bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Residual Stresses in Al2O3 Prepared by Ion Beam Assisted Deposition
Authors: Goldiner M. G. , Was G. S. , Parfitt L. J. , Jones J. W.
Published: March 2011

Alumina films synthesized by ion beam assisted deposition (EBAD) were characterized in terms of their microstructure and residual stress. Normalized energy per deposited atom, En, ranged from 0 to 130 eV/atom. The microstructure of PVD films (En=0) is a mixture of crystalline (γ-Al2O3) and amorphous phases and IBAD films are amorphous. Density and stoichiometry vary between 2.6 and 3.1 g/cm3 and 1.3 and 1.6, respectively. Neither are dependent on either ion-to-atom arrival rate ratio, R, or En. The film porosity is in the form of small (4-6 nm) voids of density 1017 - 1018 cm-3. Bombarding gas is incorporated with 80% efficiency to levels of 4-5 at. %. A tensile residual stress of 0.3 GPa exists in PVD films. A rapid transition to high compressive stresses occurs with increased En, with a saturation of -0.4 GPa occurring at high En There is a strong correlation between gas incorporation and residual film stress. However, no existing models are capable of providing a quantitative explanation of the results.
Ion Beam-Assisted Deposition of Biaxially Aligned CeO2 and ZrO2 Thin Films on Amorphous Substrates
Authors: Ressler Kevin G. , Sonnenberg Neville , Cima Michael J.
Published: March 2011

Deposition of HTSC and other films is often restricted to lattice-matched single crystal substrates to produce desired epitaxial films. Ion assisted, electron beam deposition (IBAD) has been used to evaporate biaxially aligned ceria and zirconia films on amorphous substrates, thus producing a surface for the deposition of oriented Ba2YCu3O7-δ films. The conditions at which preferential (200) film alignment is obtained has been optimized. The ion-to-atom ratio and ion beam energy are critical in determining beam effects on in-plane alignment Pole figures revealed that both (220) and (111) in-plane alignments parallel to the direction of the ion beam could be obtained depending on the ion-to-atom ratio. Certain orientations dominate at various temperature regimes on different substrates. The orientation regimes were similar on all substrates, but the temperature at which the trends were observed differed with substrate. Microstructures were correlated to orientations, with the desired (200) orientation being columnar. A mechanism to account for this biaxial alignment is proposed.
An Initial Investigation of the Electrical and Microstructural Properties of Au/Ti and Au/Pd/Ti Ohmic Contact Structures for AlGaAs/GaAs HBTs
Authors: Sandhu Kuldip S. , Staton-Bevan Anne E. , Henry Bernard M. , Crouch Mark A. , Gill Sukhdev S.
Published: March 2011

The electrical and microstructural properties of Au/Ti and Au/Pd/Ti contacts to p+-GaAs (C-doped, 5×1018cm−3) were investigated. Current-voltage measurements as a function of temperature showed that the Ohmicity of the Au/Ti contact improved upon annealing. However, the annealed binary contact featured Au spiking into the GaAs making it unsuitable for HBT applications. The addition of a Pd diffusion barrier layer between the Au and Ti metallisation layers prevented spiking, but resulted in a decrease in the Ohmicity of the contact.

For all the contact systems it was found that thermionic-field emission dominates the current transport mechanism across the metal-semiconductor interface between the temperature range 198K and 348K. The Au/Pd/Ti contact structure shows HBT potential, however higher epilayer doping levels will be required to produce satisfactory specific contact resistivities.
Ohmic Contacts to p-Type InGaAs/InP with a Graded Bandgap Heterobarrier
Authors: Leech Patrick W. , Reeves Geoffrey K.
Published: March 2011

Ohmic contacts to p-type InP with an In0.47Ga0.53As buffer layer and an interposed superlattice of 50 Å In0.47Ga0.53As/ 50 Å InP have been investigated. Initial studies of contacts to In0.47Ga0.53As/ InP without the superlattice structure have shown that Pd/Zn/Pd/Au metallization produced a lower specific contact resistance (pc = 1.1 × 10−4 Ω cm2) than Pd/Ge/Au, and over a wider range of anneal temperature than Au/Zn/Au. The incorporation of the superlattice in the p-In0.47Ga0.53As/ InP structure resulted in Pd/Zn/Pd/Au contacts with pc of 3.2 × 10−5 Ω cm2 as-deposited and 7.5 × 10−6 Ω.cm2 after a 500 °C anneal. The presence of Pd/Zn in the metallization was shown as important in reducing pc. Significant intermixing of the metal layers and In0.47Ga0.53As occured at ≥ 350 °C, as revealed by Rutherford backscattering spectrometry.
Initial Stage of Heteroepitaxial Growth of SiC on Si by Gas Source MBE Using Hydrocarbon Radicals
Authors: Fuyuki Takashi , Tarui Yoichiro , Hatayama Tomoaki , Matsunami Hiroyuki
Published: March 2011

Heteroepitaxial growth of 3C-SiC on Si in gas source molecular beam epitaxy ( GSMBE ) was carried out by a combination of carbonization of a Si surface and subsequent crystal growth on it using hydrocarbon radicals and Si2H6. The carbonization process and the initial stage of the subsequent growth during the intermittent supply of Si2H6 have been studied by a reflection high-energy electron diffraction (RHEED) observation. A Si surface was chemically converted to 3C-SiC at 750°C, and homoepitaxial growth on the carbonized layer could be obtained at 1000°C. Si atoms generated by thermal decomposition on a surface would react with hydrocarbon radicals, forming SiC through a layer by layer growth mode.
Alignment of Adsorbate-Induced Defects on Silicon(001) 2×1 Observed with STM
Authors: Seiple J. V. , Pelz J. P.
Published: March 2011

