bluuebunny/crossref_metadata_2025 huggingface dataset:
Computational Problems in Orthopaedic Biomechanics
Authors: Taylor Dean
Published: March 2011

Total joint replacements such as the hip and knee result in composite structures. Proper design of these devices and selection of particular devices requires understanding of the structural response of the resulting composite structure of plastic, metal, interface, and human bone. The problem is challenging because of complex geometry, non-homogeneous material properties (dense cortical bone and spongy cancellous bone), and time varying material properties (bone remodeling). Bone is a active material which responds over time to applied load, changing the density and Young's modulus.

This paper addresses several computational issues. Remote sensed data such as computerized tomography scans are used to create finite element models. Nonhomogeneous material properties are represented in finite element models using shape functions. This results in a unique material property for each Gauss point. Finally, stochastic finite elements methods are used to model material variation and uncertainty. Both Monte Carlo and First Order Second Moment methods are used. These problems are particularly well suited for high-level parallelization schemes on multiple instruction multiple data machines.
Density Functional Methods and Applications to Materials Problems
Authors: Li Y. S. , Daelen M. A. van , King-Smith D. , Wrinn M. , Wimmer E. , Newsam J. M. , Klitsner T. , Sears M. P. , Carlson G. , Nelson J. , Allan D. C. , Teter M. P.
Published: March 2011

Density functional theory provides a first-principles approach for computing the geometric and electronic structures, and a wealth of corresponding properties, of a wide range of materials types and compositions, including bulk solids, surfaces, defects and clusters of molecules. Parallel advances in hardware performance, implementation strategies and algorithms have all contributed to a rapid growth in the number of important applications. Recent developments under each of these themes are outlined and the breadth of current applications is illustrated by typical examples. Issues associated with the implementation and performance of density functional methods on parallel computer architectures are discussed.
Molecular Modeling of the Crystal Structure of LARC-CPI Thermoplastic Polyimide
Authors: Brilihart Mark V. , Teverovsky Justyna , Nagarkar Pradnya , Cebe Peggy
Published: March 2011

Electrical components place high demands on the properties and performance of materials. Potential service environments have both broad temperature ranges and widely varying stress states. Polyimides are a class of polymers that possess the necessary performance characteristics for electronic applications. LARC-CPI, a novel semicrystalline thermoplastic polyimide developed by the NASA Langley Research Center [1], combines the excellent properties of polyimides with an ability to crystallize. This enhances mechanical performance and chemical resistance and imparts the processing benefits associated with thermoplastic materials. The high Modulus of Elasticity (2.5 to 3.6±0.2 GPa [2]), glass transition temperature (Tg = 222 °C [3]) and melting temperature (Tm = 350 °C [3]) combined with a relatively low dielectric constant (ε = 3.2 [4]) of LARC-CPI appear to meet the criteria for a wide range of electronic materials applications. Since many of the properties are attributed to the crystalline region and its orientation, thorough characterization of any ordered structures present in LARC-CPI is essential. The chemical repeat unit for LARC-CPI and a model repeat unit can be seen in Figure 1.
Bending of Flex Leads During Thermal Cycling
Authors: Shi L. T. , Tong H.
Published: March 2011

A three dimensional finite-element stress model was used to simulate the lead bending incurred during thermal cycling of a Flex connector joined to a silicon carrier via an eutectic solder. Three different coating conditions (no coating, with a polyimide coating, and with a silicone coating) were simulated. With the polyimide coating, lead bending was found to occur at the corner inner leads of the Flex as a result of the plastic strains accumulated there during thermal cycling. In the case of silicone, the corresponding plastic strains grew during the first thermal cycle but saturated subsequently, confirming the negligible lead bending observed experimentally. For the case of no coating, the highest plastic strain was found to be borne in part by the polyimide film at its edge and thus no significant bending was observed. In all cases, the results provided by the model agree well with the experimental observations.
Characterization of Conductive Anodic Filament (Caf) by X-Ray Microtomography and by Serial Sectioning
Authors: Stock S. R. , Dollar L. L. , Freeman G. B. , Ready W. J. , Turbini L. J. , Elliott J. C. , Anderson P. , Davis G. R.
Published: March 2011

X-ray microtomography is used to nondestructively section printed wiring boards in which conductive anodic filaments (CAFs) had grown, Quantification of the spatial distribution of copper is compared for microtomography and for serial sections obtained in SEM with backscattered electrons. The agreement between the techniques is excellent and indicates that microtomography may be used confidently to follow the subsurface growth of CAFs.
Reliability Studies on Ge High Density Interconnect (Hdi) Modules
Authors: Paik Kyung W. , Bernard Edward S.
Published: March 2011

Considerable mechanical and environmental reliability testing as defined by MIL-STD-883 has been performed on GE HDI modules in both hermetic and nonhermetic configurations. The tests involving temperature cycling, temperature bakes, thermal shock, power cycling by self-heating, vibration, centrifuge and drop shock showed no change in the overlay or in the performance of the underlaying chips on the substrate. As an additional reliability test, the effect of humidity cycling (45° - 95° relative humidity) on nonhermetic HDI substrates has been also investigated. Any noticeable failures and degradation of metallization were not observed by humidity cycling itself at room temperature. Both the 883 and humidity cycling test could lead to the conclusion that HDI is a robust MCM-D technology. In addition, extensive studies on the residual stress analysis of the thin film layers of metal and polymer during fabrication and thermal cycling have been performed using the Flexus laser beam bending instrument. The study results predicted that failure of overlay HDI such as delamination between layers is less likely because of lower in-plane stresses than in conventional spin-coated and cured polyimide.
Light Scattering Measurements of Surface Roughness in Molecular Beam Epitaxy Growth of GaAs
Authors: Lavoie C. , Nissen M. K. , Eisebitt S. , Johnson S. R. , Mackenzie J. A. , Tiedje T.
Published: March 2011

