bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Characterization of Buried Ingaas/GaAs Wires Overgrown by MBE
Authors: Pieger K. , Straka J. , Gréus Ch. , Forchel A.
Published: March 2011

We have prepared buried InGaAs/GaAs wires by high resolution electron beam lithography, wet chemical etching and subsequent MBE overgrowth. Wires with lateral widths of less than 40nm have been realized.

For optimized regrowth conditions such as growth temperature, growth rate, III/V ratio, and arsenic flux a smooth surface morphology of the 100nm thick overgrown (Al)GaAs layer is obtained.

Etched only ultra narrow wires show a decrease of radiative recombination due to process induced defects and surface recombination at the open sidewalls. Optical investigations of narrow overgrown wires show a significant enhancement (up to two orders of magnitude) of the photoluminescence intensity. This is due to the disappearance of the open sidewalls and carrier capture from the overgrown barrier.

From studies of the influence of the crystallographic orientation on the quantum efficiency we find, that <111>B surfaces of the <011> wires offer the best conditions for MBE overgrowth.
Interfacial Effects in Polycaproamide-Aramide Polymer Systems
Authors: Dmitrenko Vladimir P.
Published: March 2011

The peculiarity of interdiffusion and phase equilibrium has been studied for poly-m-phenyleneisophthalamide and poly-p-amidobenzimidazole systems during formation of a transitional layer in conditions of organoplastics. The investigation of this process has been based on the method of electron-probe X-ray spectral microanalysis. The effect of temperature, pressure and time of thermal treatment on dimensions of diffusional zones and kinetics of their formation was shown. The parameters of solubility and mutual diffusion of components were determined and phase diagrams were obtained.
Adhesion of Tungsten Fine Lines on SiO2 by Micro-Wedge Scratching
Authors: de Boer M. P. , Huang H. , Nelson J. C. , Wang F. , Gerberich W. W.
Published: March 2011

Microscratch testing of thin films has mainly been done with a conical tip. In the wedge scratch technique introduced in this paper, thin film fine lines are scratched by a wedge-shaped diamond tip until a spallation occurs. A near plane strain situation arises, and finite element method (FEM) analysis is applied for more accurate evaluation of the work of adhesion. The material system used to demonstrate the micro-wedge scratch technique is rf-sputtered tungsten on thermally grown SiO2. When scratching a long line, delamination occurs by two mechanisms. At loads above 8-9mN/µm (normal load per unit line width), tensile stresses behind the indenter tip cause the tungsten to crack, and the thin film subsequently curls up. At loads above 1lmN/µm, high shear stresses in front of the indenter cause delamination of the tungsten at the interface. This latter event is modeled by FEM using a bimaterial fracture mechanics approach to obtain a practical work of adhesion value.
Characterization of Ti/TiN Films and SiO2/Ti Interfaces by Use of X-Ray Photoelectron Spectroscopy
Authors: Bernard Joffre , Adem Ercan , Ramaswami Seshadri
Published: March 2011

The deposition and processing of thin films, such as barrier metals and anti-reflective coatings, can be enhanced using the information provided by various surface analysis techniques. We will show the application of x-ray photoelectron spectroscopy(XPS) to the production of Ti and TiN films suitable for use in ULSI CMOS integrated circuits. XPS can separate Ti and N photoelectron peaks and detect low (1.0-5.0 atomic%) contamination levels while providing surface and interface chemical state information. In this paper we will show that a) the effect of TiN deposition on subsequent Ti film quality from the same Ti target was determined to be minimal, b) the relation of anneal temperature to the extent of SiO2 reduction by Ti metal was characterized on SiO2/Ti/TiN structures for temperatures from 600°C to 800°C, and c) the absorption of O into TiN films from ambient air was detected and confirmed.
STM Studies of Ultra-Thin Overlayers of Cu on SrTiO3(001) Surfaces
Authors: Liang Yong , Carroll D. L. , Bonnell Dawn A.
Published: March 2011

Scanning tunneling microscopy has been used to study the initial stage of Cu growth on SrTi03(001) surfaces. Our STM results show that Cu grows initially into 3-D island-like structures. Two different morphologies were observed. In some areas loosely bound individual Cu islands appear preferentially attached to step edges. The islands were frequently relocated by the STM tip during the scanning as a result of tip-surface interaction. Other areas have higher densities of Cu islands that exhibit a narrow size distribution with an average diameter of 70 Å and are homogeneously distributed on those areas. The driving force for the morphological evolution of Cu on the SrTiO3(001) surface is discussed in terms of surface free energy and interfacial interaction of metal on transition metal oxide surfaces.
Microstructural Evolution and Stress Relaxation in Sputtered Tungsten Films
Authors: Ross F. M. , Kola R. R. , Hull R. , Bean J. C.
Published: March 2011

We have investigated the relationship between microstructure and stress in very thin sputtered W films. We discuss features of the microstructure, in particular the presence of voids in compressively stressed films, in terms of the evolution of the structure from a metastable β-phase. By developing a novel specimen geometry for the transmission electron microscope (TEM), we present dynamic observations of the β-W→α-W transformation.
The Role of Gel Processing in The Preparation of Catalyst Supports
Authors: Cairns J.A. , Segal D.L. , Woodhead J.L.
Published: March 2011

