bluuebunny/crossref_metadata_2025_split huggingface dataset:
Controlling Defect Formation in Thin Films
Authors: Nandedkar A. S. 
Published: March 2011

ABSTRACTComputer simulations were used to study nucleation and development of misfit dislocations in coherent films on lattice mismatched substrates. Nucleation of a misfit dislocation was characterized as insertion of vacancies in the top layer of the film, whereas further development of the misfit dislocation was accompanied by the movement of a half dislocation loop towards the interface (1). The energetics of nucleation phenomenon was studied in the presence or absence of surfactants (a Monolayer of different atoms on top of the thin film) and also under different compressive stresses. An Au/Ni film substrate system and Au films with Ni or Ag as surfactants were used for calculations. In absence of a surfactant or when the surfactant atom lattice constant was larger (Ag) than the film atoms (Au), the energy of vacancy insertion (EVI) decreased with increase in compressive strains. When the surfactant atom was smaller (Ni), EVI increased with increase in compressive strains. This should inhibit insertion of vacancies into the film and thus formation of defects such as misfit dislocations.
Periodic Arrangement of GE Islands on SI(111)
Authors: Hibino H. , Shimizu N. , Shinoda Y. , Ogino T. 
Published: March 2011

ABSTRACTWe describe periodic arrangements of Ge islands grown on Si (111) using Ge deposition at room temperature and post-deposit annealing. A Mesh pattern of relaxed Ge islands is obtained under conditions of a Ge thickness of 10 Å and an annealing temperature of 400°C. The Mesh pattern is due to the preferential crystallization of α-Ge films at steps and at out-of-phase boundaries of 7×7 reconstructions. We also demonstrate that the Ge island pattern is modified when Ge is grown on a substrate changed by Si homoepitaxy or In adsorption.
The Effect of Solute Drag on Grain Growth in Thin Films
Authors: Frost H.J. , Hayashi Y. , Thompson C.V. , Walton D.T. 
Published: March 2011

ABSTRACTWe have modelled the microstructural evolution of polycrystalline thin films during grain growth under the situation in which grain boundary migration becomes impeded by solute drag. For this we use a two-dimensional simulation of capillarity-driven grain growth in which grain boundaries migrate at velocities proportional to local curvature. At high driving forces, corresponding to high curvatures, the boundaries are given a mobility corresponding to drag-free motion. At low driving forces, corresponding to curvatures less than some critical value, the boundaries are given a lower mobility which models the effect of solute drag. During grain growth the average curvature of boundary segments decreases. When the boundary curvatures begin to fall below the critical curvature, the grain size distribution evolves to a lognormal distribution, which is maintained as significant further grain growth occurs. This is in accordance with many experimental grain size distributions which are commonly observed to be lognormal.
Diffusive Creep in Polycrystals
Authors: Laks David B. , Maroudas Dimitrios , Pantelides Sokrates T. , Watson IBM Thomas J. 
Published: March 2011

AbstractWe report quantitative mesoscopic calculations of diffusive creep in polycrystals under external stress. The analysis includes mass transport both in the grains and along the grain boundaries, fully coupled with elastic deformations in the grains and the evolution of the displacement field. We find that the net creep rate depends strongly on the details of grain boundary arrangements. The calculations represent a first step toward a comprehensive first-principles theory of plasticity.
Structural and Electrical Properties of Thermally Annealed InN Thin Films on Native and Ain-Nucleated (00.1) Sapphire
Authors: Kistenmacher T. J. , Ecelberger S. A. , Bryden W. A. , Hawley M. E. 
Published: March 2011

ABSTRACTThe effects of thermal annealing at 400°C in 5 MTorr of N2 on the structural and electrical properties of thin films of InN grown at 100°C on native and AIN-nucleated (00.1) sapphire by reactive magnetron sputtering have been studied. The variations in the properties of the two sets of films have qualitatively similar, yet quantitatively different dependencies on anneal time. In each case, surface decomposition to give (101) textured rods of elemental indium is seen at short anneal times, and markedly so in the more highly strained films on the AIN-nucleated substrates. The electrical properties in both cases improve with annealing time, yielding a Hall Mobility that is enhanced 2–3 times relative to as-deposited films and similar to that for films grown at a substrate temperature of 400°C. The evolution of the electrical properties appears to be relatively insensitive to the surface decomposition and to largely reflect the nature of the bulk InN Matrix.
Depth Profiling of Molybdenum Thin Films Using Grazing Incidence X-Ray Scattering
Authors: Malhotra Sandra G. , Rek Z. , Vill M. , Karpenko O.P. , Yalisove S.M. , Bilello J.C. 
Published: March 2011

