bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo Simulations of Growth Kinetics and Phase Transitions at Interfaces: Some Recent Results
Authors: Nielaba P. , Binder K.
Published: March 2011

In the first part Monte Carlo studies of the kinetics of multilayer adsorption (without screening) are described. The approach to the jamming coverage in each layer is asymptotically exponential. The jamming coverages approach the infinite-layer limit value according to a power law. In the second part, studies of phase transitions in two dimensional fluids are reviewed. With a combination of Monte Carlo and finite size scaling block analysis techniques, accurate values are obtained for the critical temperatures, coexistence densities and the compressibilities of an adsorbed fluid layer in an NVT ensemble.
Facet Formation on Single Crystal TiO2 Surfaces Studied by Atomic Force Microscopy
Authors: Antonik M. D. , Edwards J. C. , Lad R. J.
Published: March 2011

Atomic force microscopy (AFM) and low energy electron diffraction (LEED) have been used to study the faceting behavior on (001) and (100) surfaces of a TiO2 single crystal. On the TiO2 (001) surface, LEED patterns characteristic of {011} facet planes develop after annealing below 900 °C in agreement with previous studies, but AFM shows a complex surface morphology consisting of a large distribution of facet sizes and orientations. After annealing at 1300 °C, facets do not form but rather a network of 5 – 30 nm high ridges develops over the entire surface. These ridges may be the result of surface defects produced by changes in bulk stoichiometry during annealing. On the TiO2 (100) surface, facets are also observed after annealing below 900 °C. However, these facets have extremely small height to width aspect ratios and are not discernible with LEED.
Molecular Beam Epitaxial Growth of (Al,Ga)As Tilted Superlattices on Vicinal GaAs (110)
Authors: Krishnamurthy Mohan , Wassermeier M. , Weman H. , Merz J. L. , Petroffa P. M.
Published: March 2011

A study of the molecular beam epitaxial (MBE) growth on singular and vicinal (110) surfaces of GaAs is presented. Quantum well structures and tilted superlattices (TSL) were grown on substrates misoriented 0.5°-2° towards the nearest [010] and [111]A azimuths at growth temperatures ranging from 450° C to 600° C under different growth conditions. The structures were characterized by Nomarski optical microscopy, transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy.

Two types of faceting were observed on the surfaces. The structures grown at temperatures above 540°C and As beam fluxes below l×10-5 torr showed V-shaped facets pointing in the [001] direction and are attributed to As deficient island growth. Lower temperatures and higher As beam fluxes lead to surfaces with microfacets that are elongated along the respective step directions on the vicinal surface and are due to step bunching during growth. Their density and height decrease with decreasing vicinal angle and they disappear on the singular (110) surface. The photoluminescence of the GaAs quantum wells grown on these samples is redshifted with respect to that of the quantum wells grown on the flat surface. This is being ascribed to the fact that on the vicinal surface, the recombination takes place at the facets where the quantum wells are wider.

The contrast in the TEM images of the TSL show for the samples misoriented towards [010] that the lateral segregation to the step edges on this surface is appreciable. The TSL spacing and the tilt however show that during growth the vicinal surfaces tend towards a surface with smaller miscut.
Radio Frequency Power Dependence of Defect Density at Hydrogenated Amorphous Silicon Interface
Authors: Ihara Hisanori , Sakakubo Takeo , Nozaki Hidetoshi
Published: March 2011

A hydrogenated amorphous silicon (a-Si:H) interface fabrication technology for the plasma CVD method, which can produce low interface defect density, is presented. The relation between the interface defect density and radio frequency (RF) power was investigated. As a result, the difference between the interface defect density and the bulk defect density decreased with increasing the RF power. A high RF power (25 W) a-Si:H buffer layer 5 nm thick was deposited on the interface before depositing low RF power (5 W) a-Si:H layer with a low bulk defect density. It has been found that the ideal defect density distribution, which shows the uniform distribution with the very low defect density (4.2×1014 cm) from the i/i interface to the bulk, can be accomplished by 5 nm buffer layer.
In-Situ Studies of the Formation Sequence of Silicides During Vacuum (10-7 TORR)Thermal Annealing of TI/Polysilicon Bilayers
Authors: Ma Z. , Allen L. H. , Lee S.
Published: March 2011

The formation of suicides during the thermal reaction of Ti/polysilicon bilayers has been investigated using both in-stu four point sheet resistance measurements and ex-situ measurements including X-ray diffraction, cross-sectional transmission electron microscopy and Auger electron spectroscopy. For a series of samples annealed at a ramp rate of 10°C/min the following sequence of changes in the bilayers occurred. At temperatures exceeding 350°C and prior to the silicidation oxygen from the vacuum system diffuses into the Ti film forming a solid solution of Ti(O) with O levels up to 20 %. An amorphous TixSiy layer is the first major suicide reaction observed at temperatures near 440°C. The first major crystalline phase is observed at 500°C and identified as C49 TiSi2. This phase was found to coexist at these temperatures with the partially consumed Ti(O) and the amorphous TixSiy layers. Further annealing above 700 °C results in the final structural transformation from C49 TiSi2 to C54 TiSi2.
Structures and Properties of Quasi-Multilayered Nanocomposites
Authors: Motohiro T. , Watanabe Y. , Takeda Y. , Noda S. , Toklzakl T. , Nakamura A.
Published: March 2011

