bluuebunny/crossref_metadata_2025 huggingface dataset:
Raman Spectroscopy of Tin Films Deposited on Silicon (001) Substrate by Laser Physical Vapor Deposition
Authors: Jagannadham K. , Chowdhury R. , Biunno N. , Narayan J.
Published: March 2011

We have carried out the Raman spectroscopy of titanium nitride films grown on Si(001) substrate by laser physical vapor deposition. The first order Raman defect induced acoustic and optical phonon peaks have been recorded for films grown at different substrate temperatures ranging from room temperature 25°C to 600°C.The ratio of the acoustic and the optical peak intensities and the width of the peaks are correlated with the nitrogen deficiency, crystalline size and stresses in the films. The results of Auger analysis, resistivity measurements and microstructural observations substantiate the finding that the stoichiometry of the films in terms of nitrogen concentration is improved at higher substrate temperatures.
Microstructure and Electromigration Properties of Submicron Al (.5%Cu) Lines
Authors: Prybyla J. A. , Kola R. R. , Hull R. , Eaglesham D. J. , HUGGINS H. A.
Published: March 2011

The evolution of the microstructure of submicron Al (.5wt%Cu) lines has been examined as a function of annealing and electromigration stressing time. We have studied lines of two different thicknesses (4000 and 2000 Å) and a range of widths from 0.2 to 1.0 Μm. Pre- and post- stressing studies of the microstructure have been performed, as well as real-time studies during stressing inside the transmission electron Microscope (TEM). We report the results of temperature cyclings over the range 400–525 C for both passivateci and unpassivated lines. IMprovements in the microstructure were observed in all cases. The Most dramatic improvement occurred for the unpassivated lines when annealed to 450 C and for the passivated lines upon annealing to 525 C. In both cases a true bamboo structure was very nearly achieved for lines of width ≤0.5 Μm. Grain growth was by far the greatest in the pads. In the 2000 Å thick passivated lines, voiding upon temperature cycling is more pronounced than for the thicker lines. Also, the bamboo microstructure is more difficult to obtain compared to the 4000 Å lines. Finally, we report our preliminary results on the microstructural changes which occur as a result of electromigration. Voiding and hillock formation are examined. Microstructure is correlated with electromigration reliability.
Thermal Stability of the TiSi2 Film Under the Dielectric Capping Layer
Authors: Kim Y.W. , Lee N.I. , Ahn S.T.
Published: March 2011

The thermal stability of titanium disilicide (TiSi2) film under dielectric capping layers was studied. Dielectric capping layers prevent changes in sheet resistance and the film stress of the TiSi2 film during annealing at 900°C. The enhancement of thermal stability of the TiSi2 film was dependent on the nature of dielectric; thermal stability of the TiSi2 film was enhanced more effectively by the plasma-enhanced silicon nitride (PE-SiN) capping layer rather than the undoped silicate glass (USG; S1O2) capping layer. The dependence of thermal stability of the TiSi2 film with the nature of dielectrics was due to the difference in stress of dielectrics at anneal temperature. At 900°C, stress of the USG film was nearly twice of that of the PE-SiN film. Agglomeration of the TiSi2 film under the dielectric capping layer at high temperature annealing can be explained by a diffusional flow of atoms called Nabarro-Herring Microcreep. As the size of Ti-polycide lines becomes smaller, the nature of the dielectric film on the TiSi2 film will be more important for achieving thermal stability.
An in Situ Transmission Electron Microscopy Study During NH3 Ambient Annealing of Cu-Cr Thin Films
Authors: Atzmon Z. , Sharma R. , Mayer J.W. , Hong S.Q.
Published: March 2011

