bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pressureless Sintering of MoSi2 Materials
Authors: Scholl Roland , JÜngling Thomas , Kieback Bernd 
Published: April 2011

AbstractVarious powder mixtures were prepared by a modified mechanical alloying technique. Starting from elemental Mo-, Si- and C-powders the influence of milling conditions on phase formation during the milling process and the subsequent heat treatment was investigated. Phase formation during sintering and sintering kinetics of activated starting mixtures were studied by differential scanning calorimetry (DSC), thermal graphimetry (TG), X-ray diffraction (XRD) and dilatometry. The results show that phase formation during milling or sintering strongly depends on milling conditions. Optimized powder mixtures of single phase and reinforced molybdenum silicides show high densities up to 98,5 % TD by pressureless sintering in various atmospheres. Full density is possible by post-HIP because the samples show only closed porosity. The microstructure was studied in dependence of sintering parameters. The level of impurities, i.e. C, O2 was determined. Hardness, fracture toughness and bending strength were measured for single phase and particle reinforced materials.
Properties of SiC-SiC Composites Produced Using CVR Converted Graphite Cloth to SiC Cloth
Authors: Kowbel W. , Kyriacou C. , Gao F. , Bruce C. A. , Withers J. C. 
Published: April 2011

ABSTRACTNicalon fiber is the primary reinforcement in SiC-SiC composites currently produced by a variety of techniques including CVI and polymer infiltration. Low strength retention at high temperatures of the Nicalon fibers limits the choice of manufacturing processes which can be employed to produce low cost SiC-SiC composites. MER has developed a new SiC reinforcement based upon a conversion of low cost carbon fabric to SiC via a Chemical Vapor Reaction (CVR) process. This new SiC filaments exhibit an excellent creep resistance at temperatures up to 1600°C. Several SiC-SiC composites were fabricated using graphite fabric converted to SiC fabric utilizing the CVR process combined with a slurry infiltration and CVI densification. A correlation between processing conditions, microstructure and properties of the SiC-SiC composites are discussed in detail.
Fiber Twist Test: A New Test Technique to Measure Composite Interface Properties
Authors: Chepolis William M. , Ertürk Turgay 
Published: April 2011

ABSTRACTThis paper discusses the work accomplished, thus far, in the development of the Fiber Twist Test (FTT) as an alternative and improved technique for testing the interface properties of continuous fiber composite materials. The unique features of the fiber twist test include the absence of Poisson effects during testing. This eliminates the nonlinear variation, with changing embedded fiber lengths, of fracture modes and accompanying debond energy, and of friction along the interface. Since the fiber is not removed from its surrounding matrix during testing, the interface area remains constant. This facilitates a more accurate measurement of friction properties at the interface.
Rapid Processing of Carbon-Carbon Composites by Forced Flow-Thermal Gradient Chemical Vapor Infiltration (FCVI)
Authors: Vaidyaraman S. , Lackey W. J. , Agrawal P. K. , Freeman G. B. , Langman M. D. 
Published: April 2011

ABSTRACTCarbon fiber-carbon matrix composites were fabricated using the forced flow-thermal gradient chemical vapor infiltration (FCVI) process. Preforms were prepared by stacking 40 layers of plain weave carbon cloth in a graphite holder. The preforms were infiltrated using propylene, propane, and methane. The present work showed that the FCVI process is well suited for fabricating carboncarbon composites; without optimization of the process, we have achieved uniform and thorough densification. Composites with porosities as low as 7% were fabricated in 8–12 h. The highest deposition rate obtained in the present study was ∼3 μm/h which is more than an order of magnitude faster than the typical value of 0.1–0.25 μm/h for the isothermal process. It was also found that the use of propylene and propane as reagents resulted in faster infiltration compared to methane.
Fiber Coatings and the Fracture Behavior of a Continuous Fiber Ceramic Composite
Authors: Miller J. H. , Lowden R. A. , Liaw P. K. 
Published: April 2011

ABSTRACTFiber coatings have been used to modify fiber-matrix interfacial forces, and thus control mechanical properties of continuous fiber ceramic composites. It has been shown that the properties and thickness of the interlayer influence composite properties such as matrix cracking and ultimate strength, toughness and interlaminar shear. The effects of fiber coating properties and thickness on fiber-reinforced SiC matrix composites fabricated employing CVI techniques have been examined. Correlations between interface condition, mechanical properties and failure mechanisms have been made.
Elevated Temperature Static Fatigue of a Nicalon Fiber-Reinforced SiC Composite
Authors: Lin Hua-Tay , Becher Paul F. , Tortorelli Peter F. 
Published: April 2011

