bluuebunny/crossref_metadata_2025_split huggingface dataset:
Species-resolved imaging and gated photon counting Spectroscopy of laser ablation plume dynamics During krf- and arf-laser pld of amorphous diamond films
Authors: Geohegan David B. , Puretzky Alexander A. 
Published: April 2011

ABSTRACTGated photon counting spectroscopy and species-resolved ICCD photography have been applied to study the weak plasma luminescence which occurs following the propagation of the initial ablation plume in vacuum and during the ‘rebound’ of the plume with a substrate during pulsed laser deposition of amorphous diamond. These time- and spatially-resolved spectroscopic techniques were required in order to investigate notable differences between amorphous diamond-like carbon films formed by pulsed laser deposition from ArF (193 nm) and KrF (248 nm) irradiation of pyrolytic graphite in vacuum. Three principal regions of plume emission have been characterized: (1) a bright luminescent ball (v ∼3-5 cm/(μ.s) displaying nearly entirely C+ emission which appears to result from laser interaction with the initial ejecta, (2) a spherical ball of emission (v ∼1 cm/μs) displaying neutral carbon atomic emission lines and, at early times, jets of excited C2, and (3) a well-defined region of broadband emission (v ∼ 0.3 cm/μs) near the target surface first containing emission bands from C2, then weak, continuum emission thought to result from C3 and higher clusters and/or blackbody emission from hot clusters or nanoparticles. For both lasers, the measurements reveal an explosive interaction within the plume which results in a variety of new gas dynamic observations in vacuum:. These include (a) generation of instabilities or jets, (b) confinement of a residual part of the plume near the pellet surface, (c) cluster formation in the collisional, confined regions of the plume, and (d) reflection of the confined region backward to splash and redeposit on the pellet surface. Evidence for gas-phase formation of these clusters in vacuum is indicated from the dynamic evolution of the same cluster bands observed during the collision of the plume with the substrate surface during film growth. Addition of background gases strongly enhances the third (cluster) component, in accordance with plume-splitting phenomena. The combination of sensitive imaging and photon-counting diagnostic techniques permit an understanding of the importance of gas dynamic effects, such as clustering, on the time-of-flight distributions of species arriving during the deposition of thin films in both vacuum and background gases.
In Situ Diagnostics of Vuv Laser Cvd of Semiconductor Interfaces by Ftir Spectroscopy and Spectroscopic Ellipsometry
Authors: Barth M. , Knobloch J. , Hess P. 
Published: April 2011

ABSTRACTThe growth of high quality amorphous hydrogenated semiconductor films was explored with different in situ spectroscopic methods. Nucleation of ArF laser-induced CVD of a-Ge:H on different substrates was investigated by real time ellipsometry, whereas the F2 laser (157nm) deposition of a-Si:H was monitored by FTIR transmission spectroscopy. The ellipsometric studies reveal a significant influence of the substrate surface on the nucleation stage, which in fact determines the electronic and mechanical properties of the bulk material. Coalescence of initial clusters occurs at a thickness of 16 Å for atomically smooth hydrogen-terminated c-Si substrates, whereas on native oxide covered c-Si substrates the bulk volume void fractions are not reached until 35 Å film thickness. For the first time we present a series of IR transmission spectra with monolayer resolution of the initial growth of a-Si:H. Hereby the film thickness was measured simultaneously using a quartz crystal microbalance with corresponding sensitivity. The results give evidence for cluster formation with a coalescence radius of about 20 Å. Difference spectra calculated for layers at different depths with definite thickness reveal that the hydrogen-rich interface layer stays at the substrate surface and does not move with the surface of the growing film. The decrease of the Urbach energy switching from native oxide to H-terminated substrates suggests a strong influence of the interface morphology on the bulk material quality.
Selective Area Epitaxy of GaAs Optical Waveguides by Laser Assisted Chemical Vapor Deposition
Authors: Roberts J.C. , Boutros K.S. , Bedair S.M. 
Published: April 2011

ABSTRACTDirect writing of GaAs optical waveguides has been achieved by laser assisted chemical vapor deposition (LCVD). The multimode waveguides have gaussian-like cross sections, smooth surfaces, and exhibit losses as low as 5.4 dB/cm. The LCVD technique offers the capability of maskless in situ selective epitaxial growth of diverse multilayer structures, and is therefore a novel alternative for the monolithic integration of optoelectronic integrated circuits.
Transient and Athermal Nucleation of Solids in Rapidly Quenched Liquid Si
Authors: Gupta Vikas V. , Im James S. 
Published: April 2011