Catalyst supports are required to meet a wide range of objectives, including chemical purity and composition, optimised surface area/porosity and thermal stability. Gel processing offers means by which many of these requirements can be achieved. In addition, the use of sols of controlled rheology allows the support material to be prepared in a form which facilitates its application to substrates (including metals) as a coating, thereby greatly improving its versatility for producing novel catalysts. The preparation of typical support materials will be discussed, together with examples of their use in catalysis.
Synthesis, Characterization, and Processing of Monosized Ceramic Powders
Authors: Fegley Bruce , Barringer Eric A.
Published: March 2011

Controlled alkoxide hydrolysis reactions for the synthesis of monodispersed oxide powders are described. The chemical and physical properties of representative monodispersed powders of TiO2, doped TiO2, ZrO2, doped ZrO2, SiO2, doped SiO2, and ZrO2-Al2O3 are described. The importance of surface chemistry for control of powder dispersion and packing is discussed and related to the control of sintered microstructures.
Lead Zirconate-Lead Titanate (PZT) Ceramics From Organic-Derived Precursors
Authors: Dosch R. G.
Published: March 2011

Organic-derived precursors can facilitate the preparation of PZT ceramics, particularly in the areas of processing and batch reproducibility. The use of partially alkoxide-derived precursors and completely organic-derived precursors has been studied. Two methods of alkoxide hydrolysis were evaluated for preparing zirconia which included direct hydrolysis in water and hydrolysis of alkoxide-base reaction products in acetone-H2O mixtures. The chemistry of these methods is discussed along with pertinent aqueous surface chemistry of the hydrated zirconia products. This work suggests that alkoxide-derived precursor properties are related to the solution chemistry used in their preparation.
Chemical Analyses of Sol/Gel Surfaces and Thin Films
Authors: Pantano Carlo G. , Houser C. A. , Brow R. K.
Published: March 2011

The application of surface analysis techniques to the characterization of sol/gel surfaces and thin films is described. Secondary-ion mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS) and sputter-induced photon spectroscopy (SIPS) are used to measure the composition of multicomponent silicate films, the relative water content of alumina films, the nitrogen content of ammonia treated silica films, and the depth profiles for films on black chrome. The determination of chemical structure using XPS and SIMS is also discussed. Finally, a brief introduction to temperature-programmed desorption (TPD) and its potential for studying surface chemical reactions, in situ, is presented.
In Situ FT-IR Studies of Oxide and Oxynitride Sol-Gel-Derived Thin Films
Authors: Haaland David M. , Jeffrey Brinker C.
Published: March 2011

A high-temperature infrared cell was developed to study the gel-to-glass conversion of sol-gel-derived thin films. FT-IR spectra of matched thin-film borosilicate sol-gel samples were taken as the samples were heated at 100°C intervals to 700°C in either air or ammonia. The gels were converted to oxide and oxynitride glasses, respectively, by these heat treatments. The gel-to-glass conversion could be followed and compared for these two treatments by monitoring changes in the vibrational bands present in the spectra. Comparisons between the infrared spectra of NH3-treated and air-treated films heated above 500°C reveal the appearance of new B-N bonds at the expense of B-O-Si bonds for the NH3-fired films. These spectra also exhibit changes which may indicate the formation of Si-N bonds. Thus, ammonolysis reactions can result in thin-film oxynitride glass formation at relatively low temperatures.
Characterisation of Concentrated Colloidal Suspensions for Ceramic Processing
Authors: Stewart R F , Sutton D
Published: March 2011

Characterisation and control of the structure and properties of particulate solids suspensions is of widespread importance with respect to many operations, such as separation, dispersion and densification in the ceramics and related industries. In this paper we describe techniques which have been used to study the effects of changes in basic parameters, for example solids content, particle size, electrolyte concentration and added polymer on the aggregated suspension morphology and characteristics. Suspension morphology was examined by a number of methods, notably freeze-etch microscopy. The mechanical properties of suspensions such as their compressional modulus and rheological behaviour was also examined.
Tetraethylorthosilicate (Teos)
Authors: Klein L. C. , Garvey G. J.
Published: March 2011

Two series of gels were prepared by hydrolyzing TEOS with HCl or NH4OH catalyst. In the first series, the molar ratio of water to TEOS was 4:1 and the catalyst addition was (1 × 10−3), (4 × 10−3), (1 × 10−2), (4 × 10−2), and (1 × 10−1). In the second series, the catalyst addition was (1 × 10−3) moles and the molar ratio of water to TEOS was 2:1, 4:1, 8:1, 16:1, and 32:1. Dried samples were characterized for surface area, porosity and C and H content. Samples were heated to 800°C and thermogravimetric weight loss was recorded. Both HCl and NH4OH are catalysts for hydrolysis, but during polymerization, the relative rates of hydrolysis and condensation determine resulting dried microstructures.
Sol-Gel Derived Ceramic-Ceramic Composites using Short Fibers
Authors: Lannutti J. J. , Clark D. E.
Published: March 2011

Short ceramic fibers or whiskers may be ideally suited for the fabrication of ceramic-ceramic composites using the sol-gel process. The fibers can be uniformly dispersed in a low viscosity sol and then frozen into the matrix through gelation. Several ceramic composites were prepared by synthesizing an Al2O3 precursor from aluminum sec-butoxide and then dispersing fibers of either zirconia, graphite or SiC. The composites were dried at room temperature and fired up to 1200°C. The fibers reduce the volume shrinkages in comparison to that obtained with pure Al2O3 during processing. Structures with dimensions of several cm2 can be rapidly produced with this method without cracking.
Long Fiber Reinforced Sol-Gel Derived Al2O3 Composites
Authors: Lannutti J. J. , Clark D. E.
Published: March 2011