ABSTRACTStatic fatigue tests of a Nicalon fiber-reinforced SiC matrix composite were conducted in four-point bending over a temperature range of 425° to 1150°C in air at selected stress levels. The composite consisted of a Nicalon cloth with a 0.3 μm graphite interfacial coating and a Forced Chemical Vapor Infiltration (FCVI) SiC matrix composite; samples were tested with or without a final protective SiC seal coat. The results indicated that the fatigue life of the Nicalon-SiC composite decreased with an increase in either applied stresses or test temperatures. However, the composite exhibited a fatigue limit of ∼ 100 MPa at temperatures ≤ 950°C which decreased to ∼ 70 MPa at 1150°C. Both electron microscopy and thermogravimetric studies suggested that the lifetime of the composites was dictated by the oxidation of graphite interfacial layer at temperatures ≤700°C and by oxidation of graphite coating accompanied by formation of silicate interfacial layer via oxidation of the Nicalon fiber (and the SiC matrix) at temperatures ≥ 950°C. Use of a SiC seal coat effectively retarded the oxidation reactions and increased the lifetime by at least one order of magnitude at 425°C. On the other hand, the SiC seal coat made little (if any) difference in fatigue life at 950 °C.
Reaction Synthesis of MoSi2-Al2O3 Composite Using MoO3, Al and Si Powders
Authors: Deevi Seetharama C. , Deevi Sarojini 
Published: April 2011

ABSTRACTIn-situ synthesis of a composite of MoSi2-Al2O3 was carried out by reacting a thermite mixture consisting of MoO3, Al, and Si powders. The reaction was found to be extremely fast and violent, and a diluent was required to moderate the reaction. Thermal behavior of the thermite mixture was studied using DTA at different heating rates, and DTA was interrupted at different temperatures to determine the reaction mechanism. X-ray characterization of the products obtained at different temperatures reveals that the mechanism consists of a reduction of MoO3 by Al to MoO2 followed by a simultaneous oxidation of Al to Al2O3 and synthesis reaction between reduced Mo and Si to form MoSi2. The rate determining step is found to be reduction of MoO2 by Al and oxidation of Al to Al2O3. The thermite reaction was moderated by adding Mo and Si to the mixture of MoO3, Al, and Si such that the ratio of MoSi2 to the thermite was in the range of 60:40 to 90:10.
Radiation Enhanced Diffusion in Mgo
Authors: Van Sambeek Andrew I. , Averback R.S. , Flynn C.P. , Yang M.H. 
Published: April 2011

AbstractMeasurements of marker spreading following 2.0 MeV Kr+irradiation at 25 to 1300°C have been performed on MgO samples containing O18, Ca and Zn buried tracer atoms. Ion beam mixing at room temperature on both sublattices was approximately 2.0 to 3.0 A5/eV. From 600 to 1000°C, the apparent activation enthalpy for diffusion on the anion sublattice (O18) was 0.35 eV and the diffusion coefficient was linear in the irradiation flux. From 1150 to 1300°C the measured activation enthalpy was 4.1 eV and the diffusion coefficient was proportional to the square root of flux. The measured activation enthalpy on the cation sublattice was roughly 0.30 eV up to 700°C for both Ca or Zn doped samples. Measurable extrinsic thermal diffusion from vacancies present for trivalent impurity charge compensation occurred above this temperature, complicating the analysis at higher temperatures. The observed kinetics in the lower temperature range are most likely controlled by interstitial loop formation. In the higher temperature range, vacancy traps with a binding energy of approximately 2 eV could account for the high activation enthalpy.
Electron Beam Irradiated Effects of SiO2 in Stem
Authors: Lee Tan-Chen , Silcox John 
Published: April 2011

AbstractElectron beam irradiation effects in SiO2 have been studied by STEM (Scanning Transmission Electron Microscopy). Oxygen loss and the corresponding transformation from SiO2 to Si in SiO2 are confirmed and consistent with previous reports 1,2. A “flower-like” Si rich area, which might not be observed in STEM BF (Bright Field) or ADF (Annular Dark Field) images, was found in Si plasmon energy filtered images. Quantification of the observations and the formation mechanisms leading to the Si-rich area are discussed.
Application of Channeling Techniques and High Resolution Transmission Electron Microscopy to Ion-Beam Damaged Zircon
Authors: Bordes N. , Ewing R.C. 
Published: April 2011