Nitridation of Cu-Cr alloy films under an NH3 ambient was studied using in situ transmission electron Microscopy. Cu-Cr thin films (40–100 nm) were deposited on a single crystal NaCl substrate by electron beam coevaporation, and were heat treated up to 750°C at 2.5–3.0 Torr NH3. The films were also vacuum (10-6 Torr) annealed under the same conditions for comparison. Initial observation of Cu and Cr crystallization occurred at 470°C for both environmental conditions. The nitridation process of Cr to form CrN was observed initially at 580°C and was followed by evolution of faceted Cu grain growth in the CrN Matrix.
The Study of Seam Line Defects in Silicon-On-Oxide by Merged Epitaxial Lateral Overgrowth
Authors: Shih Yangchin , Lou J. C. , Oldham W. G.
Published: March 2011

Selective Epitaxial Growth of silicon through windows in SiO2 using low-temperature SiH2Cl2/H2 chemistry in a hot wall LPCVD system was used to form Epitaxial Lateral Overgrowth (ELO) regions of Silicon-on-insulator. In cases where pattern ‘width was less than two times epi film thickness, the ELO regions merged to form a continuous epitaxial film. In this study, 2.5 μm thick single crystal silicon layers were grown perfectly over oxide regions with very low dislocation density (< 104/cm2). The epitaxial Si/oxide interfaces were smooth and defect-free. However, a “seam”-like defect was occasionally observed in the epitaxial film on top of the oxide, at the locations where two growth fronts merged together. This crystallographic defect in some case extends through the whole Silicon-on-Oxide film and would be expected to be detrimental to electronic devices built on or close to it. The sturctures of these seam line defects were investigated in detail by transmission electron Microscopy (TEM). The formation mechanisms of these seam line defects and possible origins are discussed.
Effects of Nitrogen Doping in the Insulational Character of Anodically Oxidized Films of Tantalum
Authors: Nakamura Y. , Yamamoto T. , Okamoto Y. , Morimoto H. , Akagi Y.
Published: March 2011

The effects of nitrogen doping as a terminator in an anodically oxidized film of tantalum have been investigated.

In the oxide film of nitrogen-free tantalum, the electric leakage current abruptly increased with the applied voltage. It is well-known as the Poole-Frenkel effect [1] [2]. After annealing at 623K in a hydrogen atmosphere, the leakage current increased.

On the other hand, in the oxidized films of nitrogen-doped tantalum the leakage current increased in proportion to the applied voltage, but it was very small as compared with the nitrogen-free oxide. Moreover the leakage current decreased after annealing. The decrement strongly depended on the amount of doped nitrogen.
Modeling of mechanisms of Formation of Quasi-Epitaxial Organic Interfaces
Authors: Zhang Yajiong , Forrest S. R.
Published: March 2011

We introduce a model to calculate the static equilibrium configuration between two monolayers of large, planar organic molecules bonded by van der Waals (vdW) forces. The Model significantly simplifies analysis by replacing the conventional atom-atom potential summation with a single ellipsoidal potential centered in the molecular plane. Our results indicate that recent observations of crystalline “quasi-epitaxial” growth of these planar molecular films in ultrahigh vacuum results from the relatively large intralayer elasticity as compared to the small interlayer stress. Good agreement between calculated and observed structures is achieved using no adjustable parameters. The Model is used to predict molecular structures which are likely to form quasi-epitaxial layers. Quasi-epitaxy is a general feature of large planar molecules of similar shape and size in adlayers and substrates where there is comparatively weak vdW bonding between layers.
Surface Stress, Morphological Development, and Dislocation Nucleation During Strained-Layer Epitaxy
Authors: Jesson D. E. , Pennycook S. J. , Baribeau J.-M. , Houghton D. C.
Published: March 2011

Utilizing Marker layer experiments and Z-contrast imaging, we have observed the formation of surface cusps during SixGe1−x alloy growth. The formation of cusps can be understood in terms of stress-driven surface diffusion, and we consider the large stress build-up at the cusp tip as a potential source for the nucleation of misfit dislocations.
Epitaxy of Germanium on SI(001) Grating Templates
Authors: Umbach C.C. , Blakely J.M.
Published: March 2011