A simple casting technique was used to fabricate composites comprised of long fibers in an alumina matrix. Random fiber preforms were placed in trays and subsequently a liquid alumina sol was added and gelled. Dried sheets approximately 6 cm in diameter and 0.2 cm thick were prepared without cracking. The addition of glycerol to the sol improved drying properties, made the dry gel flexible, and permitted the lamination (plying) of several sheets.
The Ceramist as Chemist - Opportunities for New Materials
Authors: Uhlmann D. R. , Zelinski B.J.J. , Wnek G.E.
Published: March 2011

The use of sol-gel techniques to prepare glasses and crystalline ceramics offers outstanding opportunity for breakthroughs in technology. The areas of particular promise include novel glasses; crystallineceramics with exceptional microstructures; coatings for modification of electrical, optical, mechanical and chemical properties; porous media with high surface area and tailored chemistry; ceramic powders with high chemical homogeneity and narrow distributions of particle size; matrix materials in ceramicceramic composites; and a wide spectrum of specialty ceramic materials, ranging from abrasives and fibers to glass ceramics and films. Opportunities in each of these areas will be discussed and related to the advances in understanding and process technology required for their achievement. The theses will be advanced that creative chemistry provides the key to many of these advances, that ceramists simply MUST learn more chemistry, but that we dare not rest from our labors when the chemistry is done.
Local Structure Surrounding Implanted As+ Ions in Polysulfone Films
Authors: Mayanovic R. A. , Feng Y. , Groh K. W. , Wang Y. , Giedd R. E. , Moss M.G.
Published: March 2011

Results from As K-edge XAFS studies on polysulfone films implanted with 50 KeV As+ in the dose range of 1015 to 1016 ions/cm2 indicate that As reacts chemically with O atoms to form As- (3) 0 based molecular structures having As-0 bond lengths equal to 1.81±0.02 Å. In comparison to samples implanted in the dose range 101S to 1016 ions/cm2, the molecular environment surrounding As in polysulfone implanted at 1017 ions/cm2 has additional structure beyond the nearest-neighbor O atoms.
Structural Analysis of Amorphous Phosphates Using High Performance Liquid Chromatography
Authors: Sales B. C. , Boatner L. A. , Chakoumakos B. C. , Mccallum J. C. , Ramey J. O. , Zuhr R. A.
Published: March 2011

The technique of high-performance liquid chromatography (HPLC) provides unique detailed information regarding the structure of partially disordered or amorphous phosphate solids. Applications of the experimental technique of HPLC to phosphate solids are reviewed, and examples of the type of information that can be obtained with HPLC are presented.
Generalized Activation Energy Spectrum Theory: A New Approach for modeling Structural Relaxation in Amorphous Solids
Authors: Shin Jung H. , Atwater Harry A.
Published: March 2011

A general approach to the dynamics of structural relaxation in amorphous solids is developed. A form of the recombination kinetics of defects is chosen which removes the ad hoc assumption made in previous theories that defects recombine only with others of identical activation energy. The generalized theory is tested quantitatively by modelling the structural relaxation of amorphous silicon, and comparing the results with the experimental data on structural relaxation. It is found that the generalized theory is necessary in order to accurately describe the time-resolved relaxation data. The generalized theory is also applied to estimate the effect of irradiation on the nucleation kinetics of crystal silicon, and is found to agree well with experimental data.
Relaxation of New-Tpi Thermoplastic Polyimide Studied by Thermally Stimulated Depolarization Current
Authors: Lu Sharon X. , Russell Wendy C. , Cebe Peggy
Published: March 2011

Semicrystalline polyimide, Regulus™ NEW-TPI, is a thermoplastic polyimide produced by mitsui Toatsu. This aromatic polyimide possesses outstanding heat resistance, high tensile strength, excellent electrical properties, and strong solvent resistance. It has become the subject of recent study in our group [1–6] and others [7–13]. The flexible ether and meta linkages in the monomer unit lower its glass transition temperature (Tg) to 250°C in quenched amorphous material.
Strain Relaxation and Oxide Formation on Annealed W/C Multilayers
Authors: Geisz J. F. , Phang Y. H. , Kuech T. F. , Lagally M. G. , Cardone F. , Potemski R. M.
Published: March 2011

Tungsten-carbon (W/C) Multilayer structures are used as X-ray mirrors and other optical elements. The optical properties of such elements are highly sensitive to changes in strain due to thermal processing. Sensitive curvature measurements were performed on 40A period W/C Multilayer structures on Si substrates using a two beam laser reflection technique. A compressive stress of approximately 1530 MPa was measured in these sputtered multilayer films. Thermal annealing to 500 C in air and under vacuum resulted in very little strain relaxation in the multilayers but X-ray diffraction data show a slight increase of the multilayer period. Significant strain relaxation, though, was observed when a 400Å W buffer layer was included. Thermal annealing of these samples to 400–500°C resulted in large strain relaxation due to the formation of a-W crystals in the buffer layer. Moderate oxide formation on air annealed samples as measured by SIMS was shown not to be a dominant mechanism of strain relaxation.
Evidence of Silica Polymerization During Internal Nucleation of Glassy Lithium Disilicate
Authors: Adams Jane W. , De Jong Bernard H.W.S.
Published: March 2011

