bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Coating Thickness on Interfacial Shear Behavior of Zirconia-Coated Sapphire Fibers in a Polycrystalline Alumina Matrix
Authors: Hellmann John R. , Chou Yeong-Shyung 
Published: April 2011

ABSTRACTThe effect of zirconia (ZrO2) interfacial coatings on the interfacial shear behavior in sapphire reinforced alumina was examined in this study. Zirconia coatings of thicknesses ranging from 0.15 to 1.45 μm were applied to single crystal sapphire (Saphikon) fibers using a particulate loaded sol dipping technique. After calcining at 1100°C in air, the coated fibers were incorporated into a polycrystalline alumina matrix via hot pressing. Interfacial shear strength and sliding behavior of the coated fibers was examined using thin-slice indentation fiber pushout and pushback techniques. In all cases, debonding and sliding occurred at the interface between the fibers and the coating. The coatings exhibited a dense microstructure and led to a higher interfacial shear strength (> 240 MPa) and interfacial sliding stress (>75 MPa) relative to previous studies on the effect of a porous interphase on interfacial properties [1]. The interfacial shear strength decreased with increasing fiber coating thickness (from 389 ± 59 to 241 ± 43 MPa for 0.15 to 1.45 μm thick coatings, respectively). Sliding behavior exhibited load modulation with increasing displacement during fiber sliding which is characteristic of fiber roughnessinduced “stick-slip”. No effect of fiber coating thickness on the interfacial sliding stress was observed for single pushout or pushback events. Heat treatment at 1550°C in air coarsened the fiber surface roughness, resulting in significantly higher interfacial shear strengths (>30%) and interfacial sliding stresses (>60%) relative to the coated fibers in an as-hot-pressed condition. Interfacial sliding resistance decreased significantly after the first sliding cycle. Evidence of substantial “stick-slip” behavior was eliminated from the load displacement plots after one pushout/pushback cycle; however, the pushback plots exhibited evidence of fiber reseating, followed by a decreasing trend in load with increasing displacement of the fiber back to the original position. These results directly support the interphase fragmentation scenario proposed for interface fatigue in ceramic composites.The high interfacial shear strengths and sliding stresses measured in this study, as well as the potentially strength degrading surface reconstruction observed on the coated fibers after hot pressing and heat treatment, indicate that dense zirconia coatings are not suitable candidates for optimizing composite toughness and strength in the sapphire fiber reinforced alumina system.
Ceramics in the System NbB2 – CrB2
Authors: Talmy I. G. , Wuchina E. J. , Zaykoski J. A. , Opeka M. M. 
Published: April 2011

ABSTRACTPhase equilibria and properties of ceramics in the NbB2 – CrB2 system were studied. Continuous solid solutions were found showing high activation energy (96 kcal'mol) of formation which is due to large disparity of atomic radii between Cr and Nb. Pure NbB2 and CrB2 ceramics were prepared by hot pressing at 2100 and 1800°C, respectively, at 20 MPa for 0.5 hour. Both materials exhibited closed porosity which was eliminated by the addition of Al2O3 and SiC. Thermogravimetric studies showed different mechanisms of oxidation of the diborides. The presence of Al2O3 and SiC improved the oxidation resistance, hardness, and fracture toughness of CrB2 ceramics. The additives increased the hardness of NbB2 ceramics but did not significantly affect their toughness.
Metal-Ceramic Microstructures in the Fe-Mn-O System – Morphology Control by Impurity Addition
Authors: Subramanian R. , Üstündağ E. , Sass S.L. , Dieckmann R. 
Published: April 2011

ABSTRACTThe influence of the addition of impurities and changes in the oxygen partial pressure on the formation of metal-ceramic microstructures by partial reduction of ternary or higher ceramic oxides was experimentally investigated in the model system Fe-Mn-C at constant temperature and total pressure. Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis. It was observed that the addition of dopants such as BaO, CaO, MgO, SrO, Al2O3, Cr2 O3 or ZrO2 to the initial, polycrystalline oxide solid solution (Fel−xMnx)1−ΔO strongly influences the location and rate of metal precipitation during reduction. Experimental observations are discussed based on solubility limits and the segregation of dopants.
Characterization of Phosphorus Segregation in Neutron-Irradiated Pressure Vessel Steels by Atom Probe Field Ion Microscopy
Authors: Miller M. K. , Jayaram R. , Russell K.F. 
Published: April 2011