Epitaxial Ge films (< 3 ML) have been grown at elevated temperatures on Si (001) grating substrates (repeat spacing of 2.0 μm) and imaged using room temperature scanning tunneling Microscopy (STM). The Ge films exhibit the 2×n reconstruction associated with missing dimer rows. The value of n and the growth morphology are influenced by the deposition rate and by annealing. At substrate temperatures of 600° C and deposition rates >0.5 ML/Min., islands elongated along the the dimer row direction nucleate at steps and on terraces. With sufficient annealing at 800° C, the islands coarsen and are eventually eliminated. The roughness of the A-type step becomes greater than that of the B-type step, which is the reverse of the situation with pure Si (001). The separation between missing dimer rows and hence the value of n are increased by annealing. Differences in substrate terrace widths due to the periodically varying step density of thegratings affect the growth Modes: two-dimensional islands occur near the extrema of the gratings whereas step flow occurs when steps are separated by ∼150 Å or less.
Dislocation Nucleation from a Surface CUSP
Authors: Li Jiangwei , Chiu Cheng-hsin , Gao Huajian
Published: March 2011

Theoretical and experimental studies have suggested that surface roughness may significantly enhance the nucleation of misfit dislocations in a strained heteroepitaxial film, especially in view of a stress-induced roughening instability which tends to form cusp-like stress singularities along the film surface. In this paper, the process of dislocation nucleation is perceived as a single dislocation emerging from a gradually sharpening surface groove. An analysis similar to the Rice-Thomson model for dislocation nucleation from a crack tip is carried out to determine the nucleation condition in terms of the depth and curvature of the surface groove. Specific applications are made to Si1−xGex alloy films on Si (100) substrates.
Evolution of Surface Roughness of a Strained Epitaxial Film Due to Interface Misfit Dislocations
Authors: Jonsdottir F. , Freund L. B.
Published: March 2011

The appearance of misfit dislocations at the interface between a strained layer and its substrate induces a nonuniform chemical potential along the surface of the layer. Under the assumption that the resulting chemical potential gradient will drive coherent mass rearrangement by surface diffusion, a model of evolution of surface shape is considered which leads to estimates of the surface roughness induced by this mechanism.
Surface Alloying and Surfactant Action of Sb ON Ag (111)
Authors: Oppo Sabrina , Fiorentini Vincenzo , Scheffler Matthias
Published: March 2011

We report ab initio calculations for Sb and Ag adsorption on Ag (111): evidence is found for substitutional adsorption and surface segregation of Sb, and for the formation of a disordered surface Sb-Ag alloy. The average diffusion barrier for Ag is enhanced on Sb-covered Ag (111), which favors the formation of a high density of small-sized islands: this is suggested to be the cause of the surfactant action of Sb on Ag reported recently.
An Investigation of PT/PT (111) Homoepitaxy with Molecular Dynamics Simulation and Static-Energy Calculation.
Authors: wang Ruoping , Kalp Bryan S. , Fichthorn Kristen A.
Published: March 2011

We present the results of a study of Pt/Pt (111) epitaxial thin-film growth with Molecular-dynamics simulation and static-energy calculation. Interatomic forces are modeled with Corrected-Effective-Medium theory. Atomic details of deposition, such as dissipation of the kinetic energy of an impinging gas atom, adatom motion on and approaching descending step edges, effects of the geometry of a step edge on the interlayer transport of adatoms, etc., have been intensively investigated. We have observed a novel mechanism for adatom incorporation into descending-step edges which involves a concerted motion of the adatom and edge atoms. Our study supports the “island size and shape” model which has been proposed to explain the reentrant layer-by-layer growth mode seen experimentally in Pt/Pt (111) homoepitaxy.
Facet Formation on One-Dimensionally, Periodic Si Substrates
Authors: Adams D.P. , Yalisove S.M.
Published: March 2011

