bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crystal Nucleation and Growth in Glassy and Liquid Pd40Ni40P20
Authors: Evans P. V. , Garcia-Escorial A. , Donovan P. E. , Greer A. L. 
Published: April 2011

AbstractTurnbull pointed out that good glass formability should correlate with a high reduced glass transition temperature, Trg. The alloy Pd40Ni40P20 has an unusually high Trg of ∼0.66 and indeed it can be formed into a glass at rather low cooling rates (≲ 1 Ks−1 ). In this paper a number of experiments are described which take advantage of the high resistance to crystallization in this alloy to study behavior in the labile temperature range between Tg and Tm. The anomalously low crystal growth velocities arise because the product is a three phase mixture. Nucleation kinetics are derived from crystal size distribution analysis. Heterogeneous nucleation at the surface of melt spun ribbon is characterized; significant surface relief develops on crystallization because of the low number of nuclei. In bulk glass produced by fluxing, good crystal size statistics show that internal nucleation is predominantly also heterogeneous, but with a significant transient time. Measurements of the specific heat of the undercooled liquid reveal that the free energy of crystallization deviates significantly from a linear dependence on undercooling (expected for pure metals) in the way predicted by Dubey and Ramachandrarao.
The Importance of Transient Nucleation and Non-Equilibrium Viscosity for Glass Formation
Authors: Kelton Kenneth F. 
Published: April 2011

AbstractThe process of nucleation and growth in glasses and undercooled liquids is modeled by directly simulating the evolution of the molecular cluster distribution under both isothermal and non-isothermal conditions. Results of that simulation for the nucleation rate during the quench, and for the number of nuclei produced and the volume fraction transformed at the end of the quench are presented. The following three points are discussed: (1) The importance of transient, or non-steady state, nucleation rates on glass formation is assessed by considering three model glass forming systems: lithium disilicate, a relatively good glass former, and two metallic glasses, (Au85Cu15)77Si9Gd14 and Au81Si19. (2) Using experimentally determined values for the steady state nucleation rates and growth velocities for Pd40Ni40P20, it is demonstrated that, in agreement with recent experimental results, this alloy may be cycled at rates on the order of 1 K/sec between the melting and glass transition temperatures without crystallization. Transient effects are shown to be unimportant under these conditions in this system. (3) The effect on glass formation of a non-equilibrium viscosity during the quench due to configurational freezing is evaluated by assuming a phenomenological model for the changing viscosity.
Amorphous Alloys from Microsecond Current Pulses
Authors: Clemens Bruce M. , Buchholz Jeffrey C. , Gilgenbach Ronald M. , Bidwell Steven 
Published: April 2011

AbstractWe report the use of microsecond current pulses to produce an amorphous metal alloy. Starting materials consisted of electron beam deposited films of elemental crystalline zirconium and nickel layers with a composition modulation wavelength of 46 nm, a total thickness of about 2.5 μn, and an average composition of Zr38Ni62 deposited onto sapphire substrates. Current pulses had a total ring time of several microseconds and were produced with a low inductance capacitor and a spark gap switch. Integration of current traces showed that 85% of the energy was deposited into the sample within 2 microseconds. The energy in the pulses could be controlled in a range where their effect on the films went from no visible change to total vaporization. Pulses with a peak current in the kiloampere range produced melting in 1 cm wide samples. The cooling rate following this treatment was sufficient to produce amorphous material. We report structural changes resulting from rapid melting and resolidification as well as results of a search for solid state transformations resulting from current pulses below the melting threshold.
The Emergence of Modern Nucleation Theory
Authors: Cahn John W. 
Published: April 2011

AbstractA series of important papers by David Turnbull and his collaborators in the late 1940's and early 1950's laid the experimental and theoretical foundation of modern nucleation theory. The elegance, versatility, and generality of the phenomenological approach, coupled with brilliant and insightful experimental confirmation, sparked widespread application which continues today. Much of David Turnbull's subsequent work in other subjects grew directly or indirectly from this work.
Crystal Growth Mechanisms and Kinetics
Authors: Glicksman M. E. , Selleck M. E. 
Published: April 2011