In-situ measurements of diffuse light scattering at λ = 457 nm are reported from the surface of GaAs films during growth by molecular beam epitaxy. Three different scattering angles are measured simultaneously corresponding to spatial frequencies in the surface roughness of q = 0.9, 12, and 17 μm−1. During growth the initial surface roughness caused by the oxide desorption decreases at high spatial frequencies and increases at low spatial frequency. The low spatial frequency roughness corresponding to scattering vectors parallel to [110] increases more rapidly during growth than for scattering parallel to [111].
The Utility of Laser Light Scattering in Assessing the Mixability of Reagents for Chemical Vapor Deposition
Authors: Ni Bin , Reck Gene P. , Proscia James W.
Published: March 2011

The premixability of reagents used in chemical vapor deposition reactors is important to insure that gas feed lines and nozzles do not become clogged with particulates during operation. Even if reactants are to be kept separate until introduced into a reaction chamber, it is desirable to limit the number of particles formed. A reactor which utilizes laser light scattering to monitor particulate formation when gaseous reagents are mixed is described. The reaction of tin (IV) chloride with water is commonly used to produce tin oxide films by chemical vapor deposition. It was found by the light scattering experiment that at temperatures above about 110°C the number of particulates formed is greatly reduced. Therefore, it would be most desirable that these reagents be mixed above this temperature when depositing tin oxide from this reaction. The reaction of titanium tetrachloride with various amine was also investigated by this method. This reaction has been demonstrated to produce titanium nitride above 450°C. For each case, it was observed that there was a temperature above which the number of particulates was significantly reduced. This temperature was always below the optimal temperature for producing titanium nitride films.
Photoreflectance Characterization of Etch-Induced Damage in Dry Etched GaAs
Authors: Glembocki O.J. , Tuchman J.A. , Ko K.K. , Pang S.W. , Giordana A. , Stutz C.E.
Published: March 2011

Photoreflectance has been used to characterize the etch-induced damage in GaAs processed in an Ar/Cl2 plasma generated by an electron-cyclotron resonance (ECR) source. We show that the damage is localized to the surface and that it is most influenced by the RF power, with little effect from the microwave power. The Fermi-level is observed to be unchanged in n-GaAs and remains near midgap, while for p-GaAs, the Fermi level shifts from near the valence band to midgap. Etch-induced anisite defects are proposed as a possible source of the damage.
Photoreflectance Characterisation of Reactive Ion Etched Silicon
Authors: Murtagh M. , Beechinor J. T. , Herbert P. A. F. , Kelly P.V. , Crean G. M. , Jeynes C.
Published: March 2011

Reactive ion etching (RIE) of p-type 2-3 †cm resistivity silicon (100) was characterised using Photoreflectance (PR), Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE). Isochronal (5 minutes) etching was performed at various DC etch biases (0-500V) using a SiCl4 etch chemistry. The substrate etch rate dependence on applied bias was determined using mechanical profilometry. A distinct shift in the A3–A1 Si transition and significant spectral broadening of the room temperature PR spectra was observed as a function of etch bias. Photoreflectance results are correlated with RBS, SE and etch rate analysis. It is demonstrated that the PR spectra reflect a complex, competitive, plasma-surface interaction during the RIE process.
In-situ Multilayer Film Growth Characterization by Brewster Angle Reflectance Differential Spectroscopy
Authors: Dietz N. , Stephens D.J. , Lucovsky G. , Bachmann K.J.
Published: March 2011

Brewster Angle Reflectance Differential Spectroscopy (BARDS) has been proposed as an optical method for real-time characterization of the growth of thin films. BARDS is based on changes in the reflectivity, Rp, of parallel (p)-polarized light incident at, or near, the Brewster angle of the substrate material. Changes in R are sufficiently large to monitor layer growth, and to determine the thickness and the optical constants of the deposited film. In this paper we extend the method to multilayer film deposition. The derivative properties of R are correlated with differences in the optical constants of the two materials, and with the sharpness of their interface. We present spectra for SiO2/Si3N4/SiO2/Si, demonstrating some of these aspects of this new and effective approach to in-situ monitoring.
Characterization of Cd1-x ZnxTe Alloys Using Infrared Reflectivity and Raman Scattering Spectroscopy
Authors: Talwar D. N. , Feng Z. C. , Becla P.
Published: March 2011

Study of impurity-induced phonon disordering in Cdl-xZnxTe alloys is reported for a variety of samples by using far-infrared reflectivity and Raman scattering spectroscopy. Substantial differences were noted among the various published values for the optical phonon frequencies versus x. Contrary to an earlier Raman study on MBE grown Cdl-xZnxTe/GaAs films, our results within a twomode behavior, yield an increase of both the CdTe- and ZnTe-like transverse optical phonons with x. Unlike earlier speculations for a gap-mode in ZnTe : Cd of ∼140∼145 cm−1, our Greens function theory predicts it to be at a relatively higher frequency of ∼153 cm−1.
Reactive Sputtiering in Oxidizing/Reducing Atmospheres
Authors: Klein J. D. , Yen A. , Clauson S. L.
Published: March 2011

