bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of Rapidly Solidified Nickel Base Superalloys Prepared by Melt Spinning and Plasma Deposition
Authors: Taub A.I. , Jackson M.R. , Huang S.C. , Hall E.L.
Published: March 2011

The microstructure and yield strength of two nickel base superalloys prepared by melt spinning and plasma deposition are compared in the as-solidified condition and after annealing. The results support the interpretation of the yield strengths obtained by tensile testing melt spun ribbon as representative of the values obtained for bulk specimens with equivalent microstructures. The effectiveness of grain size strengthening in a nickel base superalloy is also examined. The Hall-Petch relation appears to be obeyed, with a slope k = .77±.15 MPa−m1/2.
A Microstruciure Investigation on Rapidly Solidified Ni3Al Containing Boron
Authors: Ciiang K.M. , Huang S.C. , Taub A.I.
Published: March 2011

A small amount of boron addition in rapidly solidified Ni3Al has been found to yield remarkable improvements in bolh room-temperature strength and ductility. In this study, the microstructure of melt-spun Ni3Al ribbons with various boron modifications ranging from 0 to 6.0 at% was investigated in detail by using transmission electron microscopy. All alloy compositions studied reveal a completely ordered fcc L12matrix phase, in which polygonized dislocation networks and subgrain boundaries are observed. The boron-free Ni3Al contains a dispersion of an Al-rich martensitic phase consisting of alternate twins. The boron addition tends to suppress the formation of the martensitic phase, but excessive boron (≥ 2.0 at%) causes the precipitation of M23B6type borides.
Microstructure of Rapidly Solidified Cu-Fe Alloys
Authors: Köster Uwe , Caesar Christoph
Published: March 2011

Rapidly solidified ribbons of Cu-Fe alloys with iron contents up to 20 at.−% have been prepared by melt-spinning. Optical and electron microscopy as well as x-ray and electron diffraction techniques were used to characterize quantitatively the microstructure, i.e., grain size and shape, solubility of iron, lattice parameter, volume fraction and distribution of precipitated iron-particles, etc.

Whereas the free surfaces of melt-spun Cu-Fe ribbons have been found to be very smooth, the contact surfaces usually consist of isolated areas of good thermal contact with small equiaxed grains separated by bands without contact during casting and therefore poor heat transfer. The cross sections of the ribbons generally exhibit a strong anisotropy in their microstructure: very fine crystals adjacent to the contact surface develop into narrow columnar grains, generally significantly elongated and extending across the whole section. The average columnar width of the grains has been found to decrease significantly with increasing iron content. Precipitation of iron not only depends on the iron content but also on the distance from the contact surface.
The Effect of Quenching Variables on the Transformation Characteristics of Some Rsp Shape-Memory Alloys
Authors: Wood J.V.
Published: March 2011

Ribbons of a Cu-Al-Ni shape memory alloy have been rapidly solidified by planar flow casting. Attempts have been made to vary casting and secondary quench conditions in order to identify the predominant process variable in determining the subsequent β1↔γ1′ transformation temperatures. By varying wheel speed, wheel material and secondary quenching rate it is concluded that the large excess vacancy concentration has most influence on the as cast ribbon, but that after subsequent heat treatment, the grain size dominates.
Monte Carlo Simulations of Film Profile Evolution During Nonplanar CVD Processes
Authors: Coronell Daniel G. , Jensen Klavs F.
Published: March 2011

A Monte Carlo simulation approach has been developed to model transport and film profile evolution for rarefied gas flows during nonplanar CVD over trenches and contact holes. A systematic study of the effect of various parameters on the film conformality including intermolecular collisions, reactant sticking coefficient and feature geometry is reported.
X-Ray Grazing Angle Scattering and Fluorescence Studies of Interfacial Microstructures in Si1-xGex/Si Multilayers
Authors: Ming Z. H. , Krol A. , Soo Y. L. , Kao Y. H. , Park J. S. , Wang K. L.
Published: March 2011

Angular dependence of grazing incidence x-ray scattering and Ge fluorescence yield were measured for the heterostructures of Si1-xGex/Si and the inverted bilayer Si/Si1-xGex as well as two 10-period superlattices. Interfacial roughness, correlation of height fluctuations between interfaces and Ge density profiles in the multilayers were investigated.
Interface Roughness, Composition, and Alloying of Low-Order ALAS/GAAS Superlattices Studied by X-Ray Diffraction
Authors: Miller W. R. , Pellegrino Joseph G. , Comas James
Published: March 2011

Low-order, monolayer by monolayer (1×1) AlAs/GaAs superlattices grown by MBE using different growth techniques have been studied by X-ray diffractometry. High-resolution multiple-crystal diffractometry was used to study diffraction features near the [004] peaks due to the substrate and epilayers. Using this technique, we have investigated the effect of growth techniques on the strain and tilt of the superlattices. High-resolution X-ray diffraction (HRXRD) results suggest that the sample grown by migration-enhanced epitaxy (MEE) is more highly strained and has more tilt than the same superlattice sample grown using the interrupted growth (IG) technique.
Growth Morphologies of Steps on Vicinal Surfaces in Molecular-Beam Epitaxy
Authors: Xiao Rong-Fu
Published: March 2011

