bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic Monte Carlo Annealing Simulation of Damage Produced by Cascades in Alpha-Iron
Authors: Gao F. , Bacon D. J. , Barashev A. V. , Heinisch H. L. 
Published: April 2011

AbstractThe mobile defects created in displacement cascades can either interact within the cascade region or undergo long-range diffusion in the crystal. The kinetic Monte Carlo code ALSOME has been used in the present work to carry out annealing simulations of electron irradiation and single cascades with energy in the range of 2 to 40 keV in α-Fe as a function of temperature. Isochronal annealing of electron irradiation shows a temperature-dependence of the recovery stages that is reasonably close to experiment, but Stage I is controlled by the rotation energy of the <110> dumbbell to the <111> crowdion. The annealing of single cascades has demonstrated that nearly 60% of SIAs formed in the primary state of cascade damage escape from the cascade at temperatures above stage I. Most of the escaping SlAs are in clusters, for only 10% of them are mono-interstitials. Although the number of escaping defects increases with increasing cascade energy, the relative fraction is almost constant for the recoil energies considered. The results are compared with those for copper obtained using the same code [1].
Local Structural Changes of Ion Damaged InGaAs
Authors: Yu Kin Man 
Published: April 2011

AbstractIon damage and amorphization behavior in InGaAs with InAs mole fractions in the range of 0 to 50%are studied. We found that the degree of dynamic annealing increases as the InAs mole fraction increases in the InGaAs when the implantation is carried out at room temperature (RIT). Extended x-ray absorption fine structure measurements reveal that in the amorphous state the InAs nearest neighbor distance, RIn-As is very different from that in the crystalline InGaAs and is ∼0.01 Å longer than that in pure crystalline InAs. For RT implanted materials, before a complete amorphous layer is formed, the RIn-As remains close to its crystalline value even when the layer is heavily damaged. A sudden increase of the RIn-As is observed when a complete amorphous layer is formed. The behavior of the measured values of RIn-As for InGaAs implanted with various doses, indicates that at RT the formation of amorphous InGaAs occurs by the simultaneous nucleation of the amorphous phase when the critical free energy in the damage layer is exceeded. At liquid nitrogen temperature, when dynamic annealing is negligible, the RIn-As value increases as the damage in the layer increases, suggesting that the amorphous InGaAs is formed by the accumulation and overlapping of amorphous zones created along the individual ion tracks.
Fabrication of Piezoelectric Ceramic / Polymer Composite Transducers using Fused Deposition of Ceramics
Authors: Lous G. M. , Cornejo I. A. , McNulty T. F. , Safari A. , Danfortha S. C. 
Published: April 2011

AbstractThe Fused Deposition of Ceramics (FDC) technique was used to fabricate ceramic skeletons for development of piezoelectric composite transducers for medical imaging. The green parts were designed in order to have 30 vol% of PZT-5H ceramic in the final composites. Physical characterization of the sintered samples revealed that 96% of the theoretical density was achieved. Optical microscopy showed that defects, such as small roads and bubbles were eliminated due to powder processing improvements. The electromechanical properties of the final composites were found to be similar to properties obtained for conventionally made composites.
Effects of Additives on Thermomechanical Properties of Composites Formed from Thermoset Polymers
Authors: Radisic A. , Valimbe P. S. , Malhotra V. M. 
Published: April 2011

AbstractAutomotive and heavy-duty friction materials are complex multimaterial composites that contain, besides polymers and fibers, a number of constituents whose exact role is not well delineated. Since the performance of these composites requires not only uniform frictional properties but also complex shapes, advanced formation techniques are required. However, before these techniques can be harnessed, we attempted to understand how nitrile rubber-modified phenolic polymer's structural and thermal behaviors were modified by the incorporation of materials such as BaSO4, graphite, coal tar pitch, slag fibers, alumina, and silicon carbide, typical friction composite ingredients. The formed composites were examined by FTIR, DSC, and DMA techniques at 300 K < T < 600 K. Our results suggested that the incorporation of ingredients, singly and additively, strongly affected the thermomechanical properties of the formed
Gradient and Discrete Region Composites Produced by Solid Free Form Fabrication Techniques
Authors: Crockett R. S. , Gervasi V. R. 
Published: April 2011