ABSTRACTIt is important that inherent strains (or stresses) be controlled during thin film processing. This study used grazing incidence x-ray scattering (G1XS) to determine the strain gradient present in a ∼1700 Å sputtered molybdenum thin film. In particular, the gradient in the hydrostatic strain was Measured. This observation corresponded to assessing the average change in the lattice parameter as a function of depth throughout the thickness of the film. In addition, the strain ellipsoids, which represent the state of strain in three dimensions, were calculated as a function of film depth. It was shown that the strain varied throughout the ∼1700 Å Mo film thickness and that the principal strains were anisotropic, with one principal strain much larger than the others in Magnitude.
Molecular Dynamics Study of Ion Impact Phenomena and Compressive Stress in Thin Films
Authors: Marks N.A. , Guan P. , Mckenzie D.R. , PailThorpe B.A. 
Published: March 2011

ABSTRACTMolecular dynamics simulations of nickel and carbon have been used to study the phenomena due to ion impact. The nickel and carbon interactions were described using the Lennard-Jones and Stillinger-Weber potentials respectively. The phenomena occurring after the impact of 100 e V to 1 keV ions were studied in the nickel simulations, which were both two and three-dimensional. Supersonic focussed collision sequences (or focusons) were observed, and associated with these focusons were unexpected sonic bow waves, which were a major energy loss mechanism for the focuson. A number of 2D carbon films were grown and the stress in the films as a function of incident ion energy was Measured. With increasing energy the stress changed from tensile to compressive and reached a maximum around 50 eV, in agreement with experiment.
Mechanism of Diamond Growth on Carbide Substrates Using Fluorocarbon Gases
Authors: Grannen K.J. , Chang R.P.H. 
Published: March 2011

ABSTRACTThe etching and growth behavior of diamond in CxFy / O2 / H2 plasmas have been investigated. Using this gas Mixture, diamond can nucleate on untreated tungsten carbide and silicon carbide substrates up to a density of 108 crystallites/cm2. This compares to a density of 102 crystallites/cm2 when using a methane gas mixture and these same substrates. The increase in nucleation density is attributed to the selective etching of the non-carbon component of the carbide with subsequent nucleation on the carbon enriched surface. The effect of temperature on the nucleation rate has been studied with a lower nucleation density at higher growth temperatures.
Effects of the Substrate Temperature on the Crystallization and Development of Texture of Mn-Zn Ferrite thin Films Deposited by Ion Beam Sputtering
Authors: Cho Hae Seok , Ha Sang Ki , Kim Min Hong , Kim Hyeong Joon 
Published: March 2011

ABSTRACTWe investigated the effects of the substrate temperature (Ts) on the crystallization and the development of texture of Mn-Zn ferrite thin films on SiO2/Si (100) under ion bombardment during ion beam sputtering. As-deposited films showed ferrimagnetic properties in spite of their crystallographic structure of wustite. The crystallographic structure of as-deposited films changed from (111) wustite structure to (222) spinel structure as oxygen partial pressure increased. The (222) preferred orientation seems to originate from oxygen-deficit ambient and preferential resputtering of oxygen ions in films during sputtering. The interplanar distance of the films deposited without oxygen flow decreased with increasing Ts due to release of compressive stress. The saturation Magnetization (Ms) of the film had maximum value at about 275°C, while the resistivity was almost of the same value irrespective of Ts. The unusual fact that crystallization and preferred orientation were less progressed at higher Ts was discussed.
Heteroepitaxial Growth of Strontium Titanate on Lanthanum Aluminate Using the Metallo-Organic Decomposition Technique.
Authors: Braunstein Gabriel , Paz-Pujalt Gustavo R. , Elman James F. 
Published: March 2011