Vertical sections of multilayers (VSM) should provide excellent testing grounds for physics and chemistry on surfaces with densely populated heterogeneous interfaces. Although VSM can be obtained from usual horizontal multilayers stacks by crushing them into pieces or by partial ion etching through masks from the top surfaces, a better way to get VSM is to form vertical multilayers. Employing simultaneous oblique deposition of ZnTe and SiO2 from opposite azimuthal directions, we have obtained nanometer-scale heterogeneous structures with anisotropie optical properties for the light coming perpendicularly to the surface. TEM revealed that successive annealing caused relaxation and recrystalllzation of ZnTe in the framework of SiO2 porous nano-structure. The resultant mosaic image of dark ZnTe regions and bright Sio2 regions of 5–10 nm wide and 30nm (or more) long told the development of VSM over the substrate although the perfect periodicity and two-dimensionality were missing. The structural modification of these quasi-multilayers was studied making reference to the similar but horizontal system of ZnTe particles periodically buried between Sio2 isolation layers.
Interface Stabilization of W-N Coatings by Chromium Alloying
Authors: Knotek O. , Löftier F. , Barimani A.
Published: March 2011

New metastable materials can be deposited using low temperature physical vapour deposition (PVD) techniques. During reactive sputtering, the atoms condensing in an intermixed state attempt to achieve a stable configuration. Due to low mobility of the adatoms, equilibrium phases cannot form and metastable structures are observed. Reactive sputtering can be used to deposit films with different stoichiometries and structures in the W-N system. The metastable phases α-W. β-W. W2N and WN1−x are obtained. All coatings are, however, thermally unstable. At temperatures above 570 °C. all phases are transformed into the a-W modification. By alloying chromium to the coatings in the W-N system, it is possible to stabilize all tungsten and tungsten nitride modifications as well as the interface layer between the substrate and the thin films.
Wetting of a Smooth Substrate by Crystal
Authors: Courtemanche David J. , van Swol Frank
Published: March 2011

We report on a molecular dynamics (MD) study of the wetting state of a system of hard spheres near a smooth planar hard wall. A direct simulation at the melting point of a two-phase system between two walls develops all the way from complete wetting by fluid (cos(θ) = 0) via partial wetting state to a final arrangement of complete wetting by crystal (cos(θ) = 1). This implies that a hard sphere fluid spontaneously crystallizes at a smooth hard wall, contrary to existing beliefs.
Characterization of P+-Implanted Silicon
Authors: David Theodore N. , Knoch Lynnita , Christiansen Jim , Pan M.
Published: March 2011

Dopant species can interact in different ways with interfaces, layers of varied microstructures, and with extended-defects. An understanding of such interactions is relevant to semiconductor processing and device-fabrication. In this study, the behavior of phosphorus-implanted silicon wafers was characterized using transmission electron microscopy (TEM), for as-implanted as well as post-implant rapid thermal-anneal (RTA) conditions. The top layers of as-implanted wafers were found to be amorphized. A correlation was seen between the presence of the amorphous-to-crystalline silicon interface and a drop in phosphorus concentrations in depth-profiles obtained using SIMS (secondary-ion mass-spectrometry). Reasons for the drop in concentration are explored, one of which is a higher diffusivity for phosphorus in amorphous silicon than in crystalline silicon. The top layers of wafers subjected to a RTA had recrystallized. A band of extended defects was present in the vicinity of the original amorphous-to-crystalline silicon interface. A correlation was seen between the presence of these defects and a secondary peak in phosphorus concentrations (in depth profiles) obtained using SIMS. These effects are explained in terms of gettering of phosphorus to the extended-defects. The band of extended-defects consists of dislocation loops, point-defect clusters, and extended dislocations that arise due to coalescing of point defects followed by annealing of the resulting extended-defects. The point-defects themselves arise from the implantation.
Principles and Performance of a PC-Based Program for Simulation of Grazing Incidence X-Ray Reflectivity Profiles
Authors: Wormington M. , Bowen D. K. , Tanner B. K.
Published: March 2011

We describe PC- based software which calculates grazing incidence X-ray reflectivity profiles from model thin film structures, including interface grading. We discuss the mathematical principles of the model and benchmark tests for speed of operation on two PC compatible machines are presented. Curvature of the specimen results in selective loss of fringe visibility at low scattering vectors and is treated rigorously. We discuss the treatment of roughness and use a generalized formula that is valid at large and small values of the reflectivity; its effects are illustrated using the program.
Tilts in Thin Strained Layers.
Authors: Beanland Richard
Published: March 2011

There is considerable interest at present in the mechanisms of tilting of epitaxial films, such that low index planes in layer and substrate have slightly different orientations. There are two primary causes of this effect: a) coherency strains and b) the action of misfit dislocations. It is important to distinguish between the two effects, particularly in the case of strained layers used for band-gap engineering. Using a recent formulation of the Frank-Bilby equation for the dislocation content of interfaces, it is shown how planes may be rotated in coherent layers due to both the Poisson effect and anisotropic misfit. An advantage of the Frank-Bilby equation is that it allows consideration of semicoherent layers. It is shown that a side effect of misfit dislocation introduction can be to introduce a further rotation of the epitaxial layer. Both these effects have been measured experimentally. The amount and the sense of rotation is compared to theory.
The Influence of Grain Boundary Inclination on the Structure and Energy of Σ3 Twin Boundaries in Copper
Authors: Wolf Ulrich , Ernst F. , Muschik T. , Finnis M. W. , Fischmeister H. F.
Published: March 2011