AbstractAn atom probe field ion microscopy characterization of A533B and Russian VVER 440 and 1000 pressure vessel steels has been performed to determine the phosphorus coverage of grain and lath boundaries. Field ion micrographs of grain and lath boundaries have revealed that they are decorated with a semi-continuous film of discrete brightly-imaging precipitates that were identified as molybdenum carbonitride precipitates. In addition, extremely high phosphorus levels were measured at the boundaries. The phosphorus segregation was found to be confined to an extremely narrow region indicative of monolayer-type segregation. The phosphorus coverages determined from the atom probe results of the unirradiated materials were in excellent agreement with predictions based on McLean's equilibrium model of grain boundary segregation. The boundary phosphorus coverage of a neutron-irradiated weld material was significantly higher than that observed in the unirradiated material.
Gamma Ray-Induced Embritilement of Pressure Vessel Alloys
Authors: Alexander Dale E. , Farrell K. , Stoller R. E. , Rehn L. E. 
Published: April 2011

AbstractHigh-energy gamma rays emitted from the core of a nuclear reactor produce displacement damage in the reactor pressure vessel (RPV). The contribution of gamma damage to RPV embrittlement has in the past been discounted. However, in certain reactor designs the gamma flux at the RPV is sufficiently large that its contribution to displacement damage can be substantial. For example, gamma rays have been implicated in the RPV embrittlement observed in the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory.In the present study, mechanical property changes induced by 10-MeV electron irradiation of a model Fe alloy and an RPV alloy of interest to the HFIR were examined. Tensile specimens were irradiated with high-energy electrons to reproduce damage characteristic of the Compton recoil-electrons induced by gamma bombardment. Substantial increases in yield and ultimate stress were observed in the alloys after irradiation to doses up to 5.3x10−3 dpa at temperatures (~50°C) characteristic of the HFIR pressure vessel. These measured increases were similar to those previously obtained following neutron irradiation, despite the highly disparate nature of the damage generated during electron and neutron irradiations.
Precipitation in Zr-2.5Nb During 10 MeV Electron Irradiation
Authors: Woo O.T. , Hutcheon R.M. , Coleman C.E. 
Published: April 2011

AbstractThe corrosion resistance of Zr-2.5Nb is increased by neutron irradiation at 570K. This is due to the radiation-enhanced precipitation of β-Nb within the ∝-Zr grains, and the associated reduction in the Nb concentration in the ∝-Zr matrix during irradiation. This microstructure was observed in annealed Zr-2.5Nb irradiated with neutrons at 670K and 770K, and also with protons between 770 and 720K to 0.9 dpa. In this study, the same annealed Zr-2.5Nb, in the form of four 8 mm diameter, 0.5 mm thick discs, was irradiated with 10 MeV electrons for 370 hours. The damage accumulated on the discs ranged from 0.5 to 1.2 dpa, while the temperature of each disc varied from 720K at the centre to 600K at the edge. TEM examination of the 1.2 dpa, 710K sample revealed needle-like precipitates in the ∝-Zr matrix. These precipitates, having widths of I or 2 nm and lengths up to 70 nm, were shown by EDX analysis to contain Zr and Nb. Dark field observations using a precipitate reflection confirmed that the precipitates were β-Nb with about 88 % Nb. Specimens made from the same Zr-2.5Nb that were annealed at 720K for 370 hours but unirradiated had clear ∝-Zr grain interiors, with no precipitates. Thus electron irradiation produced a microstructure similar to that produced by neutrons and protons.
Medium-Range Order in Metamict Silicas
Authors: Qin L.C. , Hobbs L.W. 
Published: April 2011

AbstractThe first sharp diffraction peak from various forms of aperiodic silica was studied. Materials examined include vitreous silica, electron-metamict quartz, neutron-metamict quartz, and Si+ ion-implanted quartz. The peak is attributed to the dominant structural rings existing in the materials, or modification thereof. The anomalous behavior of this peak is also discussed.
The Effect of Crystal Structure on Sputtering: Molecular Dynamics Calculations
Authors: Chang Che-Chen , Chen Horng Huah , Wu Paul 
Published: April 2011