The deposition of thin films by magnetron sputtering is readily influenced by the reduction/oxidation characteristics of the plasma. Unfortunately, the redox state of the sputter plasma is often inadvertently determined by uncontrolled factors such as transient evolution of species from the target. Undesirable variations in film and target properties can be avoided by actively setting the redox conditions. This is most readily accomplished by including two competing species, one oxidizing and the other reducing, in the chamber gas mixture. Optical emission spectroscopy, an in-situ process monitor, was employed to observe redox interactions in nominally unreactive dc sputtering of YBCO and reactive rf sputtering of IrO2. Optical spectroscopy of YBCO sputtering reveals that the intensity of atomic oxygen emissions decreases with H2 additions to the sputter gas blend.
Evaluation of Dry Etching Induced Damage of Gainas Using Transmission Lines and Schottky Diodes
Authors: Thomas S. , Pang S. W.
Published: March 2011

Plasma etching of GaInAs and AlInAs has been carried out in a system which consists of an electron cyclotron resonance (ECR) source and an rf-powered stage. Since the ECR source can generate a plasma with low ion energy, dry etching induced damage is expected to be minimal. In this study, Schottky diodes and transmission lines were fabricated on the etched GaInAs surface. The diode and transmission line characteristics were evaluated as a function of etch conditions. For the etching of GaInAs and AllnAs, C12 and Ar were used as the etch gases. In addition to the ratio of the two gases, microwave power, rf power, pressure, and source distance were varied and their effects on etch rate, morphology, and surface damage were analyzed. Etch rate increased monotonically with microwave power, rf power, and C12 percentage. Etch rate decreased with increasing distance and reached a maximum for a pressure of 1 mTorr. The etch conditions for the damage study were chosen to maintain smooth morphology. One of the most important factors influencing damage was the ion energy which can be limited by using low rf power and short source distance. Minimum damage was obtained at 1 mTorr which provides the optimal balance between high etch rate and low ion energy. Besides limiting ion energy, the addition of Cl2 reduced etch-induced damage. The specific contact resistivity and sheet resistivity obtained from transmission line measurements of dryetched n-GaInAs were lower than the wet-etched samples. Schottky diode analysis show reduction in barrier height and breakdown voltage after Ar sputtering. Addition of 10% C12 is sufficient for full recovery of the diode characteristics.
Characterization of Cadmium Zinc Tellurium Obtained by Modified - Bridgman Technique
Authors: Acosta D.R. , Rabago F.
Published: March 2011

The growth of ternary semiconductor compounds Cd1-ZZnx. Te leads to possible uses of this material like optoelectronic devices. In the present work we report the structural characterization of Cd0.96Zn0.04Te obtained by modified - Bridgman technique. Structural studies were carried out using Scanning Electron Microscopy (SEM) and Conventional and High Resolution Electron Microscopy (TEM and HREM, respectively). Selected Area Electron Diffraction (SAED) was used to determine local variations in composition. Characteristics of the growth of the bulk samples were observed and structural details that might be related with the stability of ternary phase were derived.
In-Situ Dual-Wavelength Ellipsometry and Light Scattering Monitoring of Si/Si1−xGex Heterostructures and Multiuantum Wells
Authors: Pickering C. , Hope D.A.O. , Leong W.Y. , Robbins D.J. , Greef R.
Published: March 2011

In-situ dual-wavelength ellipsometry and laser light scattering have been used to monitor growth of Si/Si1−x,Gex heterojunction bipolar transistor and multi-quantum well (MQW) structures. The growth rate of B-doped Si0 8Ge0.2 has been shown to be linear, but that of As-doped Si is non-linear, decreasing with time. Refractive index data have been obtained at the growth temperature for x = 0.15, 0.20, 0.25. Interface regions ∼ 6-20Å thickness have been detected at hetero-interfaces and during interrupted alloy growth. Period-to-period repeatability of MQW structures has been shown to be ±lML.
Determination of BPSG Thin-Film Properties using IR Reflection Spectroscopy of Product Wafers
Authors: Niemczyk Thomas M. , Franke James E. , Zhang Lizhong , Haaland David M. , Radigan Kenneth J.
Published: March 2011

Three BPSG calibration sets were analyzed using infrared external reflection-absorption spectroscopy: 1) 21 films deposited on undoped silicon coated with 0.1 pm of silicon dioxide, 2) 21 films deposited on undoped silicon, and 3) 9 films deposited on microelectronics product wafers. A multivariate partial least squares analysis of the spectral data for the first large data set showed that boron content, phosphorus content, and film thickness can be quantified with precisions of 0.10 wt%, 0.12 wt%, and 30 Å, respectively. The second large data set yielded similar results. The precisions obtained for the nine product wafer samples were 0.13 wt% B, 0.09 wt% P, and for film thickness 103 Å.
Deep Level Defects, Luminescence, and the Electro-Optic Properties of SiGe/Si Heterostructures
Authors: Bhattaci-Iarya Pallab , Li Shin-Hwa , Lee Jinju , Smith Steve
Published: March 2011

Deep levels and luminescence in SiGe/Si heterostructures and quantum wells have been investigated. We have studied the effects of Be- and B-doping on the luminescent properties of Si1−xGex/Si single and multiquantum wells. No new levels, or enhancement of luminescence, from that in undoped samples, is detected in samples which are selectively doped in the well-regions, implying that the observed luminescence in the undoped quantum wells is a result of alloy disordering. Slight enhancement of luminescence is observed in disordered wells and in quantum wires made by electron beam lithography and dry etching. Deep levels have been identified and characterized in undoped Si1-xGex alloys. Hole traps in the p-type layers have activation energies ranging from 0.029-0.45 eV and capture cross sections (σ∞) ranging from 10−9 to 10−20 cm2. Possible origins of these centers are discussed. Some possibilities of obtaining enhanced electro-optic coefficients in SiGe/Si heterostructures are discussed.
Contact-Related Deep States in AI-GaInP/GaAs Interface
Authors: Huang Z.C. , Wie C.R.
Published: March 2011