In a combined theoretical and experimental study, the energies and structures of Σ3 [011] twin boundaries in Cu were investigated. The atomic structures and the grain boundary energies were calculated using the Embedded Atom Method (EAM). Grain boundary energies of welded Cu bicrystals of the same boundary orientations were also obtained by the thermal grooving technique. The atomic structure of the symmetric {211} incoherent twin boundary (SITB) was investigated by High Resolution Transmission Electron Microscopy (HRTEM). Calculated grain boundary energies γb plotted against the inclination angle Φ of the boundary plane relative to the {111} coherent twin boundary (CTB) plane show a mininmm for the CTB (Φ = 0°) and a second minimum at Φ = 82°. This dependence on the inclination is also confirmed by the measured energies. Common to all calculated boundary structures is a microface 11 ing into CTB and SITB segments with a symmetric orientation of the adjacent crystals. Additionally, strong relaxations occur for the grain boundaries near the second energy minimum. This relaxation can be interpreted as a sequence of stacking faults located almost perpendicular to the mean boundary plane. They are terminated by partial dislocations which form a small angle boundary. The most apparent feature of these structures is a bending of the {111} planes running across the boundary. The structural properties were confirmed by HRTEM.
Reactions at Solid Interfaces
Authors: Sinclair R. , Ko D. H. , Konno T. J. , Nolan T. P.
Published: March 2011

This article discusses some of the changes which can occur at interfaces due to reaction or annealing. For chemically unstable interfaces, the atomic recombinations result in formation of new phases, which can even be amorphous in the initial stages. When no further chemical evolution takes place, physical rearrangement can have important consequences on the structure and properties. Examples are drawn from work on Ti-Si, Pt-GaAs, Ti-Si-O-N, Al-Si and TiSi2-Si.
Accommodation of Substrate Steps in the Growth of CoSi2 on (lll)Si
Authors: Daykin A. C. , Kiely C. J. , Pond R. C.
Published: March 2011

Thin films of CoSi2 have been grown on (111) substrates of Si, and studied using transmission electron microscopy. In 2nm films, steps initially on the substrate were found to be transformed into interfacial dislocations following deposition of the films. The Burgers vectors of the dislocations were consistent with ½<101>, which includes a component ½[111] perpendicular to the interface. The contrast behaviour of these dislocations exhibited characteristic effects, which are consistent with the short-range displacement field of the defects resembling that of a disclination dipole.
Grain Boundary Structure Control for Intergranular Stress-Corrosion Resistance
Authors: Palumbo G. , King P. J. , Lichtenberger P. C. , Aust K. T. , Erb U.
Published: March 2011

A geometric model for intergranular stress corrosion cracking (IGSCC) is presented and used to evaluate the influence of grain boundary structure on the IGSCC resistance of polycrystalline materials. Preliminary observations regarding the structure of intergranular fracture paths in Alloy 600 C-ring specimens exposed to high temperature caustic media are noted to be consistent with the general predictions of the proposed geometric model and demonstrate that significant enhancement to bulk IGSCC resistance may be achieved through material processing considerations which result in (1) moderate increases in the frequency of structurally ‘special’ grain boundaries (i.e., interfaces close to low Σ CSL's) and (2) refinement in grain size.
Study of the Defect Levels and Interface Properties of CdTe and CdS Polycrystalline Thin Films
Authors: Abou-Elfotouh F. , Ashour S. , Alkuhaimi S. A. , Zhang J. , Dunlavy D. J. , Kazmerski L. L.
Published: March 2011

The properties (electrical and structural) and the defect levels dominating cadmium telluride (CdTe) films prepared by radio frequency (rf) planar magnetron sputtering, and electrochemical deposition have been determined and compared. The properties of the deposited CdTe film and the behavior of its interface with cadmium sulfide (CdS) depend strongly on the method of depositing the CdTe film, and on postdeposition heat treatments. These treatments determine various parameters crucial to the device performance, including the type and concentration of the dominant defects, interface states, and deep trap levels. Photoluminescence (PL) emission from p-type CdTe polycrystalline thin films and single crystals is reported at low temperatures (9–50 K) as well as at room temperature. The room temperature PL peak at 1.58 eV due to band-to-band recombination was observed for the first time in polycrystalline thin films. The peak location of the exciton emission is indicative of the structure perfection of the film, which is also related to the deviation from stoichiometry. The as-grown polycrystalline films are composed of a close-packed array of preferentially oriented (the [100], [110], and [111] axes aligned perpendicular to the substrate) single-crystal grains of a size in the range of 0.25–2.0 μm for the electrochemically deposited films (E-film) and 0.3–4.0 μm for rf sputtered material (rf-film). The resistivity of the heat treated E-film was substantially lower than that of the rf-film (ρ = 1.0–5.0 and 300–500 Ωcm). The performance of the CdS/(E-CdTe) devices is limited by deep levels, while the performance of die rf-CdTe device is affected by a high density of interface states.
Fracture Strengths of Individual Grain Boundaries in Ni3Ai Using a Miniaturized Disk Bend Test
Authors: Meyers Douglas E. , Ardell Alan J.
Published: March 2011