ABSTRACTWe have theoretically investigated the nature and kinetics of solid nucleation in supercooled liquid Si within the framework of the classical nucleation theory, and corresponding to the cases in which the liquids are quenched at extremely high quenching rates (from 109 to 1011 K/s). In doing so, we identify and draw a general conclusion that in addition to the well-treated phenomenon of transient nucleation, one must also consider the mechanism of athermal nucleation in order to properly elucidate the situations that are encountered at such high quenching rates. Moreover, contrary to the common notion that the transient effect is relevant at low temperatures where sluggish kinetics prevail, it is noted that the effect can also become prominent at near-equilibrium conditions due to the increase in the time needed by the embryos to reach the exceedingly large critical size.
Tem/Hrem Structural Characterization of Directionally Solidified Gaas-Cras Eutectic Crystals
Authors: Ruvimov Sergei , Liliental-Weber Zuzanna , Swider Wendy , Washburn Jack , Holmes Douglas E. 
Published: April 2011

ABSTRACTConventional and high resolution electron microscopy have been applied to characterize the microstructure of the CrAs-GaAs eutectic. The CrAs-GaAs eutectic crystals were directionally solidified by the Czochralski method in order to produce an ordered array of CrAs rods embedded in a GaAs matrix. The CrAs rods of 2-3 μm in diameter align parallel to the growth axis of the ingot. Where the GaAs matrix is found to contain structural defects, the CrAs rods are effectively defect-free. The CrAs has an orthorombic structure with the parameters a=3.5±0.1 Å, b=6.2±0.1 Å,c=5.7±0.1 Å.The c-axis is close to the direction of solidification.
Interfacial Reactions in Metal-Matrix Composites
Authors: Heffelfinger J. R. , Kieschke R. R. , Carter C. B. 
Published: April 2011

ABSTRACTThe interfacial reaction between Al2O3 (alumina) and a β-Ti alloy has been characterized by transmission electron microscopy, scanning electron microscopy, and X-ray energy-dispersive spectroscopy. Diffusion bonding single-crystal alumina and a β-Ti alloy was found to produce three interfacial regions: a region of intermetallics (Tl3Al and TiAl) located near the alumina interface, an α-Ti region, and a β-Ti region (rich in Mo, the β-phase stabilizer). Of the intermetallics to form, Ti3Al was found to form first and have an aligned, planar interface with the alumina. TiAl formed second and was found to separate grains of Ti3Al and the alumina. Reaction products observed in the diffusion-bonded alumina/β-Ti couples are compared with those observed in metal-matrix composites (MMCs), where a β-Ti alloy matrix is reinforced with alumina fibers. Different coatings used in MMCs are investigated for their ability to prevent the reaction between the matrix and fibers.
Interfacial Reactions Between Ain Substrate And 4-A Family Elements
Authors: Du Yong , He Xiangjun , Tao Kun 
Published: April 2011

ABSTRACTInterfacial reactions between A1N substrate and 4A-family elements including Ti, Zr and Hf were studied. The samples were prepared by Physical Vapour Deposition and annealed at different temperatures from 200°C to 800°C. X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) were employed to detect the compounds formed at the interfaces between them. For Ti/AIN system, when the samples were annealed from 600°C to 800°C for 1 hour, it was found from XRD patterns that TiAl3, TiN, and Ti4N3.x including Ti2N were formed at Ti/AIN interface. With the temperature increasing, the intensities of Ti, TiN(200), Ti2N and Ti4N3.x diffraction peaks decreased while that of TiAl3 and TiN(111) increased. For Zr/AlN system, it was found that the reactions between Zr and AlN resulted in the formation of Al3Zr at about 300°C and Al2Zr at about 500°C. According to RBS spectra, it can be assumed that Al3Zr was the direct product by the reaction between AlN and Zr and Al2Zr was formed by the reaction between Al3Zr and Zr. For Hf/AlN system, however, even the sample was annealed at 800°C, no compound resulted from interfacial reactions was detected.
Atomistic Image of the Kinetics of ‘Order-Order’ Reactions in Ni3Al+B
Authors: Kozubski R. , Pfeiler W. 
Published: April 2011