ABSTRACTWe demonstrate the heteroepitaxial growth of thin films of SrTiO3 prepared by the method of Metallo-organic decomposition on LaAlO3 substrates. The SrTiO3 films are prepared by spin coating and thermal decomposition of a solution of Metallo-organic precursors on single-crystal, <100> oriented, LaAK>3 substrates. Subsequent heat treatment at 1100 – 1200 °C for 1 h results in the epitaxial alignment of the SrTiO3 films with respect to the LaAlO3 substrate.The degree of alignment of the films appears to depend on their thickness, with thinner films showing better alignment (as determined by ion-channeling measurements). This behavior is interpreted as a result of the competition between solid-phase epitaxy and random nucleation, observed during the crystallization of films prepared by Metallo-organic decomposition. However, since thinner films have been prepared by dilution of the precursor solution, there is also the possibility that the concentration of the precursor solution may influence the crystallization behavior of the films.The potential influence of the precursor formulation on the crystallization mechanism is discussed.
Initiation and Evolution of Epitaxial Growth of GaAs on CaF2/Si (111) Substrates
Authors: Li Weidan , Anan Takayoshi , Thundat Thomas , Schowalter Leo J. 
Published: March 2011

AbstractIn this work, MBE growth of GaAs on CaF2/Si (111) substrates has been studied with both Rutherford backscattering spectrometry, transmission electron microscopy and atomic force Microscopy. It has been observed that, under certain conditions, a chemical reaction between As adatoms and the CaF2 layers can be induced, by which a more stable As layer on the CaF2 surface is formed. The existence of the As layer modifies the CaF2 surface free energy, which, if properly controlled, leads to two-dimensional (2D) nucleation of GaAs on the CaF2/Si (111) surface as opposed to the more commonly observed three-dimensional (3D) growth. Artificial Modification of the CaF2 (111) surface by introducing Ca prior to GaAs growth is also discussed as a promising way to achieve 2D nucleation. In subsequent growth, two kinds of twins have been observed. All samples were observed to have Micro-twins near the GaAs/CaF2 interface. These twins can be suppressed during the first 1000Å, if the layer is grown in a narrow optimal growth window. Otherwise, the growth will be in a 3D Mode at lower temperatures, or it will suffer from the formation of large rotational twins at higher temperatures. It has been observed that growth on vicinal substrates tilted toward [112] azimuth is helpful in suppressing the development of rotational twins so that growth on these substrates have a wider optimal growth window. Surface Morphology of CaF2 epitaxial layers grown on Si (111) substrates with different vicinal angles has also been investigated. It May have significant impact on the twin development during subsequent GaAs growth.
Surface Morphology of Gallium Phosphide Deposited by Chemical Beam Epitaxy and Interrupted Cycle Chemical Beam Epitaxy
Authors: Kelliher James T. , Thornton John T. , Russell Phillip E. , Bachmann Klaus J. 
Published: March 2011

ABSTRACTIn this paper, we describe the relation of the surface morphology of GaP grown by chemical beam epitaxy (CBE) and interrupted cycle chemical beam epitaxy (ICCBE) to the deposition conditions on (001) Si. The films were examined with scanning electron Microscopy (SEM) and atomic force Microscopy (AFM). Initial stages of the films grown by CBE using triethylgallium (TEG) and tertiarybutylphosphine (TBP) examined by SEM reveals in addition to GaP nuclei at 10–100 nm scale, whiskers of typically 100 nm diameter at their bases. AFM Measurements yield an average height of these whiskers of 50 nm that self-terminate and are incorporated into the GaP film upon further growth without loss of epitaxy as determined by x-ray diffraction. Nevertheless, the whiskers are a possible source for defects and surface roughness in thicker films. Whisker formation can be suppressed under conditions of ICCBE by the addition of hydrogen flow, sealing the silicon surface by a smooth thin film of GaP.
Interface Phenomena in very thin Si-Ge Heterostructures
Authors: Baribeau J.-M. , Lockwood D.J. , Lu Z.-H. , Headrickt R.L. 
Published: March 2011

