bluuebunny/crossref_metadata_2025 huggingface dataset:
Tensile Tests of Low Density Multilayer Thin Films
Authors: Heerden D. van , Josell D. , Shechtman D.
Published: April 2011

Although mechanical studies of multilayer thin films are increasingly more abundant, the majority of studies merely determine film hardness using micro- or nanoindentation techniques. Actual tensile tests are still quite rare. We have therefore conducted tensile tests of free standing aluminum-titanium multilayer thin films. This system was selected for its potential use as a low density (3.3 g/cm3) structural material with potential aerospace applications. The strongest multilayers produced, with bilayer thicknesses 7nm Ti/16 nm Al, fractured at tensile stresses (UTS) of 900 MPa - well beyond the UTS of either of the constituent materials. Specimen characterization by xray diffraction as well as transmission electron microscopy (TEM) revealed near perfect texturing and an intriguing hcp to fec transformation of the titanium layers during preparation of samples for TEM viewing.
Measurement of the Interfacial Shear Strength of thin Copper Films on Sapphire by Microindentation Experiments
Authors: Dehm G. , Raj R. , Rühle M.
Published: April 2011

Microindentation experiments were carried out on 500 nm thick films of copper grown on sapphire substrates, containing titanium interlayers of different thicknesses. The films were near single crystal and were grown by molecular beam epitaxy. The width of the titanium interlayers was varied from 0.7nm to I 10nm. The load-displacement data obtained from the indentation experiments was analyzed in terms of a new model. Just 0.7nm of titanium produced a 40% increase in the interfacial shear strength. Further increase in the thickness of the titanium interlayers produced only a slightly larger increase in the interfacial strength, suggesting that the measurement reflected the influence of the atomic bonding at the interface. The technique and the model present a simple way to estimate the relative change in the interfacial strength of metal-ceramic interfaces.
X-Ray Residual Stress Measurement in Films with Crystallographic Texture and Grain Shape
Authors: Yu L. G. , Hendrix B. C. , Xu K. W. , He J. W. , Gu H. C.
Published: April 2011

X-ray diffraction provides an easy and powerful method for measuring residual stress in thin films. However, nonlinearity of the d vs. sin2ψ relation can lead to the misinterpretation of results, especially when one of the measurements is made at low values of ψ relation for different combinations of ideal crystallographic textures and grain shapes are given. In all cases, a high ψ angle range exists where the d vs. sin2ψ relation in the low ψ angle range.
Annealing Effects of Indium-Tin Oxide Films Produced by Atmospheric RF Plasma Deposition Technique
Authors: Moss R. W. , Lee D. H. , Vuong K. D. , Ryan J. , Fagan J. , Condrate R. A. , Wang X. W.
Published: April 2011

Thin-films of indium-tin oxide (ITO) on soda-lime-silicate (SLS) glass were fabricated using an atmospheric RF plasma mist deposition process. Some of the films were deposited at substrate temperatures between 400 C and 500 C, and were subsequently annealed at 400 C and 530 C for 1 hour. Conductivity was improved due to post-annealing. Film thickness, particle size, film morphology and crystallite size were characterized. The structural changes on the glass and the ITO film were investigated by DRIFT spectroscopy.
Thermodynamics and Microstructure Development in the Thin Film Reaction of Aluminum on Silicon Carbide
Authors: Hayes T. S. , Ray F. T. , Trumble K. P. , Kvam E. P.
Published: April 2011

A refined thernodynamic analysis of the reaction between molen Al and SiC is presented. The calculations indicate much higher Si concentrations for saturation with respect to AkC 3 formation than previously reported. Preliminary microstructural studies confirm the formation of interfacial A14C3 for pure Al thin films on SiC reacted at 9000C. The implications of the calculations and experimental observations for the production of ohmic contacts to p-type SiC are discussed.
Massively Parallel Molecular Dynamics and Simulations for Many-Body Potentials
Authors: Wille L. T. , Cornwell C. F. , Morrey W. C.
Published: April 2011

We discuss the implementation of classical molecular dynamics simulations on Single- Instruction Multiple-Data computers with two-dimensional mesh connectivity. Specific timing results are given for the MasPar MP-1, complemented by a general time complexity analysis. Our main interest is in simulations with a number of particles N that is comparable to the number of processors P. In particular, we discuss results for large Si-clusters with up to 2000 particles, using a Stillinger-Weber potential. Particular attention is paid to the problem of handling in an efficient way the calculation of the three-body potential and force.
Early Stages of Sintering of Si3N4 Nanoclusters Via Parallel Molecular Dynamics
Authors: Tsuruta Kenji , Omeltchenko Andrey , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