The principal problem in developing a theory of internal nucleation lies in the constitution of the nascent nuclei. To get at this constitution in an internally nucleating glass, oxygen and lithium core level x-ray photoelectron spectra have been measured on glassy and nucleated lithium disilicate and on the three stable crystalline compounds in the Li2O-SiO2 system. Our results indicate that nucleated lithium disilicate glass consists of completely polymerized silica in the formation of which non-bridging oxygens are consumed. During this silica polymerization lithium atoms move away from presumably four-fold coordinated sites towards higher coordinated ones.
Simulation By Cellular Automata Of The (Re) Crystallization Of A Matrix Containing An Inert Second Phase
Authors: Pezzee C. F. , Dunand D. C.
Published: March 2011

Two-dimensional cellular automata simulations were carried out to study the case of the crystallization (or recrystallization) of a matrix containing an inert, immobile second phase. A range of particle area fractions and aspect ratios were investigated under continuous grain nucleation conditions, assuming that the effect of particles is limited to geometric impingement upon contact with the growing grains. Systematic deviations from the classical Johnson, Mehl, Avrami, Kolmogo-rov equation for single-phase materials are observed with increasing particle aspect ratio and particle fraction. Inert particles also influence both mean size and mean aspect ratio of the final grains.
Two-Stage Crystallization Of Poly (Ether Ether Ketone) And Its Blends With Poly (Ether Imide)
Authors: Chen Hsin-Lung , Porter Roger S.
Published: March 2011

Thermal Mechanical analysis (TMA) has been used to study the crystallization behavior of poly (ether ether ketone) (PEEK) and its blends with poly (ether imide) (PEI). The two crystallization stages of PEEK are clearly distinguished by measuring the variation of film thickness with time during isothermal crystallization. Upon blending with PEI, the distinction of the two PEEK crystallization stages becomes obscure. This is attributed to the depressions in both nucleation density and spherulite growth rate upon blending with PEI.

An Avrami analysis, Modified by considering both primary and secondary crystallization, is used to extract the respective kinetic behavior of these two crystallization stages. The results indicate that the secondary crystallization proceeded slower than the primary crystallization in the diffusion-controlled crystallization region. On the other hand, these two crystallization stages proceeded at comparable rate in the thermodynamically-controlled crystallization region. It is also found in the diffusion-controlled crystallization that blending with PEI induced a larger depression in the secondary crystallization rate than in the primary crystallization rate. Explanations for these observations are proposed and discussed.
High Temperature Dynamic in-Situ Raman Spectral Characterization of Sodium Borosilicate Glasses
Authors: Jillavenkatesa Ajit , Condrate Robert A.
Published: March 2011

Dynamic Raman spectra of sodium borosilicate glasses containing large amounts of boron oxide have been studied as functions of temperature and holding time. Such characterization enabled measuring the changes in the nature and states of the molecular species that were present in the glasses and their Melts. The data indicate that boroxol rings involving one or more four-coordinated boron ions in the sodium oxide-containing glasses decreased in concentration as they were heated through melt temperatures as was noted earlier for boroxol groups involving three-coordinated boron ions in pure borosilicate compositions.
Study Of Nucleation And Growth Ev Al-Zn Alloys Using TEM
Authors: Sundar G. , Kenik E. A. , Hoyt J. J. , Spooner S.
Published: March 2011

Nucleation and growth studies were conducted on Al-Zn alloys at several temperatures using transmission electron Microscopy (TEM) with an in-situ furnace. The value of the critical undercooling was established by noting the lowest temperature at which precipitates were no longer observed, following a quench into the two-phase metastable region. These results were compared with the Langer-Schwartz Model of nucleation and growth in which it is predicted that the half-completion time (i.e, the time required for the supersaturation to reach half its initial value) diverges for initial supersaturations which are higher than those predicted by the classical nucleation theory.
Ion Beam Synthesis of Luminescent Si and Ge Nanocrystals in a Silicon Dioxide Matrix
Authors: Atwater H. A. , Shcheglov K. V. , Wong S. S. , Vahala K. J. , Flagan R. C. , Brongersma M. L. , Polman A.
Published: March 2011

Ion beam synthesis of Si and Ge nanocrystals in an SiO2 Matrix is performed by precipitation from supersaturated solid solutions created by ion implantation. Films of SiO2 on (100) Si substrates are implanted with Si and Ge at doses 1 × 1016/cm2 - 5 × 1016/cm2. IMplanted samples are subsequently annealed to induce precipitation of Si and Ge nanocrystals. Raman spectroscopy and high-resolution transmission electron microscopy indicate a correlation between visible room-temperature photoluminescence and the formation of diamond cubic nanocrystals approximately 2–5 nm in diameter in annealed samples. As-implanted but unannealed samples do not exhibit luminescence. Rutherford backscattering spectra indicate a steepening of implanted Ge profiles upon annealing. Photoluminescence spectra are correlated with annealing temperatures, and compared with theoretical predictions for various possible luminescence Mechanisms, such as radiative recombination of quantum-confined excitons, as well as possible localized state luminescence related to structural defects in SiO2 Potential optoelectronic device applications are also discussed.
Ion Beam Induced Epitaxial Crystallization of Single Crystalline 6H-SiC
Authors: Heera V. , Kögler R. , Skorupa W. , Glaser E.
Published: March 2011