A Monte Carlo model has been used to study growth morphologies of steps on vicinal surfaces in molecular-beam epitaxy. The model accounts for molecule attachment, detachment, and surface diffusion. Through variation of surface temperature, impingement rate of source molecules, and the orientation of vicinal surface, we have explored the surface diffusion and the conditions under which two dimensional nucleation (2DN) growth and step flow (SF) growth occur. We have found optimum growth windows for 2DN growth and SF growth. For SF growth we have found that morphological stabilitity of steps are closely dependent on their step height. Steps with multi-molecular-layers are seen to be less stable than single-layer steps in a surface diffusion field, due to a decrease in the attachment of growth units from the upper terrace.
Stepped Surfaces and Internal Film Microstructures
Authors: Chernov A. A.
Published: March 2011

It is known since long ago that “birth defects” of crystals appearing during their nucleation and growth may hardly be eliminated by further “education,” like heat treatment. Even less hope, if any, exists for fabricating fancy device structures unless we use detailed techniques of crystal growth, techniques based on interfacial processes, and determine the real defect structure of the crystal or film.

These practical issues encourage those who are excited by the goal to penetrate into processes at solid surfaces and should encourage those who make decisions on funding this research.

In what follows I emphasize selected general issues that seem to be hot today and that have been addressed at Symposium B of the 1992 Fall MRS Meeting. Of course, the selection is a matter of taste.
Phases and Phase Transitions in the First Few Layers of Methane, Argon and Krypton Adsorbed on Graphite
Authors: Goodstein David , Day P. , LaMadrid M. , Lysek M.
Published: March 2011

The equilibrium phase diagrams of monolayers of many substances adsorbed on graphite have long been studied as examples of 2-dimensional (2D) matter. One typically observes 2D gas and liquid phases, and solid phases that may be commensurate or incommensurate with the substrate lattice. Many experimental techniques have been used, but thermodynamic measurements are generally the most useful for tracing out phase boundaries.

Recent advances in technique have made it possible to use thermodynamic measurements to study the phase diagrams of the second and higher layers, up to the fifth or sixth. These advances include ultra high resolution scanning calorimetry, and a detailed understanding of the role of capillary condensation in corners and pores of the graphite foam substrate. We find a rich array of phases and phase transitions in multilayer methane, argon and krypton. The second and third layers typically have distinct 2D gas, liquid and solid phases evidenced by 2D triple points and critical points. We observe phase transitions between solid phases that are commensurate and incommensurate with the layer below. We also observe melting of the first layer at higher temperatures, even when one to five additional layers are adsorbed on top of it.

In argon and krypton, but not in methane, a strange new phenomenon is observed at temperatures above the gas-liquid critical point of the nth layer for n> 3. Below that temperature, nthlayer gas coexists with a condensed nth layer. At some temperature above it, a new coexistence region is observed in which a partial nth layer coexists with a partial n + 1st layer. This behavior is thought to be evidence for a theoretically predicted phase transition of the bulk interface, called the preroughening transition.
Morphology of Monolayer Films Observed by Photoelectron and Low-Energy-Electron Microscopy
Authors: Mundschau M. , Bauer E. , Świech W.
Published: March 2011

Many of the fundamentals of epitaxial growth, long predicted by theories of crystal growth, have been seen during the molecular beam epitaxial growth of monolayer films. In general, high temperatures and low deposition flux favor nucleation at atomic steps. The opposite extreme of low temperature and high flux favors island nucleation in terraces, and steps play little role. For intermediate conditions a wide variety of growth morphology is seen. High temperatures and high flux have been seen to produce two-dimensional dendritic growth. Atomic steps on substrates have been observed to migrate during sublimation. Pinning of steps during migration gives rise to complex atomic step and terrace structures and a distribution of terrace widths. For terraces wider than the diffusion length of adsorbed atoms, nucleation of islands is favored in the terraces, whereas narrow terraces favor nucleation at the atomic steps. For a constant substrate temperature and deposition flux, morphology can vary profoundly depending upon local terrace width. Complex structures in monolayer films are produced during sublimation. These include lockeime or hole nuclei which are one atomic step deep. Steps are seen to oscillate during step flow apparently due to considerable mass transport between steps and terraces.
Defect-Mediated Growth of YBa2Cu3O7-δ Films
Authors: Schlom D. G. , Anselmetti D. , Bednorz J. G. , Gerber Ch. , Mannhar J.
Published: March 2011

The evolution of the surface microstructure of sputtered c-axis oriented epitaxial YBa2Cu3O7-δ films has been monitored by scanning tunneling microscopy (STM). The results indicate that growth is dominated by the incorporation of depositing species at defect sites. These defect sites, which provide energetically favorable positions for accommodating the arriving species, are at ledges—either along growth spirals emanating from screw dislocations, or due to the closely spaced surface steps arising from the macroscopic tilt of the substrate. If the substrate is misoriented sufficiently, the depositing species may diffuse to and be accommodated by these surface steps, without the supersaturation on the terraces attaining a high enough level for two-dimensional nucleation to occur. Under these conditions, growth occurs by step propagation. Otherwise, a high density of screw dislocations (≈109 cm-2) is nucleated during the initial stages of growth, which provides a continual supply of ledge incorporation sites in the vicinity of the depositing species. The surface evolution reported appears to be an intrinsic feature of c-axis oriented YBa2Cu3O7-δ films for a wide range of growth conditions, irrespective of the substrate material or vapor phase deposition method.
Irreversible Island Formation During Deposition: Island Size and Separation Distributions
Authors: Bartelt M. C. , Tringides M. C. , Evans J. W.
Published: March 2011