We investigate early stages of sintering of silicon nitride (Si3N4) nanoclusters by molecular-dynamics (MD) simulations on parallel computers. Within 100 pico seconds, an asymmetric neck is formed between nanocrystals at 2,000K. In the neck region, there are more four-fold than three-fold coordinated Si atoms. In contrast, amorphous nanoclusters develop a symmetric neck, which has nearly the same number of three-fold and four-fold coordinated Si atoms. In the case of sintering among three nanoclusters, a chain-like structure forms in 200 pico seconds. The present study shows that sintering is driven by rapid diffusion of surface atoms and cluster rearrangement.
Lattice Instabilities, Anharmonicity and Phase Transitions in PbTiO3 and PbZrO3
Authors: Rabe K. M. , Waghmare U. V.
Published: April 2011

Most perovskite structure oxides exhibit structural phase transitions from a hightemperature cubic phase to a distorted low-temperature phase which can be described by the freezing-in of one or more phonon modes of the cubic structure [1]. The first-order cubic-tetragonal ferroelectric transition in PbTiO3 at Tc = 763 K involves the freezing-in of a single F15 polar mode. In PbZrO3 , the structure of the antiferroelectric low-temperature orthorhombic phase is far more complicated, with forty atoms per unit cell and the freezing-in of R25 and Σ3 modes, perhaps accompanied by other modes as well [2][3].
Molecular Dynamics Study of Structural Transitions and Melting in Two Dimensions
Authors: Boyer L. L.
Published: April 2011

Simple pair potentials are constructed which give hexagonal- or squarelattice ground states in two dimensions, depending on the value of a single parameter controlling the width of the potential well. Molecular dynamics calculations for free clusters of a few hundred particles are used to examine a structural transition from the square lattice, at low temperatures, to the hexagonal lattice at high temperatures. Another structural transition (melting) is identified by the onset of diffusion. The melting temperature is found to be a minimum near the point where the barrier between the two structures, as a function of lattice strain, is also a minimum.
Molecular-Dynamics Simulations of Hydrogenated Amorphous Silicon Thin-Film Growth
Authors: Ohira T. , Ukai O. , Noda M. , Takeuchi Y. , Murata M. , Yoshida H.
Published: April 2011

We have performed molecular-dynamics (MD) simulations of hydrogenated amorphous silicon (a-Si:H) thin-film growth using realistic many-body semiclassical potentials developed to describe Si-H interactions. In our MD model, it was assumed that SiH3, SiH2 and the H radicals are main precursors for the thin-film growth. In MD simulations of a-Si:H thin-film growth by many significant precursor SiH3 radicals, we have evaluated average radical migration distances, defect ratios, hydrogen contents, and film growth rates as a function of different incident radical energies to know the effect of the radical energization on the properties. As a result of the comparison between the numerical and experimental results, it was observed that the agreement is fairly good, and that an increase of radical migration distance due to the radical energization is effective on a- Si:H thin-film growth with a low defect.
Full-Potential LMTO Calculation of Ni/Ni3Al Interface Energies
Authors: Price D. L. , Cooper B. R.
Published: April 2011

Solid solution precipitates, including Ni3Al in Ni, play an important role in modifying and improving properties of structural and high temperature alloys. The nature of the interface between the host alloy and the precipitate has a large influence on the nature of the precipitate properties, and upon the energetics of their formation. We present here a brief summary of initial ab-initio electronic structure calculations of the Ni/Ni3Al interface, and present results for the interfacial energy. Our results indicate that that the spin-moment transition from high moment Ni to low moment Ni3Al accounts for much of the (zero temperature) interface energy. Corresponding paramagnetic calculations give a significantly lower interfacial energy, and one that is more consistent with high temperature (above the Curie temperature) experimental results.
Simulations of the Structure and Properties of the Polyethylene Crystal Surface
Authors: Wilhelmi J. L. , Rutledge G. C.
Published: April 2011