AbstractThe scientific contributions by David Turnbull and his co-workers toward understanding crystal growth span over 35 years from the late 1940's to the present. Turnbull's early attempt (1950) to correlate interfacial energies derived from droplet supercooling measurements with other thermochemical data still provides a significant data base for estimating such energies in a variety of materials. His work with Hillig in 1956 on quantification of the screw dislocation mechanism for interfacial molecular attachment remains as a predictive theory for defect-assisted growth of faceted, and therefore kinetically hindered, interfaces. The Hillig-Turnbull screw dislocation mechanism is now ranked among such notable kinetic models for crystal growth as the Wilson-Frenkel random attachment theory and the nucleationlimited layer spreading models of Burton, Cabrera, and Frank. Turnbull's contributions and interest in elucidating crystal growth kinetics have continued throughout his long and productive career, as evidenced by his recent work with Coriell (1982) on estimates of collision limited rapid crystal growth in highly supercooled transition metals. Progress in unraveling the kinetic contributions of interfacial attachment from those of heat and solute transport will also be reviewed to provide a current context of Professor Turnbuli's contributions to the field of rapid crystallization.
Self-Assembled InAs Islands on (AI,Ga)As, an In Situ Scanning Tunneling Microscopy Study
Authors: Ballet P. , Smathers J.B. , Salamo G.J. 
Published: April 2011

ABSTRACTWe report an in-situ molecular beam epitaxy – scanning tunneling microscopy study of three dimensional (3D) self organized InAs islands on (AI,Ga)As surfaces. The influence of the presence of Al atoms on the roughness of the starting surface and on the island density is shown by investigating several Al compositions. We emphasize the case of InAs/AlAs and point out the major differences between this system and the widely studied InAs/GaAs system.
Stress-Driven Formation of Self-Assembled InGaAs Islands on Sub-Micron Metal-Patterned Substrate
Authors: Son Maeng Ho , Jung S. K. , Min Byung Don , Hyun Chan Kyung , Choi Bum Ho , Kim Eun Kyu , Kim Yong , Lim Jong Soo 
Published: April 2011

ABSTRACTA stress-driven formation of self-assembled InGaAs islands has been studied by the growth on GaAs (100) substrates with sub-micron platinum stripe pattern. Islands or quantum dots preferentially nucleate at the boundary of metal patterns. In addition, a quantum dot-free region near the boundary of the metal pattern is found. Those results are attributed to the stress between metal stripe and GaAs surface, which produces a laterally stressed region around the metal stripe. Adatoms on this region preferentially migrate toward the edge of metal stripes with maximum stress. This result may show a possible way for the interconnection between randomly distributed self-assembled quantum dots and metal stripes.
Quantum Confined Electron-Hole States in ZnSe Quantum Dots
Authors: Lee H. W. H. , Smith C. A. , Leppert V. J. , Risbud S. H. 
Published: April 2011

ABSTRACTWe observed the quantum confined bandedge emission from ZnSe quantum dots and the size dependence of the energy states, spin-orbit interaction, and Stokes shift. The bandedge emission occurs in the UV-blue. The energy gap = Eg + C/dn where d is the diameter and n is 1. 19 ± 0.13 and 1.21 ± 0.13 for the first and second electron-hole transitions, respectively. The separation between these transitions approaches the bulk spin-orbit splitting, while the Stokes shift decreases with particle size. Effective mass theories can not explain these results. Trap emission is observed in some samples in the green and red, resulting from Se-related traps.
Manipulating InAs Dots with GaAs Patterns: Effect of GaAs Buffer Layer Growth and Pattern Profiles
Authors: Jeppesen Søren , Gerling Maria , Samuelson Lars , Miller Mark S. 
Published: April 2011

ABSTRACTWe report on our efforts to selectively place chemical beam epitaxy grown Stranski-Krastanov InAs dots on GaAs patterns. The pattern profiles for placement depends on the growth conditions of a GaAs buffer layer grown on the lithographic patterns. Because we seek to suppress dot formation on (100)-oriented surfaces outside of the features, we investigated the effects buffer layer growth conditions have on dot nucleation using reflected high energy electron diffraction, atomic force microscopy and photo-luminescence. We conclude that buffer conditions favorable for patterns have negligible effect on the dots formed on the (100)- oriented surface, and that selective dot placement can be engineered by As pressure, InAs deposition and buffer growth conditions.
Intraband Absorption in Ge/Si Self-Assembled Quantum Dots
Authors: Boucaud P. , Le Thanh V. , Sauvage S. , Brunhes T. , Fortuna F. , Debarre D. , Bouchier D. 
Published: April 2011