For the first time, ion beam induced epitaxial crystallization (IBIEC) has been found in SiC. The effect of 300 keV Si+ irradiation through an amorphous surface layer in single crystalline 6H-SiC at 477+5°C has been investigated by RBS/C and XTEM. A shrinkage of the amorphous layer was found after ion irradiation at this temperature which is caused by both an ion dose independent thermal regrowth of about 20 nm and an additional ion beam induced epitaxial crystallization with a rate of about 1.5 nm/ 1016 cm−2.
Induced Crystallization In CW Laser-Irradiated Sol-Gel Deposited Titania Films
Authors: Exarhos Gregory J. , Hess Nancy J.
Published: March 2011

Isothermal annealing of amorphous TiO2 films deposited from acidic sol-gel precursor solutions results in film densification and concomitant increase in refractive index. Subsequent heating above 300°C leads to irreversible transformation to an anatase crystalline phase. Similar phenomena occur when such amorphous films are subjected to focused cw laser irradiation. Controlled variations in laser fluence are used to density or crystallize selected regions of the film. Low fluence conditioning leads to the evolution of a subtle nanograin-size morphology, evident in AFM images, which appears to retard subsequent film crystallization when such regions are subjected to higher laser fluence. Time-resolved Raman spectroscopy has been used to characterize irradiated regions in order to follow the crystallization kinetics, assess phase homogeneity, and evaluate accompanying changes in residual film stress.
Layer by Layer Amorphization in Si: Temperature, Ion Mass and Flux Effects
Authors: Battaglia A. , Romano G. , Campisano S. U.
Published: March 2011

The layer-by-layer amorphization process is explored in a temperature range in which the kinetics of crystallization can be neglected. It has been found that the pure amorphization rate increases exponentially as the substrate temperature is decreased with an apparent activation energy of 0.48 eV. Moreover the rate increases with both the ion flux and the energy deposited into elastic collisions. A phenomenological model is proposed to explain the experimental results.
A Critical Regime for AMorphization of Ion Implanted Silicon
Authors: Goldberg R. D. , Williams J. S. , Elliman R. G.
Published: March 2011

A critical regime has been identified for ion implanted silicon where only slight changes in temperature can dramatically affect the levels of residual damage. In this regime decreases of only 5° C aie sufficient to induce a crystalline-to-amorphous transformation in material which only exhibited the build-up of extended defects at higher temperatures. Traditional Models of damage accumulation and amorphization have proven inapplicable to this regime which exists whenever dynamic defect annealing and damage production are closely balanced. Irradiating ion flux, Mass and fluence have all been shown to influence the temperature—which varies over a range of 300° C for ion species ranging from C to Xe—at which the anomalous behaviour occurs. The influence of ion fluence suggests that complex defect accumulation plays an important role in amorphization. Results are presented which further suggest that the process is nucleation limited in this critical regime.
The Application of Solid Phase Epitaxy for the Incorporation of Substitutional Carbon in Silicon
Authors: Candelaria Jon J. , Watanabe J. K. , Da Vid Theodore N. , Gregory Richard B. , Schroder Dieter K. , Stout Lawrence M. , Cave Nigel G.
Published: March 2011

Carbon was substitutionally incorporated into silicon using ion implantation and solid phase epitaxy (SPE) to regenerate a high quality crystalline substrate. Carbon was implanted into Si (100) substrates using a single implant of 25 keV ai doses ranging from 1.75 × 1015 to 1.05 × 1016/cm2. After carbon implantation half of the substrates were amorphized using a silicon implant. All of the wafers were subjected to a 700°C anneal in N2 ambient for 30 Minutes to induce SPE regrowth of the implanted regions. FTIR, SIMS, RBS, and TEM were used to characterize the samples. Results indicate that carbon was substitutionally incorporated into the silicon lattice, but that some carbon did precipitate to form silicon carbide. Post-amorphization improved regrowth of implanted regions in lower dose implanted wafers. Electrical Measurements on diode structures indicate that the band gap was reduced for carbon incorporation at these concentrations.
Trends in Solute Segregation Behavior During Silicon Solidification
Authors: Reitanot Riccardo , Smith Patrick M. , Aziz Michael J.
Published: March 2011

At the high growth rates accessible during pulsed-laser induced melting and solidification and explosive crystallization, crystal growth kinetics are dominated not by equilibrium thermodynamics, but by the atomistic mechanisms by which crystallization proceeds. These Mechanisms can be probed by testing the predictions of solute trapping models based on various crystal/Melt interface structures against Measurements. We have measured the dependence of solute trapping of several group III, IV, and V elements in silicon on both interface orientation and crystallization speed. The Aperiodic Stepwise Growth Model of Goldman and Aziz accurately fits both the velocity and orientation dependence of the solute trapping observed in these systems. The success of the model implies a ledge structure for the crystal/Melt interface and a step-flow mechanism for crystal growth. In addition, we have observed an empirical inverse correlation between the two free parameters (“diffusive speeds”) in this model and the equilibrium solute partition coefficient of a system. This correlation may be used to estimate values of the diffusive speeds for other systems in which solute trapping has not been or cannot be Measured.
Interface Stability During Solid Phase Epitaxy Of Strained GexS1-x Films on Si (100)
Authors: Zeng Xiaobiao , Lee Tan-Chen , Silcox John , Thompson Michael O.
Published: March 2011