ABSTRACTInterfacial properties of thin Si/Ge heterostructures are discussed. It is shown that (SimGen) p superlattices with well defined periodicity can be synthesized on both (100) Si and Ge using low temperature (350 °C) Molecular beam epitaxy. Multilayer structures are however intermixed over one or two monolayers and exhibit a roughness with lateral scale > 100 nm and an amplitude of the order of two Monolayers. On Si the roughness is strongly correlated from interface to interface, possibly due to small surface mobility during growth. Segregation of Ge during growth has also been evidenced by x-ray photoelectron spectroscopy and may explain some of the interface Mixing. The strong composition dependence of Ge diffusion in Si1−xGex alloys causes anisotropie diffusion upon annealing whereby a large composition gradient can be preserved at the heterointerfaces due to the very slow diffusion rate of Ge atoms in pure Si. This effect is important in structures which alternate thin Ge and thick Si layers and is thus more prominent in superlattices grown on Si substrates.
Coupled Diffusion Equation Solutions To Ag/Ge (L 11) And Cs/Si (100) Interactions
Authors: Venables J. A. , Persaud R. , Metcalfe F. L. , Milne R. H. , Azim M. 
Published: March 2011

ABSTRACTSurface diffusion has been studied in the Ag/Ge (111) and Cs/Si (100) systems using UHV-SEM based techniques, biassed secondary electron imaging (b-SEI), Micro-AES and RHEED. Ag and Cs were deposited through a mask of holes held close to the substrate at room temperature, and annealed at higher temperatures Ta. Under certain conditions, the Ag and Cs patches split into two distinct regions with different sub-Monolayer (ML) coverages θ, observable using b-SEI; the sensitivity for Cs/Si (100) is below 0.5% ML. These patch widths were measured as f(ø,Ta,t), and effective diffusion coefficients extracted. Both systems were modelled using coupled diffusion equations, involving adatoms in two different surface phases. Comparison with experiment yields activation energies for adsorption (Ea) and diffusion (Ed).
Interdiffusion Enhancement in AIGaAs/GaAs Superlattices in the Presence of Carbon
Authors: Jamal Zul , Goodhew P J 
Published: March 2011

AbstractThe mechanism of C diffusion through short period GaAs-A1GaAs superlattices has been investigated. The diffusion coefficient of C and the interdiffusion rates of the Ga and Al atoms were estimated by analysing, respectively, SIMS data and TEM image intensity traces. The TEM and SIMS results shows that C diffuses with an activation energy of about 2.8eV in the range 850-1000°C and that interdiffusion of Al and Ga on the group III lattice is enhanced by a factor of 5 or more when the C concentration exceeds about 5 × 1019cm−3.
Tem Studies of Impurity Induced Defects in GaAs Grown by CBE
Authors: Jamal Zul , Goodhew P J 
Published: March 2011

AbstractDefects generated from a thin impurity layer between a CBE-grown epilayer and its GaAs substrate have been studied by TEM. Line defects were observed to emerge randomly from the impurity layer in the various <110> directions either as single lines or as various vshaped dislocation pairs. The origin, frequency and significance of these defects is discussed.
Determination of The State of Deformation in Epitaxial Layers Using High Resolution X-Ray Diffraction
Authors: Dugdale P.J. , Pond R.C. , Barnett S.J. 
Published: March 2011

AbstractThe state of deformation in epitaxial layers of InGaAs grown by MBE on GaAs substrates has been determined using high resolution X-ray diffraction. This method enables the strains and rigid body rotations which occur in the layers to be measured and these are described by means of a tensor. Layers of different thicknesses have been grown on substrates whose dislocation densities differ by three orders of magnitude in order to assess the influence of this parameter on layer relaxation through the motion of misfit dislocations to the interface. Transmission electron microscopy has also been used to provide additional information on the relaxations.
A Novel Approach for The Production of Low Dislocation Relaxed Sige Material.
Authors: Powell A.R. , Iyer S.S. , Legoues F.K. 
Published: March 2011