ABSTRACTIsothermal ‘order-order’ relaxations in Ll2-ordered N76Al24+0.19at.%B were studied by means of residual resistometry. This method made it possible to register very fine changes in the degree of LRO occurring about 1000K below the disordering temperature.
The experimental results of two simultaneous processes being involved in these order-order relaxations with a high activation energy of 4.6eV are explained with an atomistic model of atomic jumps to nn vacancies. The parallel processes are connected with selected jumps of atoms to nn vacancies on different sublattices with a high activation energy of vacancy formation being involved.
Analysis of TPD Spectra on Semiconductor Surfaces by Monte Carlo Simulations
Authors: Venkataramani Rajesh , Jensen Klavs F. 
Published: April 2011

ABSTRACTThis work aims to provide a systematic approach for deriving desorption mechanisms on semiconductor surfaces from a coupling of temperature programmed desorption (TPD) experiments and Monte Carlo (MC) simulations. MC simulations are used to evaluate different desorption schemes to identify mechanisms consistent with experimental results. Effects of nearest neighbor interactions, island formation, and surface reconstructions are quantified through the simulations. Methyl desorption from Ga-rich GaAs is used as a case study to illustrate the MC procedure for interpretation of TPD spectra.
GaAs-on-Ge Heteroepitaxy by Atomic Hydrogen-Assisted Molecular Beam Epitaxy (H-MBE)
Authors: Okada Yoshitaka , Harris James S. , Sutoh Atsushi , Kawabe Mitsuo 
Published: April 2011

ABSTRACTThe purpose of this work is to achieve a high-quality epitaxy of GaAs-on-Ge system at low growth temperatures of 300 ∼ 400°C, by atomic hydrogen-assisted molecular beam epitaxy (H-MBE), in attempt to reduce Ge segregation to a minimum and to realize a layer-by-layer two-dimensional (2D) growth mode from the initial stages of the growth. A high-quality heteroepitaxy is expected in H-MBE technique as atomic H is known to act as an effective surfactant modifying the kinetics and energetics of the growth, which are practically difficult to control on atomic-scale unless a third element like a surfactant is introduced into the growth system. It is shown with the support of reflection high-energy electron diffraction (RHEED), secondary ion mass spectroscopy (SIMS), and atomic force microscopy (AFM) characterization that an enhanced layer-by-layer 2D growth can actually be realized and (2×4) GaAs(001) surface can be achieved in low-temperature heteroepitaxy on vicinal Ge(001) substrates at 400 °C by H-MBE.
Interdiffusion During the Growth of Fe on Ag/Fe(110)
Authors: Persaud R. , Noro H. , Venables J. A. 
Published: April 2011

ABSTRACTWe have previously shown the growth mode of Ag on Fe(110) to be Stranski-Krastanov with Ag islands growing on top of two intermediate Ag layers. In the present studies, Fe was deposited on thin annealed Ag layers on Fe(110). The growth and interdiffusion of these layers were monitored by reflection high energy electron diffraction (RHEED) and Auger electron spectroscopy (AES). For deposition at room temperature (RT), Fe islands grow in a (HO) orientation on the Ag/Fe(110) substrate. These islands form facets similar to those obtained at an equivalent coverage for the Fe/Fe(110) system. AES indicates that there is some intermixing between the deposited Fe atoms and underlying Ag layers at RT. During annealing, or for deposition at 250°C, Ag floats to the top while the Fe islands flatten to form layers at the Ag/Fe(110) interface.
Strain Relaxation at Low Misfits: Dislocation Injection vs. Surface Roughening
Authors: Perovic D.D. , Bahierathan B. , Houghton D.C. , Lafontaine H. , Baribeau J.-M. 
Published: April 2011

