bluuebunny/crossref_metadata_2025_split huggingface dataset:
Atomistic Study of Boron-Doped Silicon
Authors: Fearn M. , Jefferson J. H. , Pettifor D. G. 
Published: April 2011

AbstractAtomistic simulations using both tight-binding and density-functional approaches have been performed to investigate boron-related defects in silicon. In agreement with experiment, the boron interstitial is shown to be a negative- U center in the sense that its neutral charge state, with an associated Jahn-Teller distortion off the ideal tetrahedral site, is never the ground state for any value of the chemical potential in the gap. The possible consequences for an electron-assisted migration of the interstitial are discussed. We also find the boron substitutional defect to be a next-nearest neighbor of a silicon vacancy in agreement with EPR spectra.A semi-empirical tight-binding model of the boron-silicon system is validated by direct comparison with the accurate density-functional results and is then used to perform molecular dynamics simulations of boron diffusion at high temperatures. The mobility of the interstitial is found to be strongly charge-state dependent. Termination of the boron interstitial migration path by recombination with a silicon vacancy is shown to be a very likely process with a number of configurations having no barrier to capture when the boron is a near-neighbor of the vacancy.
Molecular Dynamics Simulations for Xe Absorbed in Zeolites
Authors: Kantola J. -H. , Vaara J. , Rantala T. T. , Jokisaari J. 
Published: April 2011

AbstractWe have carried out molecular dynamics simulations for Xe atoms absorbed in two different zeolites, NaA and AlPO-11. The main emphasis is in the distribution of Xe in the zeolites, Xe-Xen, interactions in NaA, and structural data on Xe-zeolite cage interactions. We report single-particle and pair correlation data, along with diffusion constants of Xe at 300 K. NMR chemical shifts of Xe were estimated using ab initio parametrization.
Critical Evaluation of Atomistic Simulations of 3D Dislocation Configurations
Authors: Shenoy Vijay B. , Phillips Rob 
Published: April 2011

AbstractThough atomistic simulation of 3D dislocation configurations is an important objective for the analysis of problems ranging from point defect condensation to the operation of Frank-Read sources such calculations pose new challenges. In particular, use of finite sized simulation cells produce additional stresses due to the presence of fixed boundaries in the far field which can contaminate the interpretation of these simulations. This paper discusses an approximate scheme for accounting for such boundary stresses, and is illustrated via consideration of the lattice resistance encountered by straight dislocations and simulations of 3D bow out of pinned dislocation segments. These results allow for a reevaluation of the concepts of the Peierls stress and the line tension from the atomistic perspective.
Representation Of Finite Cracks By Dislocation Pileups: An Application To Atomic Simulation Of Fracture
Authors: Shastry Vijay , Farkas Diana 
Published: April 2011

AbstractThe elastic displacement field solution of a semi-infinite crack in an anisotropic body, calculated using a complex variable approach due to Sih and Liebowitz, is usually used by atomistic simulations of fracture. The corresponding expression for the displacement field of a finite crack is numerically cumbersome since it involves multiple square roots of complex numbers. In this study, displacement field of the crack is calculated by superposing the displacements of dislocations in an equivalent double pileup, equilibrated under mode I conditions. An advantage of this method is its extensibility to atomistic studies of more complex systems containing multiple cracks or interfaces. The pileup representation of the finite crack is demonstrated as being equivalent to its corresponding continuum description using the example of a double ended crack in a-Fe, loaded in mode I. In these examples, the interatomic interaction in α-Fe is described by an empirical embedded atom (EAM) potential.
Experimental Evidence For Sulfur Induced Loss Of Ductility In Copper Shaped-Charge Jets
Authors: Chan D. K. , Lassila D. H. , King W. E. , Baker E. L. 
Published: April 2011