Deep levels have been measured in molecular beam epitaxy grown Ga0.51In0.49P/GaAs heterostructure by double correlation deep level transient spectroscopy. Gold(Au) and Aluminum (Al) metals were used for Schottky contact. A contact-related hole trap with an activation energy of 0.50-0.75eV was observed at the A1/GaInP interface, but not at the Au/GaInP interface. To our knowledge, this contact-related trap has not been reported before. We attribute this trap to the oxygen contamination, or a vacancy-related defect, VIn or VGa. A new electron trap at 0.28eV was also observed in both Au- and Al-Schottky diodes. Its depth profile showed that it is a bulk trap in GaInP epilayer. The temperature dependent current-voltage characteristics (I-V-T) show a large interface recombination current at the GaInP surface due to the Al-contact. Concentration of the interface trap and the magnitude of recombination current are both reduced by a rapid thermal annealing at/or above 450°C after the aluminum deposition.
Hydrogen Passivated Carbon Acceptors in GaAs and AlAs: no Evidence for Carbon Donors
Authors: Davidson B. R. , Newman R. C. , Pritchard R. E. , Bullough T. J. , Joyce T. B. , Jones R. , Öberg S.
Published: March 2011

GaAs and AlAs layers grown by CBE and doped with either 12C or 13C have been passivated with hydrogen or deuterium. Infrared absorption lines due to hydrogen stretch modes, symmetric A1 modes and “carbon-like” E modes of H-CAs and D-CAs pairs have been assigned for both isotopes in both hosts. Comparisons have been made with new ab initio local density functional theory and simple harmonic models. Anticrossing behaviour is found for the two types of coupled E modes in the two hosts. The dynamics of the H-CAs centre are very similar in GaAs and AlAs.
Effects of Ion-Irradiation and Hydrogenation on the Doping of InGaAIN Alloys
Authors: Pearton S. J. , Abernathy C. R. , Hobson W. S. , Ren F.
Published: March 2011

Carrier concentrations in doped InN, In0.37 Ga0.63 N and In0.75 Al0.25 N layers are reduced by both F+ ion implantation to produce resistive material for device isolation, and by exposure to a hydrogen plasma. In the former case, post-implant annealing at 450–500°C produces sheet resistances > 106 Ω/ℹ in initially n+ (7 x 1018 − 3 x 1019 cm−3) ternary layers and values of ∼5 x 103 Ω/ℹ in initially degenerately-doped (4 x 1020 cm−3) InN. The evolution of sheet resistance with post-implant annealing temperature is consistent with the introduction of deep acceptor states by the ion bombardment, and the subsequent removal of these states at temperatures −500°C where the initial carrier concentrations are restored. Hydrogenation of the nitrides at 200°C reduces the n-type doping levels by 1-2 orders of magnitude and suggests that unintentional carrier passivation occurring during cool down after epitaxial growth may play a role in determining the apparent doping efficiency in these materials.
Deep Level Structure of Semi-Insulating Movpe Gaas Grown by Controlled Oxygen Incorporation
Authors: Huang J. W. , Kuech T. F.
Published: March 2011

Semi-insulating oxygen-doped GaAs layers have been grown by low pressure metalorganic vapor phase epitaxy (MOVPE) using aluminum-oxygen bonding based precursor diethyl aluminum ethoxide (DEALO). Resistivities of more than 2x109 Ω-cm at 294 K have been achieved. Deep level structure responsible for the high resistivity was investigated by deep level transient spectroscopy (DLTS) using DEALO and disilane co-doped GaAs p+-n homojunction. Multiple deep level peaks were observed, and the relative peak heights were found to vary with the dopant concentrations. Major deep levels were electron traps with ionization energy between 0.75 and 0.95 eV below conduction band edge minimum. An activation energy of 0.81 eV was deduced from temperature-dependent resistivity measurement, and should be closely related to the major0.75 eV peak in DLTS spectra.
Defects in Low—Temperature—Grown MBE GaAs
Authors: Look David C.
Published: March 2011

Defect concentrations in molecular beam epitaxial (MBE) GaAs range from 1012 to 1020 cm-3 as the growth temperature is lowered from 600 to 200 °C; however, very high quality layers can be grown over this whole range. The dominant defect is the As antisite, but there is also good evidence for As interstitials and gallium vacancies. The particular form of the As antisite center in low—temperature (LT) MBE GaAs is not known at this time, but it is definitely not EL2, because both the thermal activation energy and the electron capture cross section differ significantly. However, other features, such as the EPR spectrum and metastable—to—normal recovery kinetics are identical to those of EL2. The donor (As antisite) to acceptor ratio seems to hold at about one order of magnitude as growth temperature is varied from 200 — 400 °C; thus, the Fermi level stays near mid—gap over this whole range. However, hopping conduction among the As antisite centers is strong for samples grown between 200 and 300 °C and keeps the material from being semi—insulating, while for those grown between 350 — 480 °C, the resistivity is greater than 107 Ω cm. The annealing dynamics are particularly interesting and include such features as the mobility going through a sharp maximum at an annealing temperature of 400 °C for a layer grown at 200 °C. The donor and acceptor concentrations can be determined both by Hall effect and absorption measurements as the layer is annealed up to 600 °C. Above 550 °C, large precipitates are formed. The relative roles of the precipitates and point defects in influencing compensation, lifetime, and device characteristics are a source of much controversy and will be discussed.
Clusters and the Nature of Superconductivity in Ltmbe-GaAs
Authors: Bert N.A. , Chaldyshev V.V. , Goloshchapov S.I. , Kozyrev S.V. , Kunitsyn A.E. , Tretyakov V.V. , Veinger A.I. , Ivonin I.V. , Lavrentieva L.G. , Vilisova M.D. , Yakubenya M.P. , Lubyshev D.I. , Preobrazhenskii V.V. , Semyagin B.R.
Published: March 2011