ABSTRACTTwo competing strain relaxation mechanisms, namely misfit dislocation generation and surface roughening, have been extensively studied using the GexSi1-x/Si (x< 0.5) system as an example. A predictive model has been developed which accurately describes the nature of misfit dislocation nucleation and growth under non-equilibrium conditions. Using optical and electron microscopy, coupled with a refined theoretical description of dislocation nucleation, it is shown that strain relieving dislocations are readily generated at low misfits with a characteristic activation energy barrier regardless of the growth technique employed (i.e. MBE, RTCVD and UHVCVD). Secondly we have studied the alternative elastic strain relaxation mechanism involving surface undulation; x-ray diffraction, electron and atomic force microscopy have been used to characterize GexSi1-x/Si (x<0.5) structures grown by UHVCVD and MBE at relatively higher temperatures. A theoretical model has been used to model the critical thickness for surface wave generation. The conditions governing the interplay between dislocation formation and surface buckling are described in terms of a "morphological instability diagram".
Observations on the Mechanics of Strained Epitaxial Island Growth
Authors: Freund L. B. , Johnson H. T. , Kukta R. V. 
Published: April 2011

ABSTRACTAn epitaxial material island which has a lattice parameter differing by a small amount for that of its substrate is considered within the framework of continuum mechanics. The strain distribution in the island is determined for a range of aspect ratio, taking into account the compliance of the substrate. It is demonstrated that the total free energy of a strained island is minimum for some value of aspect ratio, and that this value depends on the volume of the island. To consider strain relaxation, the nucleation of a dislocation at the edge of a strained island is examined and the equilibrium aspect ratio of a dislocated island is computed. In particular, it is shown that an island can reduce its free energy by reducing its aspect ratio and, simultaneously, forming an interface misfit dislocation. The simulations are based on the numerical finite element method.
Strain-Induced Diffusion in Heteroepitaxially Grown CuInSe2 on GaAs Substrates
Authors: Fons P. , Niki S. , Yamada A. , Okada A. , Tweet D.J. 
Published: April 2011

ABSTRACTA series of CuInSe2 thin films of varying thicknesses were grown on both GaAs(001) substrates and nominally lattice-matched In0.29Ga0.71As (001) linearly graded buffers by MBE at 450°C. Transmission electron microscopy and high resolution x-ray diffraction measurements revealed the presence of a second phase with chalcopyrite symmetry strained to the CuInSe2 thin film in-plane lattice constant for CuInSe2 films grown on GaAs substrates. Further examination confirmed that the second phase possessed chalcopyrite symmetry. No second phase was observed in films grown on nearly lattice-matched In0.29Ga0.71As (001) linearly graded buffers. Secondary ion mass spectrometry confirmed the presence of interdiffusion from of Ga from the substrate into the CuInSe2layer. It is speculated that this diffusion is related to the state of stress due to heteroepitaxial misfit.
Highly Refined Microstructures in Devitrified Alloys
Authors: Battezzati L. 
Published: April 2011

AbstractThe formation of nanosized microstructures from controlled devitrification of amorphous alloys is reviewed. The driving force for copious nucleation of crystals is discussed in terms of thermodynamic models for the free energy of crystallization and for the interfacial free energy. After fast nucleation and growth of crystals to nanometric size, there are evidences of a change in diffusion mechanism to slow growth. Examples are provided of primary processes in Fe-Zr-B and Al-Sm with data of XRD, TEM, DSC. Cases of eutectic and polymorphic transformations are also at hand (Ni-P, Cu-Ti-Al, Cu-Ti-Ni, Ti-Zr-Co-Cu-Al) showing that the thermodynamic and kinetic conditions leading to nanostructured materials are not unique.Finally chemical effects are discussed such as those of impurities in crystallization (e. g. Zr-based alloys), in leaching of Ni-Zr-Al and in deposition reaction of electroless Ni-P.
Structural and Mechanical Properties of a Simulated Nickel Nanophase
Authors: D’Agostino G. , Van Swygenhoven H. 
Published: April 2011

AbstractThe present paper is aimed at studying the physics of a nickel nanophase at the atomic level. A dense polycrystal has been designed by ideally growing many nano-crystals from randomly distributed seeds and truncating them through a Voronoi construction. The sample has been brought to thermodynamic equilibrium and quenched to its local minimum energy thus leading to a mechanically stable system. The dynamic evolution has been simulated by means of classical molecular dynamics employing a Finnis-Sinclair interactive potential. Owing to the large number of atoms required, a parallel code has been developed. Elastic and plastic behaviour of the simulated sample has been compared with that of a perfect crystal. Evidence of an enhanced plastic behaviour has been observed when severe tensile stresses are applied.
Physical Properties of Partially Crystallized Fe80B20 Amorphous Alloys
Authors: Fiorani D. , Malizia F. , Ronconi F. , Vittori Antisari M. 
Published: April 2011