AbstractZircon (ZrSiO4) samples were irradiated at 100K with 400 keV Ar+ and Xe+ ion beams to fluences ranging from 5x1013 to 5x1015 ions/cm2. Rutherford backscattering spectroscopy (RBS) experiments were completed to study the dechanneling of He ions in the irradiated zircons. Cross-sections of some irradiated samples were prepared, and the zircon microstructure was examined by highresolution transmission electron microscopy (HRTEM). At doses greater than 8x1014 ions/cm2 or 0.8 dpa (displacements per atom), RBS channeling experiments showed the presence of a disordered or amorphous layer. The electron microscopy confirmed the presence of an amorphous layer extending over a depth of 300 to 350 nm (Ar+ irradiation) and 200 nm (Xe+ irradiation) in agreement with the damage layer depth calculated by TRIM. At depths extending beyond the damage peak, TEM reveals an amorphous layer with “islands” of crystalline material of σ 30 nm in size. These experiments show that RBS and TEM are complementary techniques in investigating radiation effects in irradiations of bulk ceramic.
Room Temperature Damage, Annealing and Dislocation Growth in Silicon
Authors: Elliman R.G. , Mitchell I.V. 
Published: April 2011

AbstractThe concentration of residual defects produced by self ion implantation of silicon has been shown to be a sensitive function of implantation temperature at temperatures near room temperature. In this study samples were heated to temperatures of 20°C and 60°C and implanted with 540 keV Si ions to a fluence of 2x1015Si.cm-2 using a constant scanned ion flux of 0.2 μA.cm-2. The resultant primary defect concentrations, measured by Rutherford backscattering spectrometry and channelling (RBS-C), were 2.3±0.1x1022 cm-l and 1.8±0.2x1021 cm-3, respectively, i.e. a reduction by a factor of σ13 for a temperature increase of 40°C. Such differences were not evident in the concentration of secondary defects formed by annealing these samples at 900°C for 15 minutes: the defect concentrations were equal within the experimental uncertainties of the RBS-C and transmission electron microscopy (TEM) measurements. This result appears to lead to the surprising conclusion that the number of displaced atoms that survive high temperature annealing to form extended defects is largely independent of the dynamic annealing processes operating during implantation but depends instead on parameters which scale with the ion fluence.
Effect of Copper and Nickel on the Neutron Irradiation Damage in Iron Alloys
Authors: Hoelzer D.T. , Ebrahimi F. 
Published: April 2011

AbstractIron alloys containing copper and nickel were irradiated at 288°C to a fluence of 4.63 × 1019 neutrons/cm2. Neutron irradiation produced defects which were observable by TEM in all of the iron alloys studied. The TEM analysis of the defects showed them to be interstitial dislocation loops with a < 100 > and a/2 < 111 > Burgers vectors. The size, the number density, and the Burgers vector of dislocations were affected by the alloy composition. The addition ofcopper and nickel decreased the dislocation loop size and increased the fraction of a/2 < 111 > loops. No voids or vacancy loops were observed in the irradiated iron alloys. The results are discussed in terms of dislocation loop nucleation and growth.
Development of Neutral-Density Infrared Filters Using Metallic Thin Films
Authors: Zhang Z. M. , Dada R. U. , Hanssen L. M. 
Published: April 2011

AbstractBroadband infrared filters with uniform spectral transmittance are used for spectrometer calibration and other applications. However, commercially available neutral-density filters with optical density (GD) greater than 2 exhibit significant variations in OD over the wavelength region from 2 μm to 25 μ m. In this work, we found a single-layer alloy film that, for appropriate thicknesses, yields a flat transmittance for OD near 3 and 4. The transmittance and reflectance of the filters were measured using a Fourier-transform infrared spectrometer. The optical constants of the alloy films were obtained from transmittance and reflectance measurements, which can be used for future design optimization.
Surface Reaction Mechanism During Deposition of a-Si: 11 by PECVD
Authors: Maeda Keiji , Kuroe Atsushi , Umezu Ikurou 
Published: April 2011