We present precise simulation results for a simplified model of irreversible nucleation and growth of islands during deposition. We characterize the scaling of the island and adatom densities, the complete island size distribution, and the adatom-island and island-island separation distributions, with the ratio of diffusion to deposition rates (for fixed coverages,θ<1). We also make some comparisons with rate equation predictions.
Microstructural Evolution During Epitaxial Growth of Chemically Derived Ba2YCu307-x. Thin Films
Authors: Mclntyre Paul C. , Cima Michael J.
Published: March 2011

Microstructure development in thin films of Ba2YCu3O7-x (BYC) synthesized on (001) LaA1O3 using an ex situ process was characterized by TEM and STEM examination of specimens quenched from different points in the growth heat treatment. The microchemistry of the growing oxide films was characterized by EDS in STEM. Phase development was also studied by X-ray diffraction. Several investigators have suggested that growth of BYC during ex situ processing occurs by nucleation and growth of BYC into an amorphous precursor film. Our observations indicate that this process involves growth into a substantially crystalline matrix. X-ray diffraction was used to identify three phases, BaF2, BaCuO2, and CuO, which are present prior to BYC nucleation. Nucleation of both c-axis normal and a-axis normal BYC occurred at approximately 760°C during rapid heating to 830°C in the growth heat treatment. Rapid growth of the c-axis normal material parallel to the substrate surface caused this orientation to become dominant in the fully converted films. Chemical microanalysis of the quenched films suggests that the BYC grows into an overlying layer that, after quenching, is composed of relatively large (25–100 nm diameter) yttrium- and copper-rich particles in a nanocrystalline barium-rich matrix.
Epitaxial Growth in Large Lattice Mismatch Systems: Characteristics of Domain Epitaxy
Authors: Zheleva Tsvetanka S. , Jagannadham K. , Narayan J.
Published: March 2011

The characteristics of epitaxial growth in large lattice mismatch TiN/Si and TiN/GaAs systems are analyzed. The epitaxial growth in these large mismatch systems is modelled in terms of various energy contributions to the epilayer. The new mode of growth, defined as domain epitaxial growth in these high mismatch systems is maintained by the formation of misfit dislocations at repeated intervals. The epitaxial relationship within the domain consists of n interplanar distances of the overlayer film closely matching with m interplanar distances of the substrate, where m and n are integers. The interfacial energy is found to be a very important term in determining the orientation relationships. The results of the model calculations are compared with the experimental observations.
Evaluation and Control of Plastic Deformation in GaAs Film on Si Substrate by Means of Crystal Plasticity Analysis
Authors: Ohashi Tetsuya
Published: March 2011

Dislocation accumulation in patterned gallium-arsenide film, which is deposited on silicon substrate and cooled down from the deposition to room temperature, is numerically simulated under a continuum mechanics approximation. A new approach to suppression of dislocation accumulation is proposed where selective growth of the film and partial doping of impurities into it are combined. The results show the possibility to keep the surface region of the film almost dislocation free.
Strain Distribution in Heterolayers with low Misfit as Revealed by Convergent Beam Illumination Methods
Authors: Ljjleental-Weber Zuzanna , Kaneyama T. , Terauchi M. , Tanaka M.
Published: March 2011

Convergent beam electron diffraction (CBED) was applied to the local measurement of lattice parameter across a strained interface with small mismatch. GaAs layers grown at low temperature with excess As (with 0.15% misfit) on a GaAs substrate were chosen for these studies. Tetragonal distortion was detected in the layer up to 0.5μm from the interface. With an increase of the layer thickness lowering of the symmetry of these CBED patterns was observed. This lowering of symmetry is most probably due to saturation of As solubility and the strain build into these layer.
In-situ X-ray Measurements of the Initial Epitaxy of Fe(001) Films on MgO(001)
Authors: Lairson Bruce M. , Payne A. P. , Brennan S. , Rensing N. M. , Daniels B. J. , Clemens B. M.
Published: March 2011

We have studied die evolution of the lattice parameter of epitaxial Fe(001) on MgO(001) vs. thickness between 1 and 200 monolayers using Grazing Incidence X-ray Scattering. We show that an interaction exists between the islanded film and the substrate, which allows the film to be incommensurate, even when the islands are too small to allow full dislocations to exist. For the conditions studied, the Fe lattice parameter increases toward the MgO lattice parameter with increasing thickness in the 1–10 monolayer coverage regime, and then relaxes back toward the bulk Fe lattice parameter at greater thicknesses. We employ a model for the interaction between film islands and the substrate which explains large changes in the lattice parameter of the Fe in the 1–10 monolayer thickness range. Relaxation at larger thicknesses is described by continuum elasticity theory.
An Investigation of the Structural Strains and the Breakdown of Poisson'S Effect in Lattice-Mismatched BCC(110)/FCC(111) Metallic Superlattices
Authors: Fartash A. , Schuller Ivan K. , Grimsditch M.
Published: March 2011

The strain profiles of individual layers of a selected group of stable bcc(110)/fcc(111) metallic superlattices which have been determined by x-ray diffraction methods are compared, and discussed in terms of a number of mechanisms proposed for explaining their anomalous properties. The superlattices in this group are distinguished in terms of a highly anisotropic lattice spacing mismatch of their adjoining bcc and fcc layers (∼20% vs. 3%). The most prominent structural feature of the bcc layers consists of a highly anisotropic in-plane contraction accompanied with a small out-of-plane strain. The fee layers are found to show large out-of-plane expansions which based on their small in-plane expansions cannot be explained within framework of standard elasticity theory.
A Study of Thin Films of Indium Tin Oxide Using Spectroscopic Ellipsometry
Authors: Maloney Colette , Bogdanova Arn N.
Published: March 2011

Transparent, electrically conducting, indium tin oxide films were prepared by r.f. reactive sputtering and electron beam evaporation. The refractive indices, n, and extinction coefficients, k, of the films together with their thicknesses were determined from spectroscopic (250nm–750nm) ellipsometry measurements. Elucidation of these parameters allowed an evaluation of the influence of the deposition conditions on the morphology, stoichionietry and microstructure of the films.