AbstractMolecular dynamics calculations have been used to study the ion-etching process by a focused-ion beam. Ion-induced atomic displacement in a Ag surface initiates collision cascades which lead to particle sputtering from the surface. Tracing collision cascades reveals that the sputtering is mainly caused by a surface atom being sideswiped by its neighboring atom traveling in a surface channel oriented a certain angle away from the direction of ejection. Depending on the angle of detection and on the kinetic energy of sputtering, the ejecting particles may proceed along crystallographic directions parallel to either the close-packed or the non-close-packed rows of atoms in the surface. The preferred direction of ejection is sensitive to variations in the polar angle of detection and in the ejection energy. For those residual atoms initially located within four lattice spacings from the target atom, the most probable distance of displacement is less than one eighth of the equilibrium bond length in the crystal bombarded by Ar† ions of I keV energy. The structural perturbation increases as the ion energy is increased from 0.2 keV to I keV, but decreases as the energy is increased further.
Microstructure of Ybco Irradiated with 200 Kev Protons and 1 Mev Fluorine Ions
Authors: Kulik Joseph , Wu J.Z. , Zhang Z.H. , Yu N. , Chu W.K. 
Published: April 2011

AbstractTransmission electron microscopy (TEM) has been used to study the effects of 200 keV proton and 1 MeV fluorine ion irradiation on the microstructure of YBa2Cu3O7-δ (YBCO). Proton irradiation at fluences on the order of 1016 cm−2 results in more visible defects than can reasonably be expected solely from high energy transfer events; medium energy transfer events also contribute to visible defects. Defects arising from cascade events can be as large as 2 to 3 nm, and high resolution imaging suggests that they consist of small volumes of structurally disordered material. Fluorine irradiation to similar displacement levels results in significantly more visible defects.
Peculiarities in the Epitaxial Regrowth of Ion-Implanted Si1−xGex Alloy Layers Grown on Compositionally Graded Buffers
Authors: Fyhn M. , Shiryaev S. Yu. , Larsen A. Nylandsted , Hansen J. Lundsgaard 
Published: April 2011

AbstractSolid phase epitaxial regrowth of ion-implanted relaxed Si1-xGex layers was studied as a function of alloy composition (0.15< x <0.5) by a combination of Rutherford backscattering/ channeling spectrometry and transmission electron microscopy. The samples were grown by molecular beam epitaxy on compositionally graded buffers at different growth conditions. It was found that the regrowth velocity follows an Arrhenius curve in the investigated composition range and increases with increasing Ge content. The activation energies of the epitaxial regrowth were found to be higher than those expected from a linear interpolation between the values for pure Si and Ge. It is demonstrated that the regrowth velocities in the samples grown at 550 and 750°C and with low-rotational speed of the substrate during growth depend on the lateral position on the wafer and that they can be reduced by a preannealing treatment at high temperatures (σ920°C). We suggest that these effects arise from a compositional modulation in the alloy layer and, therefore, from a symmetrized strain, which can be reduced by a high temperature annealing.
Numerical Simulation of Thermal Effects in Nonlinear Optical Materials
Authors: Kowalski Gregory J. , Wahl Edward H. , Roach Joseph F. 
Published: April 2011

AbstractA numerical simulation of the nonlinear optical and thermal response of a material is described. The code is divided into preprocessor, simulation and postprocessing functions. The simulation function is a transient, three dimensional, finite difference algorithm which describes the thermal response and the optical phase change that occurs due to 3rd order nonlinearity and thermal effects. Irradiance changes due to linear and nonlinear absorption mechanisms are included in the code. In the postprocessing function a Gaussian beam decomposition technique is used to calculate the irradiance and transmitted power at a far field location and the temperature time response of the material. Examples of using the code to simulate Z-scan experiments are presented and compared to those reported in the literature. Results are presented that demonstrate that the code can be used as a tool to investigate using thermal transport mechanisms to modify the nonlinear optical response of the material. Limitations of the code are discussed.
Solvent Effects on C60 Excited State Cross Sections
Authors: McLean Daniel G. , Brandelik Donna M. , Brant Mark C. , Sutherland Richard L. , Frock Lynn 
Published: April 2011