AbstractStereolithography patterns have been used to create composites with gradient properties. Patterns are produced with an open cellular or columnar structure inside a surface shell. This serves as a host for filler materials, generally epoxies or polyurethane matrices loaded with various fibers or microspheres. Regions within a single object may be separated by thin barriers, allowing filling with different matrix materials to create regions of differing local properties.
The internal structure can also be continually gradated in dimension to produce composites with properties ranging from that of the filler material to that of the SFF material, currently epoxy or ABS plastic. This is a general set of processes that can be applied to a variety of existing Solid Freeform Fabrication systems.
Synthesis and Thermoelectric Properties of Cs2Bi7.33Se12, A2Bi8Se13 (A = Rb, Cs), Ba4-xBi6+2/3xSe13, and Ba3±xPb3±xBi6Se15
Authors: Iordanidis Lykourgos , Brazis Paul W. , Kannewurf Carl R. , Kanatzidis Mercouri G. 
Published: April 2011

AbstractWe are continuing our synthetic investigations in the ternary A/Bi/Se systems and also expanded our interests into the quaternary A/M/Bi/Se (A = Rb, Cs, Sr and Ba; M = lanthanide or Pb) systems. We have synthesized several new ternary and quaternary bismuth selenides with band gaps <0.6eV such as Cs2Bi7.33Se12, A2Bi8Se13 (A = Rb, Cs), Ba4-xBi6+2/3xSe13, and Ba3±xPb3±xBi6Se15. The synthesis, crystal structures and charge transports properties of these new compounds are presented.
Solid State Chemistry Approach to Advanced Thermoelectrics. Ternary and Quaternary Alkali Metal Bismuth Chalcogenides as Thermoelectric Materials
Authors: Kanatzidis Mercouri G. , Chung Duck-Young , Iordanidis Lykourgos , Choi Kyoung-Shin , Brazis Paul , Rocci Melissa , Hogan Tim , Kannewurt Carl 
Published: April 2011

AbstractOur exploratory research to identify new promising candidates for next generation thermoelectric applications has produced several interesting new materials which are briefly described here. We present their compositions, solid state structures, properties and charge transport behavior. The compounds CsBi4Te6, β-K2Bi8Se13, Ba4Bi6Se13, Eu2Pb2Bi6Se13, KBi6.33S10, Eu2Pb2Bi4Se10, Ba2Pb2Bi6S13 and K1.25 Pb3.5Bi7.25Se15 are particularly noteworthy.
Bi1-xSbx Alloy Thin Film and Superlattice Thermoelectrics
Authors: Cho S. , Vurgaftman I. , Shick A. B. , DiVenere A. , Kim Y. , Youn S. J. , Hoffman C. A. , Wong G. K. L. , Freeman A. J. , Meyer J. R. , Ketterson J. B. 
Published: April 2011

AbstractWe have grown Bi1-xSbx alloy thin films on CdTe(111)B over a wide range of Sb concentrations (0≤x≤0.183) using MBE. We have observed several differences with the bulk system. The 3.5 and 5.1% Sb alloys show semiconducting behavior, and the Sb concentration with the maximum bandgap is shifted to a lower Sb concentration, from 15% in bulk to 9%. The power factor S2/ρ (where S is thermoelectric power(TEP) and ρ electrical resistivity) peaks at a significantly higher temperature (250K) than previously reported for the bulk alloy (80K). The magnetotransport properties of Bi1-x,Sbx thin films (x = 0, 0.09, and 0.16) and Bi/CdTe superlattices have been determined by applying the Quantitative Mobility Spectrum Analysis (QMSA) and multicarrier fitting to the magneticfield- dependent resistivities and Hall coefficients, using algorithms which account for the strong anisotropy of the mobilities. The calculated S values are in good agreement with experimental results. The structural stability of bulk Bi is studied using the local density linear muffin-tin orbital method. It is shown that the internal displacement changes the Bi electronic structure from a metal to a semimetal, in qualitative agreement with a Jones-Peierls-type transition. The total energy is calculated to have a double well dependence on the internal displacement, and to provide a stabilization of the trigonal phase. We show that an increase of the trigonal shear angle leads to a semimetal-semiconductor transition in Bi.
Electronic Structure and Transport Properties of CoSb3: A Narrow Band-Gap Semiconductor
Authors: Sofo J. O. , Mahan G. D. 
Published: April 2011