Strained solid phase epitaxial (SPE) regrowth of amorphous GexSi1-x on Si (100) substrates was studied using time-resolved reflectivity (TRR). Films of CVD-grown Ge0.13Si0.87 on Si were amorphized by Si ion implantation, and subsequently regrown at temperatures between 550°C and 610°. Information on regrowth dynamics and interface roughness evolution was obtained by accurately modeling the complicated TRR data for GexSi1-x regrowth using a Moving, statistically roughening interface. The SPE regrowth rate slowed as the interface crossed into the GexSi1-x layer and the originally planar interface roughened, as confirmed by transmission electron Microscopy. A Minimum in the regrowth velocity was observed after regrowing approximately 60 nm into the GexSi1-x layer; the SPE rate subsequently increased to a final, thickness-dependent velocity that was still below that for pure Si. Upon entering the GexSi1-x layer, the interface roughened quickly to a 15–20 nm amplitude, increasing only slightly more during the remainder of regrowth. The degree of roughening and velocity reduction was found to be dependent on the anneal temperature. In contrast, samples with low Ge concentrations (< 3 at.%) prepared by ion implantation exhibited minimal interface roughening and essentially identical SPE velocities as pure Si.
Nanometer-Scale Oxide Particles in Gesi Films Grown by Wet Oxidation
Authors: Lee Tan-Chen , Soave Robert J. , Shacham-Diamand Yosi Y. , Silcox John
Published: March 2011

Amorphous GeSi films with different thicknesses and oxygen contents were electron beam evaporated onto Si (KK)) wafers and wet oxidized at 900 °C for 30 Min. If there was no oxygen in the as-deposited film, an epitaxial GeSi film would be grown after wet oxidation. For the samples with oxygen, epitaxial growth broke down when the thickness of the epitaxy exceeded about 200 A and polycrystalline GeSi films were formed. A dedicated STEM (scanning transmission electron Microscope) was used to characterize the sample after oxidation. STEM BF (bright field), ADF (annular dark field), and energy filtered images revealed the presence of small oxide particles in the polycrystalline GeSi films. X-ray microprobe analysis with a windowless detector was employed to identify the oxide particles. The failure of the epitaxy is explained by the random nucleation and growth of GeSi grains on the oxide particles.
Crystallization of Amorphous Metastable Ceramic PVD-Coatings
Authors: Knotek O. , Löffler F. , Wolkers L.
Published: March 2011

Ceramic PVD coatings have got very often an X-ray Amorphous structure. This is regarded for all classes of ceramics like covalent and ionic Materials. These Amorphous materials start to crystallize at temperatures about 800 °C, a quite low temperature for the practical use of such Materials. This prevents the propagation of this materials in applications like high temperature wear protection, oxidation resistivity etc.

This paper describes several possible techniques to increase the thermal stability of the Amorphous state of ceramic PVD-coatings like A1203 and SiC up to 1200 °C. The best way is the incoporation of an additional element like nitrogen into the thin filmsl. The change of the mechanical properties of alumina leads to new applications like diffusion barriers.
Effects of Glass and Carbon Fiber on Nylon 6,6 Crystallization
Authors: Siangchaew Krisda , Davidson Theodore , Libera Matthew
Published: March 2011

The effects of addition of glass fiber and HMS4 carbon fiber on the crystallization of nylon 6,6 has been investigated using DSC and polarized optical Microscopy (POM). DSC observations indicate that HMS4 fiber lowers the supercooling required to initiate crystallization. A transcrystalline layer is also observed in the near-fiber region of carbon fiber-reinforced composites after DSC. The presence of transcrystallinity and the earlier onset of crystallization for this composite are due to heterogeneous nucleation on carbon fiber surfaces. DSC Measurements of nylon 6,6 with glass fibers show supercoolings similar to those of neat nylon 6,6. Transcrystallinity is also absent in the glass-reinforced composites. These glass fibers appear to be weak nucleation catalysts. Different transcrystalline layer thickness is found to be influenced by thermal processing condition. In addition to transcrystallinity, the HMS4 carbon fiber also influences the bulk morphology of the nylon 6,6.
Multiple Pulse Irradiation Effects in Excimer Laser-Induced Crystallization of Amorphous Si Films
Authors: Kim H. J. , Im James S.
Published: March 2011

We have experimentally Investigated the effects that are associated with Multiple-pulse irradiation in the excimer laser processing of thin Si films on SiO2. Double-pulse irradiation experiments revealed results, which are consistent with that which is known from single-pulse crystallization experiments, and these experiments confirm the applicability of the transformation scenarios, which were derived from single pulse-induced crystallization experiments [1,2]. The results from the Multiple-pulse irradiation experiments clearly show that gradual and substantial grain enlargement can occur — and only occurs — when the irradiation energy density is close to but less than the level that is required to melt the film completely. Based on these findings, we argue that the grain enlargement effect is a near-complete melting phenomenon that is associated with polycrystalline Si films, and we present a grain boundary melting model to account for this phenomenon. A brief discussion on the apparent similarities and physical differences between the observed phenomenon and the solid state grain growth processes is provided herein.
Large Grain Creation and Destruction in Excimer Laser Crystallized Amorphous Silicon
Authors: Boyce J. B. , Anderson G. B. , Fork D. K. , Johnson R. I. , Mei P. , Ready S. E.
Published: March 2011