We have observed that a build-up of gas-phase adsorbates on Si(001) followed by mild annealing at temperatures in the range 500 - 800°C can lead to a quasi-periodic array of line defects, which in STM images appear similar to lines of dimer vacancies aligned perpendicular to the surface dimer rows. These line defects can be eliminated by annealing at temperatures above 900°C, indicating that Ni contamination is not the cause. Adsorbed O2 or H2O followed by an anneal do not exhibit the same behavior.
Diffusion-Segregation Equation for Simulation in Heterostructures
Authors: Gafiteanu R. , You H.-M. , Göesele U. , Tan T.Y.
Published: March 2011

Diffusion of impurity atoms or point defect species occurs simultaneously with segregation in materials that are inhomogeneous or consisting of heterostructures. Based on thermodynamic principles, a general diffusion-segregation equation (DSE) simultaneously describing the species’ diffusion and segregation behavior has been derived. The DSE treats the diffusion-segregation problems on the same fundamental level as the diffusion problems are treated by Fick’s Laws. A critical comparison of modeling diffusion-segregation phenomena using the DSE vs. previous formulations is given. The wide range of applications of the DSE is demonstrated by several examples.
Control of Interfacial Mechanical Properties in Ti/Al203 Composites
Authors: Wang Hsin-Fu , Gerberich William W. , Angelo Jim E. , Mills Mike J.
Published: March 2011

The fracture energy of Ti/Al203 composite interfaces has been determined by four point bending tests of sandwich specimens for different thicknesses of metal interlayers at 900°C. The interfacial fracture was found to be brittle. An intermetallic reaction product (Ti3Al) was produced at the interface after the diffusion bonding process. When the metal interlayer is thicker, there is more plastic energy dissipation in the metal during the fracture process. Therefore, the interfacial fracture energy increases. This can be seen from the fact that there is a larger plastic zone size with increasing thickness of the metal interlayer. The measured interfacial fracture energy Ti/Al203 ranges from 9.6 J/m2to 45.1 J/m2. The intrinsic interfacial fracture energy is obtained to be 0.26 J/m2. The embrittlement of the interface after the diffusion bonding process causes this value to be smaller than work of adhesion for Ti/Al203 (2.0 J/m2).
Influence of Segregation Effects on the Energies of Lead/Graphite and Gold/Graphite Interfaces
Authors: Gangopadhyay Utpal , Wynblatt Paul
Published: March 2011

This paper reports the results of solid state wetting studies of graphite by Pb and Au alloyed with Ni. It is shown that additions of Ni ranging from 0 to 0.2 wt%Ni reduce the contact angle of Pb on graphite from 117 to 80°, and that a 5 wt% Ni addition to Au decreases the contact angle of Au on graphite from 131 to 123°. These contact angle changes are used to compute the interfacial energy at both Pb/graphite and Au/graphite interfaces. Direct evidence of Ni segregation at those interfaces is also obtained by crater edge profiling measurements. It is found that the enrichment factor of Ni is much larger in the Pb- than in the Au-based system. Also, for similar changes in interfacial energy, the effects of Ni segregation on contact angle are larger in the Pb- than in the Au-based system. These effects are discussed in terms of the relative surface and interfacial energies in the two systems.
Measurement of Plasticity Gradients with Scanning Probe Microscopy
Authors: Kiely James D. , Bonnell Dawn A.
Published: March 2011

Scanning Tunneling and Atomic Force Microscopy were used to characterize the topography of fractured Au /sapphire interfaces. Variance analysis which quantifies surface morphology was developed and applied to the characterization of the metal fracture surface of the metal/ceramic system. Fracture surface features related to plasticity were quantified and correlated to the fracture energy and energy release rate.
Sputter Etching Effect on Magnetic Properties in TaOx/TbFeCo/Ag Layered Films
Authors: Shimamori Takumi , Yoshida Hidemi , Kobayashi Yoshimitsu
Published: March 2011

Sputter etching effect on magnetic properties was investigated in TaOx/TbFeCo/Ag layered films. With sputter etching, smooth interfaces of about lnm roughness were obtained. In films with smooth interfaces, magnetization was stabilized and magnetization reversal was sharpened at around the Curie temperature. As a result, recorded marks were stabilized, and the media became sensitive to the magnetic field for writing. 49dB was obtained as C/N even at 0.45μm mark length, which is sufficient for digital recording.
The Influence of Grain-Boundary Structural Disorder on the Magnetic Properties of Nanocrystalline Nickel
Authors: Szpunar Barbara , Erb Uwe , Aust Karl T. , Palumbo Gino , Lewis Laurent J.
Published: March 2011

The influence of grain boundaries on the magnetic properties of nanocrystalline nickel, in particular the ∑ = 3 and ∑ = 5 special grain boundaries and the extreme case of a purely amorphous sample, has been investigated. Our calculations reveal that the magnetic moment is rather insensitive to the structural disorder varying by at most 15 %. These results correlate extremely well with the recent observation in electrodeposited nickel that the magnetic moment depends very little on grain size, down to about 10 nm.
NH3-Plasma Treatment of Gaas Surface at High Temperature in Remote Plasma and Direct Plasma Reactor
Authors: Wan Park Kyoung , Jae Lee Seong , Shin Mincheol , Lee El-Hang
Published: March 2011

