bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation, Structure, And Electronic Properties Of Amorphous Gaas By Tight-Binding Molecular Dynamics
Authors: Molteni C. , Colombo L. , Miglio L. 
Published: March 2011

ABSTRACTWe investigate the short-range structural properties of a-GaAs as obtained in a computer experiment based on a tight-binding molecular dynamics simulation. The amorphous configuration is obtained by quenching a liquid sample well equilibrated at T=1600 K. A detailed characterization of the topology and defect distribution of the amorphous network is presented and discussed. The electronic structure of our sample is calculated as well. Finally, we discuss the reliability and transferability of the present computational scheme for large-scale simulations of compound semiconductor materials by comparing our results to first-principles calculations.
First Stages of Nano-Crystallization of Amorphous Fe75.5Cu1Si12.5B8 Studied by the Positron Annihilation Lifetime Technique
Authors: Kruk A. J. , Schut H. , Sietsma J. , Van Veen A. 
Published: March 2011

ABSTRACTThe first stages of the nano-crystallization process of amorphous Fe75.5Cu1Nb3Si12.5B8 into a nano-crystalline structure are investigated by the positron annihilation lifetime technique. Samples have been isothermally annealed at 643 K for times varying between 600 and 105 seconds. The positron lifetime spectra have been analyzed allowing for three lifetimes. The shortest and the longest lifetime, τ1 = 150 ± 2 ps and τ3 = 1500–2000 ps respectively, are attributed to annihilation of positrons in the amorphous phase and to the formation and annihilation of ortho-positronium at the surface of the stacked foils and did not change significantly upon the annealing. The intermediate positron lifetime τ2 increased from 324 ps to 387 ps. The intensity of this component increased from 5 to 15%. Comparison with resistivity measurements indicates that the change of this lifetime component occurs at an early stage in the crystallisation process, i.e. when the fraction of crystalline material is on the order of 10−3. The increase of τ2 is attributed to positrons annihilating in a region with lower average density surrounding the small crystallite.
High Temperature Calorimetric Study of Mixing, Phase Separation, and Crystallization in Silicate Glasses
Authors: Navrotsky Alexandra 
Published: March 2011

ABSTRACTSeveral glass forming systems have been studied by in situ scanning calorimetry and by solution calorimetry in Molten 2PbO.B2O3 at 973 K. In systems which show macroscopic glass-glass phase separation on annealing, namely K2O-La2O3-SiO2 and Li2O-SiO2, the enthalpies of solution of optically clear quenched glasses and milky annealed glasses are almost identical. This behavior, coupled with a linear variation of heat of solution with composition along joins which have a large change in overall degree of polymerization, support the contention from spectroscopy that short range clustering dominates even in nominally single phase Materials, with exsolution observed as the initially present heterogeneous regions grow in size. Alkali titanosilicate melts show Cp anomalies consistent with breakdown of alkali titanate complexes or changes in Ti coordination. Calorimetry is a sensitive quantitative probe of crystallization as a function of time in both ceramic and geologic systems.
Nucleation And Growth Rates in Isothermal Crystallization Op Amorphous Si50Ge50 Films
Authors: Song J. H. , Im James S. 
Published: March 2011

ABSTRACTIsothermal crystallization behavior of as-deposited thin amorphous Si50Ge50 films (∼1000Å-thick) at 580°C has been investigated using transmission electron Microscopy (TEM). The crystal counting method was employed in order to obtain directly the two-dimensional steady-state crystal nucleation rate of 3.9×103 #/cm2sec (equivalent volumetric nucleation rate of 3.4×108 #/cm3sec). The Modified two-dimensional Johnson-Mehl-Avrami analysis, in which the growth rate of the crystals was the only adjustable parameter, and in which the time-dependent nucleation rate and the size effect associated with the onset of the observation are considered, was developed in order to extract the crystal growth rate of 16.5 Å/sec. When compared to the crystallization of a-Si films, these nucleation and growth rates confirm the observation that it is possible to achieve significantly faster crystallization at lower temperatures while producing substantially better Microstructures (i.e., > 5 μ grain-sized poly-Si50Ge50 obtained within two hours at 580°C vs. 1–2Μm grain-sized poly-Si obtained in about > 10 hours at 600°C).
Ion-Beam-Driven Amortization of Ca2La8 (SiO4)6O2 Single Crystals
Authors: Weber W. J. , Hess N. J. , Wang L. M. 
Published: March 2011