Using effective medium theory the effect of the oxygen concentration on the void content of the sputtered films could be modelled. At concentrations greater than 15–20%, a saturation in the optical properties was observed as the films approached ideal stoichionietry. The refractive indices of both annealed and untreated evaporated films exhibited a decrease with increasing substrate temperature (up to 300°C) which is consistent with an increase in the microcrystallite size. Measurements on the annealed samples revealed a blue-shift in both n and k spectra as the oxygen pressure during evaporation was reduced to the background value of about 106 mbar. This, we attribute to the Burstein-Moss shift associated with the increased number of oxygen vacancies.

Supplementary investigations using profilometry, atomic force microscopy and optical transmission spectroscopy confirm the reliability of the results obtained by this technique.
Microstructure and Defects in Implanted Hipox-Structures
Authors: David Theodore N. , Pegler Peter L.
Published: March 2011

High-pressure oxidation of silicon (HIPOX) is one of various techniques used for electrical-isolation of semiconductor-devices on silicon substrates. The effect of HIPOX-related stresses on isolation structures is of interest because structural-defects, if formed, could electrically degrade devices. The present investigation was performed to study the origin and behavior of defects in recessed HIPOX structures. The structures were exposed to a boron implant. The experimental observations indicate that glide dislocations arise when the following features are present: (i) HIPOX, (ii) recessed edge, (iii) boron implant. The origin and behavior of the defects are modelled and explained in terms of implant-induced dislocation-sources creating glide-dislocations in the structures. The microstructure of the structures described above, and defect-modelling is presented.
High-Resolution Electron Microscopy of Olivine-Magnetite Interfaces.
Authors: Mckernan Stuart , Barry Carter C.
Published: March 2011

In the oxidation of iron-rich olivine (Mg,Fe)2SiO4 at elevated temperatures interfaces between olivine and the magnetite spinel (Fe3O4) are formed. The orientation relation between these structures is such that the planar spacing for the principal low index planes are very closely matched in the two materials. Regions of different contrast are observed in the olivine up to 5–10 nm from the interface. It is proposed that this contrast is due to enhanced iron concentration in this region caused by the strain field around the magnetite precipitates.
A Study of Extended Defects in Silicon Crystals After Exposure to a Hydrogen Plasma
Authors: Chen Y. L. , Maher D. M.
Published: March 2011

The distribution, number density, and nature of extended defects in crystalline silicon which is exposed to plasma-generated atomic hydrogen at a temperature of 250°C are characterized by transmission electron microscopy. Cross-sectional and plan-view modes are used for these characterizations. Extended defects are typically detected in the near surface region of a < 001 > crystal and their number density may exceed 109 defects-cm2, depending on die plasma exposure time, wafer temperature, gas pressure, and power. These defects exhibit contrast features which are characteristic of small dislocation loops (> 50nm in dia) and the nature of their associated strain field is assessed by diffraction-contrast techniques. The relationship between loop-like contrast features and die so-called hydrogen-induced platelet is established by both diffraction-contrast and phase-contrast imaging techniques. The results show that loop-like and platelet-like images exhibit contrast features which are consistent with a compressive strain field and therefore it is concluded that the extended defects in this study are interstitial in nature.
High Spatial Resolution Tem Study of Thin Film Metal/6H-Sic Interfaces
Authors: Bow J. S. , Porter L. M. , Kim M. J. , Carpenter R. W. , Davis R. F.
Published: March 2011

Thin films of titanium, platinum, and hafnium were deposited on single crystal n-type, (0001) 6H-SiC at room temperature in UHV. Microstructure and chemistry of their interfaces were analyzed by high spatial resolution TEM imaging and spectroscopy. Ti5Si3and TiC were the two phases found in the reaction zone of Ti/SiC specimens annealed at 700°C. A carbon-containing amorphous layer formed between Pt and SiC when the annealing temperature went up to 750°C. There was no apparent reaction zone in Hf/SiC specimens annealed at 700°C for 60 min‥ The change of electrical properties of metal/6H-SiC devices was attributed to these new product phases.
Formation of Single Crystal Epitaxial β-FeSi2 Films on Si(001)
Authors: Konuma K. , Zagwijn P. M. , Vrijmoeth J. , Vlieg E. , Van Der Veen J. F.
Published: March 2011

Ultrathin (∼ 1.5 nm) epitaxial films of P-FeSi2were grown by two methods; by sequential deposition of ultrathin amorphous Si and Fe followed by annealing and by mere Fe deposition followed by annealing. During the various stages of the growth process the lattice structure, composition and morphology of the films were investigated by medium-energy ion scattering in conjunction with shadowing and blocking.