AbstractWe have observed that a change in the bulk sulfur content of oxygen-free electronic copper markedly affects its high temperature (400–1000°C), high strain-rate (> 103 s−1) deformation and fracture behavior. These conditions are typical of those found in "jets" formed from the explosive deformation of copper shaped-charge liners. Specifically, an increase in the bulk sulfur concentration from 4 ppm to 8 ppm shortens the breakup time, tb, of the copper jets by nearly 20% as measured using flash x-ray radiographs recorded during breakup of the jets. At bulk concentrations of 4 ppm, the jet was observed to be uniform and axisymmetric with a breakup time of 186 µs. Jet particles exhibited length-to-diameter ratios of roughly 8:1. The addition of sulfur transformed the jet breakup behavior to non-uniform, non-axisymmetric rupture and reduced the breakup time to 147 µs. The length-to-diameter ratios decreased to roughly 5:1 in the sulfurdoped samples. Previously measured sulfur solubilities and diffusivities in copper at the temperatures where this material was processed indicates nearly all of the sulfur was localized to grain boundaries. Therefore, we infer that the increase in sulfur content at grain boundaries is directly responsible for the change in breakup performance of the shaped-charge jets.
Effects Of Externally Generated Dislocations On Brittleness/Ductility Of Crystals
Authors: Mesarovic Sinisa DJ. 
Published: April 2011

AbstractDirect interactions of externally generated dislocations with a moving, non-emitting crack tip, have been investigated. Dislocations of the appropriate Burgers vector, initially residing in a strip ahead of the incoming crack tip, are funneled toward the tip, with their motion restricted to the slip plane. Once drawn into the vicinity of the tip, these dislocations inevitably cause local, atomic scale blunting of the tip. The resulting crack trapping process is modelled, resulting in the temperature, crack velocity, and dislocation density dependent, tip toughness.
Preparation Of Silicon Carbide Nanofibrils From Vapor Grown Carbon Nanotubes
Authors: Niu Chunming , Moy David 
Published: April 2011

ABSTRACTSiC nanofibrils are of interest for their potential applications, particularly for the development of nanostructured ceramic (or metal) matrix composites. Methods of production of SiC nanofibrils in bulk quantity are essential for realization of these applications. We have prepared SiC nanofibrils with average diameters of 15 nm by direct reaction of carbon nanotubes with vapor phase SiO. The carbon nanotubes were prepared catalytically by decomposition of hydrocarbons in our commercial process; they are characterized by having uniform diameter of ∼10 nm and multiple graphitic carbon layers arranged concentrically around the tube axis. Total conversion of the carbon nanotubes to SiC nanofibrils was easily achieved; the resulting SiC nanofibrils were highly crystallized β-SiC, essentially free of SiC particles. The reaction between carbon nanotubes and SiO vapor was a pseudo-topotactic transformation since the macroscopic textures of the starting carbon nanotubes remained almost unchanged in the product. This synthetic approach utilizes high quality carbon nanotubes of high uniformity which are available on a commercial scale; thus applications of SiC nanofibrils in matrix composites on a commercial scale can be envisioned.
A New Monoclinic Structure for “Compressed Hexagonal Boron Nitride”
Authors: Horiuchi S. , He L. L. , Akaishi M. 
Published: April 2011

ABSTRACTA prominent contraction of the interplanar spacing between sp2 sheets from 3.33 to 3. 10Å in so-called “compressed h-BN”, which appears on the phase transition from h(hexagonal)- to c(cubic)-boron nitride (BN) under high pressure (7.7GPa) at high temperature (1800°C), is examined by high-resolution transmission electron microsco)py (HRTEM). It is attributable to a monoclinic lattice distortion of the residual h-BN, which originates from the difference in the compressibility as well as the thermal expansion between adjoining h- and c-BN grains. The parameters of the monoclinic unit-cell are am=4.33, bm=2.50, cm,=3.1–3.3Å and β=92 - 95°. Thin plates of h-BN are often folded and the folding also causes the monoclinic structure.
Ti/TiN Barrier Improvement for VLSI Metallization
Authors: Chen Chun-Cho , Chao Jay L. C. , Wang K. C. , Chiang Eric , Hsu J. J. 
Published: April 2011

ABSTRACTIn this study deposition temperature and post-deposition treatments, such as vacuum break, furnace anneal and RTA, were coupled together to improve Ti/TiN barrier properties. Raising substrate temperature during deposition resulted in lower sheet resistance and stresses, but worse Sheet resistance (Rs) uniformity, suggesting larger-grain growth and non-uniform silicidation. The RTA treatment appeared to be the most effective one to improve barrier integrity due to high temperature densification and oxygen rich along grain boundaries. To include contact geometry effect, the barrier processes were incorporated with hot Al on the contact level of 0.6µm SRAM. After alloying at 430°C for 45 min, the yields turned out to be similar, although the RTA treatment resulted in lower P+ contact resistance, implying more complete activation, silicidation and less dopant segregation. The result suggests that it is feasible to deposit Ti/TiN insitu with hot Al process to enhance throughput. The yield result after a second alloying set at 500°C for 30 min showed that RTA treated Ti/TiN was the only one to survive.
Dopant Incorporation Efficiency in CVD Silicon Carbide Epilayers
Authors: Larkin D. J. 
Published: April 2011