ABSTRACTSingle crystals of Ca2La8(SiO4)6O2, with 1% Nd substituted for La, were irradiated with 0.8 MeV Ne+ and 1.5 MeV Kr+ ions over the temperature range from 15 K to 773 K. The irradiations were carried out using the HVEM-Tandem Facility at Argonne National Laboratory. The structural changes and the ion fluence for complete amorphization were determined by in situ transmission electron Microscopy. The ion fluence for complete amorphization increased with temperature in two stages associated with defect annealing processes. The critical temperature for amorphization increased from -360 K for 0.8 MeV Ne+ to -710 K for 1.5 MeV Kr+. During in situ annealing studies, irradiation-enhanced recrystallization was observed at 923 K. Spatially-resolved fluorescence spectra of the Nd ion excited with 488.0 nm laser excitation showed marked line-broadening toward the center of the amorphous regions. Initial Measurements indicate the subtle shifts of the 9I9/2 groundstate energy levels can be measured by pumping directly into the excited state 4F3/2 Manifold suggesting that the line broadening observed originates from a distribution of geometrically distorted Nd sites.
Ion Beam Induced Graphitization of Phenolformaldehyde
Authors: Ila D. , Evelyn A. L. , Jenkins G. M. 
Published: March 2011

ABSTRACTWe have studied MeV ion beam induced phase transformation in phenolformaldehyde cured at 170°C by both Raman Microprobe spectroscopy and in situ resistance measurement of the irradiated area. Samples were irradiated using various doses of protons, alphas and nitrogen beams. Irradiated volumes in each sample were tested in situ for enhanced electrical conductivity and later on by Raman Microprobe spectroscopy. The results have shown changes in the resistance as much as seven orders of magnitude by alpha particles, six orders by nitrogen bombardment and three orders by hydrogen. Raman Microprobe spectroscopy of the darkened phase shows development of the D- and G-lines which are characteristic of the production of a carbonized resin. These spectra indicate that maximum carbonization was caused by the nitrogen beam.
The Effect of Strain and Strain-Gradients on the Crystallisation Kinetics of S1−xGex Alloy Layers
Authors: Kringhøj Per , Elliman Robert G. , Hansen John L. 
Published: March 2011

ABSTRACTA comparison of strain relief in SiGe alloy layers during high temperature annealing and solid phase epitaxial crystallisation (SPEC) has shown that layers which are thermodynamically stable are also fully strained following SPEC, whereas metastable layers that relax at high temperatures also relax during SPEC. This is illustrated by the fact that a uniform SiGe layer with x=0.085 is stable during annealing at 1100°C for 60 sec and is fully strained following SPEC. In contrast, a uniform layer with x=0.17, which was fully strained as-grown by molecular beam epitaxy (MBE), is shown to relax during high temperature annealing and during SPEC.A depth dependent SPEC velocity is observed for metastable layers, with a decrease in velocity as the alloy layer begins to crystallise and an increase in velocity as strain relaxation proceeds.
A Positron-Annihilation-Lifetime study of Polymer Blends
Authors: Liu J. , Jean Y. C. , Yang H. 
Published: March 2011

ABSTRACTPositron-annihilation-lifetime (PAL) spectroscopy has been utilized to investigate the free-volume properties of two types of polymer blends, a miscible blend of bisphenol-A polycarbonate (PC) and tetramethyl bisphenol-A polycarbonate (TMPC), and an immiscible blend of PC and polystyrene (PS). In the miscible blend, the free-volume hole size and its fraction follow a linear relationship with respect to the weight fraction while in the immiscible blend, the relationship is not linearly additive. The free-volume hole distributions in the immiscible blend are found to be significantly broader than those in the pure polymers. The difference is thought to be a result of the free volume formed and associated with the conformation and interchain packing between the dissimilar chains in incompatible polymers.
Solid Phase Epitaxy Process Of Ar-Ion Bombarded Silicon Surfaces and Recovery of Crystallinity by Thermal Annealing Observed With Scanning Tunneling Microscopy
Authors: Uesugi Katsuhiro , Yoshimura Masamichi , Yao Takafumi 
Published: March 2011