The results of our initial efforts at measuring the fracture strengths of grain boundaries In Ni3Al using a miniaturized disk-bend test are presented. The samples tested were 3 mm in diameter and between 150 and 300 μm thick. An Ingot of directlonally-solidlfled, boron-free Ni3Al containing 24% Al was annealed between 1300 and 1350 °C to induce grain growth, producing many grain boundaries In excess of 1.5 mm in length. Specimens were cut from these In such a way that one long grain boundary was located near a diameter of the specimen. The relative orientations of the grains on either side of the boundary were determined from electron channeling patterns. Low-angle boundaries are so strong they do not fracture; Instead the samples deform In a completely ductile manner. High-angle boundaries always fracture, but only after considerable plastic deformation of the two grains flanking them. Fracture is Indicated by a load drop in the load vs. displacement curves. A method involving extrapolation of the elastic portion of these curves to the displacement at fracture is used to estimate the fracture stresses. This procedure yields consistent values of the fracture strengths of high-angle boundaries. The measured stresses are large (∼2 to 3 GPa), but considerably smaller than those required for the fracture of special boundaries, as predicted by computer simulations. No correlation was found between the fracture stresses or loads and the geometry of the high-angle boundaries, many of which are close to, but deviate from, coincident site lattice orientations.
An Atomistic Study of Hydrogen Effects on the Fracture of Tilt Boundaries in Nickel.
Authors: Moody N. R. , Foiles S. M.
Published: March 2011

In this study, molecular dynamics simulations were used to fracture Σ9 tilt boundaries in nickel lattices containing a range of trap site hydrogen concentrations. These lattices were created in a previous study using Monte Carlo simulations and the Embedded Atom Method to duplicate room temperature exposure to a hydrogen environment. The molecular dynamics simulations were run at absolute zero to immobilize the hydrogen distributions for determination of trap site occupancy effects on grain boundary fracture. In all lattices, fracture began by the breaking of bonds next to polyhedral defect sites that characterize the boundary structure followed by rapid failure of the remaining bonds. The effect of hydrogen was to lower the stress for fracture from 18 GPa to a lower limiting value of 8 GPa as the trap sites along the boundary plane filled. The simulations showed that the atoms at these sites were the only atoms involved in the fracture process. Within the constraints imposed on these calculations, the results of this study showed that the ‘inherent’ effect of hydrogen in the absence of plastic deformation is to reduce the cohesive force between atoms across the boundary.
Atomic Structure of Internal Interfaces in A Ti3AI-TiAI Two-Phase Alloy
Authors: Penisson J. M. , Bonnet R. , Loubradou M. , Derder C.
Published: March 2011

TiAI/Ti3AI colonies in an as-cast Ti-40 at.%AI alloy have been studied using HREM. Their microstructures consist mainly of alternating parallel lamellae of y (TiAI, L10) and α2 (Ti3AI, DO19) phases. The γ phase is often twinned with extended boundaries {111] parallel to the adjacent Ti3AI-TiAI interphase boundaries. The detailed atomic structures of the two possible (111)-γ σ3a and (111)γ σ3b twin boundaries have been observed as well as the facetted (0001)α2//(11)γ interphase boundaries. The facetted boundaries contain transformation dislocations whose elastic displacement fields conform well to the fields computed from the Somigliana dislocation model.
Effects Of Rare-Earth On Properties Of Heat-Resistant Steels And Its Interaction With Interfaces
Authors: Jihua Xu , Guichun Han , Guorong Lu , Shuping He , Dasheng Jin
Published: March 2011

Effects of rare-earth (RE) addition on creep, workability and the scaling behavior of Cr-Si, Cr-Ni and Cr-Ni-N steels were investigated. By RE additions both the creep strength and the workability of the tested steels were increased and the spalling resistance was improved. Analysis snowed that RE atoms segregated to grain boundaries, inhibiting segregation of other harmful impurities, and enhanced the cohesive strength of grain boundaries. SEM, EDX, ICP and X-ray investigations of scales showed that although no RE oxides were formed, RE modified the constituent of the scales, promoted the formation of a dense and protective scale and enhanced the cohesion between the scale and the matrix.
Prediction of First Phase Formation at Au-METAL Interfaces Using the Effective Heat of Formation Model
Authors: Pretorius R. , Marais T. K. , Muller A. E. , Knoesen D.
Published: March 2011

The effective heat of formation model enables heats of formation to be calculated as a function of concentration. By choosing the effective concentration at the growth interface to be that of the liquidus minimum, the model correctly predicL. first phase formation for 14 binary systems for which experimental data was found, except for the Au-Cu system which does not have a well-defined minimum on the liquidus curve.
Grain Boundary Diffusivity Measurement Through Kinetic Analysis Of Discontinuous Precipitation
Authors: Manna I. , Jha J. N. , Pabi S. K. , Gust W.
Published: March 2011

Discontinuous precipitation involves formation of a two phase aggregate from a supersaturated solid solution behind a migrating boundary. It is established that the solute transport occurs primarily through the migrating boundary, called the reaction front. This report presents a systematic study of discontinuous precipitation in a Zn-Ag alloy and measurement of grain boundary chemical diffusivity of Ag in Zn-Ag using a suitable analytical model for the first time. The necessary kinetic parameters were determined by optical and scanning electron microscopes. The activation energy for boundary chemical diffusion of Ag in Zn-Ag has been estimated to be 65.8 kJ/mol.
Observations Of Grain Growth In Thin Films
Authors: Smith D. A. , Townsend S. J. , Nichols C. S.
Published: March 2011