At RT the deposited Fe reacts with the Si(001) substrate and forms a continuous film of average composition FeSi for both growth methods. Upon annealing to 670 K a conversion into epitaxial β-FeSi2 takes place. β-FeSi2 films grown by mere Fe deposition are composites of two orientational domains. On the other hand, films grown by sequential Si and Fe deposition are essentially of single orientation (>90% A orientation).
Surface and Interface Morphology of Small Islands of TiSi2 and ZrSi2 ON (001) Silicon
Authors: Kropman B. L. , Sukow C. A. , Nemanich R. J.
Published: March 2011

The morphology of small islands of TiSi2 and ZrSi2 on Si(100) is investigated and compared to larger islands in terms of a solid state capillarity model. The silicide islands are formed by deposition of very thin layers of titanium and zirconium (3–50Å) followed by an anneal at high temperatures (700–1200 °C). SEM and cross-sectional HRTEM are used to study respectively the surface and interface morphology. It is found that the C49-phase for TiSi2 is stable for layers as thin as 8Å, and annealing temperatures as high as 1200°C. An explanation for the fact that the formed islands align parallel to the Si<110> directions is given in terms of interplanar lattice spacings.
Effect of the Crystallographic Orientation of Underlying Poly-Si on the Thermal Stability of the TiSi2 Film
Authors: Kim Y. W. , Kim I. K. , Lee N. I. , Ko J. W. , Ahn S. T. , Lee M. Y. , Lee J. G.
Published: March 2011

The effect of the crystallographic orientation of underlying poly-Si film on the thermal stability of the TiSi2 film was studied. Different preferred orientations of the poly-Si film were obtained by annealing poly-Si or amorphous Si films at various temperatures. The TiSi2 film was formed by the solid-state reaction of the Ti film sputtered on the poly-Si film. The thermal stability of the TiSi2 film was evaluated by changes in the sheet resistance and microstructural evolution during furnace anneals. The TiSi2 film on poly-Si with the <110> preferred orientation shows more stable conductivity during high temperature anneals than with the <111> orientation. The surface energy of underlying poly-Si is expected to influence the thermal stability of the TiSi2/poly-Si structure significantly. Better thermal stability of the TiSi2 film can be obtained by the higher surface energy of underlying poly-Si.
Evolution of Epitaxial SixGei1-x Alloys on Si(100) During Thermal Annealing a-Ge/Au Bilayers Deposited on Si Substrate
Authors: Ma Z. , Allen L. H.
Published: March 2011

Solid phase epitaxial (SPE) growth of SixGei1-x alloys on Si (100) was achieved by thermal annealing a-Ge/Au bilayers deposited on single crystal Si substrate in the temperature range of 280°C to 310°C. Growth dynamics was investigated using X-ray diffraction, Rutherford backscattering spectrometry, and cross-sectional transmission electron microscopy. Upon annealing, Ge atoms migrate along the grain boundaries of polycrystalline Au and the epitaxial growth initiates at localized triple points between two Au grains and Si substrate, simultaneously incorporating a small amount of Si dissolved in Au. The Au is gradually displaced into the top Ge layer. Individual single crystal SixGei1-x islands then grow laterally as well as vertically. Finally, the islands coalesce to form a uniform layer of epitaxial SixGe1-x alloy on the Si substrate. The amount of Si incorporated in the final epitaxial film was found to be dependent upon the annealing temperature.
Microstructural Characterization of Low Temperature GaAs(111)B MBE Growth by AFM and Tem
Authors: de Boer M. P. , Angelo J. E. , Dabiran A. M. , Cohen P. I. , Gerberich W. W.
Published: March 2011

Atomic Force Microscopy (AFM) images are correlated with Transmission Electron Microscopy (TEM) plan-view images in a structure consisting of <111> oriented GaAs layers grown by molecular beam epitaxy (MBE) at 500°C. We present results on the applicability of AFM, which requires short sample preparation and imaging time relative to TEM, in obtaining information on twin density and growth pits of these low temperature samples. Also, we discuss the behavior of twin boundaries by comparing plan-views and cross sectional TEM images.
Stringlike Chemisorption and Rapid Dissociation of As4 and Sb4 on Si(100)
Authors: Gryko J. , Allen R. E.
Published: March 2011

Dodson-type potentials have been constructed for As-As, Si-As, Sb-Sb, and Si-Sb interactions. The parameters were determined by fitting to the energies obtained in first-principles calculations for As-Si and Sb-Si clusters with a variety of geometries. These potentials have been applied in molecular dynamics simulations of As4 and Sb4 chemisorbing on Si(100) at high temperature (900K). We find that both molecules tend to chemisorb in stringlike configurations, and that dissociation into two dimers can occur within only a few picoseconds.
Effects of Initial Substrate Surface on Microstructure of Si3N4 Deposited by LPCVD
Authors: Lee Woo Y.
Published: March 2011

The morphology of Si3N4 deposited on Al2O3, BN, and SiC by low pressure chemical vapor deposition (LPCVD) was characterized as a function of deposition temperature. At 1200°C, faceted Si3N4 crystallites were deposited on SiC whereas Si3N4 deposited on the other substrates tended to be amorphous. With an increase in temperature to 1430°C, Si3N4 deposited on these substrates was polycrystalline. At this temperature, the microstructure of Si3N4 was not significantly influenced by the changes in substrate surface.
Early Homoepitaxy of Au and pt (100) with Surface-Embedded-Atom Potentials
Authors: Haftel Michael I. , Rosen Mervine
Published: March 2011