ABSTRACTHydrogen contents were investigated in a-Si:H films prepared by PECVD under various conditions. The H atom contents were divided into SiH and SiH2 densities by spectral deconvolution of the IR absorption. Dehydrogenation of SiHo simultaneously occurs with Si-Si bonding in the surface reaction. The mechanisms of surface reaction were proposed based on an analysis of the variation in S1H2 density with the deposition condition. There are two kinds of processes, the fast process and the slow process. The fast process incorporates SiH2 into the network. The activation energy of the slow process is 0.3 eV, which is due to the surface migration of adsorbed radicals.
The Limitations of the Constant Photocurrent Method for Determining Subgap Absorption
Authors: Stradins P. , Fritzsche H. , Tran M. 
Published: April 2011

ABSTRACTThe subgap absorption αcpm measured by the constant photocurrent method (CPM) was studied between 4.2K and 300K for different dopings and defect concentrations N in hydrogenated amorphous silicon (a-Si:H). We found that αcpm is reduced by up to a factor 100 between 50K and 200K due to infrared selfquenching which changes the charge state of the defects and enhances recombination. The effect is diminished at high N and large doping. The relative change Δα/α reflects ΔN/N both at very low and high temperatures. For undoped samples αcpm is about four times larger at 4.2K than at 300K. For doped samples the two values are essentially the same.
Structural Defects in thin Film Amorphous Silicon Films Deposited on Textured TCO Material
Authors: Knoesen D. , Schropp R. E. I. , Van Der Weg W. F. 
Published: April 2011

ABSTRACTA cross sectional TME study has been conducted into the structure and morphology of p- and i-type a-Si:H layers of device quality deposited on textured TCO on glass. The layer thickness over peaks is shown to be equivalent to that for flat regions, while defective regions are found in narrow valleys, initiating from the pit of the valleys. These regions may act as regions of excessive recombination and/or shunting regions, thus leading to a reduced Voc and fill factor in thin solar cells. A cosine relationship was found between the deposited thickness and the facet angles of the surface TCO crystals. It is concluded that for best performance of the deposited layer, the deposition has to be completely isotropie, and that the preferred surface morphology of textured TCO be sharp peaks with wider valleys.
The Effect of ZnO Sputtering Deposition Parameters on the Performances of Back Reflector Enhanced Amorphous Silicon Solar Cells
Authors: Terzini E. , Rubino A. , De Rosa R. , Addonizio M. L. 
Published: April 2011

ABSTRACTLow resistivity (5×10−4Ω cm) and high transmittance (T > 82 %) ZnO films have been obtained by RF magnetron sputtering deposition of ZnO/Al2O3 (2.5 % wt.) target. The doped oxide films have been investigated by optical and electrical measurements and by scanning electron microscopy. The optimized recipes have been applied to the realisation of amorphous p-i-n solar cells back reflector in the structure: TCO/pin/ZnO/Ag.The application of ZnO/Ag leads to an increase of the Jsc current of about 13% but a poorer fill factor steadily affects the characteristics of the devices. We demonstrate that a thicker n+ layer of about three times the standard one is effective in driving the FF toward the normal values.The cells' behaviour has been ascribed to a thinning of the n+ layer resulting from a sputtering action of energetic oxygen atoms during the ZnO deposition process. This effect has been evidenced by measuring the absorbance of SnO2/a-Si (20 nm) /ZnO in comparison with SnO2/a-Si (20 nm) structure.
A New Linear Array Thin Film Position Sensitive Detector (LTFPSD) for 3D Measurements
Authors: Fortunato E. , Soares F. , Lavareda G. , Martins R. 
Published: April 2011

ABSTRACTA Linear array Thin Film Position Sensitive Detector (LTFPSD) based on hydrogenated amorphous silicon (a-Si:H) is proposed for the first time, taking advantage of the optical properties presented by a-Si:H devices we have developed a LTFPSD with 128 integrated elements able to be used in 3D inspections/measurements. Each element consists on an one-dimensional TFPSD, based on a p.i.n diode produced in a conventional PECVD system, where the doped layers are coated with thin resistive layers to establish the required device equipotentials. By proper incorporation of the LTFPSD into an optical inspection camera it will be possible to acquire information about an object/surface, through the optical cross-section method1. The main advantages of this system, when compared with the conventional CCDs, are the low complexity of hardware and software used and that the information can be continuously processed (analogue detection).
Electron Spin Resonance Evidence for a Localized EP (E’δ-Like) Defect Structure
Authors: Conley John F , Lenahan PM 
Published: April 2011