ABSTRACTMid-infrared intraband absorption in Ge/Si self-assembled quantum dots is reported. The self-assembled quantum dots are grown by ultra-high-vacuum chemical vapor deposition. The intraband absorption is observed using a photoinduced absorption technique. The mid-infrared absorption, which is in-plane polarized, is maximum around 300 meV. The absorption is attributed to a quantum dot hole transition between bound and continuum states. The absorption cross section is deduced from the saturation of the photoinduced intraband absorption. An inplane absorption cross section as large as 2 × 10−13 cm2 is measured for one dot plane.
Inverse Magnetoresistance In Manganite/SrTiO3/Co Tunnel Junctions
Authors: Teresa J. M. De , Barthélémy A. , Contour J. P. , Fert A. , Lyonnet R. , Montaigne F. , Vaurès A. , Seneor P. 
Published: April 2011

AbstractIn La0.7Sr0.3MnO3/SrTiO3/Co tunnel junctions, the half-metallic nature of La0.7Sr0.3MnO3 allows probing the spin polarization of Co. For applied voltage bias around zero volts, an inverse tunnel magnetoresistance is found, indicating the negative spin polarization of Co at the Fermi level as expected from the density of states of the “d” band in Co. The bias dependence of the magnetoresistance reflects the structure of the “d” band density of states of Co. In this article we underline the important consequences for the knowledge of the spin-dependent tunneling in solids brought by these results and describe in detail the effect of temperature and high magnetic field on the magnetoresistance.
Detailed C-V Analysis for YbMnO3/Y2O3/Si Structure
Authors: Yoshimura Takeshi , Fujimura Norifumi , Ito Daisuke , Ito Taichiro 
Published: April 2011

AbstractYbMnO3 (Yb/Mn = 0.96) thin films were prepared on Y2O3(111)/Si(111). Although the sample exhibited ferroelectric type C-V hysteresis, the window width changed depending on the applied bias voltage. Hence, the ferroelectric type hysteresis might include the effect of space charge. To make clear the C-V behavior caused by only ferroelectricity, and to obtain the optimal relationship between ferroelectric and insulator layer thicknesses, the C-V behavior at high frequency was computed for MFIS structure. Relationships between the counter bias voltage applied to the ferroelectric layer and the thickness of dielectric layer were also demonstrated. Compared with the calculated results, experimental C-V characteristics are discussed.
Energy Dispersion Contour Approach to Calculate Optical Properties of Quantum Well Structures
Authors: Osotchan T. , Shi W. , Zhang D.H. 
Published: April 2011

ABSTRACTIn order to calculate optical properties i.e. dielectric function, refractive index and absorption coefficient, the evaluation of integration including ground and excited wavefunctions is required over entire k-space. The contour of energy dispersion was proposed to form the criteria to select and limit the value of k in the integration. With the contour approach the integration can be determined to truncate at certain k value where the weight factor of Fermi-Dirac distribution function become very small and the fraction of integration can be ignored. The approach was applied to AIGaAs/AlAs/GaAs double barrier quantum well structures with 14-band k.P Hamiltonian. By systematically modifing this quantum well structure the dependence of absorption peak width was investigated in bound-to-bound and bound-to-quasibound intersubband transitions. The energy dispersion contours of each involved state were illustrated in two dimensional k-space including the compositions in perpendicular and parallel directions to the interface. The calculated refractive index and absorption as a function of wavelength can be simply extracted from the contour characteristic especially at the constant Fermi energy surface.
Optical Properties of Silicon Nanocrystals: A First Principles Study
Authors: Ögüt Serdar , Chelikowsky James R. , Louie Steven G. 
Published: April 2011

ABSTRACTAb initio quasiparticle gaps. self-energy corrections. exciton Coulomb energies. and optical gaps of Si nanocrystals are calculated using the higher-order finite difference psendopotential method. The calculations are performed in real space on hydrogen-passivated Si clusters with diameters up to 30 A (> 1000 atoins). The size-dependent self-enerkgy correction is enhanced substantially compared to bulk. and quantum confinement and reduced electronic screening result in appreciable excitonic Coulomb energies. Calculated optical gaps are in very good agreement with absorption data from Si nanocrystals.
Ab Initio Calculations of Response Properties Including the Electron-Hole Interaction
Authors: Olevano Valerio , Albrecht Stefan , Reining Lucia 
Published: April 2011