The structure and properties of GaAs layers grown by molecular-beam epitaxy at low temperature (150-250 °C) have been studied. The samples were found to contain up to 1.5 at.% extra As, which formed nano-scale clusters under annealing. The dependences of the excessive As concentration and As-cluster size and density on the growth and annealing conditions were established. LT-GaAs layers were found to have high electrical resistivity, however, our investigations of microwave absorption in a weak magnetic field revealed a characteristic signal usually attributed to the superconducting phase. It has been proved that this microwave absorption is unlikely to be due to either the arsenic clusters in LT-GaAs films or indium in the substrate, as it was assumed previously. We suggest a new hypothesis that the superconducting phase in LT-GaAs is Ga nanoclusters formed on the growth surface.
Effects of Defects in GaAs/AlGaAs Quantum Wells
Authors: Russo O.L. , Rehn V. , Nee T.W. , Dumas K.A.
Published: March 2011

High Resolution transmission electron microscopy (HRTEM) and electroreflectance (ER) were used to explain the role of point defects in the molecular beam epitaxy (MBE) grown PIN structure containing five coupled (50Å/28Å) GaAs/AlxGa1−xAs quantum wells with x = 0.25. The ER data were taken at 300K and 77K for energies from 1.4 to 2.1 eV from which sub-band energy transitions were determined. Data at 300K showed three transitions whereas four were readily resolved at 77K. HRTEM data determined the uniformity of both the wells and barriers to be within ± 2Å, which neither caused appreciable broadening nor a decrease in the transition probability. However, the data at different temperatures suggest that point defects may be responsible for the decrease in the transition probability.
Temperature and Polarization Dependence of the Optical Absorption in ZnGeP2 at two Micrometers
Authors: Shah M. , Ohmer M. C. , Fischer D. W. , Fernelius N. C. , Manasreh M. O. , Schunemann P. G. , Pollak T. M.
Published: March 2011

The temperature and polarization dependence of the optical absorption in ZnGeP2 at two micrometers is reported for the first time over the temperature range from 10K to 300K. The radiation was normally incident upon the face of a cubic sample which contained the c-axis. The absorption of o-rays (E parallel to c), and erays (E perpendicular to c) was determined. It was found that the e-ray absorption coefficient was always significantly larger than the o-ray absorption coefficient and that it had a less significant temperature dependence. For example, the ratio of e-ray to o-ray absorption coefficient was approximately two at 300K and five at 77K. Correspondingly the o-ray absorption coefficients were reduced upon cooling to 77K by a factor of 2.5, while the e-ray absorption coefficients were reduced only slightly (10%-20%). These results indicate that for Type I optical parametric oscillators (OPOs) which use an oray pump beam, that performance may be improved by cooling the crystal.
A Tight-Binding Theory of the Electronic Structures for Rhombohedral Semimetals and Sb/GaSb, Sb/AlSb Superlattices
Authors: Xu J.H. , Wang E.G. , Ting C.S. , Su W.P.
Published: March 2011

The band structures of three group-V semimetals As, Sb, and Bi with rhombohedral A7 symmetry are studied using a second-neighbor tight-binding model including spin-orbit interaction with an sp3s* basis. Then the bulk tight-binding parameters are used to investigate the electronic properties of semimetal-semiconductor superlattices made of alternating (111) layers of Sb and GaSb or AlSb. It is found that the band gap can be adjustable depending primarily on the thickness of the Sb layers. An interface state is observed in the region of the gap.
Cathodoluminescence Spectroscopy Studies of Growth Induced Deep Levels at GaInP.
Authors: Enrique Viturro R. , Varriano John D. , Wicks Gary W.
Published: March 2011

We report a cathodoluminescence spectroscopy study of growth-induced deep levels at GaInP epilayers grown by Molecular Beam Epitaxy under various conditions. This approach allows the identification of deep levels which appear to play an important role in the band to band radiative recombination efficiency of these GaInP films. Control of these electronic defects is crucial for the performance of visible optoelectronic devices.
Fabrication of Quantum Wires by Wet Etching Techniques
Authors: Yang H. W. , Horng S. F. , Hwang H. L.
Published: March 2011

Quantum Wires Structures Were Fabricated By Patterning Quantum Well Samples With Electron Beam Lithography And Various Wet Chemical Etching Procedures. Wire Structures With 800Å Wire Width Were Achieved By Wet Etching In Nh4Oh / H2O2/ H2O (20:7:973). These Samples Were Characterized By Scanning Electron Microscopy (Sem), Photoluminescence (Pl), And Polarization-Dependent Photoluminescence Excitation (Ple) Measurements. The Pl Spectra Show Significantly Strongpr Peaks Than That Taken From An En-Etched Quantum Well Sample. A Wire Width Of 400Å Was Estimated From The Blue Shift Of Pl Peaks. A 22% Anisotropy Was Observed From Polarization-Dependent Ple Spectra, Further Corroborating The Existence Of Two-Dimensional Quantum Confinement.
The Organometallic Chemical Vapor Deposition of Transition Metal Carbides: the Use of Homoleptic Alkyls
Authors: Healy Matthew D. , Smith David C. , Rubiano Rodrigo R. , Springer Robert W. , Parmeter John E.
Published: March 2011