For fast-pulse laser-crystallized thin-film Si on non-crystalline substrates, the average grain size exhibits a peak as a function excimer laser energy density at a characteristic laserfluence FM. The average grain size increases with increasing laser fluence and can reach a maximum value on the order of 10 pm or about 100 times the film thickness. The grain size then decreases with further increases in fluence. This peak in grain size is accompanied by a similar peak in the Hall electron mobility and x-ray scattering intensity. Our experiments have investigated as-deposited and ion-implanted samples, using a double-scan laser crystallization process. Devices have also been fabricated and studied. The results are consistent with the increase in grain size occurring because of the destruction of nucleation sites with increasing laser fluence (i.e., increased heating and complete Melting). But substrate damage occurs in the vicinity of FM, creating nucleation sites which give rise to small grain sizes in the solidified film. The disruption of the interface causes substantial current leakage through the dielectric of bottom-gate transistors, implying that devices should be laser fabricated below Fm.
Selective Crystallization of A-Si:H Films on Glass
Authors: Yin Aiguo , Fonash Stephen J.
Published: March 2011

We have found that an oxygen plasma exposure of a-Si:H films can cause these films to crystallize with a much lower thermal-budget than that required for the same a-Si:H films without this plasma exposure. Based on this unique finding, a selective area crystallization process has been developed to successfully form patterned polycrystalline Si films. In this study, 1500 Å PECVD a-Si:H films were first covered by 500 Å sputtered SiO2 which was then patterned by lithography to form various islands covered by the SiO2. These patterned films were exposed to an oxygen plasma and were then thermally annealed in a furnace at 600 °C for 6 hours. After this annealing it was found that the islands covered by SiO2 during the oxygen plasma treatment remained a-Si while the oxygen plasma exposed regions were crystallized completely. Both XRD and TEM were used to establish the existance of these controlled regions of a-Si and poly-Si in these films.
Excimer Laser Induced Crystallization of Amorphous Silicon-Germanium Films
Authors: Slaoui A. , Deng C. , Talwar S. , Kramer J. K. , Prevot B. , Sigmon T. W.
Published: March 2011

Application of excimer laser crystallization of Amorphous silicon (a-Si) has introduced a new, interesting potential technology for the fabrication of polycrystalline (poly-Si) thin film transistors. We are currently studying polycrystalline Si1−xGex thin films in order to determine whether this material can lead to improved electrical properties or to better processing requirements when compared with polycrystalline Si films. In this work we analyze by RBS, TEM, Raman spectroscopy and surface reflectance, the structure of thin Amorphous Si1−xGex films after irradiation with a XeCl excimer laser. The Amorphous SiGe films were prepared by evaporation of Si and Ge onto oxidized Si substrates using an electron gun in vaccum. The effects of laser energy fluence during irradiation are investigated. The Amorphous to crystalline transition is followed by in-situ measurement of time-resolved reflectivity.
Kinetics Of Hydrogen Evolution And Crystallization In Hydrogenated Amorphous Silicon Films Studied By Thermal Analysis And Raman Scattering
Authors: Sridhar Nagarajan , Chung D. D. L. , Anderson W. A. , Yu W. Y. , Fu L. P. , Petrou A.
Published: March 2011

We observed the processes of hydrogen evolution and crystallization in hydrogenated Amorphous silicon 0.5–7 μm thick films (deposited by dc glow discharge on Molybdenum) by differential scanning calorimetry (DSC), Raman scattering and thermogravimetric analysis (TGA). Investigation was made as a function of doping, deposition temperature and film thickness. For all the films, an endothermic DSC peak was observed at 694 °C (onset). That this peak was at least partly due to hydrogen evolution was shown by TGA, which showed weight loss beginning at 694 °C, and by evolved gas analysis, which showed hydrogen evolution at 694 °C. This temperature (658–704 °C) increased with increasing heating rate (5–30 °C/min). Doping reduced this temperature from 694 to 625 °C for boron doping and to 675 °C for phosphorous doping. Hydrogen evolution kinetics and FTIR results suggest that the silicon-hydrogen bonding in the intrinsic film was a mixture of SiH and S1H2, and was predominantly SiH in the phosphorous doped films and SiH2 in the boron doped films. Crystallization was independent of silicon-hydrogen bonding in the as-deposited Amorphous silicon film. It was bulk (not interface) induced. No exothermic DSC peak accompanied the crystallization. The film deposition temperature had little effect on the DSC result, but crystallization was enhanced by a higher deposition temperature.
The Mechanism of Excimer Laser-Induced Amorphization of Ultra-Thin Si Films
Authors: Eiumchotchawalit T. , Im James S.
Published: March 2011

To better understand the involved phase transformation Mechanism, we are studying the excimer laser-induced amorphization (ELA) of ultra-thin Si films on oxidized Si substrates. In this paper, we show that the onset of amorphization of hydrogen-free Si films on SiO2 substrates upon increases in the energy density is associated with the onset of complete melting of the film. Once complete melting occurs, further increases in the incident energy density and/or increases in the substrate temperature can lead to incomplete amorphization of the film. Planar view TEM analysis of nearly-amorphized Si films reveals a heterogeneous microstructure, which consists of a mixture of densely dispersed amorphous-like annular regions (∼20 to 40 μm−2), embedded within and typically separated by a region containing finegrained small crystals. Such a cellular microstructure strongly suggests that amorphization occurred not via a homogeneous but via a heterogeneous transformation. In particular, the microstructure paints a scenario in which amorphization proceeded via nucleation of solids, which is then followed by interfacial amorphization. The experimental results unambiguously reveal (1) that the previously proposed criteria of the melt duration and the vertical temperature gradient are irrelevant in determining amorphization of supercooled liquid Si films and (2) that the quenching rate, not surprisingly, is the important parameter.
Thin Film Transistors Made From Hydrogenated Microcrystalline Silicon
Authors: Wang K. C. , Chen B. Y. , Hsu K. C. , Yew T. R. , Hwang H. L.
Published: March 2011