Using embedded atom potentials fit to both bulk and surface properties, we explore the submonolayer vapor deposition of Au and Pt onto reconstructed (100) surfaces with the MD code DAMSEL. The surface geometries are determined by computational annealing over .6 ns. Surface reconstruction has a strong influence on the effects of adatoms. In Au and Pt the deposited atoms are absorbed into the surface and surface structures form by atomic replacement sequences and collective motion over the surface and substrate. On Au the reconstructed corrugated surface evolves into one characterized by two-dimensional mounds as coverage is increased. On reconstructed Pt, which exhibits alternately quasihexagonal and bulk-like regions, adatoms initially form strings above the bulk-like regions parallel to the (110] corrugation rows. At about .5 monolayer coverage the quasihexagonal structure of the top substrate layer transitions to a bulk-like structure in both Au and Pt
The Influence of Diamond Surface Perfection on the Preferential Nucleation of SP2 Carbon During Methane Pyrolysis
Authors: Lin B. Y. , Beetz C. P. , Brown D. W. , Lincoln B. A.
Published: March 2011

We report a set of CH4 pyrolysis experiments in a UHV system on diamond surfaces having varying degrees of surface roughness or perfection. Scanning electron microscopy (SEM), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED) were used to examine the formation of graphite and the resulting surface morphologies. A (100) type Ha natural diamond having 3 sputtered craters on the surface was used as the substrate, sp2 carbon was formed preferentially on the structurally defective crater surfaces after ∼3×1010 L of CH4 exposure at 900°C, whereas essentially no sp2 carbon was found on the flat portions of the diamond surface. Similar experiments were also carried out on a polycrystalline CVD diamond film and sp2 carbon was formed on that surface afte ∼4×109 L of CH4 exposure at 900°C. These results indicate that structural defects on diamond surfaces are a crucial factor in the preferential nucleation of sp2 carbon during CH4 pyrolysis.
AFM Study of Nucleation and Void Formation in SiC Carbonization of Si
Authors: Li J. P. , Steckl A. J.
Published: March 2011

In this paper the nucleation mechanisms for SiC thin film growth are studied by rapid thermal CVD and atomic force microscopy (AFM). The nucleation mode was found to be strongly dependent on the hydrocarbon partial pressure in the gas stream, for a fixed reaction time. In the case of three-dimensional (island) growth at low precursor concentration, cross-sectional SEM micrographs indicate that no voids are present at the center of each nucleus (or island). Voids begin to form when two neighboring nuclei come in contact. AFM has shown that trenches are present in the Si substrate around each isolated nucleus. The trench depth increases with the diameter of the island. AFM analysis of films grown for a nominal reaction time of 1 sec at different propane concentrations indicates that: (1) SiC grain size and surface roughness decreases with increasing propane concentration; (2) SiC grain density increases with increasing propane concentration. Based on the above evidence, the following nucleation mechanism is proposed: (a) the initial nucleation density is determined by the precursor concentration in the reaction gas; b) each nucleus grows larger, both laterally and vertically, by consuming Si around it; (c) voids are formed when nuclei grow large enough to come in contact, and not at the original nucleation sites.
Electrochemical Sulfur Treatments of GaAs Using Na2S and (NH4)2S Solutions: A Surface Chemical Study
Authors: Yota J. , Burrows V. A.
Published: March 2011

Chemical sulfur treatments of GaAs have been shown to improve the GaAs surface electronic properties. These treatments result in lower surface state density, lower surface recombination velocity, and shifting or unpinning of the Fermi level, in addition to improvement in the performance of devices. However, there is still considerable controversy regarding the chemical nature of the surface film which results from this chemical sulfidation. It has been shown that this film is not stable chemically and electronically. The improved surface electronic properties decay with time and are sensitive to the chemical environment of the material. In this study, using surface infrared reflection spectroscopy (SIRS) and x-ray photoelectron spectroscopy (XPS), we have investigated the electrochemical sulfidation of GaAs as a possible new method to produce a GaAs surface that is stable chemically and electronically. We have found that anodic treatments with Na2S and (NH4S solutions result in the removal of the pre-existing oxide of GaAs and the formation of films comprising sulfur, sodium carbonate, ammonium thiosulfate, and sulfide and sulfur-oxygen compounds of arsenic. Rinsing the GaAs with water removes the bulk of the film, leaving behind a surface on which only arsenic sulfide was detected.
Surface Chemistry of GaAs(100) after Treatment with Aqueous H3PO4 Solution
Authors: Burrows V. A. , Kondapuram V. S. G.
Published: March 2011

The interaction of semiconductor surfaces with aqueous acid solutions is important in chemical cleaning and etching. Wet chemical treatments are advantageous because they cause little damage to the surface and do not usually require high temperatures. The surface chemistry of GaAs after treatment with phosphoric acid was studied using multiple internal reflection infrared spectroscopy. The treatment left behind a thin film containing several types of PxOy bonds. The chemical nature of the film was observed to change with time as new species would form on the surface.
Repair of Flat Panel Display Substrates by Laser Direct Writing of Metallic Platinum, Copper and Aluminum and Insulating Aluminum Oxide Utilizing Gas Phase Reactants
Authors: David Casey J. , Comunale Richard A.
Published: March 2011