NH3-plasma treatment has been used for passivation of native-oxide-contaminated GaAs surface. Ex situ band-gap photoluminescence(PL) measurement shows enhanced intensity for the treated surfaces in direct plasma. Auger electron spectroscopy(AES) shows that the treated surface contains nitrogen atoms but no arsenic atoms, which leads us to speculate that the graded GaN thin layer was formed on the surface. Long-term stability of the enhanced PL intensity is attributed to the formation of GaN on the surface.
Electronic Structure of the ∑3[111] Grain Boundary and Doping Effect in Ni
Authors: Chongyu Wang , Dongliang Zhao
Published: March 2011

Based on the tight-binding bond recursion method, the energetics parameters of ∑3[111] grain boundary in nickel are investigated. The theoretical results indicate that the boron enhances interatomic energy between the host atoms, and between impurity and nickel atoms. Calculations of the energy of the grain boundary segregation show that boron, nitrogen, and phosphorus have the tendency to segregate onto the grain boundary and segregation property of boron is stronger than that of nitrogen and phosphorus.
Effects of Near Interfacial Microstructure on Interlaminar Fracture Toughness of Hybrid Metal-Polymer Composites
Authors: Grabilnikov Alexander S. , Zinevich Oleg M.
Published: March 2011

Results of detailed study on interlaminar fracture toughness of hybrid aramid-epoxy/aluminum laminate composites are presented. A fracture mechanics approach has been adopted and Mode-I, Mode-II tests for a wide range of loading rates have been used. Hybrid composite failure loci has been studied using SEM technique. Results were analyzed from the point of view of metal substrate/aramid fibre surface free energy effect on near interfacial (in the boundary layers) microstructure and fracture toughness of elastomer modified epoxy resins. It has been shown, that toughened epoxy resin morphology (rubber particles size and volume content) and, as a result, fracture resistance of the boundary layers were strongly dependent upon the adsorption processes, that could take place during adhesion contact formation and curing. To increase interfacial fracture toughness of hybrid composites due to the improvement of near interfacial resin microstructure and boundary layer fracture resistance, as for aluminum-epoxy and for aramid-epoxy failure loci, metal sheets/aramid fibres surface properties and interfacial residual thermal stresses should be optimized. The last result has been achieved by means of si lane primer treatment of aluminum laminates and tensile loading of cured composite.
Structural Imperfections in Ulrathin Oxides Grown on Hydrogen Terminated Silicon Surfaces
Authors: Hattori Takeo , Ohishi Kazuaki
Published: March 2011

The initial stage of oxidation of 40wt-% NH4F treated Si(111) surface at 300 °C in dry oxygen with a pressure of 133 Pa and the subsequent oxidation at 600 and 800°C were studied. It was found from the analysis of Si 2p photoelectron spectra that non-uniform layer by layer oxidation proceeds at 300°C, while the layer by layer oxidation proceeds at 600 and 800°C. Furthermore, at these temperatures the interface becomes atomically flat with the progress of oxidation.
The Study of Silicon Diffusion into GaAs by Rapid Thermal Oxidation
Authors: Chen W. S. , Fu C.
Published: March 2011

The diffusion of silicon into GaAs was investigated in this work. Shallow silicon carrier profile with doping levels in excess of 1018 cm−3 were obtained in GaAs by rapid thermal oxidation (RTO) of Si cap film in pure O2 with pressure 2 torr at 800 ∼ 900 ° C. SIMS revealed the presence of various degrees of interdiffusion in / near the interface between Si and GaAs as being a function of oxidation temperature and cap thickness. Ga and As atoms were observed in Si film. Silicon and oxygen were also found in the GaAs wafer. The silicon and arsenic atoms were segregated in / near the interface. The Si atoms could be driven further into GaAs by additional rapid thermal annealing (RTA) process. The above phenomena were confirmed by the electrical measurements taken on sheet resistance, doped dose, and mobility. The TaSix / GaAs Schottky barriers were also fabricated. The ideality factor, Schottky barrier height, and breakdown voltage are the functions of the doping level. This behavior could be accounted for by the theory of tunnel effect of Schottky barrier.
Surface Smoothing Process of YBa2Cu3O7−x Thin Film for Fabrication of Superconducting Multi-Chip Modules
Authors: Liang S. , Shi Z.Q. , Chern C. , Lu Y. , Safari A. , Lu P. , Kear B.H.
Published: March 2011

In this paper, we report the development of surface smoothing process for YB2CU3O7. x (YBCO) films. The SrTi03/YBCO interface characteristics were investigated as functions of polishing agent and polishing time. It was found that the 7% HF solution gave the best results both in structural and electrical properties. The leakage current through the SrTiÛ3 film grown on polished YBCO was reduced to about 3 orders of magnitude. The dielectric constant was also increased from 110 to over 300. The superconducting properties of the YBCO bottom layer degraded insignificantly after undertaking the surface smoothing process and the overlayer growth of STO. This surface smoothing process without post treatment is suitable for subsequent growth of epitaxial STO films and the fabrication of MCM’s.
Conductive Polymer / Superconductor Sandwich Structures
Authors: Haupt Steven G. , Zhao Jianai , Lo Rung-Kuang , Zhou Ji-Ping , McDevitt John T.
Published: March 2011

Methods for characterizing the interface of conductive polymer/high-Tc superconductor sandwich structures are reported. Electrochemical procedures, such as cyclic voltammetry and chronoamperometry, are utilized to deposit conductive polymers directly onto bulk ceramic and thin film samples of YBa2Cu3O7-δ. Moreover, similar methods are utilized to cycle the polymer structures between their neutral (non-conductive) and oxidized (conductive) forms. Through changes in the polymer doping level, the superconducting properties of the high-Tc component can be modulated in a controllable and reproducible fashion. This paper focuses on an analysis of conductive polymer/superconductor interface phenomena as explored by electrochemical, resistivity vs. temperature and contact resistance measurements.
Biaxial State of Stress in SiGe Epilayers on Patterned Si Substrates
Authors: Fischer Armin , Richter Hans
Published: March 2011