ABSTRACTThe solid-phase epitaxy (SPE) process of Ar+-ion bombarded Si (001) surfaces and recovery of crystallinity by thermal annealing are studied “in situ” by using a scanning tunneling Microscope (STM). As-bombarded surfaces consist of grains of 0.63–1.6 nm in diameter. The grains gradually coalesce and form clusters of 2–3.6 nm in diameter at annealing temperature of 245° C (2×1) and (1×2) reconstructed regions surrounded by amorphous regions are partially observed on the surface by prolonged annealing, which suggests the onset of SPE. Successive observation reveals that the smoothing of the surface occurs layer by layer. As annealing temperature is raised up to 445 °C, the amorphous layer epitaxially crystallizes up to the topmost surface, and (2×1) reconstructed surface with Monatomic-height steps is observed. The smoothing of the surface structures and the formation of nucleation of Si islands are observed during annealing at 500 °C.
Bulk Semicrystalline Polymers: A Status Report
Authors: Keith H. D. 
Published: March 2011

ABSTRACTDiscovery several decades ago that long-chain molecules crystallize by folding prompted vigorous basic research on structure-property relations in bulk semicrystalline polymers with expectation of insights that, paralleling experience in metal physics, would lead to better materials for technology. However, complexity of the crystallization process and difficulty in exploring morphology in adequate detail were both underestimated. Important aspects of behavior were recognized but improved polymeric materials have resulted more from exploratory engineering with composites and blends than from basic research on homopolymers. A summary of this research is presented with emphasis upon developments key to present status; also upon the truly formidable challenges that remain, Most readily accessible questions for research being of limited technological significance.
Shear Induced Morphology Of Semicrystalline Block Copolymers
Authors: Kofinast Peter , Cohen Robert E. 
Published: March 2011

ABSTRACTA series of semicrystalline diblock copolymers of poly (ethylene) / poly (ethylene-propylene) (E/EP) were subjected to high levels of plane strain compression using a channel die. Deformations were imposed both below and above the melting point of the E block. The crystallographic and morphological textures were examined using wide-angle x-ray diffraction pole figure analysis and two dimensional small-angle x-ray scattering. The lattice unit cell orientation of the crystallized E chains with respect to the lamellar superstructure was determined, as well as the lamellar orientation relative to the specimen boundaries. When the diblocks are textured above the E block melting point at various compression ratios, the lamellae orient perpendicular to the plane of shear, while texturing below Tm causes the lamellae to orient parallel to the plane of shear. The orientation of the crystallized E chains was perpendicular to the lamellar normal, irrespective of the texturing temperature. The various shear-induced lamellar morphologies have potential applications in gas transport control to develop membranes for use in gas separations or as barrier Materials.
In-Situ TEM Crystallization of Anorthite-Glass Films on α-Al2O3
Authors: Mallamaci Michael P. , Bentley James , Barry Carter C. 
Published: March 2011

ABSTRACTAnorthite-glass films have been grown by pulsed-laser deposition on single-crystal α-Al2O3 substrates which were pre-thinned to electron transparency. The glass films were crystallized in the transmission electron Microscope (TEM), which allowed direct observation and video-recording of the crystallization process. Crystallization of these films in the TEM resulted in the formation of hexagonal and orthorhombic anorthite. The orthorhombic phase was the predominant product of glass films grown at elevated substrate temperatures and displayed strong epitaxy with the underlying substrate. In contrast, the hexagonal phase was the major constituent of films grown at ambient substrate temperature and displayed no clear epitaxy with the substrate. The differences in degree of epitaxy and phase structure may be evidence of ordering at the original glass/oxide interface.
High Resolution In Situ TEM Studies of Silicide-Mediated Crystallization of Amorphous Silicon
Authors: Hayzelden C. , Batstone J. L. 
Published: March 2011

ABSTRACTWe report in situ high resolution transmission electron microscopy studies of NiSi2-Medi-ated crystallization of Amorphous Si. Compared to conventional solid phase epitaxy of (111) Si, an enhancement of the growth rate by three orders of magnitude was observed and high quality twin-free needles of <111> Si were formed. Crystallization occurred via a ledge growth mechanism at the epitaxial Type A NiSi2/crystalline Si (111) interface. A Model for NiSi2-Mediated crystallization of Amorphous Si involving the passage of kinks along <110> ledges at the NiSi2/crystalline Si (111) interface is proposed.
Crystallization of Glass Films on Single-Crystal MgO Substrates
Authors: Ramamurthy Sundar , Mallamaci Michael P. , Barry Carter C. 
Published: March 2011