The development of surface morphology during homoepitaxial growth on one-dimensionally periodic, patterned Si substrates and subsequent annealing has been investigated using transmission electron Microscopy. Si layers grown by MBE are characterized in terms of facets which develop at a trench edge. 1000 Å thick films deposited at ∼ 600°C on Si substrates develop large (311) facets at the bottom and top of the sidewall. After annealing at high temperatures for short times (∼ 1 hour), the amplitude of corrugation decreases but the surface profile is facetted along its length. The “annealed shape” at the trench edge is shown to consist of several surfaces including: (211), (311), (511), and (711). This evidence suggests that (311) facets develop as a result of the growth kinetics.
Numerical Simulation of Diffusion Controlled Surface Evolution
Authors: Chiu Cheng-Hsin , Gao Huajian
Published: March 2011

As a model for Stranski-Krastanow island formation in strained heteroepitaxial layers, this paper investigates the surface-diffusion controlled morphological evolution of a two dimensional semi-infinite solid loaded in the lateral direction. Numerical Methods are developed to simulate the surface diffusion process, and examples are presented to demonstrate three distinct evolution patterns which are characterized by two critical wavelengths. The results show that, according to the wavelength, a slightly wavy surface can evolve into a cusped, a smoothly undulating, or a flat configuration. The diffusion wavelength and cusp-formation time compare favorably with recent experimental observations.
Controlling Defect Formation in Thin Films
Authors: Nandedkar A. S.
Published: March 2011

Computer 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

We 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

We 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

We 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

The 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

It 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

Molecular 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

The 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

We 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

We 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

In 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

In 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

Interfacial 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

Surface 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

The 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

Defects 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

The 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

In 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

When 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

Selective 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

Various 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

While 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

The 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”.
A Multi-Plane Model for Defect Nucleation at Cracks
Authors: Beltz G. E. , Schmauder S.
Published: March 2011

A mathematical model (2D) of dislocation generation at cracks on interfaces is presented, which takes into account the role of slip processes on several slip planes in the vicinity of a crack. The work investigates the effects of other incipient dislocations on the nucleation and emission of the primary dislocation that emits first and is responsible for crack-tip blunting on atomic length scales. The modeling makes use of the recently-developed Peierls-Nabarro framework for dislocation nucleation. It is found that there is a moderate increase in the critical load necessary to emit a dislocation, when incipient slip activity is allowed to occur on the prolongation of the crack plane. Furthermore, the slip at the tip, the quantity which characterizes to what extent an incipient dislocation forms before it emits, decreases when the dual slip-plane model is used. Implications for the ductile versus brittle response of Ni are discussed.
Migration Dynamics of a Σ=3 {112} Boundary in Aluminum
Authors: Medlin D.L. , Stobbs W.M. , Weinberg J.D. , Angelo J.E. , Daw M.S. , Mills M.J.
Published: March 2011

We present a study of the structure and migration mechanisms of the Σ=3 {112} boundary in aluminum. Measurements of the static boundary, using both High Resolution Transmission Electron Microscopy (HRTEM) and the α-fringe technique, are consistent with the lowest energy boundary structure that is predicted by the Embedded Atom Method (EAM). HRTEM observations of the migrating boundary are also presented. The boundary is mobile and upon translation produces coherent {111} twin boundary steps. The atomistic processes that are involved in this migration are considered in terms of the required twinning shears and the results of molecular dynamics simulations using the EAM. The initial nucleation of steps in the boundary appears to be electron beam induced.
Interactions of Dislocations and Deformation Twins with Interfacial Boundaries in Titanium Aluminides
Authors: Appel Fritz , Wagner Richard
Published: March 2011