Grain growth occurs during the deposition and subsequent processing of metallic films. Observation of the grain structure by scanning ion probe microscopy and grain growth by in situ transmission electron microscopy using a heating stage serves to define some characteristic grain structures and their evolution in pure metal and alloy films used for metallisation.
Morphology of Si/Tungsten-Silicide/Si Interlayers
Authors: David Theodore N. , Secco d'Aragona F. , Blackstone Scott
Published: March 2011

Tungsten and tungsten-silicides are of interest for semiconductor technology because of their refractory nature, low electrical-resistivity and high electromigration-resistance. This paper presents the first formation of buried tungsten-silicide layers in silicon, by proximity adhesion. The interlayers, created by a combination of chemical vapor-deposition (CVD) and proximity-adhesion were studied using transmission electron-microscopy (TEM). The behavior of the layers in the presence and absence of an adjacent silicon-dioxide interlayer was also investigated. Buried suicide layers were successfully formed with or without the adjacent silicon-dioxide. The suicide formed continuous layers with single grains encompassing the width of the interlayer. Individual grains were globular, with cusps at grain boundaries. This caused interlayer-thicknesses to be non-uniform, with lower thickness values being present at the cusps. Occasional voids were observed at grain-boundary cusps. The voids were smaller and less frequent in the presence of an adjacent oxide-layer, due to flow of the oxide during proximity adhesion. Electron-diffraction revealed a predominance of tungsten-disilicide in the interlayers, with some free tungsten being present. Stresses in the suicide layers caused occasional glide dislocations to propagate into the silicon substrate beneath the interlayers. The dislocations propagate only ∼100 nm into the substrate and therefore should not be detrimental to use of the buried layers. Occasional precipitates were observed at the end of glide-loops. These possibly arise due to excess tungsten from the interlayer diffusing down the glide dislocation to finally precipitate out as tungsten-silicide.
Microstructure and Properties of MoSi2/Nb Interfaces with and Without Alumina Coating
Authors: Xiao L. , Abbaschian R.
Published: March 2011

This study explores the relations between processing routes, microstructures and mechanical properties of the matrix/reinforcement interfaces in MoSi2/Nb composites. It was found that the fracture energy of the interfacial region depended on the interfacial bond strength, roughness of interface, and the nature of the interfacial compounds. The fracture energy between the oxide coating and intermetallic interfacial compounds was found to be lower than that between two intermetallics or between Nb and an intermetallic. Processing routes were found to affect the fracture energy of the interfacial region by changing interphase formation, changing microstructure of materials adjacent to the interface, or changing roughness of interface.
The Evolution of Titanium-Silicon Interfaces as Monitored by X-Ray Diffraction
Authors: Novet Thomas , McConnell John , Johnson David C.
Published: March 2011

Reactions in solids occur at interfaces. Following interfacial reactions has been difficult due to the small fraction of material making up the interfaces. In this paper, variable-temperature grazing x-ray diffraction is used to probe interfacial reactions in modulated ultra-thin film layered composites. This technique permits the monitoring of solid-state reactions in their earliest stages. The initial evolution of titanium-silicon interfaces within a superlattice is discussed. Our data suggest that the classical approach of modeling diffusion via Fick's laws is insufficient to describe the initial interdiffusion or mixing reaction at an interface.
CoSi2 Formation Through Co/Ti Multilayer Reacting with Si-(100) Substrate
Authors: Hong Feng , Patnaik Bijoy , Rozgonyi George A.
Published: March 2011

In this work, Co/Ti multilayers were deposited on Si-(100) substrates by dual source thermal evaporation. Oxygen was found to be selectively incorporated into the Ti layers during the deposition. The samples were then treated by a two step annealing process. A —6nm Co2Si + CoSi2 layer was formed at the original Ti/Si interface after a 550°C, 2hr. annealing. The Ti(O) layers acted as selective diffusion membrane for Co and Si during this interaction. The morphology of the suicide layer was dependent on the thickness of the Ti(O) barrier layer. Selective removal via wet etching of the upper layers and a 750°C annealing produced stoichiometric and uniform epitaxial cobalt disilicide with a reduced film resistivity. A very flat top surface with no sign of groving or agglomeration and a much improved interface with the Si substrates were obtained.
Variable Angle Spectroscopic Ellipsometric Characterization of Polycrystalline Silicon thin Film Multilayer Structures
Authors: Snyder Paul G. , Xiong Yi-Ming , Woollam John A. , Krosche Eric R.
Published: March 2011

Variable angle spectroscopie ellipsometry (VASE), a nondestructive optical technique, was used to characterize two different multilayer samples, each having a low-pressure chemical vapor deposited polycrystalline silicon (poly-Si) layer. Analysis of these samples by cross-sectional transmission electron microscopy (XTEM) revealed large changes in grain size, between the undoped, as-deposited, and doped, annealed poly-Si layers. Roughness at the top of the poly-Si layers was also observed by XTEM. These features, together with the other structure parameters (thickness and composition), were analyzed ellipsometrically by fitting the measured VASE spectra with appropriate multilayer models. Each composite layer (surface overlayer, interfacial layer, and poly-Si layer) was modeled as a physical mixture, using the Bruggeman effective medium approximation. The ellipsometrically determined thicknesses were in very good agreement with the corresponding results measured by XTEM. Furthermore, VASE analysis provided additional information about the relative fractions of the constituent materials in the different composite layers. Thus, it quantitatively characterized the surface and interracial properties, and also the doping and annealing effects on the microstructure of poly-Si layers.
Structural Studies Of (ZnSe/FeSe) Superlattices By Transmission Electron Microscopy
Authors: Park K. , Salamanca-Riba L. , Jonker B. T.
Published: March 2011