AbstractWe report calculations which show that the band structure of CoSb3 is typical of a narrow band-gap semiconductor. The gap is strongly dependent on the relative position of the Sb atoms inside the unit cell. We obtain a band gap of 0.22 eV after minimization of these position. This value is more than four times larger than the result of a previous calculation which reported that the energy bands near the Fermi surface are unusual. The electronic states close to the Fermi level are properly described by a two-band Kane Model. The calculated effective masses and band gap are in excellent agreement with Shubnikov de Haas and Hall effect measurements. Recent measurements of the transport coefficients of this compound can be understood assuming it is a narrow band gap semiconductor, in agreement with our results.
Fabrication, Characterization and Electronic Properties of Bismuth Nanowire Systems
Authors: Zhang Zhibo B. , Dresselhaus M. S. , Ying Jackie Y. 
Published: April 2011

AbstractWe have fabricated ultra-fine Bi nanowire (10–120 nm) arrays with packing densities as high as 7.1 × 1010/cm2 by pressure injecting its liquid melt into the evacuated nano-channels of an anodic alumina template. Using this fabrication technique, we have also prepared Te-doped n-type Bi nanowires. Free-standing Bi nanowires with an aspect ratio (length/diameter) higher than 500 are obtained by etching away the anodic alumina matrix without attacking the Bi. The resulting Bi nanowires are shown to be single crystals (with the same crystal structure as bulk Bi) and all the wires of a nanowire array are similarly oriented along the wire axis. The small electron effective mass of Bi, the high anisotropy of its Fermi surface, and the large aspect ratio of the Bi nanowires make this a very promising material for low-dimensional thermoelectric applications and an excellent system for studying quantum confinement effects in a quasi-one-dimensional (1D) electron gas. A theoretical model based on the basic band structure of bulk Bi, suitably modified for the 1D situation, is constructed to explore the electrical transport properties of Bi nanowires, which are expected to be very different from those of bulk Bi.
Thermionic Refrigeration
Authors: Mahan G. D. 
Published: April 2011

AbstractThe principles of thermionic refrigeration are explained. The simplest device is composed of two metal plates separated by a vacuum gap. This device is efficient at room temperature only for plates with small work functions (eø <0.3 eV). Small barriers are available in semiconductor-semiconductor interfaces (band off-sets) and in metal-semiconductor interfaces(Schottky barriers). An efficient refrigerator is modeled for these systems. Possible realizations are discussed.
Thermoelectric Transport in Superlattices
Authors: Broido D. A. , Reinecke T. L. 
Published: April 2011

AbstractA quantitative description of the power factor for thermoelectric transport in quantum well and quantum wire superlattices has been developed. The size dependence of the carrier scattering rates as well as carrier tunneling between layers are included, and results are obtained for full three-dimensional superlattice systems. In addition, model calculations of the lattice thermal conductivity of free standing wells and wires have been obtained, and their implications for the thermoelectric figure of merit are discussed. Illustrative results are given for GaAs and PbTe systems.
Performance of Ultra Hard Carbon Wear Coatings on Microgears Fabricated by Liga
Authors: Ager Joel W. , Monteiro Othon R. , Brown Ian G , Follstaedt David M. , Knapp James A. , Dugger Michael T. , Christenson Todd R. 
Published: April 2011

AbstractStiction and friction are of concern for the reliable, long-term application of Ni-alloy micromachines. We have found that the application of a 30 - 70 nm hard carbon coating produces a significant reduction in the friction coefficient and wear rate of electroformed Ni substrates in reciprocating sliding contact under simulated MEMS operating conditions. To evaluate the performance of coated components, a series of 70-μm-thick microgears ranging in diameter from 0.2 to 2.2 mm were fabricated from electroformed Ni via standard LIGA processes and fixtured on posts in preparation for the coating procedure. A pulsed vacuumarc deposition process was used to deposit a carbon coating on the gears with the plasma incident at a shallow angle to the gears' top surface. A sample bias of −2 keV was used in order to produce a coating with relatively low stress and good adhesion while maintaining high hardness. This coating process is known to be somewhat comformal to the component surfaces. The coating uniformity, particularly in the high-aspect-ratio areas between the gear teeth, was evaluated with micro-Raman spectroscopy. It is shown that the coating can be applied uniformly on the top gear surface. Between the gear teeth the coating was the same thickness as on top of the gear down to a point 50 μm below the top surface. Below that point (i.e. between 50 and 70 μm), the coating thickness is somewhat thinner, but is still present. These results demonstrate that it is possible to a deposit hard carbon coating on microgears to reduce friction and wear in micromachines.
Torsion Testing Of Diffusion Bonded Liga Formed Nickel
Authors: Christenson T. R. , Buchheit T. E. , Schmale D. T. 
Published: April 2011