The organometallic chemical vapor deposition (OMCVD) of transition metal carbides (M = Ti, Zr, Hf, and Cr) from tetraneopentyl-metal precursors has been carried out. Metal carbides can be deposited on Si, A120 3, and stainless steel substrates from M[CH 2C(CH3)3]4 at temperatures in the range of 300 to 750 "C and pressures from 10-2 to 10-4 Torr. Thin films have also been grown using a carrier gas (Ar, H2). The effects of variation of the metal center, deposition conditions, and reactor design on the resulting material have been examined by SEM, XPS, XRD, ERD and AES. Hydrocarbon fragments generated in the deposition chamber have been studied by in-situ mass spectrometry. Complimentary studies examining the UHV surface decomposition of Zr[CH2C(CH3)3]4 have allowed for a better understanding of the mechanism leading to film growth.
Synthesis and Characterization of a New Ternary Transition Metal Nitride, FeWN2, from the Transition Metal Oxide Precursor, FeWO4
Authors: Bem David S. , Houmes Joel D. , Loye Hans-Conrad Zur
Published: March 2011

The ternary nitride, FeWN2, has been synthesized via ammonolysis of the transition metal tungstate, FeWO4. FeWN2 is hexagonal with a unit cell of a = 2.8724(1) Å and c =10.973(4) A. Rietveld refinements were performed in the space group P3–1C with Rwp=9.91%, and Rp=7.23%. The structure consist of alternating octahedrally coordinated iron-nitrogen layers and trigonal prismatically coordinated tungsten-nitrogen layers. Mössbauer data at 250K indicates an isomer shift δ=0.85 and shows no quadrupole splitting, which is consistent with the octahedral iron coordination in the proposed structure.
New Organosilicon Polymers for Ceramics Applications
Authors: Seyferth Dietmar , Strohmann Carsten , Dando Neal R. , Perrotta Anthony J. , Gardner James P.
Published: March 2011

The preparation, characterization and pyrolytic conversion to silicon-containing ceramics of two types of polymers – a series of poly(ureidosilazanes) and poly(silylenecarbodiimides) – are described. The former appears to have some promise as a preceramic polymer.
Oxygen Sinks in SiC-Based Ceramics
Authors: Braue Wolfgang , Chowdhury K. Das , Carpenter Ray W.
Published: March 2011

During an HREM/AEM investigation, two different oxygen sinks were identified for a variety of SiC-ceramics involving different sintering mechanisms: segregation of oxygen to i) internal interfaces, and ii) “excess-carbon” secondary phases consisting of basically turbostratic graphite and an intermediate amorphous Si-C-O phase. Si-C-O glasses and polycarbosilanebased nonstoichiometric SiC materials (Nicalon fibers) are well suited as model systems to evaluate the structure and the stability range of the amorphous Si-C-O phase in SiC-based ceramics.
Synthesis and Characterization of Nanophase Metal, M and Metal Carbide, M2C Particles of The Group 6 Elements, Cr, Mo and W.
Authors: Zeng D. , Hampden-Smith M. J.
Published: March 2011

Reduction of MCln, n = 3 for M = Cr, Mo, n = 4 for W with LiBEt3H in THF results in formation of nanometer-sized crystalline metal carbide, M2C particles whereas the same reduction reaction in toluene results in formation of the corresponding metal particles. As an example of this methodology, the reduction of MoC13(THF)3 and WC14 in THF by Li/C10H8 is described in detail. Reduction of MoC13(THF)3 in THF by Li/C10H8 resulted in formation of a black suspension from which black powder can be isolated. Electron diffraction and X-ray powder diffraction data showed the black powder is amorphous. Energy dispersive spectroscopy confirmed the presence of molybdenum, and no chlorine was detected. Ex-situ variable temperature X-ray powder diffraction experiments showed the presence of fec Mo2C which upon further heating underwent a phase transformation to hexagonal Mo2C. Crystalline molybdenum was also observed after heating to 750°C for 3 hours. Reduction of WC14 in THF by Li/C10H8 results in formation of a black powder which on heating underwent phase transitions from amorphous to fcc W2C to hexagonal W2C as determined by X-ray powder diffraction.
Microstructure and Mechanical Properties of Hot-Pressed and Pressureless Sintered WC-Al2O3 Ceramic Composites
Authors: Endo Hidehiro , Ueki Masanori
Published: March 2011

Fully densified WC-A12O3 composites were successfully consolidated by both hot-pressing and pressureless sintering. The optimum hot-pressing condition for the composites was 1700°C for 2h under a pressure of 40MPa. A remarkable improvement in mechanical properties was achieved in the composite system, especially in WC-30 and -70vol%A12O3, compared to the monolithic WC and A12O3 ceramics. The addition of MgO as a sintering aid had a great effect on the properties of the composites. WC-30vol%A12O3 composite with 1.Owt% MgO addition exhibited flexural strength higher than 1000MPa up to 1200°C, fracture toughness; KIC≥7MPa√m, and hardness; HV ≥2450. In pressureless sintering with the addition of MgO as a sintering aid and subsequent HIP treatment, the WC-30vol%A12O3 composite exhibited the flexural strength higher than 900MPa up to 1200°C.
Intercalation of Li into Single Crystals of MoS2
Authors: Papageorgopoulos C. A. , Jaegermann W.
Published: March 2011