We present a two-dimensional analysis of the in-plane misfit stress and its elastic relaxation in rectangular patterned heteroepitaxial multilayer structures on rigid substrate. Based on the generally acknowledged model of relaxing film stress we calculate the distribution of the misfit stress versus distance from the free surface of a multilayered mesa edge. By superposition of the isolated stress fields of the mesa edges, we obtain the biaxial misfit stress distribution in a finite heteroepitaxial thin film structure on thick substrate. The formalism developed permits the determination of the variation of stress values as a function of material and size characteristics of the patterned multilayer-substrate system. The theoretical analysis will be applied to the SiGe/Si strained layer epitaxy and III-V compound semiconductor integration with Si or Ge.
Gels and Gel-Derived Glasses in the SiO2 GeO2 System
Authors: Mukherjee Shyama P.
Published: March 2011

Gels and gel-monoliths in the SiO2 -GeO2 system were prepared by different procedures using metal alkoxides as starting materials. Several gel compositions with increasing GeO2 were prepared. Crystallization behavior of gels in relation to the preparation procedures, homogeneity, and molecular structure of gels is discussed. Supercritically dried porous gel-monoliths of high silica compositions were densified into glass by sintering at 1280°C.
Ferroelectric Ceramics--The Sol-Gel Method Versus Conventional Processing
Authors: Wu Edward , Chen K.C. , Mackenzie J.D.
Published: March 2011

The sol-gel method for the preparation of ceramics and glasses has frequently been mentioned as more advantageous as compared to conventional methods. However, there are few known examples of a direct comparison for the same material. In the present work both the processing and resultant properties for ferroelectrics such as BaTiO3, KTaO3, KNbO3 and K(Ta,Nb)O3 made by both methods are directly compared. The uniformity is evaluated by high-angle x-ray diffraction, electron microscopy and EDAX and the dielectric properties are compared. The advantages and disadvantages of the sol-gel method are discussed.
Chemical Synthesis of Single and Mixed Phase Oxide Ceramics
Authors: Mazdiyasni K. S.
Published: March 2011

Thermal and hydrolytic decomposition of metal alkoxides, M(OR)n, is employed to obtain ultra-high-purity submicron-size < 50 nm refractory, ferroelectric, and electro-optic oxide powders. The high surface activity associated with these powders makes possible relatively low temperature processing of the powder compacts to near theoretical density with uniform fine-grain-size bodies. Transmission electron microscopy, high-temperature X-ray, and infrared and Raman spectroscopy are used to observe nucleation, growth, crystallite morphology of the synthesized powder, and microstructural features.
Preparation and Optical Properties of Polycrystalline Aluminum Germanate
Authors: Prochazka S. , Slack G. A.
Published: March 2011

Aluminum germanate, the germanium analog of mullite, 3 AlO2O3. 2 GeO2, was first prepared by Gelsdorf, Muller-Hesse and Schweite (Ref. 1), who demonstrated that both partial and complete substitution of SiO2by GeO2in mullite was possible. They also determined the lattice constants of the solid solutions. The following studies reported some physical properties of aluminum germanate such as density (Ref. 2) optical constants (Ref. 2) crystal structure (Ref. 3) and I. R. absorption (Ref. 4). Phase equilibria in the system AlO2O3−GeO2were investigated by Miller et al. (Ref. 5) and Perez-y-Jorba (Ref. 6). The ratter author found several compounds of which germanium mullite was the most stable and showed a relatively wide compositional range. Miller et al. observed only 3 Al2O3. 2 GeO2with no evidence of solid solutions. The compound was reported to melt incongruently at 1530° C. Recently Yamaguchi et al. (Ref. 7) prepared aluminum germanates of a wide range of stoichiometry from alkyl oxides and found, in addition to germanium mullite, the compound Al2O3−2GeO2which was stable between 1190° and 1310° C. The authors also report infrared absorption spectra.
Structure Data from Light Scattering Studies of Aerogel
Authors: Hunt Arlon J. , Berdahl Paul
Published: March 2011

This paper reports a recent advance in the understanding of the structure of microporous optical materials such as aerogel through the interpretation of light scattering data. The Fourier transform of the densitydensity correlation function is used to relate measurements of the angular dependence of scattered light to material structure parameters. The results of the approach fit the unusual dependence of the intensity of scattered light as a function of angle for two polarizations. The fit shows that light scattering from aerogels may be interpreted as having two origins; one from the small scale structure of linked particles that comprise the material, and the second due to weak fluctuations in the average density of the microporous structure over distances significantly larger than the pore size.
The Pyrolytic Decomposition of Owens-Illinois Resin Gr650, an Organosilicon Compound
Authors: Bagley B. G. , Gallagher P. K. , Quinn W. E. , Amos L. J.
Published: March 2011

The pyrolytic conversion of an organosilsesquioxane (Owens-Illinois resin GR650) to SiO2 is characterized by ir spectroscopy, thermogravimetry and evolved gas analysis (line-of-sight mass spectroscopy). Scanning calorimetry, ramping at 10°C/min, on the as-received (room temperature annealed) resin indicates a glass transition temperature of 67°C which decreases to 58°C for an unrelaxed sample. The ir spectra have bands which can be assigned to Si-CH3 and Si-O-Si modes. For 30 minute isothermal anneals at temperatures above 420°C there is a continuous decrease in the bands associated with the Si-CH3 groups such that after 30 minutes at 650°C the ir spectrum has evolved to that for SiO2. Evolved gas analysis indicates that there are four major components evolving. Over the temperature range (ramping at 10°C/min) ∼180 to ∼500°C we observe C2H5OH and H2O, both of which are condensation reaction products from the curing reaction. Methane is a major evolving species over the temperature range ∼500 to ∼800°C and the thermal spectrum is double peaked which we attribute to CH3+ bound to the inside and outside of the polymer cage structures. The final major component detected was H2, over the temperature range ∼600 to ∼1100°C, which was attributed to pyrolysis of the organic components, both trapped and evolving. The features of the weight loss curve can be accounted for by the measured evolving species spectra.
Micro-Raman Spectroscopy of Fresh and Aged Silica Gels
Authors: Klein L. C. , Nelson C. , Higgins K. L.
Published: March 2011