AbstractA test technique has been devised which is suitable for the testing of the bond strength of batch diffusion bonded LIGA or DXRL defined structures. The method uses a torsion tester constructed with the aid of LIGA fabrication and distributed torsion specimens which also make use of the high aspect ratio nature of DXRL based processing. Measurements reveal achieved bond stengths of 130 MPa between electroplated nickel with a bond temperature of 450°C at 7 ksi pressure which is a sufficiently low temperature to avoid mechanical strength degradation.
Influence of Specimen Size and Sub-Micron Notch on The Fracture Behavior of Single Crystal Silicon Microelements and Nanoscopic Afm Damage Evaluation
Authors: Minoshima Kohji , Inoue Shigemichi , Terada Tomota , Komai Kenjiro 
Published: April 2011

AbstractSimple bending tests of single-crystal silicon microelements fabricated by photoetching were performed. Silicon microelements deform elastically until final catastrophic failure, showing a brittle nature. The fracture strength increases with a decrease in specimen size, and the maximum strength reaches about 8 GPa. A Focused ion beam was used to machine a sub-µm deep notch. Such a small notch decreases the fracture strength of a microelement. Some fatigue tests were conducted in laboratory air and in distilled water: water reduces the strength of microelement under fatigue loading. Fracture surface and sample surface were closely examined with a scanning electron microscope and an atomic force microscope, and the fracture mechanisms are discussed from the nanoscopic points of view.
Dry Etching of Sol-Gel Pzt
Authors: Zeto R. , Rod B. , Dubey M. , Ervin M. , Conrad J. , Piekarz R. , Troliermckinstry S. , Su T. , Shepard J. 
Published: April 2011

AbstractTwo techniques for dry etching of sol-gel lead zirconate titanate (PZT 52/48) thin films were investigated: reactive ion etching and argon ion milling. Etched profiles were characterized by scanning electron microscopy. For reactive ion etching, a parallel plate etcher was used with HC2ClF4, an environmentally safe etch gas, in a process described by other researchers. Etch rates were measured and compared as a function of electrode shield material (ardel, graphite, alumina) and RF input power (100 to 500 W). These etch rates varied from 10 to 100 nm/min. Reactive ion etched sidewall angles 12° off normal were consistently produced over a wide range of RF powers and etch times, but overetching was required to produce a clean sidewall. For argon ion milling, a 300 mA/500 V beam 40° off normal to the substrate operating in a 72 mPa argon pressure was used. These ion milling conditions produced an etch rate of 250 nm/min with a sidewall slope angle of about 70°. The ion milling etch rate for sol-gel PZT was significantly faster than rates reported for bulk PZT. The 500 nm thick PZT films used in this study were prepared by the sol-gel process that used methoxyethanol solvent, spin coating on t/Ti/SiO2 silicon substrates, and rapid thermal annealing for 30 s at 650 °C for crystallization of the perovskite phase.
Sol-Gel Casting of Ceramic Microcomponents
Authors: Chan C. M. , Cao G. Z. 
Published: April 2011

AbstractDevelopment of ceramic microcomponents can open up the current silicon-based MEMS technology to new applications, especially for use in high temperature, chemically reactive environments. We report a study of sol-gel technologies applied to the fabrication of microcomponents. Organic/inorganic hybrid materials, particularly silica-based hybrids, were developed by sol-gel processing. A weak silica network was made possible by using acid catalyst, low functionality organic precursor in the sol preparation. Since the weak network has a high tendency to collapse, the result is a denser material. Incorporation of organic ligands modifies the surface chemistry of gel network so that a greater drying stress was developed and a denser hybrid structure was achieved without high temperature treatment. In addition, the incorporation of organic ligands prevented formation of cracks. Nanoscale oxide particles were dispersed and incorporated into the gel network by surface condensation. The incorporation of solid nanoparticles into sols greatly reduced the shrinkage of gels and enhanced the mechanical strength of the components. In addition, silica sol was applied to coat metallic microcomponents and a thin uniform was formed.
Microstructural Evolution of Co-fired Ceramic Tapes for MEMS Applications
Authors: Charoenmechaikul Suebpong , Luzzi David E. 
Published: April 2011