ABSTRACTThin, calcium magnesium silicate glass films have been deposited onto (001) -oriented single-crystal MgO substrates by pulsed-laser deposition (PLD). The substrates were thinned to electron transparency and characterized in the transmission electron Microscope (TEM) before and after the deposition and following different heat treatments. Energy Dispersive X-ray Spectroscopy (EDS) was used in the TEM to characterize the chemistry of the films. The heat treatments were performed both in situ and ex situ. Direct evidence for crystallization was obtained by in-situ experiments at 950°C. Subsequent heat treatments were performed for longer times in air between 950°C and 1100°C. The crystallized phase was found to be Monticellite (CaMgSiO4) and the crystallites show moderate epitaxy with the underlying substrate. Films contaminated with aluminum resulted in the growth of magnesium aluminate spinel (MgAl2O4) epitaxially from the substrate. These observations of epitaxy indicated that crystallization initiated at the surface of MgO.
Crystallization Of Silicon Thin Films Prepared By Ecr Pecvd
Authors: Lee Seok-Woon , Jeon Yoo-Chan , Joo Seung-Ki 
Published: March 2011

ABSTRACTSilicon thin films were deposited by Electron Cyclotron Resonance PECVD using silane as a source gas at room temperature. Deposited films were crystallized either by conventional furnace annealing(FA) or by rapid thermal annealing (RTA) process. The films deposited on SiO2/Si wafer substrates were Amorphous or microcrystalline depending on the microwave power. Deposited films were annealed at 600TC in a furnace. As expected, higher crystallinity was obtained in the case of the Amorphous films than the microcrystalline films after 7.5 hours annealing. It took 15 hours at 600δC for the Amorphous films to reach their maximum crystallinity in case of FA, but it only took 1 second at 900 δC for RTA. In addition, it was shown that RTA can be applied to the rapid crystallization of Amorphous silicon thin films deposited on a fused quartz substrate utilizing a new film structure.
Solid State Ordering of Wholly Aromatic Copolyesters of Random Monomer Sequence
Authors: Blackwell J. , Schneider A.-I. , McCullagh C. M. 
Published: March 2011

ABSTRACTX-ray diffraction and computer molecular modeling Methods are being used to investigate the ordering of random sequence copolyesters when cooled for the nematic Melt. Data will be presented for the copolymers prepared from p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid. The non-periodic diffraction patterns arising from the random monomer sequences are also indicative of the presence of limited three dimensional order. For both polymer systems, we can generate the qualitative feature of the x-ray data using models in which short non-identical segments of 10–12 Monomers on adjacent chains are approximately in register at their center. Molecular Mechanics calculations show that mese non-identical sequences can be packed on the observed hexagonal lattice with only small energy differences when compared to analogous homopolymer structures. Data will also be presented showing how x-ray diffraction can be used to follow transesterification of copoly (HBA/HNA) in the nematic MelL
Reliability of Flex Coatings for High-Performance Applications
Authors: Tong H. , Wilson C. , Graham T. , Shi L. 
Published: March 2011

AbstractA study was undertaken to select a suitable coating for a high-pin-count flexible edge connector (Flex) that interconnected a multichip thin-film silicon carrier to a printed circuit board. The Flex with cantilevered inner leads were joined to the contact pads at the perimeter of the carrier. 15 polymeric coatings were evaluated by subjecting coated Flexes to tests consisting of inner lead bending, temperature/humidity/bias (85°C/80%/15 V/350 hours), corrosion, line peel, and/or pressure cooker (126°C/20 psig/120 hours). Inner lead bending measurements were performed to assess the potential of lead shorting at the inner lead bonding sites during thermal cycling. From this study, a low-stress silicone evolved as the best candidate. The results leading to this conclusion will be shown and discussed.
A Study of Sn-Pb-Re Solder
Authors: Ying Zhu , Hongyuan Fang , Yiyu Qian 
Published: March 2011