Raman spectra were obtained from fresh and aged silica gels using micro-Raman techniques. Comparison of the spectra from wet and dried gels reveals the stages of reaction in the ethanol-TEOS-water system and the gradual development of the silica structure. The steady disappearance of bands assigned to ethanol and the appearance of bands assigned to silatious species can be traced during the drying process. Increases in either acid concentration or water level increase reaction rates to give gels in a more advanced stage of polymerization. Gels tend to develop fluorescence upon aging for several months. The source of this fluorescent could not be determined, but it's development can be prevented by heating freshly dried gels to about 155°C.
Organically Modified Silicates by the Sol-Gel Process
Authors: Schmidt H.
Published: March 2011

The introduction of organic groups into inorganic networks by the sol-gel process opens the possibility for the preparation of new materials, and typical properties resulting from inorganic as well as from organic components may be combined. Some general aspects and different examples of material developments are reviewed.
Multi-Phasic Ceramic Composites made by Sol-Gel Technique
Authors: Roy Rustum , Komarneni S. , Roy D.M.
Published: March 2011

Instead of aiming to prepare homogeneous gels and xerogels, this paper reports on work done to prepare deliberately diphasic materials. This has been achieved by three different paths: (1) mixing 2 sols; (2) mixing 1 sol with 1 solution; and (3) post formation diffusion of either one or two solutions.

By the last named process we have made SiO2, mullite and alumina based composites, with silver halides, BaSO4, CdS, etc., as the dispersed phase. The crystal size can be confined to the initial pores by rapid diffusion giving rise to extremely fine second phases in the submicron range. Subsequent reduction of appropriate metallic salts can be used to give finely dispersed metals (e.g. Cu, Ni) in essentially any xerogel matrix. The open porosity makes these metal atoms very accessible.

By the first two processes we have made both single phase and di-phasic gels of the same composition (prototype: mullite) and shown that though they cannot be distinguished by XRD, SEM, and TEM, by DTA and thermal processing, they are radically different. Such di-phasic gels store more metastable energy than any other solids.
Formation of Glass and Amorphous Oxide Fibers from Solution
Authors: Sakka Sumio
Published: March 2011

A review has been made of our works on two types of sol-gel methods for obtaining oxide fibers through low temperature process: (1) the alkoxide method and (2) the freezing-of-gel method. In the alkoxide method, metal alkoxides in an alcoholic solution are hydrolyzed and polycondensed into chain-like polymers, drawn into gel fibers near room temperature and heated to several hundred °C. Various problems encountered in the process are discussed with SiO2-based fibers. In the freezing-of-gel method, a hydrogel is unidirectionally frozen by lowering the gel cylinder into a cold bath. Thawing of unidirectionally grown ice crystals leaves a bundle of hydroxide fibers. Factors affecting the formation of fibers are discussed with titanium and zirconium hydroxide fibers as examples.
Phase Separation In Blends of Polystyrene and Poly (P-METHYLSTYRENE) Using Thermal Analysis And Small-Angle Neutron Scattering
Authors: Xenopoulos A. , Londono J. D. , Wígnall G. D. , Wunderlich B.
Published: March 2011

Differential scanning calorimetry (DSC) was used to study blends of polystyrene (PS) and poly (p-Methylstyrene) (PpmS). The presence of two glass transitions on heating after quenching was interpreted as evidence of phase separation at the temperature of the liquid before quenching. The small difference between the glass transitions of the homopolymers in the PS/PpmS system of “13 K limits the reliable detection of double glass transitions for blends to concentrations between 30 and 70%. The results of the DSC technique are supported by comparison with small angle neutron scattering (SANS) data.
Simulation Studies Of Titanium And Zirconium Wadeite Glasses
Authors: Vessal Behnam , Dickinson James E.
Published: March 2011

Molecular dynamics simulations of the structure of crystalline and glassy titanium and zirconium wadeites have been undertaken to study the microscopic origin of the striking difference between these two systems in terms of nucleation and surface crystallization. The results of simulation are in accord with Raman and EXAFS spectroscopy as well as neutron scattering and DTA scans on the same structures.
Nucleation and medium Range Order in Silicate Liquids: Inferences From NMR Spectroscopy
Authors: Stebbins Jonathan R. , Sen Sabyasachi
Published: March 2011

NMR spectroscopy is beginning to provide quantitative information on short- and medium-range structure in silicate glasses and liquids, and on molecular-scale dynamics in the liquids. Data on coordination numbers, second and higher neighbor connectivities, and larger scale heterogeneities, as determined by NMR at ambient and high temperatures, are potentially very useful in models of nucleation and growth of immiscible liquid and crystalline phases. New techniques such as dynamic angle spinning (DAS), high temperature magic angle spinning (MAS) are especially promising. Detailed studies of paramagnetic nuclear spin relaxation can characterize compositional heterogeneity in glasses to distance scales of at least several nanometers.
Relaxation and Deformation in Glassy Polymers
Authors: Chow T. S.
Published: March 2011