AbstractA study of the structure and thermodynamics of the densification process in a model alumina-based ceramic tape system during thermal processing is presented. DuPont's Green Tape™ 951, which is primarily composed of frit (>50% silica), alumina and an organic binder, is used as the model system. The microstructures of annealed specimens are characterized by scanning electron microscopy as a function of annealing time and temperature. The distribution and shape of pre-existent pores and frit particles are found to be strongly dependent on the processing conditions. With the processing temperatures significantly below conventional sintering temperature of alumina, the behavior of the frit is the critical determinant of the final microstructure and mechanical behavior.
A Direct Molding Technique to Fabricate Silica Micro-Optical Components
Authors: Lee Choon-Keat Terence , Vasile Michael J. , Goettert Jost 
Published: April 2011

AbstractA technology for the direct molding and release of silica micro-optical components in polymethyl methacrylate (PMMA) molds is developed. The objectives of this work are to bypass some of the usual steps in deep x-ray lithography (DXRL) and to determine the suitability of GR650 resin (methylpolysilsequioxane) for molding thick, high aspect ratio structures. The process is initiated by DXRL exposure of PMMA, followed by spin-on glass application, a cure at 85°C to set the shape of the resin, followed by demolding. The cure is below the glass transition temperature of PMMA and the demolding process allows re-use of the mold. There is no need for electroforming in the replication process. PMMA molds with thickness of 250, 350 and 500 um were fabricated by DXRL and standard resist development. A novel metal sacrificial layer technique is used in the release process with initial yield of about 50%. Microoptical elements that were fabricated include lenses, prisms, grating structures and transmission test structures. These components are cured above 400°C after release, to convert the organosilicon polymer to a silica-like material. Weight loss from the high temperature cure was in the range of 15 to 25%, while linear dimensions of the components decreased by about 1%. Composition of the molded, cured structures was measured by XPS depth profiles.
Rapid Thermal Annealing for Residual-Stress Relaxation in Undoped or Doped Polysilicon Thin Films
Authors: Zhang Xin , Zhang Tong-Yi , Zohar Yitshak 
Published: April 2011

AbstractThe residual stress in doped and undoped polysilicon films, before and after rapid thermal annealing (RTA), is investigated using both wafer-curvature and micro-rotating structures techniques. Microstructure characterization has been conducted as well to understand the mechanism of the stress evolution. The results show that the compressive residual stresses in undoped polysilicon films can be reduced or eliminated within a few seconds RTA. Surface nitridation and grain growth are identified as the mechanisms responsible for the stress evolution.
Deep Reactive Ion Etching of Silicon
Authors: Ayón A. A. , Chen K.-S , Lohner K. A. , Spearing S. M. , Sawin H. H. , Schmidt M. A. 
Published: April 2011

AbstractThe ability to etch deep trenches in silicon while controlling not only the profile of etched features but also the etching rate, uniformity and selectivity enable us to expand the number and scope of MEMS devices. In fact, the increase of MEMS applications in different and varied fields requiring deep silicon etching or high aspect ratio structures (HARS) has even been extended to include microturbomachinery which was recently introduced as a feasible source of power generation. Many projects also place additional demands on surface morphology. Thus, the scalloping observed on vertical walls during time multiplexed deep etching (TMDE), the roughness of horizontal surfaces exposed to the glow discharge and the radius at the bottom of etched features are also relevant. Therefore, it is important to understand not only the plasma processes involved but also the dependence of response variables on operating conditions. For this purpose we have designed, performed and analyzed sets of experiments adequate to fit quadratic models. The data was collected using interferometry, atomic force microscopy (AFM), profilometry and scanning electron microscopy (SEM). The exercise involved eight etching variables and it was conducted in an inductively coupled deep reactive ion etcher (DRIE). The mapping of the dependence of response variables on dry processing conditions produced by this systematic approach provide additional insight in the plasma phenomena involved and supply practical tools to locate and optimize robust operating conditions.