The structural properties of (ZnSe/FeSe) superlattices, grown with and without a ZnSe buffer layer on (001) G a As substrates by molecular beam epitaxy, have been studied by transmission electron microscopy. High quality (ZnSe/FeSe) superlattices are obtained when grown on a ZnSe buffer layer on (001) GaAs substrates. In contrast, nominal (ZnSe/FeSe) superlattices grown directly on (001) GaAs substrates without a buffer layer showed evidence for intermixing of the layers in the superlattice indicating that the superlattice is unstable. We observed a disordered structure and an ordered structure in the resulting Zn1−xFexSe solid solution. The ordered structure corresponds to chemical ordering of Zn and Fe atoms along the < 100 > and < 110 > directions. We have studied the effect of misfit strain in the (ZnSe/FeSe) superlattices on the film quality.
Electrical Resistivity And Crystal Structure Of Nickel-Based Multilayer Thin Films
Authors: Tan M. , Haftek E. , Waknis A. , Barnard J. A.
Published: March 2011

The electrical resistivity and crystal structure of three Ni-based periodic multilayer thin film systems (Al/Ni, Ti/Ni, and Cu/Ni) have been investigated. In each series of films the Ni layer thickness was systematically varied while the thickness of the ‘spacer’ layer (Al, Ti, or Cu) was fixed. In the Al/Ni and Ti/Ni systems films with very thin Ni layers (and consequently large volume fractions of spacer and ‘interfacial’ material) yielded very high resistivities which dropped rapidly with increasing Ni thickness. By contrast, the resistivity of Cu/Ni multilayers continuously increased with Ni layer thickness due to the decline in volume fraction of high conductivity Cu. Both the Al/Ni and Ti/Ni systems exhibit Ni(111) texture in the thicker Ni layer samples. As the Ni layer thickness decreases the Ni(111) peak loses intensity and broadens due to finer grain size and increasing disorder. Al-Ni and Ti-Ni compounds are also noted. In the Cu/Ni system, however, the sharpness of the Ni(111) peak passes through a minimum as the Ni layer thickness decreases but then increases for the thinnest Ni layer samples.
SOI Interface Structures in Selective Epitaxial Growth
Authors: Weng Zara S. , Gronsky R. , Lou J. C. , Oldham W. G.
Published: March 2011

Silicon-on-insulator structures were formed by the selective epitaxial growth (SEG) of silicon and the epitaxial lateral overgrowth (ELO) of oxide shapes using an LPCVD hot-walled reactor at 850°C. The homoepitaxial interface changed character with modifications of the gas composition during the in-situ pre-epitaxial bake at 900°C. HREM images show ellipsoid-shaped inclusions lying along the homoepitaxial interface for silicon growth conducted with no dichlorosilane (DCS) flow during the prebake in H2. SIMS analysis indicates a large oxygen, fluorine, and carbon concentration at the interface. For structures grown with a small DCS flow in addition to H2 during the prebake, the homoepitaxial structural defects and the oxygen, fluorine, and carbon peaks are removed.
Grain Growth Behaviour Of Nanocrystalline Nickel
Authors: El-Sherik A. M. , Boylan K. , Erb U. , Palumbo G. , Aust K. T.
Published: March 2011

The thermal stability of electrodeposited nanocrystalline Ni-1.2%P and Ni-0.12%S alloys is evaluated by in-situ electron microscopy studies. Isothermal grain size versus annealing time curves at 573K and 623K show an unexpected thermal stabilization in form of a transition from rapid initial grain growth to negligible grain growth. This behaviour is discussed in terms of the various grain boundary drag mechanisms which may be operative in these alloys.
Preparation And Sintering Studies Of Nanometer-Sized Polycrystalline ZrO2
Authors: Würschum R. , Soyez G. , Schaefer H.-E.
Published: March 2011

The present paper reports on the characterization and on sintering studies of nanometer-sized polycrystalline ZrO2 prepared by the technique of crystallite condensation, oxidation, and in-situ compaction. The annealing induced growth of crystallites as well as a transformation from the tetragonal to the monoclinic phase were observed. A rapid increase of the mass density and of the microhardness during annealing up to 1000 °C indicates attractive sintering characteristics. By means of positron lifetime spectroscopy the development of the pattern of structural free volumes during sintering was studied.
Equilibrium And Non-Equilibrium Metal-Ceramic Interfaces
Authors: Gao Y. , Merkle K. L.
Published: March 2011

Metal-ceramic interfaces in theimodynamic equilibrium (Au/ZrO2) and non-equilibrium (Au/MgO) have been studied by TEM and HREM. In the Au/ZrO2 system, ZrO2 precipitates formed by internal oxidation of a 7%Zr-Au alloy show a cubic ZrO2 phase. It appears that formation of the cubic ZrO2 is facilitated by alignment with the Au matrix. Most of the ZrO2 precipitates have a perfect cube-on-cube orientation relationship with the Au matrix. The large number of interfacial steps observed in a short-time annealing experiment indicate that the precipitates are formed by the ledge growth mechanism. The lowest interfacial energy is indicated by the dominance of closed-packed {111} Au/ZrO2 interfaces. In the Au/MgO system, composite films with small MgO smoke particles embedded in a Au matrix were prepared by a thin film technique. HREM observations show that most of the Au/MgO interfaces have a strong tendency to maintain a dense lattice structure across the interfaces irrespective of whether the interfaces are incoherent or semi-coherent. This indicates that there may be a relatively strong bond between MgO and Au.
Evaluation of the Interface Structure During Stranski-Krastanov Growth of GE(SI) on Si (001)
Authors: Albrecht M. , Strunk H. P. , Hansson P. O. , Bauser E.
Published: March 2011