A unified account of the structural relaxation and nonlinear deformation in glassy polymers is presented. The glassy state relaxation is derived from the local configurational rearrangements of molecular segments, and the dynamics of hole motion. We then apply this to predict the nonlinear stress-strain relationships.
Amorphous-to-crystalline transition in Tb33Fe66 films studied via EXAFS
Authors: Hams V. G. , Das B. N. , Elam W. T. , Koon N. C.
Published: March 2011

The amorphous-to-crystalline transition in sputter-deposited amorphous Tb33Fe66 films has been studied using a conversion-electron extended X-ray absorption (EXAFS) technique. Modeling of the EXAFS data using theoretical and empirical standards allowed the quantitative measurement of coordination, radial distance, and disorder of local atom shells around the Fe sites after varying degrees of heat treatments.
Transient Nucleation in Devitrification
Authors: Greer A. L.
Published: March 2011

A review is given of transient crystal nucleation in glassy or amorphous solids. The types of behaviour are surveyed. It is shown that the kinetics can be quantitatively modelled and that the matching of experiment and theory provides an important test of the classical theory. Examples are considered of homogeneous nucleation (affecting glass formation), heterogeneous nucleation, and nucleation at an interphase interface. While the emphasis is on transient effects of the kind implicit in the classical theory, it is shown that transients can arise for other reasons as well, thus potentially complicating the interpretation of experiments.
The Elastic Strain Energy of Coherent Ellipsoidal Precipitates in Anisotropic Crystalline Solids: Applications to the Aragonite-Calcite Transformation
Authors: Liu Ming
Published: March 2011

Eshelby's theory has been applied to the aragonite-calcite transformation in order to calculate the elastic strain energy of coherent ellipsoidal precipitates in anisotropie solids. Using a quasiNewton's Method and a finite-difference gradient, the elastic strain energy was incorporated in order to calculate the activation energy ΔG* for homogeneous nucleation under hydrostatic and non-hydrostatic conditions.
Analysis of Crystal Nucleation and Growth in Amorphous Cobalt Disilicede.
Authors: Smith D. A. , Evans P. V. , Koppikar S. R.
Published: March 2011

Extensive in situ investigations of the crystallization of amorphous cobalt disilicide have been conducted using a transmission electron microscope with a hot stage. Thermodynamic and kinetic parameters describing the heterogeneous transformation have been evaluated. The angle of contact betwen crystalline and amorphous material was determined from tilting experiments to be 76°. Nucleation rates in samples 40 nm thick were evaluated at various temperatures and compared with thermodynamic models to deduce an interfacial energy between amorphous and crystalline COSi2 (σca) of 121 mJ/m2 and an activation energy for crystallization of 1.27 eV. Johnson-Mehl-Avrami analysis of the observed continuous nucleation and steady state isotropie growth in 100 nm thick samples points to a gradual transition of the crystallization mode from 3-dimensional (n=4) to 2-dimensional (n=3) growth as might be expected. Comparison of the nucleation and growth rates in 40 nm and 100 nm thick samples demonstrated the influence of surfaces on crystallization phenomena in thin films.
Crystallization Kinetics In A Ni24Zr76 Amorphous Alloy
Authors: Ghosh G. , Chen F.-R.
Published: March 2011

Isothermal crystallization kinetics of Ni24Zr76 amorphous alloy has been studied by differential scanning calorimetry (DSC). Theoretically estimated transient times are found to be consistent with the experimentally observed incubation periods. The crystallization kinetics has been analyzed in terms of Kolmogorov-Johnson-Mehl-Avrami (KJMA) Model and significant departure from the linear KJMA behavior was observed. Such non-linearity is due to the surface-induced crystallization, anisotropie growth of the crystals, impingement effects and variation of the nucleation rate during crystallization etc. By applying high-resolution electron Microscopy (HREM), it has been shown that the nucleation and growth of the crystals do not take place at a constant state of disorder.
Amorphous/Crystalline Structure And Phase Transformations In Metastable Semiconducting Ge1−xSnx
Authors: Lee Susanne M. , Barmak Katayun
Published: March 2011

The semiconducting crystalline alloys, Ge1−xSnx, are of interest due to theoretical predictions about their electronic band structures which make them useful in infrared photodetectors. However the composition region where these alloys have the desired properties is greater than the equilibrium solid solubility limit of Sn in Ge (x<0.01). We have circumvented the solubility limits and produced thin (2000Å) and thick (4–8Μm) films of Gei.xSnx (x<0.31) by rf sputtering. Differential scanning calorimetry (DSC) Measurements were performed to study grain growth and crystallization processes in these highly metastable semiconductors. X-ray and electron diffraction measurements indicated the materials were amorphous, but the fact that some of the films were fine grained polycrystalline samples only became apparent in their DSC spectra. We present models that describe quantitatively the transformation behavior in both sets of films.
Heterogeneous Nucleation of Superparamagnetic Phases in “Fe-Bearing Cordierite-Glasses
Authors: Abs-Wurmbach Irmgard , Boberski Cornelia
Published: March 2011