The structures and thermodynamic properties of the (100), (010), and (110) lateral surfaces of extended-chain polyethylene crystals between 0 K and 300 K were determined by free energy minimization using consistent quasi-harmonic lattice dynamics. Slight rotations of the outermost chains from their corresponding orientations in the bulk were observed. These deviations from bulk structure were confined to the first three molecular layers (approximately 10 Å) at the surface. Surface free energy calculations found the (110) surface to be the most stable over the entire temperature range modeled, with free energies ranging from 95.4 erg/cm2 to 103.5 erg/cm2, at temperatures of 0 K and 300 K, respectively. Surface free energies of the (100) and (010) surfaces were found to be at least 15% higher than the (110) surface, with the (100) surface slightly more stable than the (010) surface, over all temperatures considered. Surface free energy increases as the density of chains at the surface decreases. The surface free energy at low temperatures was determined predominantly by intermolecular potential energy; at higher temperatures, excess entropy accounted for nearly half the surface free energy. Surface entropy was almost entirely due to lattice mode motions.
Ab Initio Core-Level Shifts in Metallic Alloys
Authors: Fiorentini Vincenzo , Methfessel Michael , Oppo Sabrina
Published: April 2011

Core-level shifts and core-hole screening effects in alloy formation are studied ab initio by constrainedl-density-functional total-energy calculations. For our case study, the ordered intermetallic alloy MgAu, final-state effects are essential to account for the experimental Mg 1s shift, while they are negligible for Au 4f. We explain the differences in the screening by analyzing the calculated charge density response to the core hole perturbation.
Atomistic Study of Boron-Doped Silicon
Authors: Fearn M. , Jefferson J. H. , Pettifor D. G.
Published: April 2011

Atomistic 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

We 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

Though 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

The 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

We 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

Direct 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

SiC 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

A 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

In 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

In 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

Chemical 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

Cells 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

Osteoblast 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

Self-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

Near-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

Polarization 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

An 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

Effects 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

Comparative 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

It 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

We 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

Thermal 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

Nanohardness, 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.
Reactive Ion Etching of the fluorinated polyimide film
Authors: Lee Y. K. , Murarka S. P.
Published: April 2011

The etch conditions affecting the etching of the fluorinated polyimide films in RF plasma using oxygen or fluorine-containing oxygen has been investigated. The effect of power, oxygen gas flow rate, and gas composition on the etch rate of fluorinated polyimide have been determined. The etch rate of the fluorinated polyimide increases linearly with the power and oxygen gas flow. The saturation at high oxygen flow rate indicates a saturation or steady state achieved at the polyimide-oxygen reaction interface. However, the etch rate increases when CF4 is added to oxygen, up to about 10% CF4 in O2, and then decreases to a smaller and CF4 concentration independent value. The etch selectivity of hard mask against fluorinated polyimide has been determined. The PECVD silicon nitride and PETEOS are found to be excellent hard mask for pattering these polyimides. The trench profile of the polyimide film also has been examined by patterning and etching the different trench sizes in fluorinated polyimide. It is concluded that this fluorinated polyimide can be etched with oxygen or fluorine containing oxygen plasma.
Evaluation of Lpcvd Boron Nitride as a Low Dielectric Constant Material
Authors: Levy R. A. , Narayan M. , Karim M. Z. , Hsu S. T.
Published: April 2011

This study characterizes low pressure chemically vapor deposited B-N-C-H as a low dielectric constant material for interlevel dielectric applications. These films are synthesized over a temperature range of 400 to 600 °C and various flow rate ratios using triethylamine borane complex (TEAB) and NH3 as precursors. The dielectric constant of these films exhibit values which varied in the range of 2.6 to 3.5 depending on processing conditions. Low dielectric constant values are achieved at film compositions which approached stoichiometry and have minimal carbon content. The variations in the structural, optical, mechanical, and chemical properties of these films as a function of deposition conditions are also discussed.
Cobalt and Titanium Metallization of SiGeC for Shallow Contacts
Authors: Bair A. E , Alford T. L. , Atzmon Z. , Marcus S. D. , Doller D. C. , Morton R. , Lau S. S. , Mayer J. W.
Published: April 2011