ABSTRACTWe discuss the current status of a computational approach which allows to evaluate the dielectric matrix, and hence electronic excitations like optical properties, including local field and excitonic effects. We introduce a recent numerical development which greatly reduces the use of memory in such type of calculations, and hence eliminates one of the bottlenecks for the application to complex systems. We present recent applications of the method, focusing our interest on insulating oxides.
Selective Aluminum CVD on Si(100) From DMAH
Authors: Bisch C. , Rogge S. , Mélin T. , Janssen G.C.A.M. 
Published: April 2011

AbstractThe influence of the dose on the crystal growth and on the selectivity of the Al-CVD process has been studied. Doses were varied from 100 L to 18000 L. Selective deposition was observed, both on passivated Si vs. SiO2, as well as on bare Si vs. passivated Si. On oxide elongated crystals have been deposited with dimensions of 1200 × 60 × 60 nm.
Nucleation and Growth In Martensitic Transformations
Authors: Pond R.C. , Nixon T. 
Published: April 2011

AbstractA mechanistic model of the nucleation and growth of martensitic products that is consistent with the phenomenological theory of martensite crystallography is described, and applied to the case of NiTi. In addition to the lattice invariant deformation specified in the phenomenological theory, an array of interfacial transformation dislocations, or disconnections, is present. The motion of these disconnections across the interface between the nucleus and matrix cause the growth of the precipitate, and the two defect arrays in combination relieve the strain in the nucleus. For such processes to be diffusionless, special crystallographic circumstances must arise, and these are explored in the paper.
3D Simulation of Coarsening of γ′ Precipitates in a Ni-Al Alloy
Authors: Vaithyanathan V. , Chen L.Q. 
Published: April 2011

AbstractPrecipitation of γ′ particles from a disordered γ matrix in a Ni-Al alloy is studied. A continuum phase-field model is employed in three-dimension(3D). The focus is on the evolution of γ′ particle morphology and development of spatial correlations during coherent nucleation, growth and coarsening. The effect of lattice mismatch on the rate of coarsening is investigated. The results are compared with those obtained from two-dimension(2D) simulations.
In Situ Ellipsometry Study of the Diamond Film Evolution Process
Authors: Cancel L.M. , Figueroa O.L. , Weiner B.R. , Morell G. 
Published: April 2011

AbstractWe employed in situ ellipsometry to monitor and study the nucleation and growth processes of diamond thin films fabricated by chemical vapor deposition. The films were grown on Si substrates in a hot filament chemical vapor deposition (HFCVD) system. We monitored the effective extinction coefficient (k) at 1.96 eV of the diamond films during growth through ellipsometry. The behavior of this parameter was found to be reproducible, making it suitable as a basis for dividing the deposition process into intervals. The film growth was aborted at various k values yielding diamond film samples that represent snapshots of the growth process at different stages. These films were removed for ex situ characterization using Raman spectroscopy and scanning electron microscopy (SEM). These characterizations were used to correlate the ellipsometric data with film microstructure, enabling us from now on to monitor the diamond film growth in real time and to design experiments targeted at modifying the film microstructure by changing growth parameters in the middle of film fabrication.
The Effects of Nucleation in the Two Step Growth of HVPE GaN
Authors: Tavernier P.R. , Etzkorn E.V. , Wang Y. , Clarke D.R. 
Published: April 2011

AbstractThe repeatable growth of high quality thick layers of GaN by hydride vapor phase epitaxy generally requires buffer layers or other surface pretreatments to produce morphologically smooth films suitable for further device growth. Of the conditions for high quality GaN growth, proper film nucleation invariably contributes most to the overall growth of high quality films and the exclusion of impurities. We have studied a two step growth process which incorporates a low temperature HVPE grown nucleation layer and have compared it to films grown without buffer layers to determine how the impurity content and the dislocation networks change the overall film quality. Additionally we observe the formation of macroscopic steps during growth with step heights of ∼0.75 μm and terrace widths of ∼ 7 μm, which we attribute to the initial conditions of the low temperature nucleation layer prior to growth and to kinetically limited growth.
Nucleation in Undercooled Co-Pd Alloys
Authors: Holland-Moritz D. , Schenk Th. , Herlach D.M. 
Published: April 2011