AbstractWe report the first observation of a hydrogen complexed EP (E’δ) center. Comparing EP/H and E’γ/H electron spin resonance spectra, we provide the first strong evidence that EP (E’δ) centers do not have a delocalized structure.
Analysis of Hydrogen Passivation Mechanisms in Poly-Si TFT’s by Employing R.F. Plasma
Authors: Choi K. Y. , Kim Y. S. , Choi H.S. , Bae B.S. , Han M. K. 
Published: April 2011

AbstractThe dominant pathways for hydrogen diffusion in poly-Si TFT’s are identified by analyzing the hydrogenation effect on the various device geometries. It is observed that the gate poly-Si thickness and channel width didn’t affect the hydrogenation. As the channel length was decreased down to 3 µm, threshold voltage was reduced and field effect mobility was increased significantly with hydrogeantion time. In the thick gate oxide (2000 Å, 4000 Å) poly-Si TFT’s, the device characteristics have been improved rapidly with hydrogenation time. The tail state density of thin gate oxide TFT wasn’t change by hydrgenation while that of thick gate oxide TFT was significantly reduced. Our experimental results may support the model that hydrogen atoms diffuse into the bulk of the active channel layer through the gate oxide and passivate the grain boundary and intragranular defects limitedly by gate oxide area.
Hydrogenation of Multicrystalline Si-Materials for Solar Cells: Discrimination Between Effects in the Intra-Grain and Grain Boundary Regions
Authors: Poortmans J. , Rosmeulen M. , Kaniava A. , Vanhellemont J. , Elgamel H. , Nijs J. 
Published: April 2011

AbstractIn this paper we describe the results of a study on the hydrogenation treatment of multicrystalline substrates by an RF-plasma with emphasis on discriminating between effects on the intra-grain material and grain boundary regions. For this purpose small mesa-type diodes were processed. Two types of multicrystalline material are being compared in this study. The main difference between these materials is their oxygen and metallic impurity content. The effects of the hydrogenation treatment were studied by means of I-V and DLTS-measurements. Finally, we will present data on small multicrystalline solar cells and the effect of hydrogenation on the main parameters of this device to illustrate the correlation and the differences between the measurements on small-scale diodes and the effects on the macroscopic device which is the solar cell.
Characterization of Growth Defects in CdZnTe Single Crystals by Synchrotron White Beam X-ray Topography
Authors: Chung H. , Raghothamachar B. , Wu J. , Dudley M. , Larson D. J. , Gillies D. C. 
Published: April 2011

AbstractSynchrotron white beam X-ray topography has been used to characterize structural defects in microgravity grown CdZnTe single crystals. Defects such as dislocations, slip bands, 180° rotation twins, precipitates and subgrain boundaries are observed but their density is much lower than those in crystals grown under normal gravity. The observed results also indicate that the defect structures of the as grown crystals are strongly influenced by cooling rates. X-ray transmission topographs recorded from regions grown at different cooling rates show that the dislocation density in rapidly cooled regions is higher than that in slowly cooled regions. The formation of dislocations is presumably attributed to the thermal stress caused by accelerated cooling rates, which is greater than the critical resolved shear stress. As the cooling rate is accelerated, the magnitude of thermal stress is increased and more dislocations are formed to relieve the accumulated lattice strain. In addition, if the cooling rates are increased further, the accentuated thermal stresses can give rise to more pronounced deformation processes, comprising the formation of dislocation slip bands, as confirmed by the extensive slip bands revealed by the X-ray reflection topographs.
Large Persistent Photochromic Effect Due to DX Centers in AlSb Doped with Selenium
Authors: Becla P. , Witt A. G. , Lagowski J. , Walukiewicz W. 
Published: April 2011

AbstractA large photochromic effect has been observed in bulk AlSb crystals doped with Se. Illumination with the light of energy higher than 1 eV leads to an increase of the absorption coefficient in the spectral range 0.1 eV to 1.6 eV. The enhanced absorption is persistent at the temperatures below about 100 K. The effect is a manifestation of a DX-like bistability of Se donors. The illumination transfers the electrons from the DX center to a metastable hydrogenic level. The increased absorption with peaks around 0.2 eV and 0.5 eV is due to photoionization from the donor level to X1 and X3 minima of the conduction band