Shallow contact metallization of SiGeC was studied in anticipation of this alloys use in low power applications. It has been shown that in the solid state reaction of Co on (100) Si, that Co is the moving species with proper annealing conditions. This prevents the formation of Kirkendal voiding in certain device structures. This work studies the Co and Ti metallization of SiGeC. A bilayer of 44 nm of Co on 7 nm of Ti, were electron beam evaporated onto epitaxially grown Si0.77Ge0.21C0.02. The samples were rapid thermal processed at 600 and 900 °C for up to two minutes in a nitrogen ambient. The analysis techniques used were Rutherford backscattering spectrometry which included the used of the 4.27 MeV 12C(α,α) 12C resonance reaction, glancing angle x-ray diffraction, During annealing at all temperatures, Co diffused through the Ti layer and formed CoSi. This phase was confirmed by x-ray diffraction. The Co displaced the Ti to the surface. At 600 °C, Ge diffused to the surface layer, while at 900 °C it was rejected back into the original SiGeC. The sample annealed at 600 °C was subsequently annealed at 900 °C. The Ge in the surface layer was rejected from the surface layer, diffused across the CoSi and back into the SiGeC.
Angle Resolved Photoemission from Ultrathin Films of Cu/Ni(001)
Authors: Subramanian K. , Mankey G. J. , Stockbauer R. L. , Kurtz R. L.
Published: April 2011

We present a study of the quantum well states observed in Cu/Ni(001). Several reports in the recent past have shown that these states, which are derived from the bulk, disperse through the Fermi level at a thickness of about 6 ML. Using angle-resolved photoemission, we have imaged the photoelectron angular distributions from several thicknesses of Cu/Ni(001). We observe that these states have s,p like symmetry and are located near the zone edge.
Mesoporous TIO2 Electrodes for Photovoltaic Applications
Authors: Barbé C. J. , Graetzel M.
Published: April 2011

During the past five years, we have developed in our laboratory a new type of solar cell based on a photo-electrochemical process. A respectable photovoltaic efficiency (i.e. 10%) is obtained by the use of mesoporous, nanostructured films of anatase particles. We will show how the TiO2 electrode microstructure influences the photovoltaic response of the cell. More specifically, we will focus on how processing parameters such as hydrothermal growth temperature, binder addition and sintering conditions influence the film porosity, pore size distribution, and consequently affect the solar cell efficiency.
Potentialities of an Innovative Technique Like 129Xe NMR and of Saxs for the Characterization of Microporous Sol-Gel Derived SiO2
Authors: de Menorval L. C. , Julbe A. , Jobic H. , Dalmon J. A. , Guizard C.
Published: April 2011

Addition of surfactants in TEOS derived sols leads to micro- or mesoporous materials whose porous texture can be varied by changing the surfactant quantity and/or chain length. This series of materials, with a relatively narrow pore size distribution, is well adapted to study the potentialities of an innovative characterization technique like 129Xe Nuclear Magnetic Resonance in comparison with Small Angle X-ray Scattering and N2 adsorption. SAXS revealed a high surface rugosity of the materials and a good correlation with pore hydraulic radius distributions measured by N2 adsorption. Using 129Xe NMR, we have studied the Xe chemical shifts (δXe,) as a function of pXe, and have pointed out several original results showing the importance, for microporous materials, of the NMR line shapes and of the slope of the lines δXe.=f(pXe).
Spectroscopy of Iron Germanium Sulfide Open-Framework Materials and Precursors
Authors: Kirkby Scott J. , Ozin Geoffrey A.
Published: April 2011

The electronic and vibrational spectroscopy of one family of metal germanium sulfide open-framework materials, designated Cat2FeGe4S10 (Cat = (CH 3)4N, Cs), along with their precursor Cat4Ge4S10 germanium sulfide clusters have been studied. Ultraviolet-visible and midinfrared reflectance spectroscopy has been used to study the electronic states. The reflectance spectroscopy of the frameworks is dominated by the d-d transitions of the Fe(II) in a S4 symmetry site. The vibrational spectroscopy has been analyzed by Fourier transform Raman. The frameworks are weakly vibrationally coupled. Their spectra contain vibrational modes that are nearly identical in frequency to those of the isolated cluster. There is a fortuitous window in the cluster vibrations in which framework modes of the Fe(II) center can be observed. In addition computational methods have been used to model the experimental results.
Microstructural Analysis and Modelling of Thin Porous Silicon Layers with Variable Angle Spectroscopic Ellipsometry
Authors: Pettersson L. A. A. , Zangooie S. , Bjorklund R. , ARWIN H.
Published: April 2011