The initial stages of heteroepitaxial growth of Ge0.85 Si0.15 on Si(001) grown from Bi solution (liquid phase epitaxy) are studid by transmission electron microscopy. Stranski-Krastanov growth is observed to take place. After growth of a pseudomorphic Ge0.85 Si0.15 layer of 4 monolayer thickness, islands form and grow pseudomorphically up to a thickness of 30 nm. Then first misfit dislocations form. The formation process of these dislocations is analyzed and discussed in terms of half loop nucleation at the surface and dislocation glide. Evidence for glide on (110) planes is put forward.
The Role Of Ion Species On The Adhesion Enhancement Of ION Beam Mixed Fe/Al2O3 Systems
Authors: Pawel J. E. , Mchargue C. J. , Romana L. J. , Horton L. L. , Wert J. J.
Published: March 2011

The role of the ion species on the adhesion enhancement of ion beam mixed Fe/Al2O3 systems has been investigated. The ion implantations were carried out after film deposition using Cr (300 keV), Fe (320 keV), or Ni (340 keV) ions. The adhesion of the films was measured by a pull test and a scratch test. While the three types of implantation result in similar ion concentration profiles (with the peak concentration at the interface) and similar damage profiles, the three species were not equally effective in improving the adhesion. The effects are proposed to be due to changes in the interfacial energy resulting from both the damage and the presence of the ion species at the interface.
Electronic And Structural Properties Of Interfaces Created By Potassium Deposition ON TiO2 (110) Surfaces
Authors: Lad R. J. , Dake L. S.
Published: March 2011

Potassium was deposited onto stoichiometric TiO2 (110) surfaces and the chemical bonding and structure were studied with UPS, XPS, LEED, and RHEED. Potassium interacts strongly with the oxygen anions of the TiO2 and reduces the valency of Ti cations at the interface. At submonolayer potassium coverages, a large charge transfer to the substrate causes a sharp drop in work function, a population of electronic states within the bulk TiO2 band gap, and surface band bending. After large potassium doses at 300 K, multilayers of K2O are formed by diffusion of oxygen anions from the substrate, creating a substoichiometric TiO2−x interface composition. No metallic potassium is present even after large doses. The K2O layers remain stable after annealing as high as 900 K, and LEED indicates that they are disordered. RHEED characterization is limited by the roughness of the stoichiometric TiO2 (110) surface.
Analytical Electron Microscopy And High-Resolution Electron Microscopy Studies Of Grain-Boundary Films In Silicon Nitride-Based Ceramics
Authors: Kleebe H.-J. , Rühle M.
Published: March 2011

The microstructures of post-sintered reaction-bonded Si3N4 materials (SRBSN) were investigated. The materials consist of large elongated β-Si3N4 grains embedded in a finegrained matrix. Amorphous secondary phases exist at triple grain junctions owing to the liquid phase sintering involved during densificacition. Those amorphous phases can be crystallized (nearly completely) by post-sintering heat treatment. Apart from these crystalline grain pockets the grains of all materials are covered with thin (<l-2 nm) amorphous intergranular films on both Si3N4/Si3N4 grain boundaries as well as on secondary-phase/Si3N4 phase boundaries. A control of the intergranular films is most desirable since they limit the high-temperature mechanical properties of Si3N4-based ceramics. Therefore, the required characterization was performed by analytical and high-resolution transmission electron microscopy (AEM/HREM). Si3N4 materials with different rare-earth and transition-element oxide additions were studied. AEM and HREM investigations revealed marked differences in thicknesses and chemical compositions of the different intergranular films depending on the system analyzed indicating a strong dependence of film thickness on chemical composition. However, a given composition of each investigated material showed a characteristic intergranular film thickness, independent of grain misorientation, with the only exception of low-energy grain boundaries. The thickness of the intergranular films was constant within 0.2 nm. In addition, the film thickness of phase boundaries was always greater (by 1–2 nm) compared to grain-boundary films.
Stress Effect on Oxidation Kinetics of Silicon with Different Surface Orientations
Authors: Imai Keitaro , Yamabe Kikuo
Published: March 2011

Thermal oxidation of different crystallographic surface orientations of Si reveals a complex rate behavior not only in the initial stage but also in sequential two step oxidation with high temperature annealing where enhanced oxidation is observed as well. These phenomena are explained by the reduction of oxygen solubility in SiO2 due to stress in the SiO2 film, which has been confirmed by isotope labeling oxidation with SIMS analysis.
An Anodic Process for the Determination of Grain Boundary and Film Thickness Strengthening Effects in Aluminum Films on Oxidized Silicon.
Authors: Venkatraman Ramnath , Bravman John C.
Published: March 2011

