around 400-500nm, which is 1/10 of the grain size of usual NiTi based shape memory alloys. In addition, the crystallization micro-mechanism of the amorphous material is discussed based on TEM observations.
Solidification Analyses for the Fabrication of Bulky Multicomponent Metallic Glasses and their Properties
Authors: Inoue Akihisa , Shinohara Yoshiyuki , Yokoyama Yoshihiko 
Published: April 2011

AbstractThe liquid-crystalline transformation during continuous cooling was examined for a Zr60Al10Ni10Cu15Pd5 alloy which was ejected into a wedge-shape cavity in a copper mold or solidified on a copper hearth by unidirectional arc melting. The structure consists of a glassy phase in the wedge angles smaller than 10 degrees and changes to glassy and crystalline phases in the higher angle range. The start (Cs) and termination (Ct) points for the transformation were determined and the continuous-cooling-transformation (C. C. T. ) curves were constructed. The nose temperature (Tn) and the time (tn) up to the nose point in the C. C. T. curves were 1018 K and 0.93 s. The critical cooling rate for glass formation defined by (Tm-Tn)/tn is 110 K/s. Furthermore, with the aim of clarifying a solidification condition for formation of a bulk glassy alloy by unidirectional arc melting, the relation between the formation of a glassy phase and the solidification parameters of moving velocity of liquid/solid interface (V), temperature gradient (G) and cooling rale (R) was examined. The glassy phase was obtained in the condition of V>3 mm/s, G>4 K/mm and R>40 K/s. The supercooling reaches 385 K at 40 K/s. The large supercooling ability is presumably due to the formation of a highly dense randomly packed structure where the nucleation of a crystalline phase and the atomic rearrangement for growth reaction are difficult.
Mechanical Properties of Porous Nanophase Materials Measured by Instrumental Indentation
Authors: Van Swygenhoven H. , Wagner W. , Löffler J. 
Published: April 2011

AbstractMechanical properties of nanostructured intermetallic Ni3Al synthesized by the inert-gas condensation technique are studied by means of instrumental indentation using the ICT-CSEMEX indenter. This instrument is a microindenter which continously measures load and displacement. Load-displacement curves are performed as function of grain size, consolidation- and annealing temperature. The mean grain size of the samples are studied by means of x-ray diffraction and small-angle neutron scattering.