AbstractA survey study of solvent effects on the linear and nonlinear absorption properties of C60 has been done. The nonlinear absorption measurements are done at 694 nm with a Q-switched Nd:YAG pumped dye laser. In conjunction with this study a three level rate equation system has been solved analytically and the model results used to extract effective excited state cross sections. A difference and a ratio are calculated from the effective excited state cross section and the ground state cross section. The analysis demonstrates that it is this difference and the initial transmission which determine the critical fluence for the onset of nonlinear absorption. The saturation behavior is determined by the ratio of the cross sections and the initial transmission. Based on these findings C60 is shown to have some of the highest reported nonlinear absorption properties at 694 nm. The effective excited state cross sections at 694 nm are reported for the solutions and correlations to the solvent types demonstrated.
Optical Limiting with Liquid Crystalline Cylindrical Guided Wave Optical Elements
Authors: Khoo I. C. , Li H. , Lee Ming , Yarnell B. K. , Wood M. V. 
Published: April 2011

AbstractUsing micro-capillaries and capillary arrays, we have fabricated dye- and C60-doped liquid crystal cored fibers and image transmission plates of various core diameters and lengths. We have observed nonlinear pulse propagation and limiting effect using nanosecond 0.53 μm Nd:Yag laser. Typical threshold fluence is on the order of < 1 J/cm2 in a 7 mm long fiber. A theoretical modelling of the observed effect is also presented.
Silicon-Hydrogen Bonding and Hydrogen Diffusion in Amorphous Silicon
Authors: Van De Walle Chris G. , Street R. A. 
Published: April 2011

ABSTRACTDespite its importance for technological applications, the behavior of hydrogen in amorphous silicon is not fully understood. In particular, the anomalously low activation energy (1.5 eV) for hydrogen diffusion has remained unexplained. We investigate the interaction of hydrogen with dangling bonds using first-principles pseudopotential-density-functional calculations. Our analysis shows that the diffusion activation energy should be measured from the hydrogen chemical potential, and that this level should be identified with the formation energy of Si-H bonds. A quantitative identification of the energy levels with experimental observables is then possible.
Properties and Crystallization of Amorphous Si1-xPx Alloy Thin Films
Authors: Carisson J. R. A. , Li X.-H. , Madsen L. D. , Hentzell H. T. G. 
Published: April 2011

ABSTRACTThe properties of amorphous Si1-xPx alloy thin films with 20–44 at.% P were studied. The results showed that these alloys have a wide bandgap Eo ranging from 1.5 to 2.15 eV, where the alloy films with 20 at.% P have the widest bandgap (1.75–1.82 eV) at annealing temperatures ≤600 °C. Conductivity measurements showed that two electron conduction processes mainly exist: hopping conduction in the band tail at low temperatures and extended-state conduction in the conduction band at high temperatures. Crystallization studies showed that the alloys are thermally stable and crystallize at temperatures between 850 and 1100 °C. A new phosphide, Si7P3 was formed by annealing the alloys with 30–44 at.% P at temperatures ≥950 °C depending on the P concentration.
Dopant Activation in Boron-Doped a-Si:H and a-SiC:H by Thermal Annealing and Light-Soaking
Authors: Isomura Masao , Hishikawa Yoshihiro , Tsuda Shinya 
Published: April 2011

ABSTRACTThe effects of thermal history and light-soaking are systematically studied on boron-doped a-Si:H and a-SiC:H. Light-soaking increases dark conductivity at a low carbon content but decreases it at a high carbon content. This reaction is reversible, and the dark conductivity recovers to the initial value with thermal annealing. The effect of thermal history is also influenced by carbon content in samples deposited at a relatively low temperature (110°C). The increase in dark conductivity occurs with thermal annealing at a higher temperature than the deposition temperature at a high carbon content. But this effect is not significant at a low carbon content. These phenomena can be explained by the hydrogen passivation of four-fold boron, and the hydrogen motion and trapping in the network. The present model suggests that a microstructure containing deep traps of mobile hydrogen contributes to improvement in the stability of a-Si:H and its alloys.
Analysis of Fill Factor Losses in a-Si and a-SiGe Alloy Solar Cells Using a New Technique
Authors: Banerjee A. , Xu X. , Yang J. , Guha S. 
Published: April 2011