Microcrystalline silicon films were deposited by diluted-hydrogen method and hydrogen-atom-treatment method at 250°C in a plasma enhanced chemical vapor deposition system and they were characterized by nuclear magnetic resonance, Raman spectroscopy, and optical bandgap Measurements. One-Mask a-Si:H thin film transistors (TFT's) were fabricated with those microcrystalline materials as the channel layer. The highest electron mobilities of the TFT's fabricated by diluted-hydrogen method and hydrogen-atom-treatment method were 1.23 and 1.04 cm2/V•s, respectively without any thermal treatment steps.
Stress Relaxation In Metals And Polymers: Theory, Experiment And Computer Simulations
Authors: Brostow Witold , Kubát Josef , Kubát Michael J.
Published: March 2011

There exist large amounts of experimental evidence on stress relaxation for metals and their alloys, synthetic and natural polymers, glasses and frozen non-polymeric organic liquids. The results, typically presented as curves a (log t) of relaxation of stress aas a function of logarithmic time t, exhibit common features, apparently independent of the type of Material. All curves consist of three regions: initial, nearly horizontal, starting at σ0; central, descending approximately linearly; and final, corresponding to the internal stress σi = σ(>). We discuss briefly the experimental evidence as well as the main features of the cooperative theory which does not involve specific features of different classes of Materials. The bulk of the paper deals with computer simulations. Simulation results obtained with the method of molecular dynamics are reported for ideal metal lattices, Metal lattices with defects, and for polymeric systems. In agreement with both experiments and the cooperative theory, the simulated σ (log t) curves exhibit the same three regions. In agreement with the theory, the slope of the simulated central part is proportional to the initial effective stress σ0* = σ0 - σi. The time range taken by the central part is strongly dependent on the defect concentration: the lower the defect concentration, the shorter the range. IMposition in the beginning of a high strain ε destroys largely the resistance of a material to deformation, resulting in low values of the internal stress σo. Since the cooperative theory assumes for particles (atoms, polymer chain segments) the existence of two states, unrelaxed and relaxed, and has a formal connection to the Bose-Einstein (B-E) distribution, we first simulate B-E systems, recording the formation of relaxed clusters of particles of different sizes. Differences in cluster sizes predicted from a B-E Model and those obtained from the simulations are recorded and analyzed. On the joint basis of experimental, theoretical
The Effect of Substrate on the Microstructure and Mechanical Behavior of Eutectic Indium-Tin
Authors: Goldstein J. L. Freer , Morris J. W.
Published: March 2011

This study was conducted in order to determine and understand the effect of substrate on eutectic In-Sn. Samples for mechanical testing were produced with either bare Cu or Ni on Cu substrates. Both the microstructure and the mechanical behavior are strongly dependent on substrate, with In-Sn on Cu having a non-uniform and irregular microstructure and In-Sn on Ni having a uniform, normal colony-based eutectic. Deformation is more uniform in the In-Sn on Ni, while it is concentrated along the length of the joint in the In-Sn on Cu. This is reflected in the different shapes of stress-strain curves between In-Sn on Cu and In-Sn on Ni. The stress exponents and activation energies for creep also vary with substrate. Creep deformation is governed by the In-rich γ phase for In-Sn on Cu and by the Sn-rich y phase for In-Sn on Ni. If In-Sn on Ni samples are aged, the microstructure coarsens and the mechanical behavior changes to resemble that of the as-cast In-Sn on Cu.
Mössbauer Parameters Describing Several Intermetallic Phases in Tin-Containing Solders
Authors: Reno Robert C. , Takacs Laszlo
Published: March 2011

We report here on the Mbssbauer parameters of two intermetallic phases expected to be present in composite solders: the Cu9Sn3Ni phase present in some forms of eutectic Sn-Pb solders and the Ag-Sn (ζ) phase which may be present in lead-free solders containing appreciable amounts of silver. Both samples were prepared by mechanical alloying techniques.

Our results show that the isomer shift of the Ag-Sn ζ phase is + 2.13 mm/sec relative to SnO2 and the phase has a room-temperature recoilless fraction that is 36% of that of SnO2. The results for Cu9 Sn3Ni are an isomer shift of + 1.78 mm/sec and a recoilless fraction 58 % of that of SnO2.
Fluence Dependence of Excimer Laser Ablation of Ain
Authors: Lumpp Janet K. , Coretsopoulos Christopher N. , Allen Susan D.
Published: March 2011

Aluminum nitride has been ablated with a KrF excimer laser (248 nm) at fluences from 1 to 60 J/cm2. Ablation depth, emission spectra and photothermal beam deflection were detected as a function of fluence. An ablation rate of 0.2 μm/pulse was achieved above 30 J/cm2 in vacuum. Ablation rate decreased with decreasing, fluence. Irradiated surfaces have a conductive metallic layer of reduced aluminum nitride. At low fluences, the metallic surface layer was spotty within the area of the laser beam. Below the fluence threshold for producing the metallized surface, emission spectra and photothermal beam deflection were still detected. Emission lines from Al, Al+ and Al-N were observed. Photothermal deflection data was used to calculate supersonic velocities for shock waves propagating from the sample surface. Shock waves resulted from rapid heating near the surface and expansion of ablated material from the laser spot.