In this paper we study in situ the intercalation of Li across and along the van der Waals planes of MoS2 single crystals. Li is intercalated according to the band model. The intercalation reaction is inhibited by a Li-S interaction. This interaction is negligible when Li is deposited along the van der Waals planes. The dominance of the intercalation reaction of Li into MoS2 is dependent on the flux of the deposited Li and the substrate temperature.
Conducting Polymer with Improved Long-Time Stability: Polyaniline-Polyelectrolyte Complex
Authors: Sun Linfeng , Yang Sze C. , Liu Jia-Ming
Published: March 2011

Conducting polymers, e.g. polyaniline, generally lack stability in their electrically conductive form due to heat and moisture induced loss of dopant. Using a template-guided synthesis scheme, we synthesized a polymeric complex of polyaniline and polyelectrolyte that showed stability against dedoping by moisture and heat. The polymeric complex consists of a strand of polyaniline twisted tightly with a strand of polyelectrolyte. The polyelectrolyte in the complex serves as a macromolecular dopant for polyaniline. These two components of the complex are tightly bound so that the dopant is not lost during tests for thermal stability and stability in water and Moisture. Since the dopant is a polyelectrolyte with high linear anion charge density, the complex resists deprotonation by water or weak base (pH < 10).
Solution Processable Conducting Polymer: Polyaniline-Polyelectrolyte Complexes
Authors: Sun Linfeng , Yang Sze C.
Published: March 2011

Conducting polymers have novel electrical and optical properties that are potentially useful for applications in electroluminescence display, rechargeable batteries, electrochromic windows, chemical sensors, electromagnetic shielding and anti-electrostatic films. However, these new materials are less adaptable to industrial processes than the traditional synthetic polymers. One of the problems is that conducting polymers are difficult to be solubilized in any solvent, thus lacking solution processability during a manufacturing process. In this article we discuss a new molecular complex of polyaniline that is soluble in water and in polar organic solvents.
Electrically Conducting Compatible Blends Of Polyaniline / Poly (Vinyl Pyrrolidone)
Authors: Stockton William B. , Rubner M. F.
Published: March 2011

Blending polyaniline (PAn) with a host polymer has the advantage of reducing the amount of polyaniline necessary for conductivity, increasing the stability of this conduction, and enhancing the overall mechanical integrity, versatility, and processability of PAn. PAn blends have generally been observed to be immiscible, reducing many of the above mentioned advantages. In this work, PAn was solution blended with poly (vinyl pyrrolidone) (PVP) in either NMP or DMAc, both polar solvents with an amide linkage. We have found PAn to be miscible with PVP under certain processing conditions. The extent of this compatibility and resulting mechanical properties were assessed by DMA, DSC, TGA, SAXS, and light Microscopy. DSC thermograms exhibit a single Tg for all blends ranging from 3 to 30 % by weight PAn. Light Microscopy and SAXS also suggest no phase separation. TGA results show that NMP binds very tightly to both PAn and PVP, with solvent cast blends retaining up to 20 wt% NMP, even after relatively vigorous drying. Electrical conductivity measurements of cast films show conductivity to range from 10-3to 2 S/cm over the same composition range.
Electrophysical Properties of Iodine Doped Acetylene/Ethylene Copolymers
Authors: Aleshin A. N. , Guk E. G. , Marikhin V. A. , Myasnikova L. P. , Belov D. G.
Published: March 2011

A new oxydative-resistant, fusible and processible ethylene/acetylene copolymer has been synthesized. The content of rigid (acetylene) and flexible (ethylene) fragments has been widely varied. The structure of the nascent powders and the films compressed at room temperature have been investigated by SEM and WAXS. DSC has been used for studying the thermal properties. DC conductivity of the iodine doped samples has been measured as a function of temperature. It is shown that the doping leads to arising conductivity in the samples even at 10 Mol % acetylene fragments in copolymer. The conductivity up to 10−3 S/cm is reached for the samples with acetylene fragment concentration about 20 Mol %. It is found that a charge carrier transport in investigated copolymers is caused by doped polyacetylene fragments and described by the hopping Mechanism.
Optical And Magnetic Properties Of Rigid Rod Conjugated Molecules
Authors: Wautelet P. , Le Moigne J. , Turek P.
Published: March 2011

A series of new stable fiinctionalised aryl ethynyl compounds bearing nitronyl-nitroxy and galvinoxyl radicals were synthesised as potential organic magnets with optical properties. Our goal is to construct biradicals in linear or broken rod molecules with the aim of probing i) the efficiency of the conjugation for the intramolecular spin exchange, and / or ii) the inter-Molecular Magnetic interaction between the neighboring radicals in the solid state Materials.

We focused our attention on the preparation of phenoxy, and galvinoxyl biradicals of the conjugated phenyl and thienyl diethynyl Moieties. The synthesis of these new components will be presented. Their optical and magnetic properties will be discussed both in solution and in the solid state.
Cyano-Derivatives Of Poly (P-Phenylene Vinylene) For Use In Thin-Film Light-Emitting Diodes
Authors: Greenham N. C. , Cacialli F. , Bradley D. D. C. , Friend R. H. , Moratti S. C. , Holmes A. B.
Published: March 2011