Glasses of stoichiometric cordierite composition Mg2(Al1−xFex)4Si5O18, containing very low iron contents (x=0.015 and 0.005) have been investigated by 57Fe Mössbauer spectroscopy. At higher Fe concentrations spinel exsolution has been observed in X-ray powder patterns. To allow Mössbauer spectroscopy at very low Fe-concentrations (<0.8 weight* Fe2O), starting materials were doped with 100% 57Fe. Glasses prepared in air at 1560°C were also oxidized In water saturated O2 stream. Glasses were crystallized to cordierite by heating In air at 1100 to 1400°C. 57Fe-Mössbauer spectra of all samples are governed by a doublet typical for Fe2+ in octahedral coordination (IS: 1.09–1.15, QS: 2.00–2.31 in MM/s relative to metallic iron). X-ray powder patterns exhibit no additional phases. But, the 295 K and 5 K Mössbauer spectra of treated and untreated glasses and of cordierltes exhibit broad lines, which have been fitted by applying internal magnetic hyperfine fields H of ca. 500 kG. These lines are attributed to heterogeneously nucleated, superparamagnetic (MgFe) (AlFe)2O4 spinels of complex compositions. From the calculated subspec-tra one may conclude that 35 to 65% of the total iron, depending on preparation conditions, is incorporated in the spinels.
Stability And Precipitation Kinetics In Si1-yCy/Si and Si1-x-yGexC/Si Heterostructures Prepared by Solid Phase Epitaxy
Authors: Strane J. W. , Picraux S. T. , Stein H. J. , Lee S. R. , Candelaria J. , Theodore D. , Mayer J. W.
Published: March 2011

This study investigates the stability of Metastable Si1-yCy/Si heterostructures during rapid thermal annealing (RTA) over a temperature range of 1000 – 1150° C Heterostructures of Si1-yCy/Si and Si1-x-yGexCy/Si (x=0.077, y ≤ .0014) were formed by solid phase epitaxy from C implanted, preamorphized substrates using a 30 Minute 700° C anneal in N2. The occupancy of C in substitution lattice sites was monitored by Fourier Transform Infrared Absorption spectroscopy. The layer strain was monitored by rocking curve x-ray diffraction and the structural changes in the layers were determined using plan-view and X-sectional transmission electron Microscopy (TEM). For anneals of 1150° C or above, all the substitutional C was lost from the Si lattice after 30 seconds. TEM verified that the strain relaxation was the result of C precipitating into highly aligned βSiC particles rather than by the formation of extended defects. No nucleation barrier was observed for the loss of substitutional C Preliminary results will also be discussed for Si1-x-yGexCy/Si heterostructures where there is the additional factor of the competition between strain energy and the chemical driving forces.
Crystallization Processes In Poly (Ethylene Terephthalate) / Polycarbonate Blends
Authors: Reinsch Veronika E. , Rebenfeld Ludwig
Published: March 2011

Blends of poly (ethylene terephthalate), or PET, and polycarbonate (PC) over a range of compositions were studied in isothermal crystallizations from the melt using differential scanning calorimetry (DSC). Both crystallization rate and degree of crystallinity of PET depend on blend composition. The glass transition temperature, Tg, of PET and PC in blends and pure polymer were also measured by DSC. Elevation of the Tg of PET and depression of the Tg of PC are observed upon blending. In cooling scans, dynamic crystallization from the melt was observed. In PET/PC blends with high PC content, a novel dual-peak crystallization of PET was observed. The effects of thermal history on crystallization kinetics and degree of crystallinity were also determined in isothermal crystallization studies. For Melt processing times between 1 and 30 Min and for processing temperatures between 280 and 300 °C, Melt processing temperature was seen to have a stronger effect than processing time.
The Evolution of Sol-Gel Films in the Environmental Scanning Electron Microscope.
Authors: Mckernan Stuart , Wright John , Francis Lorraine F.
Published: March 2011

The ability to study the surface texture of a sol-gel film of lead titanate as it is heated in-situ in an environmental scanning electron microscope is demonstrated. Measurements of the shrinkage of the film at cracks and around delaminations of several microns have been Made. Grain sizes of the final crystalline microstructure were determined to be ∼ 0.2 μm. The formation of bumps in the film 1–5 μm in size was observed. The presence of these features may correlate with the onset of crystallization.
The Pyrolytic Conversion of Perhydropolysilazane into Si3N4: X-Ray Diffraction Analysis
Authors: Blanchard Cheryl R. , Schwab Stuart T.
Published: March 2011

X-ray diffraction analysis was used to study the pyrolytic conversion of a preceramic polysilazane into Si3N4. Quantitative data for crystallite size, phase composition, and degree of crystallinity versus pyrolysis temperature and atmosphere (N2 and NH3) are presented. Pyrolytic products produced under N2 and NH3 atmospheres consist of microcrystals of silicon and a- and β-Si3N4. Under both atmospheres, a majority of the char is crystalline at ∼ 1270°C, and the entire char is crystallized at 1400°C. Pyrolysis under an NH3 atmosphere produces near stoichiometric Si3N4, while pyrolysis under N2 produces a silicon-rich material.
Crystallization Process and Chemical Disorder in Flash Evaporated Amorphous Gallium Antimonide Films
Authors: Dias Da Silva J. H. , Cisneros I. , Cardoso L. P.
Published: March 2011

In this work we describe a flash evaporation system specially built to produce Amorphous films of III-V compounds and characterize GaSb films using optical, electrical and X-Ray diffraction Measurements. Changes in the composition of the GaSb samples were obtained by the use of different crucible temperatures. In such samples, consequently, the optical absorption edge and the DC electrical conductivity were Modified. The departure from stoichiometry in GaSb films is analyzed on the basis of these results which can be used as an evidence of the chemical disorder. This kind of disorder is represented by either wrong bonds or sites with different coordination.