AbstractIn this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin Silicon On Insulator, SOl, substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced into the upper SiGe material, which appeared dislocation free to the limit of the cross sectional Transmission Electron Microscopy (TEM) analysis. We thus have a method for producing very low dislocation, relaxed SiGe films with the additional benefit of an SO substrate. This buffer structure is significantly less than a micrometer in thickness and offers distinct advantages over the thick SiGe buffer layers presently in use.
Simulations of the Dislocation Array at Ge/Si Interfaces
Authors: Kaplan Theodore , Chisholm M. F. , Mostoller Mark 
Published: March 2011

AbstractWhen Ge is grown epitaxially on Si(001), the 4% mismatch between the lattice parameters of Ge and Si can produce a regular two-dimensional grid of (a/2) [1,±1,0] edge dislocations at the interface, a checkerboard with a spacing of ∼ 100 Å. We have performed classical molecular dynamical simulations of this checkerboard in large microcrystals. The results show the expected 5-fold plus 7-fold ring structure at the cores of the individual dislocations, and a new closed symmetric structure of 18 atoms at their intersections. Tetrahedral coordination is everywhere retained, with relatively small changes in the bond lengths of less than 10% and in the bond angles of less than 25%. The energetics and dislocation offset of the system are explored for the Stillinger-Weber and Tersoff potentials.
Microstructural Examination of Extended Crystal Defects in Silicon Selective Epitaxial Growth (SEG)
Authors: Yen Haw , Bashir Rashid , Kvam Eric P. , Neudeck Gerold W. 
Published: March 2011

AbstractSelective epitaxial growth has been used to produce electronically isolated devices on patterned-oxide Si substrates. The oxide / silicon interfaces in such materials are often associated with regions of poor device performance. In this study, the extended defects at the interfacial regions are examined by transmission electron microscopy, and the defects observed are correlated to electronic behavior of diodes fabricated in the selectively grown Si region. Process modifications were made to reduce the density of these defects. The nature of the successful techniques for defect reduction suggests that a large portion of the defects were due to thermal expansion mismatch, and may be avoidable.
The Morphology of Grain Boundary Interactions with Twins in YBa2Cu3O7−δ
Authors: Wang Jenn-Yue , King A. H. 
Published: March 2011

AbstractVarious morphologies are observed where twins meet grain boundaries in YBa2Cu3O7−δ. Twins may be “correlated” at the boundary (i.e. twin boundaries from one grain may meet a twin boundary from the other grain in a quadruple junction) and the twins may be narrowed or “constricted” at the boundary. These effects are determined by the interfacial energy. We estimate the energy of the various interfaces by determining the dislocation arrays they contain, using the constrained coincidence site lattice (CCSL) model and Bollmann's O2-lattice formalism. Our approach indicates that there are significant changes in the energy of the interfaces and is thus able to explain the variety of observed morphologies.
Crystallite Rotation Experiments Revisited: the Contribution of Free-Surface Interactions
Authors: Balasubramanian L. , King A.H. 
Published: March 2011

AbstractWhile crystallite-rotation experiments of the type pioneered by Gleiter and his co-workers have provided a great deal of information about the variation of grain boundary energy with crystal misorientation, certain aspects of the experiments still remain puzzling. Notably, crystal rotation rates do not follow the form predicted by consideration of the Read-Shockley equation; and Chan and Balluffi have shown that in some cases certain crystallites are able to escape from the energy cusps that trap others [5]. In this paper we re-examine the crystallite rotation mechanism and rotation rates from the perspective of the interactions of grain boundary dislocations with the free surfaces that terminate the grain boundary.
A Modified Approach to the Modelling of Grain Boundary Structure in Materials with an Hexagonal Crystal Structure
Authors: Maclaren Ian , Aindow Mark 
Published: March 2011

AbstractThe CCSL approach for modelling dislocation configurations in high-angle grain boundaries of hexagonal materials has been re-examined. It has been shown that this model implies the existence of long range strain in both crystals and that the strain energy which would be involved makes the formation of such structures unlikely. It has been proposed that alternative methods could be developed which make no assumptions about the nature of any reference structure adopted by a boundary. If the Burgers vectors of interfacial dislocations are obtained using Pond's symmetry theory of interfacial defects and the arrangement of these defects determined using an ‘0’ lattice approach then the structure of grain boundaries may be modelled irrespective of the nature of the “reference structures”.