ABSTRACTA new technique to diagnose fill factor losses occurring in single-junction amorphous silicon (a-Si) alloy based nip solar cells has been explored. The method consists of the measurements of the fill factor of the device under blue and red light illumination and the current-collection loss obtained from the ratio of the quantum efficiency versus wavelength spectra at zero and reverse bias. Normally, the losses are higher at low and high wavelengths. It has been observed that there is a strong correlation between the values of the blue and red fill factors and the current collection losses at the pli interfaces and the bulk of the i-layer, respectively. The losses have been attributed to back diffusion of carriers at the pli interface and to the bulk of the i-Layer. There is a sensitive dependence between these losses and the texture of the substrate: textured substrates lead to higher losses compared to specular substrates. The technique has been used successfully to enhance the values of the red, blue, and AM 1.5 fill factors of both a-Si and amorphous silicon-germanium (a-SiGe) alloy single-junction cells on back reflectors by the optimization of device fabrication parameters. The optimized cells on textured back reflectors exhibit reduced losses. The paper presents an analysis of the experimental results.
Electrophotographic Patterning of a-Si:H
Authors: Gleskova H. , Wagner S. , Shen D. S. 
Published: April 2011

ABSTRACTA novel laser-printing method for the manufacturing of the backplane circuits of active-matrix liquid-crystal displays (AMLCD) is proposed and demonstrated. Xerographic toner is used as an etch mask for amorphous silicon (a-Si:H) and for the seeding of metal lines. We also demonstrate for the first time the direct-print patterning of silicon on ∼ 50 μm thick glass foil.
Detection Limit of Large Area Id Thin Film Position Sensitive Detectors Based in a-Si:H P.I.N. Diodes
Authors: Martins R. , Lavareda G. , Soares F. , Fortunato E. 
Published: April 2011

ABSTRACTThe aim of this work is to provide the basis for the interpretation of the steady state lateral photoeffect observed in p-i-n a-Si:H ID Thin Film Position Sensitive Detectors (ID TFPSD). The experimental data recorded in ID TFPSD devices with different performances are compared with the predicted curves and the obtained correlation's discussed.
Studies of a Polymer Dispersed Ferroelectric Liquid Crystal
Authors: Allan Guymon C. , Hoggan Erik N. , Bowman Christopher N. 
Published: April 2011

ABSTRACTFerrorlrtric liquid crystals (FLCs) have shown great potential for use in electro-optic and display technology due to theri inherently fast switching speeds. Recently within this area a great deal of attention has also been given to FLCs dispersed within a polymer networks. Adding the polymer may act to enhance certain electro-optic properties and will substantially increase the mechanical strenth on the FLC system. This study examines the effects of adding either a diacrylate monomer or a polymer network to a FLC mixture of known composition. The monomer depresses the phase transition temperatures to more orderd phases for both first and second order transitions and causes a marked decrease in the amount of liquid crystal which exhibits typical transitions behavior. During polymerization the network phase separates forming two cocontinuous phases and allows the liquid crystal transitions to return close to values seen in polymer systems. As a result of this decrease, the rotational viscosity decrease for these same samples. Maximum double bond conversions and polymerization rate maxima increase with monomer concentration until saturation on monomer in the liquid crystal is reached. The rate maxima then decreases as the monomer as the monomer must dissolute into the liquid crystal and diffuse to the reactive sites.
Deviation from Stoichiometry and Lattice Properties of Semiconducting SnTe Phase
Authors: Rogacheva E. I. , Gorne G. V. , Nashchekina O. N. 
Published: April 2011

AbstractThe temperature dependences of lattice thermal conductivity λp in the range of 300-650 K were obtained for SnTe1+x semiconducting phase with x =0-0.04. It is established that the nonstoichiometric vacancies are centers of effective scattering of phonons. The scattering cross-section calculated from experimental data is in a good agreement with the theoretical calculations based on the Klemens theory. The linear change of thermal resistance with temperature is observed, which evidences the prevalence of three-phonon scattering processes. The additional thermal resistance grows as the concentration of cation vacancies increases.