AbstractThe magnetic properties and hyperfine fields were investigated at low temperatures on amorphous Fe80B20 ribbons crystallized at the end of the nucleation-and-growth process without involving coarsening process. The results obtained by SQUID magnetometer and Mössbauer spectrometer show that saturation magnetization and mean magnetic hyperfine field values are greater than those in both the parent amorphous phase and in the fully crystallized structure where coarsening and grain growth processes are involved. Below 200 K irreversibility is observed in low field magnetization measurements. Transmission electron microscopy measurements reveal that spherulites of Fe3B include a radial structure made of small bcc-Fe acicular crystals about 200 nm long and 10 nm wide. In our opinion, magnetic properties and hyperfine fields are ruled by both high magnetic anisotropy of small monodomain acicular bcc-Fe crystallites and the structure of Fe atoms located at their surfaces.
Characterization of a Pulsed Arc Cluster Ion Source for the Production of Metal Clusters in Molecular Beams.
Authors: Piseri P. , Barborini E. , Milani P. 
Published: April 2011

AbstractWe have produced metal clusters with a molecular beam apparatus based on a Pulsed Arc Cluster Ion Source. The source has been optimized in order to generate intense and stable cluster beams of various elements, with a mass distribution ranging from the monomer up to several thousands of atoms. The source operation conditions can be varied in order to control the mass distribution, intensity and velocity of the aggregates. Preliminary results on the synthesis of granular thin films with this technique are also presented.
Characterization of Tib2/TISI2 Bilayer Structure Deposited by Sputtering
Authors: Sade G. , Pelleg J. 
Published: April 2011

AbstractBilayer of TiB2/TiSi2 was deposited by magnetron co-sputtering on silicon and alumina substrates, and this structure was investigated for structural and electrical properties. Substrate bias and annealing in vacuum have been applied to vary the film properties. X-ray diffraction (XRD) and cross-sectional transmission electron microscopy (XTEM) were used to characterize the structure, and chemical composition was characterized by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). Resistivity was measured by four probe method. Diffusion barrier properties were studied by AES. As deposited films are amorphous with resistivities of about 40 μΩcm. Post deposition annealing in vacuum shows that the amorphous titanium boride film is very stable. Crystallization starts above 1000°C as seen by XRD, and the crystallization temperature depends on the thickness of TiB2. TiSi2 C54 forms in the temperature range 586°C - 922°C, when TiB2 still remains in amorphous form. The TiSi2 sublayer serves as an additional effective diffusion barrier, preventing outdiffusion of boron from TiB2 into the Si substrate.
Titanium Silicidation and Secondary Defect Annihilation in ION Beam Processed Sige Layers
Authors: Larsen K. Kyllesbech , La Via F. , Lombardo S. , Raineri V. , Donaton R. A. , Campisano S. U. 
Published: April 2011

AbstractThe secondary defect annihilation by one- and two-step titanium silicidation in SiGe layers, formed by high dose Ge implantation, has been studied systematically as a function of the Ge fluence, implantation energy, silicide thickness, and silicide process conditions. In all cases the Ti thickness was kept below 20 nm, resulting in very thin Ti silicide layers typically less than 40 nm. The silicide phase was inspected by x-ray diffraction and transmission electron diffraction. Channelling Rutherford backscattering spectrometry and transmission electron microscopy were used to follow the end of range dislocation loop annihilation as a function of the silicide process conditions. The end of range loop annealing and the influence of silicidation is presented in this paper for Ge fluences above 3×1015 cm−2 and energies ranging from 70 keV to 140 keV. A model based on loop coarsening is presented which describes the observed loop annihilation behaviour.
Interpretation of the Infrared Spectra of β-FeSi2 by Molecular Dynamics Simulations
Authors: Miglio Leo , Meregalli Valeria 
Published: April 2011

AbstractWe report the vibrational spectra of β-FeSi2 calculated by molecular dynamics simulations with a tight binding potential and provide a quantitative confirmation of the anisotropic behaviour found by new Infrared (IR) measurements for small monocrystals This analysis allows for the interpretation of more complex IR results previously found for epitaxial samples.