Thermal annealing with a sequence of increasing temperatures first induced detectable variations in the optical absorption edge and in the vibrational properties of the Amorphous GaSb. These variations are compatible with the GaSb local ordering and were observed by Raman scattering and infrared absorption spectra. The annealing at higher temperatures allowed the crystallization of the material confirmed by X-Ray diffraction. From these experimental results a crystallization mechanism based on the segregation of Sb excess coming from the crystallized regions toward the Amorphous tissue is proposed.
Lateral Grain Growth in the Excimer Laser Crystallization of Poly-Si
Authors: Kuriyama H. , Sano K. , Ishida S. , Nohda T. , Aya Y. , Kuwahara T. , Noguchi S. , Kiyama S. , Tsuda S. , Nakano S.
Published: March 2011

We have succeeded in obtaining nondoped, thin poly-Si film (thickness ∼500Å) with excellent crystallinity and large grain size (Maximum grain size ∼4.5 μ m) by an excimer laser annealing Method, which offers the features of low-temperature processing and a short processing time. The grain size distribution shrinks in the region around 1.5 μ m and this poly-Si film exhibits a strong (111) crystallographic orientation. Poly-Si thin film transistors using these films show quite a high field effect mobility of 440cm2/V · s below 600°C process.
Excimer Laser Crystallization of Amorphous Silicon Films for Poly-Si TFT Fabrication
Authors: Tanabe Hiroshi , Sera Kenji , Nakamura Ken-Ichi , Hirata Kazumi , Yuda Katsuhisa , Okumura Fujio
Published: March 2011

Excimer laser crystallized silicon films have been studied as a function of the number of laser shots, and the influence of the use of such polycrystalline films in thin film transistors (TFTs) has also been investigated. It is found that electron Mobility, one of the most important of all TFT characteristics, increases monotonically with the number of irradiations, with maximum mobility being obtained at about 20 shots. This result is not due to grain size, since transmission electron microscopy indicates that the number of laser shots does not affect grain size in polycrystalline silicon films. Raman studies and TFT carrier transport analysis, on the other hand, suggest that this increase in electron mobility may be explained by the decrease in grain boundary defects and defects inside grains.
Compamson in the Growth and Properties of rf Sputtered μc-Si:H and Glow Discharge-Chemical Vapor Deposited μc-Si:H Films
Authors: Lin J. Y. , Tseng B. H. , Hsu K. C. , Hwang H. L.
Published: March 2011

Properties of μc-Si:H films grown by rf sputtering and by glow discharge-chemical vapor deposition (GD-CVD) using diluted-hydrogen and hydrogen-atom-treatment method were compared employing TEM, X-ray diffraction, Raman scattering and FT-IR. The films deposited by both methods all exhibited comparable grain sizes in the range of 10–18 nm. and showed the same tendency in almost all the Measurements.
The Sensitivity of Small Molecule Sorption to Annealing in Glassy Liquid Crystalline Polymers
Authors: Morisato Atsushi , Miranda N. R. , Willits J. T. , Cantrell G. R. , Freeman B. D. , Hopfenberg H. B. , Makhija S. , Haider I. , Jaffe M.
Published: March 2011

The sorption of organic penetrants is found to be sensitive to thermal annealing conditions in a series of glassy, nematic, thermotropic, random copolyesters. Controlled thermal annealing of two polymers in this series permitted a systematic variation of chain packing and, presumably, higher order molecular suprastructure, ranging from a disordered amorphous morphology to More ordered nematic liquid crystalline and semi-crystalline morphologies. The development of liquid crystalline order appears to reduce or preclude small molecule solubility in nematically ordered forms of these polymers.
Mechanical Properties of Plated Copper
Authors: Korhonen M. A. , Brown D. D. , Li C.-Y. , Steinwall J. E.
Published: March 2011

Both electrodeposited and electroless copper are widely used in the electronics industry to form signal lines and plated-through holes in printed circuit cards and boards. Because of widely differing thermal expansion coefficients of copper and of the ceramic and polymeric substrates, large mechanical stresses develop in the metallization during thermal cycles, as e.g. during solder reflow. To safeguard against premature fracture it is imperative that the metallization is sufficiently ductile. Plated thin foil copper of poor ductility is known to be susceptible to cracks in plated-through holes which, besides causing problems in the manufacture, poses a threat to device reliability in service. In this paper we show that such cracks arise as a combination of reduced ductility due to presence of initial porosity in copper and due to grain boundary sliding and diffusional cavity growth during the soldering cycle. We emphasize that there exists strong interactions between these ductility reducing effects, such that their coupled action may exceed the effect when each mechanism operates independently. We review recent research on deformation and fracture of bulk and plated copper between RT and 300°C. Finally, we briefly discuss approaches to improve mechanical properties of plated thin foil copper.
Models for the Thermomechanical Behavior of Metal/Ceramic Laminates
Authors: Spearing S. M. , Tenhover M. A. , Lukco D. B. , Viswanathan L. , Hollen D. K.
Published: March 2011

Metal/ceramic bilayers fracture by one of three failure modes; crazing, spalling or interfacial failure. Models for these failure modes are developed. The results are presented as maps that can be used in the design and failure analysis of electronic packages. Examples are presented for several material systems, including A1N.
Ternary Phase Formation in 95Pb-5Sn Flip-Chip Solder Bonds
Authors: Mockler Alan J. , Goodhew Peter J. , Logan Elizabeth A.
Published: March 2011

The microstructure of 95Pb-5Sn flip-chip solder bonds deposited on Cr/Cu/Au metallisation pads has been studied using both light and electron analysis techniques. The presence of Sn-Cu- Au ternary intermetallic phases was detected within the Pb-rich matrix at significant distances from the originally deposited interface. The distribution of the phases present after the solder has undergone a reflow heat treatment can be interpreted using recent equilibrium ternary diagram data. An investigation was also made into the effects of various non-reflow heat treatments at carefully chosen temperatures, to qualitatively evaluate the extent of solid state diffusion and the resultant phase distribution.