The identification and repair of defects in flat panel displays (FPD's), most especially liquid crystal, are required to achieve acceptable manufacturing yields and reasonable costs. Laser cutting and laser direct writing, from gas phase reactants, are used to repair opens and shorts in conductor lines of FPD substrates (the LI laser repair system). This paper details platinum, copper and aluminum deposition processes including deposition parameters, conductivity data, Auger evaluations and microscopy characterizations. Life-study data on repaired, fully assembled FPD's will be presented. Also the laser direct-writing process for aluminum oxide, used to repair dielectric defects and to passivate metal repairs, will be described. Finally, a unique, localized vacuum system (SPOT VAC™ ), specifically engineered for laser deposition on large (500 × 500mm) flat substrates, will be detailed.
CBE Growth Characterization of GaAs and InGaAs by Rheed and RD
Authors: Paulsson G. , Junno B. , Samuelson L.
Published: March 2011

Triethylgallium, trimethylindium and tertiarybutylarsine have been used to grow GaAs and InGaAs on (OO1)GaAs. No pre-cracking was used so that the thermal decomposition of tertiarybutylarsine on GaAs could be studied. The growth has been monitored in-situ using reflection high-energy electron diffraction and reflectance-difference. A comparison ismade between the reflectance difference signal and the intensity of the reflection high-energy electron diffraction specular spot as the surface is transformed from As rich to Garich. Using the former technique similar growth transients have also been studied as a function of the temperature. It is found that the incorporation of small amounts of In (less than 5 per cent) in the buffer layer significantly improves the oscillatory behavior of the RD-signal when growth of GaAs is commenced. Finally, the growth dynamics of InGaAs isstudied using reflection high-energy electron diffraction.
Comparison of GaAs Metallization Systems for High Temperature Applications
Authors: Scofield J. , Liu S. , Smith S.
Published: March 2011

Transition metal-germanide/silicide based ohmic contact systems to n-type GaAs have been studied using current-voltage (I-V) and transmission line measurements (TLM). The effects of substituting various metals from groups IVB and VIB into the metallization stack have been compared, as well as the effects of using germanium or silicon. Rapid Thermal Annealing (RTA) was used to facilitate the reactions. Titanium and molybdenum were shown to be more effective metallizations than chromium, even though chromium readily forms a silicide or germanide. Germanium has been found to produce an ohmic contact of low resistivity, while metallization with silicon alone does not show ohmic behavior.
Surface Investigations of Germanium Chemical Vapor Deposition on Silicon
Authors: Greenlief C. Michael , Klug Debra-Ann , Du Wei , Keeling Lori A.
Published: March 2011

The adsorption and decomposition of several Ge-containing compounds on Si(100) have been investigated with the intent of elucidating the surface processes leading to the deposition of epitaxial Ge films from these gaseous sources. Exposure of digermane, Ge2H6/ to Si(100) at 110 K results in molecular adsorption and ab initio calculations are used to help interpret the low temperature ultraviolet photoelectron spectrum. Diethylgermane, GeH2Et2, chemisorbs dissociatively on Si(100) at 110 K. The adsorption products are GeH2 and adsorbed ethyl groups. Large exposures of GeH2Et2 result in the formation of a physisorbed layer of molecular GeH2Et2 on top of the dissociated layer. The surface ethyl groups thermally decompose near 670 K via a β-hydride elimination reaction evolving C2H4 into the gas phase. The interactions of Ge2H6 and GeH2Et2 with Si(100) are discussed and compared to similar experiments with GeH4 as the Ge-containing gas source.
Investigation of the Kinetics of Surface-Limited thin Film Growth of SiGe Alloys by CVD of Si2H6/Ge2 H6 Mixtures
Authors: Sharp J. W. , Eres Gyula
Published: March 2011

The kinetics of surface-limited thin film growth of SiGe alloys was investigated by time-resolved surface differential reflectometry. The source gas, mixtures of disilane and digermane in ratios from 1:1 to 6:1 in helium carrier gas, was delivered to a heated Si(001) substrate by a fast-acting pulsed molecular jet valve. The adsorption and desorption kinetics were determined from the surface differential reflectance signal obtained using a polarized, high-stability HeNe probe laser. Thin film growth was studied in the temperature range of 400–600°C on Si(001) substrates. Preferential incorporation of digermane into the film produces an alloy composition that depends upon but does not mirror the gas composition. For all gas mixtures, there is a strong temperature dependence of the rate at which the adsorption layer decomposes into film plus by-product. The kinetic data and the alloy compositions provide a basis for deducing some of the characteristics of the reaction sequence that leads to SiGe alloy thin film growth.
Surface Decomposition Kinetics of Organosilane Precursors to Silicon Carbide
Authors: Han Bin , Hudson John B. , Interrante Leonard V.
Published: March 2011

Reactive molecular beam scattering techniques with mass spectrometric detection have been used to characterize the kinetics and mechanism of the decomposition of two 1,3-disilacyclobutane precursors to SiC on the Si(100) surface to yield SiC and gas-phase byproducts. Both compounds adsorb and desorb without dissociation at ambient temperature. Reaction probability increases with increasing surface temperature to a maximum exceeding 0.8 at 1100 K. Both compounds yield large quantities of gas-phase intermediates, while only one produces a significant yield of SiC in the initial collision. In situ and ex situ analysis of the SiC film indicate that it is stoichiometric SiC. A combination of mass spectrometric detection with time of flight analysis of surface reaction products permits formulation of a reaction scheme involving a multistep surface decomposition sequence.
Ab Initio Computation of Thermochemistry and Kinetics in the Oxidation of Gas Phase Silicon Species
Authors: Zachariah Michael R. , Tsang Wing
Published: March 2011