We have measured stress variations with temperature as a function of film thickness and a given grain size in pure Al and AI-0.5%Cu films on Si substrates. The variation in thickness for a given grain size is brought about by using the same film and the repeated controlled growth and dissolution of a barrier anodic oxide which can be grown uniformly on the film. Stress measurements were made as a function of temperature by measuring wafer curvature after successively removing each 0. Iμm of Al film. The components of strengthening due to the film thickness and the presence of grain boundaries were separated by assuming that the flow stress of the film is simply the sum of these two components. The observations are consistent with results obtained using lascr-rcflowed films in an earlier work. The variations of these two components with temperature, and under tension and compression is discussed.
Evolution of Intrinsic Stress During Nucleation and Growth of Polycrystalline Tungsten Films by Chemical Vapor Deposition.
Authors: Leusink G. J. , Oosterlaken T. G. M. , Janssen G. C. A. M. , Radelaar S.
Published: March 2011

We present in situ measurements of the intrinsic (growth) stress during nucleation and growth of thin tungsten films by chemical vapor deposition. It is shown that interfering stress sources, as recrystallization or plasic flow, do not contribute to the intrinsic stress in these films. This makes W-CVD a model system for the experimental study of the relation between the evolution of microstructure and the development ofgrowth stress.
Structure and Dose Effects on Ion Beam Modification of Polymers
Authors: Rao G. R. , Lee E. H. , Mansur L. K.
Published: March 2011

Polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethersulfone (PES) were implanted with 200 keV boron ions at three different doses. PS was also implanted with 100 keV boron. A nanoindentation technique and reciprocating sliding wear tests were used to characterize mechanical properties of the implanted polymers. The results showed that hardness increased with increasing dose as well as increasing energy. The percentage increase in hardness was reduced with increasing complexity of the side groups although absolute hardness values were higher. With increasing complexity of the main backbone, polymer chain, the percentage increase in hardness as well as numerical hardness values were lower. These effects were attributed to the relative contributions of cross-linking and chain scission which were viewed as competing processes. Wear tests showed that in general, a lower or intermediate implant dose yielded the best improvement in wear resistance. No specific trends were observed for relating friction coefficient values and improved wear resistance. The results indicate that wear is a complex phenomenon which has a sensitive dependence on hardness and elastic properties of the mating surfaces.
Determination of Strain Distributions in Aluminum Thin Films as a Function of Temperature by the use of Synchrotron Grazing Incidence X-Ray Scattering
Authors: Venkatraman Ramnath , Besser Paul R. , Brennan Sean , Bravman John C.
Published: March 2011

We have measured elastic strain distributions with depth as a function of temperature in Al thin films of various thicknesses on oxidized silicon using synchrotron grazing incidence X-ray scattering (GIXS). Disregarding minor surface relaxation effects that depend on the film thickness, it is shown that there are no gross strain gradients in these films in the range of temperatures (between room temperature and 400°C) considered. We also observe X-ray line broadening effects, suggesting an accumulation of dislocations on cooling the films, and their annealing out as the films are reheated.
Calculation of Stress Gradients in Thin Al-0.5%Cu/Ti Lines from Strain Gradients Measured as a Function of Temperature Using Grazing Incidence X-Ray Scattering
Authors: Besser Paul , Venkatraman Ramnath , Brennen Sean , Bravman John
Published: March 2011

Strain gradients in Al-0.5%Cu lines on a 1000Å Ti barrier layer have been measured during thermal cycling from room temperature to 400°C using X-rays from a Synchrotron Source in the Crazing Incidence Geometry. The stress gradient calculated from the strain gradient is shown at four temperatures during thermal cycling. The surface of the line is relaxed relative to the bulk during heating and more stressed during cooling. It was also found that the width direction of the line supports essentially no stress throughout the thermal cycle and that the much of the stress along the length of the line is relaxed during the first few minutes at elevated temperatures.
Effect of Initial Substrate Curvature on Nonlinear Bending Measurements of Thin-Film Stress.
Authors: Fahnline D. E.
Published: March 2011

A recently reported nonlinear model of the bending of a thin-film/substrate bilayer provides a means for determining stress in thin films even for large deflection and ellipsoidal bending. This model replaces the usual Stoney's equation, which is valid only for small deflections. However, the model omits consideration of the commonly observed initial curvature of the substrate before deposition. In the small deflection regime the principle of superposition justifies simply subtracting the initial curvature from the final curvature after deposition, but for large deflections this is inappropriate, because the principle of superposition is no longer valid. The present paper presents a modified form of the nonlinear model incorporating initial substrate bending. The resulting equations show that initial substrate curvature causes magnified nonlinear effects and provide a means for determining film and substrate elastic properties in addition to thin-film stress.
Influence of Adsorbate Monolayer on the Nano-Mechanics of TIP-Substrate Interactions
Authors: Rafii-Tabar H. , Pethica J. B. , Sutton A. P.
Published: March 2011

We employ constant temperature molecular dynamics simulations to study, at the atomistic level, the interactions of an Ir tip with a Pb substrate. We have considered the complete cycle of approach.contact, indentation and retraction of the tip from the substrate. We have observed the wetting of the tip by the substrate atoms, and the formation of atomic necking between the tip and the substrate.

We have carried out further simulations to study the interactions of an Ir tip with an Ir substrate covered with an adsorbate monolayer of Pb film. We show that the introduction of the adsorbate considerably reduces the work of adhesion and the extent of plastic flow, in agreement with experimental results.

Three-dimensional geometries have been generated on computer and used for the animation of the simulation runs.