Thin porous silicon (PS) layers (30–1000 nm) have been produced by electrochemical anodization of highly p-doped silicon in a hydrofluoric acid electrolyte at constant current density. Variable angle spectroscopic ellipsometry was used for characterization in the spectral range 1.24–5.00 eV. Four multilayer models were developed for the PS layers. Ellipsometric spectra were fitted for three of these models by utilizing an effective medium approximation for each sublayer containing crystalline silicon and voids. A third constituent, amorphous silicon, was added in the fourth model. Excellent fits to experimental data were obtained in the entire spectral range and thickness and composition of each individual sublayer in the models were determined. The analyses revealed a compositional gradient normal to the surface. The porosity and the fraction of amorphous silicon decreased with film depth, whereas the fraction of crystalline silicon increased. The mean porosity of a PS layer was obtained as the thickness weighted average of the porosities of the sublayers. The proposed multilayer models allow a more detailed analysis of PS layers compared to single layer models.
Proteins Encapsulated in Porous Sol-Gels: Biomolecules as Pore Structure Templates
Authors: Dave B. C. , Dunn B. , Valentine J. S. , Zink J. I.
Published: April 2011

Porous inorganic SiO2 glasses obtained by the sol-gel route represent a unique matrix for encapsulation of biomolecules wherein the pores act as enclosures for high molecular weight proteins. These hybrid materials are characterized by a pore-biomolecule interface between the pore walls and the protein surface. As a specific model protein, cytochrome c (cyt c) is used to elucidate the nature of physical and chemical interactions between the pores of the matrix and the protein. Evidence from optical absorption, and resonance Raman (RR) spectroscopy methods indicates that the dopant protein alters the structural features of the pore walls. The optical and vibrational measurements strongly suggest that the pores that contain the trapped protein undergo little or no structural change during aging and drying as compared to protein-free pores. Vibrational RR analysis of the trapped cyt c also suggests that the protein resides in a pore where the pore dimensions conform to the shape of the protein. The results indicate that noncovalent interactions between the surface of the protein and the pore walls govern the dynamics of pore formation during gelation and individual biomolecules act as structural templates to design local pore structure.
Aerogel Synthesis Using Extractive Drying
Authors: Smith D. M. , Ackerman W. C. , Roth R. , Zimmerman A. , Schwertfeger F.
Published: April 2011

The advent of ambient pressure aerogel technology may offer process advantages compared to supercritical drying. Since low density is required for most applications of interest, precursor gels must be very dilute (e.g. 6–8% SiO2). The remaining 92–94% is solvent which must be carried along for the entire process, then evaporated, condensed, separated, and recycled to be reused. These steps and associated unit operations represent a major cost (capital and operating). The drying step is problematic because of the large mass of solvent and the inherently low thermal conductivity of the gel. A new approach for drying aerogels is described whereby a wet gel containing a solvent is submerged in hot water or similar fluid which results in removal of the solvent without the drying fluid penetrating the gel. This results in a dried gel with aerogel properties but with the advantages of having a high heat transfer rate without using large temperature gradients as well as providing inherent separation of the dried material. We explore the effects of different solvents and drying temperature gradients on resulting gel microstructure.
Macroporous Thermosets via Chemically Induced Phase Separation
Authors: Kiefer J. , Porouchani R. , Mendels D. , Ferrer J. B. , Fond C. , Hedrick J. L. , Kausch H. H. , Hilborn J. G.
Published: April 2011

We have explored a new technology based on chemically induced phase separation that yields porous epoxies and cyanurates with a closed cell morphology and micrometer sized pores with a narrow pore size distribution. When the precursor monomers are cured in the presence of a low molecular weight liquid, the desired morphology results from a phase separation and a chemical quench. After phase separation, the porosity is achieved by thermal removal of the secondary liquid phase, specifically by diffusion through the crosslinked matrix. In respect to the thermodynamics and kinetics, the origin of the phase separation process can be identified as nucleation and growth. The influence of internal and external reaction parameters, such as chemical nature of the low molecular weight liquid, its concentration and the curing temperature on the final morphology are presented. Thus, the morphology can be controlled ranging from a monomodal to bimodal pore size distribution with pore sizes inbetween 1 to 10 μm. These porous thermosets are characterized by a significantly lower density, without any loss in thermal stability compared to the neat matrix. Such new materials demonstrate great interest for lowering the dielectric constant and for improving the fundamental understanding of the role of voids in stress relaxation and toughening.