Conjugated polymers can be use to provide charge transport and emissive layers in a range of thin-film electroluminescent devices. Electroluminescence results from radiative decay of excitons which are formed by electron-hole capture. Device efficiency is particularly sensitive to the balancing of electron and hole currents injected from opposite electrodes, and this is best achieved at the heterojunction between two polymer layers with different electronegativities. We report here the properties of a conjugated polymer with high electron affinity, a cyano derivative of poly (p-phenylene vinylene), PPV. This polymer shows an electron affinity considerably higher than than that of PPV, and is therefore suitable for use as the electron transporting layer in heterostructure LEDs. It shows efficient photoluminescence due to radiative decay of singlet excitons, and photoinduced absorption in the IR, similar to that in PPV, which we attribute to excitations of photogenerated triplet excitons. EL devices formed with a heterojunction between PPV and this cyano derivative of PPV, with indium/tin oxide as positive electrode, PPV, cyano-PPV layers and an aluminium negative electrode, show internal quantum efficiencies as high as 4%.
Thermally Stable Poled Polymers: Highly Efficient Heteroaromatic Chromophores In High Temperature Polyimides
Authors: Jen Alex K-Y. , Wong K. Y. , Pushkara Rao V. , Drost K. , Cai Y. M. , Caldwell B. , Mininni R. M.
Published: March 2011

In this paper, we report our recent developments in achieving thermally stable polyimides that possess large second order nonlinear optical activity. We have developed several classes of novel chromophores based on the combination of efficient thiophene conjugating units and novel electron-donating and electron-accepting functional groups. Through these developments, we have synthesized chromophores that possess non-resonant βμ values as high as 9,100 × 10−48 esu measured at 1.9 μm. These chromophores also possess improved thermal and chemical stabilities. The incorporation of these chromophores in high temperature polyimides produces E-O Materials with high linear electro-optic coefficients (in excess of 15 pm/V at 1.3 μm) and long-term temporal stability at an elevated temperature of 150°C for more than 800 hours.
Novel Experimental Protocol for Studying Temporal Decay of Second-Order Nonlinear Optical Polymer Properties: Quantitative Analysis of Coupling to Polymer Dynamics and Conditions for Temporal Stability
Authors: Dhinojwala Ali , Hooker Jacob C. , Torkelson John M.
Published: March 2011

A new experimental approach has been developed which allows characterization of rotational dynamics of NLO chromophores in amorphous polymers over 12 decades in time, from 10-6 to 106 sec. Measurements over such a broad distribution in relaxation times are important not only in determining how the chromophore orientational dynamics are coupled to polymer dynamics but also in making accurate predictions of the temporal stability of technological interest. In particular, accurate characterization over a broad range of time scales reveals that NLO polymers meet technological requirements more easily than is predicted using a less complete characterization.
Photonic Polymers For Optical Switching
Authors: Horsthuis Winfried H.G.
Published: March 2011

Photonic polymers and devices with improved performances are reported. Optical losses in electro-opic polymers below 0.5 dB/cm at 1.3 and 1.6 μm have been realized. IMprovements in thermal stability have led to poled polymers exhibiting a relaxation time of 1 12 days at 125°C. The thermo-optic switches reported here are close to the requirements in telecommunications, and electro-optic devices with low switching voltages and high extinction coefficients are described as well.
Relaxation Phenomena in Poled Electro-Optic Polymers
Authors: Singer K. D. , Dureiko R. , Khaydarov J. , Fuerst R.
Published: March 2011

The relaxation of the nonlinear optical coefficient of poled electro-optic polymers remains an important issue in the potential application of these Materials. This relaxation is due to the homogenization of the orientational distribution function of nonlinear chromophores in the polymer glass over time. We have measured the relaxation using optical second harmonic generation as a function of temperature for doped polymer materials over a range of temperatures deep in the glassy state. We relate the data to widely used physical models of the glassy state which indicate that the relaxation process occurs over a considerable range of time scales. It has been found that the decay of the nonlinear polarization exhibits two mechanisms depending on the time and temperature scales over which measurements are performed. We have carried out measurements over a range of times and show that a broad distribution of relaxation times characterizes the data. This broad distribution is an appealing model in that it not only fits the data well, but is well connected to accepted physical models of the relaxation behavior of glasses. The characteristic energy of the relaxation can be estimated from the temperature dependence and is found to be equal to or less than the energy characterizing the polymer Motion, and agrees with dielectric studies. This indicates that the chromophores are more or less coupled to the dynamics of the polymer chain. A figure of merit for the coupling of the chromophore to the polymer chain is proposed.
Blue Second-Harmonic Light Generation From A New Organic Single Crystal, 8-(4′-Acetylphenyl)-1,4-Dioxa-8-Azaspiro[4.5]Decane(Apda)
Authors: Sagawa Masakazu , Kagawa Hiroyuki , Kakuta Atsushi , Kaji Makoto
Published: March 2011

A new second-order nonlinear optical organic Material, 8-(4′-acetylphenyl)-l,4-dioxa-8-azaspiro[4.5]decane (APDA) was synthesized as a frequency doubler emitting blue light. Its crystal growth, linear and non-linear optical properties were evaluated. The APDA crystal has a short cutoff wavelength of 384 nm and high nonlinear optical coefficients d33=50 pm/V and d32=7 pm/V. The crystal is phase matchable below wavelengths of 800nm, and its maximum effective nonlinear coefficient is 14.9 pm/V. Type I phase-Matched second harmonic generations can be carried out with YAG and Ti-sapphire laser pumping.
Nonunear Absorption in Phthalocyanines and Naphthalocyanines
Authors: Shirk James S. , Flom Steven R. , Lindle J. R. , Bartoli F. J. , Snow Arthur W. , Boyle Michael E.
Published: March 2011

The wavelength dependence of the nonlinear absorption for lead tetrakis (cumyl-phenoxy) phthalocyanine (PbPc(CP)4) and lead octa (α-pentoxy) napthalocyanine (PbNc(α-PO)8) are reported. The ground state absorption and the reverse saturable absorption are substantially red shifted in PbNc (α-PO)8 as expected. Such control over the reverse saturable absorption is crucial to design optical limiting materials for specific wavelength ranges.