AbstractThe statistics of nucleation are studied for different Co-Pd alloys by electromagnetic levitation. Each alloy was undercooled approximately 100 times under the same experimental conditions. A model developed by Skripov is employed to statistically analyze the distribution of maximum undercoolings in order to obtain information on the prevailing nucleation mechanism. The results of these investigations indicate that nucleation is influenced by magnetism when the nucleation temperature is approaching the Curie temperature.
Stochastic Modeling of Grain Growth and Coarsening
Authors: Pande C.S. , Masumura R.A. 
Published: April 2011

AbstractRecent developments in the modeling of grain growth and coarsening are briefly considered. Common characteristics of both these phenomena are briefly pointed out. A formulation based on stochastic consideration is proposed. This formulation assumes that the rate of growth of an individual grain or a precipitate is not entirely determined by its size but has a random component to it. This leads to a Fokker-Planck Equation for the size distribution. It can then be shown that there is indeed a unique state (the self-similar state) which is in general reached from an arbitrary initial state. The case of two dimensional grain growth is treated in detail as an example. Grain size distribution is obtained from these considerations, which is in good agreement with experiments.
Interdiffusion Microstructure Map Topology
Authors: Morral J. E. , Chen Huimi , Meisenkothen Frederick 
Published: April 2011

AbstractWhen two alloys are placed in contact to form a diffusion couple, the microstructure that forms on heating is a function of alloy composition. This function can be illustrated on a phase diagram as an “Interdiffusion Microstructure Map” (IMM). An IMM was determined in the present work for Ni-Cr-Al diffusion couples at 1200°C. The couples consisted of one γ+γ' alloy bonded to a number of γ+β alloys. The IMM contained five fields corresponding to five different microstructures. The fields met at a five-line node, giving the map an unexpected topology. The IMM topology was deduced by considering the transition microstructures and kinetic equations that lead to the formation of interdiffusion microstructures.
Early Stages of Decomposition in Ni-Rich Ni-Ti
Authors: Kompatscher M. , Demé B. , Hecht J. , Heinrich H. , Kohlbrecher J. , Schneider J.-M. , Schönfeld B. , Kostorz G. 
Published: April 2011

AbstractIn-situ small-angle neutron scattering was performed on Ni-(10 to 12) at.% Ti polycrystals and single crystals at temperatures between 870 and 1270 K. During decomposition metastable precipitates of cuboidal shape form with preferred alignement along <100>. The Ti concentration of these precipitates is 17(1) at.% (between 870 and 950 K). Metastable precipitates precede the formation of platelets of the stable η phase even outside the hitherto accepted metastable miscibility gap.
Phase Transition and Pattern of Self-Organized Microstructures in Presence of Mobile Impurities
Authors: Ivanova K. , Ausloos M. 
Published: April 2011

AbstractA growth model starting from a surface and in presence of mobile nonreactive localized impurities has been studied for the statistical physics of the microstructure and the surface roughness through simulation. The model is based on the Eden model. The microstructure is described at the mesoscopic (particle) scale level. A dynamical repulsion effect on the front with the mobile particles has been investigated numerically. The presence of such mobile particles shifts the usual percolation transition for three-dimensional (3D) systems from 0.65 corresponding to static hindrances, to the value of 0.8. The particle pushing leads to an aggregation phenomenon with self-organizing particles near and after the interface. This leads to the formation of front facets, competition between faces of different orientations and surface roughening.
Eutectoid Decomposition in Three Ti-Co Alloys
Authors: Coomber E. , Whiting M. J. , Tsakiropoulos P. 
Published: April 2011

AbstractThe mechanisms of eutectoid decomposition are important because of the widespread use of alloys which exhibit a eutectoid transformation. However, the transformation remains a matter of controversy for a number of reasons. The Ti-Co system is examined in order to test current understanding of eutectoid decomposition.The high temperature beta phase can transform on cooling into several products - alpha plates, a non-lamellar mixture of alpha and Ti2Co which can be designated bainite, lamellar pearlite, spheroidal pearlite and Ti2Co allotriomorphs. In this study the high temperature beta phase was decomposed in hypoeutectoid, eutectoid and hypereutectoid alloys, for a range of undercoolings. The microstructure and crystallography of the transformation products was characterised by reflected light microscopy, SEM, XRD and TEM. The classification of the transformation products is discussed.