The deformation behaviour of two-phase titanium aluminide alloys with a lamellar microstructure of the intermetallic phases α2(Ti3Al) and y(TiAl) was studied. The interaction processes of dislocations and deformation twins, respectively, with the lamellar interfaces are investigated by conventional and high-resolution electron microscopy. The mechanisms of translation of shear deformation across, the lamellar boundaries depend on their structure. Semicoherent interfaces are very effective barriers limiting the propagation of shear deformation. The misfit dislocations present at these interfaces support, on the other hand, the generation of dislocations and deformation twins. The observed processes are discussed regarding plastic deformation and crack propagation in the material.
Structural Evolution and Deformation in an Aluminum-Based Solid Solution Alloy with Submicron Grain Size
Authors: Wang Jingtao , Horita Zenji , Nemoto Minoru , Furukawa Minoru , Valiev Ruslan Z. , Ma Yan , Langdon Terence G.
Published: March 2011

Superplastic ductilities may be achieved in tension using polycrystalline materials with small grain sizes (typically <10 μm). Experiments were conducted to evaluate the significance of the grain boundaries in an Al-3% Mg solid solution alloy with a submicron grain size (∼0.2 μm). The material was produced by subjecting the alloy to severe plastic strain using a pressing technique. This paper describes the nature of the microstructure in the as-fabricated condition, the evolution of the microstructure as a function of time and/or temperature, and the effect of testing in tension at a temperature of 403 K.
Experimental Measurement of the Local Electronic Structure of Grain Boundaries in Ni3Al
Authors: Muller D.A. , Batson P.E. , Subramanian S. , Sass S. L. , Silcox J.
Published: March 2011

We have examined grain boundaries in both undoped and boron doped Ni0.76Al0.24using electron energy loss spectroscopy (EELS), x-ray fluorescence (EDX) and annular dark field (ADF) imaging in a UHV STEM. A detailed study of a high angle grain boundary in nickel rich Ni3Al doped with 1000 ppm boron shows nickel enrichment occurring in a 5Å wide region. Boron segregation to the boundary is observed with EELS and is seen to vary along the boundary, coinciding with ADF contrast changes in the surrounding grains that may be due to local strain fields. Spatially resolved EELS of the Ni L2,3core edge, which is sensitive to changes in the hole density in the nickel d band, shows boron rich regions of the grain boundary to have a bonding similar to that of the bulk material. Boundary regions without boron have an electronic structure similar to that of the undoped grain boundaries where the Fermi level lies deeper in the nickel d band. In addition to studying boron segregation, EELS provides a unique opportunity to examine the changes in bonding that control the local properties of the material.
Nearly Dislocation-Free APB Termination at Pure Grain Boundary Step Defects in L10 Alloys
Authors: Singh Abha , King A.H.
Published: March 2011

L10 alloys typically derive from a high-temperature, disordered fcc phase. For example, CuAu has a face centered tetragonal structure below 380°C and is derived from its high temperature, disordered face centered cubic phase. As the material transforms from the disordered fcc phase to the ordered tetragonal phase, the four distinct Σ3 fcc twin misorientations generate twelve distinct tetragonal twin misorientations, four being characterized as Σ3 and eight as Σ6. Of particular interest is the Σ6 structure because it is possible to terminate lattice antiphase boundaries without dislocations at this interface. A pure step defect at the interface can accommodate the APB termination due to anti-site coincidence (coincidence between copper and gold sites). We term these defects “antiphase steps”. The antiphase step is a new type of interfacial defect that has not been described by other workers. The possibility of forming antiphase steps in ordered L10 alloys is related to even-Σ interfaces. Since the Σ6 boundary is common in the ordered phase, the formation of dislocation-free APB terminations may be important in L10 alloys.
Hrem Observations, Peels Analysis and Numerical Simulations of Au/Ni Mbe Multilayers
Authors: Bayle Pascale , Deutsch T. , Gilles B. , LancÇn F. , Marty A. , Thibault J. , Colliex C. , Tence M.
Published: March 2011