ABSTRACTIn order to ensure reproducible and reliable SiC semiconductor device characteristics, controlled dopant incorporation must be accomplished. Some of the many factors which greatly influence dopant incorporation are the site-competition effect, SiC(0001) substrate polarity, substrate temperature, and the dopant-source reactor concentration. In this paper, dopant incorporation is considered and compared for various dopants in the context of dopant incorporation efficiency. By using secondary ion mass spectrometry (SIMS), the relative dopant incorporation efficiencies were calculated by dividing the SIMS determined dopant concentration in the resulting epitaxial layer by the intentional gas phase dopant concentration used during the SiC CVD. Specifically, the relative magnitudes of dopant incorporation efficiencies for nitrogen, phosphorus, and boron in 6H-SiC (0001) Si-face epitaxial layers are compared as a function of the site-competition effect and the dopant-source reactor concentrations. This serves as a first approximation for comparison of the relative “doping potencies” of some common dopants used in SiC CVD epitaxial growth.
Chemical Vapor Infiltration Process Modeling and Optimization
Authors: Besmann T. M. , Matlin W. M. , Stinton D. P. 
Published: April 2011

ABSTRACTChemical vapor infiltration is a unique method for preparing continuous fiber ceramic composites that spares the strong but relatively fragile fibers from damaging thermal, mechanical, and chemical degradation. The process is relatively complex and modeling requires detailed phenomenological knowledge of the chemical kinetics and mass and heat transport. An overview of some of the current understanding and modeling of CVI and examples of efforts to optimize the processes is given. Finally, recent efforts to scale-up the process to produce tubular forms are described.
Cellular Response to Heterogeneously Charged Polystyrene
Authors: Kapur Ravi , Picciolo Grace Lee , Black Jonathan 
Published: April 2011

AbstractCells are sensitive to topological, chemical and electrical properties of substrates on which they are grown. However, most studies of cell-surface interactions have neglected electrical effects or confounded them with other substrate properties. The use of nanofabrication technology has made it possible to fabricate optically transparent surfaces, with controlled chemistry and topology, with active, controllable surface charge density in domains as small as 1–4 um1. Human monocytes incubated on polystyrene with 3.3 um wide strip domains alternately charged, so as to maintain overall charge neutrality, show significant charge density and time dependent increases (greater than twofold) in cell area and cell perimeter after challenge with a phagocytic trigger (human IgG opsonized Zymosan particles). Additional ultrastructural studies on silicon dioxide substrates show charge density dependent qualitative morphological differences. The human monocytes exhibited significant charge density and time dependent hyper-phagocytosis (> 25fold increase over control) of human IgG opsonized Zymosan particles. The charge-induced surfaces modulated the amplitude of the secreted extracellular levels of cytokines and also induced a temporal shift in the kinetics of cytokine release2.These studies demonstrate that human blood peripheral monocytes respond in-vitro to the peak magnitude of local surface charge heterogeneity in the absence of substrate topology and compositional variation.
Porous Polymer-Ceramic Systems for Tissue Engineering Support the Formation of Mineralized Bone Matrix
Authors: Laurencin C. T. , Attawia M. A. , Elgendy H. M. , Fan M. 
Published: April 2011

AbstractOsteoblast cell differentiation and bone formation using rat calvaria cells were studied on the surface of a porous 3-dimensional polymer matrix of 50:50 poly (lactide-co-glycolide) (PLAGA)/ hydroxyapatite (HA). Cell proliferation was determined at 24 hr, 3, 7, 14, and 21 days. Exponential growth was observed during the first week and a steady increase in the population continued until 21 days after cells were seeded. Cell growth kinetics on PLAGA/HA showed an exponential pattern. Environmental scanning electron microscopy revealed the formation of multilayers of cells growing throughout the polymer matrices by day 7 and through day 21. Alkaline phosphatase (AP) activity was demonstrated after 21 days of culture on PLAGA/HA using a commercial diagnostic kit. Light microscopy observations of experiment cultures revealed active osteoblastic cells forming a characteristic mineralized matrix in the presence of β-glycerophosphate as a phosphate donor. Mineralization was not seen when the matrix alone was incubated with the reagent, indicating that the mineralization was due to the cells and not the HA in the matrix. These results suggested that the 3-dimensional PLAGA/HA matrix studied provided an excellent matrix for bone cell differentiation and mineralizationin vitroand therefore may be a good candidate as a synthetic implant for bone regeneration.
Self-Assembled InP/GaInP Quantum Dot Lasers
Authors: Moritz A. , Wirth R. , Kurtenbach A. , Eberl K. , Hangleiter A. 
Published: April 2011