Ab initio molecular orbital calculations coupled to RRKM reaction rate theory have been conducted on some important reactions involved in the oxidation of silane in a high-temperature/high H2O environment. The results indicate thatH2O acts as an oxygen donor to SiH2 to form H3SiOH or SiH2O. Subsequent reactions involve the formation of (HSiOOH, H2Si(OH)2,:Si(OH)2 or SiO). In turn SiO polymerizes into planar rings, without an activation energy barrier. A list of calculated thermochemical data are also presented for a number of equilibrium species.
Chemical Vapor Deposition of SiO2 from Ozone-Organosilane Mixtures near Atmospheric Pressure
Authors: Guinn K. V. , Mucha J. A.
Published: March 2011

The kinetics of deposition of SiO2 by the reaction of tetramethylsilane (TMS) with ozone (O3) has been studied over the temperature range 180 – 380° C and compared with available data for the same process using tetraethoxysilane (TEOS). Both processes exhibit the same activation energy (17 kcal/mole) below 300 ° C which falls-off at higher temperatures due to transport limitations. Transition from first- to zero-order kinetics occurs with increasing concentrations of TMS and O3, which gives an overall O3/TMS consumption ratio of 10 at 258° C and5 at 325° C. TEOS is estimated to be 5 times more reactive than TMS above 300° C and over 10 times more reactive in the kinetically-limited regime below 300° C. Results suggest that O3-induced SiO2 deposition proceeds via surface reactions and is limited by heterogeneous decomposition of ozone.
Effect of Thermal Degradation on the Adhesion of Polyimide'Silicon Interface
Authors: Chu Y Z. , Durning C. J.
Published: March 2011

The object of this work is to identify the most important structure features in the bonding of polyimide/silicon during the curing anddegradation. An essential tool for this work is a quantitative adhesion measurement which can relate the macroscopic adhesion strength to the microscopic interfacial structures. We apply the blister test forthis purpose. In particular, the test is applied to examine the effect of thermal history on the adhesion of PMDA-ODA polyimide on siliconsurface. Our studies show that the test is accurate and sensitive. The adhesion data reveal that increases in adhesion strength coincide with the formation of certain thermal degradation products as revealedin the earlier thermal degradation studies. This suggests a mechanismfor increases in adhesion strength with curing temperature, based on chemical and physical modification of the interface.
Chemical Spray Pyrolysis of Complex Thin Solid Films
Authors: Bates Clayton W. , Varner Elizabeth B. , Alshvang Svetlana , Summers Keith
Published: March 2011

Chemical spray pyrolysis (CSP) is a technique in which compounds of the constituents of the thin film to be fabricated are dissolved in an aqueous solution which is subsequently sprayed onto a heated substrate using nitrogen as the atomizing gas. At relatively low substrate temperatures (150–400°C) chemical reactions take place in which film formation of the desired compound occurs concomitantly with the release of volatile chemical reactants. The technique has advantages that include: (1) simplicity, (2) low cost and simple equipment, (3) the ability to prepare films over large areas with various shapes with relative ease and (4) the possibility of varying the physical properties through chemical means in known ways at modest temperatures. Results on the preparation of CuInSe2 which is a defect dominated semiconductor of technological interest are presented. Both n- and p- type materials were prepared with resistivities varying from 10−2 – 104 ohm-cm illustrating the use of the control of solution chemistry to produce films with reproducibly controlled properties.
Low Pressure Diamond Growth Using a Secondary Radical Source
Authors: Hukka Terttu I. , Rawles Robin E. , D'Evelyn Mark P.
Published: March 2011

A novel method for chemical vapor deposition and atomic layer epitaxyusing radical precursors under medium vacuum conditions is being developed. Fluorine atoms are generated by thermal dissociation in a hot tube and abstract hydrogen atoms from precursor molecules injected immediately downstream of the source, generating radicals with completechemical specificity. The radical precursors are then transported to the growing substrate surface under nearly collision-free conditions. To date we have grown diamond films from CCl3 or CH3 radicals together with atomic hydrogen, generated by injecting CHCI3 or CH4 and H2 into the F atom stream at reactor pressures between 10−4 and 10−2 Torn This approach should be ideal for low-temperature growth and atomic layer epitaxy: growth rates remain relatively high because activation energies for radical reactions are typically small and because the cycle times for atomic layer epitaxy can be reduced to die msec range by fast gas-stream switching, and contamination and segregation are minimized by keeping the surface “capped” by chemisorbed intermediates.
Surface Spectroscopic Studies of the Initial Stages of Diamond Growth on Si(100)
Authors: Jackman Richard B. , Chua Lye Hing , Foord John S.
Published: March 2011

The interaction of hot filament “activated” methane and hydrogen with Si(100) surfaces has been probed in situ for the first time, using Auger electron and thermal desorption spectroscopies. It is shown that hot filament activation of methane results in thechemisorption of acetylene and ethylene on Si (100). Atomic hydrogen drives a range of surface reactions within the adsorbed phases formed. In particular hydrogen abstraction is observed which results in the efficient conversion of ethylene to adsorbed acetylene, and further reactions take place between atomic hydrogen, acetylene and C1 species, resulting in the formation of C3 hydrocarbon species. The implications of this work for diamond film growth are considered, and die results are used to develop a model to describe die growth of sp3 hybridised hydrocarbon chains on the Si surface.