The structural evolution of Au/Ni multilayers (with an increasing number of Ni monolayers (MLs)) has been investigated by HREM. As soon as the thickness of Ni becomes larger than 5 MLs, a structural change occurs which in fact has been predicted by numerical simulations. The deformation in the multilayer has been characterised by HREM image processing and has been related to the Ni profile. This profile has been compared to the chemical profile obtained by scanning PEELS analysis through the multilayer.
Localized Influence of Solute on the Stacking Fault Energy of Dilute Al-Based Solid Solutions
Authors: Rohrer C. Lane
Published: March 2011

The stacking fault energy (SFE) is widely used to classify the mechanical behavior of pure metals. In alloys, however, the experimentally observed SFE is strongly influenced by localized solute effects. To further understand these effects on dislocation structure and on the observed SFE, solute segregation to an extended edge dislocation dipole, delineating two stacking faults, was studied in dilute Al:Cu, Al:Ag, and Al:Cu, Ag solid solutions. Cu and Ag were chosen to isolate solute size and modulus effects, Cu being smaller than Al, while Ag and Al are essentially the same size. Atomistic Monte Carlo results showed little change in the partial dislocation spacing in the binary systems as compared to the spacing in pure Al, even though Cu was observed to segregate to the compressive regions of the dislocation dipoles, forming widespread atmospheres, while Ag formed randomly distributed Ag-rich zones. However, in ternary Al:Cu,Ag simulations, the Ag apparently inhibited the Cu from distributing across the width of the extended dislocations, both Ag and Cu forming small clusters near or on the partial dislocations which increased the partial dislocation spacing. Results will be discussed in light of interpretations of experimental SFE determinations, emphasizing the importance of the localized solute distribution on the SFE.
Effect of Boron and Hydrogen on the Electronic Structure of Ni3Al
Authors: Kioussis N. , Watanabe H. , Hemker R.G. , Gourdin W. , Gonis A. , Johnson P.E.
Published: March 2011

Using first-principles electronic structure calculations based on the Linear-Muffin-Tin Orbital (LMTO) method, we have investigated the effects of interstitial boron and hydrogen on the electronic structure of the L12 ordered intermetallic Ni3A1. When it occupies an octahedral interstitial site entirely coordinated by six Ni atoms, we find that boron enhances the charge distribution found in the strongly-bound “pure” Ni3AI crystal: Charge is depleted at Ni and Al sites and enhanced in interstitial region. Substitution of Al atoms for two of the Ni atoms coordinating the boron, however, reduces the interstitial charge density between certain atomic planes. In contrast to boron, hydrogen appears to deplete the interstitial charge, even when fully coordinated by Ni atoms. We suggest that these results are broadly consistent with the notion of boron as a cohesion enhancer and hydrogen as an embrittler.
Effect of Molybdenum on the Electronic Structure of Iron Grain Boundaries with Phosphorus and Boron
Authors: Krasko Genrich L.
Published: March 2011

We are reporting preliminary results on LMTO supercell calculations on a Σ3 (111) grain boundary (GB) in Fe with Mo atoms sitting at the GB plane. Calculations were performed both for the clean (CL) GB and GB with P/B atoms occupying centers of host (Fe and Mo) atom trigonal prisms (a coordination typical of the Fe GBs). The geometry of the GBs was not changed upon substituting Mo for Fe in the GB plane: all the interplanar distances and atomic radii were preserved (these were calculated earlier for the Fe GBs from GB3 relaxation modelling using the Embedded Atom Method). Comparison of the electron charge-density distributions within the atomic spheres for GBs with and without Mo, has shown that the presence of Mo at the GB plane increases both the number of d-electrons and the total charge density within atomic spheres of the atoms most important for intergranular cohesion. This should result in enhanced cohesion. The magnetic moments of the constituent atoms were also found to be strongly affected by the addition of Mo. The Mo atoms are anti-ferromagnetically coupled with the neighboring Fe atoms: mM0=-O.6OμB (CL GB), mMo=-O.14μB (GB with P), and mMo=-O.18μB (GB with B).