AbstractSelf-assembled quantum dots of InP in In0.48Ga0.52P can be formed by molecular beam epitaxy (MBE) due to the strong lattice mismatch of 3.7 %. This is a promising method to realize small quantum dots which exhibit strong quantization effects and represent real 0D systems. Lasers with quantum dots in the active region should exhibit very low thresholds due to the low discrete density of states in quantum dots. On the other hand the self organized dots exhibit a considerable size fluctuation leading to an inhomogeneous broadening of the gain spectrum. We have measured the optical gain in quantum dots at room temperature and found two gain peaks which are identified as being due to the wetting layer and the quantum dots by their polarization properties. As expected from the results of the gain measuremlents, cleaved samples under optical pumping show lasing at room temperature of either the quantum dots or of the wetting layer, depending on the experimental conditions.
Evidence for Local Atomic Strain in Pb-Doped Heavy-Metal Fluoride Glasses
Authors: Niu L. , Kortan A. R. , Kopylov N. , Citrin P. H. 
Published: April 2011

AbstractNear-edge and extended x-ray absorption fine structure (NEXAFS and EXAFS) measurements have been made as a function of Pb dopant concentration to study the changes in local geometric and electronic structure in several heavy-metal fluoride glasses (Zr/Ba/La/Al/Na, or ZBLAN). A strong correlation is found between the observed glass instability for Pb concentrations > 10% and the structural changes that are measured exclusively around the Ba atoms. Implications of these novel findings are examined in light of the present understanding of these complex glass systems.
The Effect Of Composition Modification on the Optical Polarization Independence In Semiconductor Strain Quantum Wells
Authors: Choy Wallace C. H. , Feng Hao , Kam S. K. , Li E. Herbert 
Published: April 2011

AbstractPolarization independent quantum well (QW) materials operating under electroabsorption effect in optical switching and modulation devices are of intense interest recently. This is a theoretical analysis of the optical properties of strained InGaAs/InP QWs. The method of composition modification based on interdiffusion will be introduced to merge the heavy- and light- hole states in order to achieve polarization insensitivity. Results presented here show that the diffused QWs with and without as-growth tensile strain can both serve in polarization independent electro-absorption requirements. With a suitable design in the interdiffused QW materials, the optical polarization independence can operate from 1.465 to 1.540 μm (tunability of 75 nm) with a maximum absorption change of 2000 cm−1. In the case studied here, over 75% reduction in the required as-growth tensile strain is achieved as compared with the conventional rectangular QWs. This provides us with a simpler way to achieve high strain optical polarization independence through interdiffusion.
Thermodynamics and Diffusion of Free Trions in Mixed Type GaAs/AlAs Quantum Wells
Authors: Yoon H. W. , Ron Arza , Sturge M. D. , Pfeiffer L. N. 
Published: April 2011

AbstractAn emission line which depends on the simultaneous presence of excitons and < 2×1010 cm−2 free photoexcited electrons in a 20 nm quantum well is shown to be due to the recombination of free negatively charged excitons ( “trions”). The binding energy is 1.3 meV and the lifetime is 1/4 that of the exciton. The increase in the radiative decay times of excitons and trions with increasing bath temperature is consistent with that of free particles. More directly, from time- and spatially-resolved measurements, we find that trions are localized at 5 K, and with increasing bath temperature both excitons and trions become mobile. The diffusivity of trions and excitons increases linearly with bath temperature, and at 10 K, the trion diffusivity is found to be factor of two lower than the exciton diffusivity. Our results are the first direct experimental evidence for free trions in GaAs quantum wells.
In Situ Observations of Interfacial Instability During Growth of Lead Bromide Crystals
Authors: Mani S. S. , Singh N. B. , Conrell S. R. , Glicksman M. E. , DeWitt R. , Santoro G. J. , Duval W. M. B. 
Published: April 2011