AbstractOne of the important way to improve the property of solder joints is to improve the property of solders, This paper is about a study of Sn-Pb-RE solder(RE-Rear Earth, mainly contains Ce and La). It has been shown that the final form of RE in SnPb60/40 solder is Sn-RE intermetallic compound, and a very little RE can change the solder microstructure greatly. The influence of RE on solder life of creep rupture is that Sn-Pn-RE solder has much long life than that of SnPb60/40, and the solder life increases with the increase of RE content.
Characterizing Soldering Fluxes
Authors: Turbini Laura J. , Freeman Garth B. , Cauffiel David 
Published: March 2011

AbstractFor a number of years electronic manufacturers of printed circuit assemblies have used rosin-based soldering fluxes. Post-solder cleaning was accomplished with chlorinated or chlorofluorocarbon (CFC) solvents. With the elimination of these solvent options due to their destructive effect on the stratospheric ozone layer, manufacturers are looking to alternative cleaners for rosin flux or to new flux choices which can be cleaned with water, or left uncleaned.Many of the flux formulations are new and their long-term effect on the performance of product manufactured with them is unknown. Although ionic contamination testers can alert one to the ionic levels remaining on an assembly, the corrosivity of the residues is not directly related to the total ionic level, but only to certain ionic species. Surface insulation resistance testing is used by many in the industry, but the results are complex and often misunderstood.All of these factors have been the driving force to develop a quantitative screening test for soldering flux residues. This test, originally conceived by Dr. David Bono, has been modified and developed at Georgia Tech to provide a quantitative evaluation of flux residue corrosivity. This work, in collaboration with the work being performed by the French standards group, will result in a new international industry standard. This paper reports the latest data on this important test development.
An Experimental and Modeling Study of Thermal Cyclic Behavior of Sn-Cu and Sn-Pb Solder Joints
Authors: Pao Y.-H. , Badgley S. , Govila R. , Jah E. 
Published: March 2011

AbstractThermal cyclic shear stress/strain hysteresis response of 97Sn-2Cu-0.8Sb-0.2Ag, 95.5Sn-4Cu-0.5Ag, 63Sn-37Pb, and 62Sn-36Pb-2Ag solder joints have been determined using a double beam specimen. The temperature cycle had a period of 40 minutes and extreme temperatures of 40°C and 140°C.The steady state creep properties of these solders were determined, and the associated Norton's law was implemented in a finite element program to simulate the experiment. The fatigue life of these solders joints and failure mechanism are also discussed.
In-Situ Tem Study of Copper-Tin Intermetallic Formation
Authors: Wu Yujing , Jacobs Elizabeth G. , Pouraghabagher Cyrus , Pinizzotto Russell F. 
Published: March 2011

AbstractThe formation and growth of Cu6Sn5 and Cu3Sn at the interface of Sn-Pb solder/copper substrate are factors which affect the solderability and reliability of electronic solder joints. The addition of particles such as Ni to eutectic Sn-Pb solder drastically affects the activation energies of formation for both intermetallics. This study was performed to understand the mechanisms of intermetallic formation and the effects of Ni on intermetallic growth. Cu/Sn and Cu/Sn/Ni thin films were deposited by evaporation and observed in the TEM in real time using a hot stage. The diffusion of Sn through Cu6Sn5 and Cu3Sn followed by reaction with Cu must occur for intermetallic formation and growth to take place. Ni is an effective diffusion barrier which prevents Sn from diffusing into Cu.
The Oxygen-Related Defect in Aluminum Nitride Ceramics: a Thermal Conduction Limiting Defect in a Technologically Important Material
Authors: Harris Jonathan H. , Youngman Robert A. , Enck Rudy 
Published: March 2011

AbstractAluminum nitride (AlN) sintered ceramics are a critical new material for electronic packaging applications, principally because of AlN's high thermal conductivity and close thermal expansion match to silicon. AlN is expected to play a key role in the next generation of high powder electronic packages, in applications ranging from high power discrete component substrates to co-fired, multilayer packages for integrated circuits. In the following paper, a detailed picture of the oxygen-related defect in AlN ceramics is presented. This impurity is of critical technological importance, because vacancies associated with oxygen severely limit thermal conduction when present in high concentrations. The results of thermal conductivity measurements, luminescence studies, optical absorption experiments, photo-induced absorption studies and electrical measurements on both ceramic and single crystal samples will be presented in order to understand the detailed nature of this defect and to model its control over a number of important technological properties.