AbstractEffects of convective mixing on the concentration homogeneity of the crystal has been demonstrated. Insitu observations of the solid liquid interface shape during crystal growth are presented which can be used to optimize the dopant distribution. Observations of the interface during growth are discussed varying the parameters in a controlled manner to minimize the thermosolutal effects. It has been observed that beyond a critical velocity for the particular dopant level, the interface shape changes. The change in the interface shape can be related to the fluid flow in the melt. Two different instability regions, namely convective and morphological are addressed. Experimentally observed result are compared with the existing convecto-diffusive theories.
Comparative Study on Three Types of Ordered Structures (TP-A, CuPt-A, CuPt-B) in AlInAs, GaInAs, AIInP, and GaInP – Bonding Energy Difference Effects.
Authors: Gomyo A. , Suzuki T. , Makita K. , Sumino M. , Hino I. 
Published: April 2011

AbstractComparative study on the formation of the three types of ordered structures (TP-A,CuPt-A, and CuPt-B) on group III sublattice in III-III-V type alloys are made for four kinds of alloys of AlInAs, GaInAs, AlInP, and GaInP grown by gas source molecular beam epitaxy. The bonding energy difference between the constituent binaries of a IIIA - IIIB-V type alloy is demonstrated to be an important factor for the ordered structure formation. The implications of the result for the formation mechanism is discussed.
0.1μm Technology and Beol
Authors: Ning Tak H. 
Published: April 2011

AbstractIt is clear that, at the device level, CMOS is scaleable to 0.1 μm and beyond, provided that the power supply voltage and the device physical dimensions are reduced in some coordinated manner. Contacting these devices and connecting them into circuits, and wiring the circuits at the chip level will become ever more challenging. Furthermore, the integration level of 0.1-μm technology is such that the chip will be the system or at least the core of the system. Thus, the BEOL will not be just for interconnecting the circuits on the chip, but provide the interconnect functions that are presently on the package and/or the board. To this end, copper and low-ε inter-level dielectric, on-chip decoupling capacitor, as well as wire-level hierarchy, will be needed.
Temperature Dependence of Resistivity for Tin And Ti-Si-N Films
Authors: Gottlieb U. , Sun X. , Kolawa E. , Nicolet M. -A. 
Published: April 2011

AbstractWe have measured by the four-point probe or Van der Pauw technique the resistivity in vacuum from 77 K to 873 K or 1073 K of Ti34Si23N43 and Ti53N47. These films were reactively sputter-deposited on oxidized silicon wafers, with thickness ranging from 200 nm to 500 nm. The resistivity of the Ti34 Si23N43 films decreases with temperature from 680. μΩcm at 80 K to about 570 μΩcm at 873 K. In contrast, resistivity of our Ti53N47 films rises with temperature, reaching a stable value of 62 μΩcm at above 673 K.
Thermal Stability and Failure Mechanisms of Au/Tiw(N)/Si and Au/TiW(N)/Si02/Si Systems
Authors: Chen C. R. , Chen L. J. 
Published: April 2011

AbstractThermal stability and failure mechanisms of Au/TiW(N)/Si and Au/TiW(N)/SiO2/Si systems have been studied by both conventional and high-resolution transmission electron microscopy, X- ray diffraction and Auger electron spectroscopy. For films deposited in Ar gas containing 20% N2, a single face-centered-cubic phase was the only crystalline phase detected to form. The samples were found to remain stable after annealing at 700 °C for 30 min. The stability temperature for Au/TiW(N)(Ar:N2=80:20)/SiO2/Si samples was found to be higher than those of Au/TiW(N) (Ar:N2=90:10)/SiO2/Si and Au/TiW/SiO2/Si samples.
Material Characterization and Chemical-Mechanical Polishing of Low-Dielectric Constant Fluorinated Silicon Dioxide Films
Authors: Tseng Wei-Tsu , Lin Charles C.F. , Hsieh Yuan-Tsu , Feng M.-S. 
Published: April 2011

AbstractNanohardness, modulus, and bonding structure of fluorinated silicon dioxides are characterized in order to evaluate their correlations with chemical-mechanical polishing (CM[P) performance. Alkaline-based slurry with adjusted pH is used for polishing in an attempt to delineate the chemical erosion from mechanical abrasion effects during CMIP of fluorinated oxides. The increase in CMIP removal rate and the reduction in refractive index with increasing fluorine content in the fluorinated oxides are related to the change in bonding configuration. The enhanced moisture absorption is due to the presence of fluorine in the oxide network.