bluuebunny/crossref_metadata_2025_split huggingface dataset:
Prediction of the Fiber-Matrix Interface Failure due to Longitudinal Tensile Loading Using Finite Element Methods
Authors: Mahfuz Hassan , Mian A.K.M. Ahsan , Vaidya Uday K. , Brown Timothy , Jeelani Shaik 
Published: April 2011

ABSTRACTA 3D-unit cell for 0/90 laminated composites has been developed to predict the composite behavior under longitudinal tensile loading condition. 3D contact element has been used to model the fiber matrix interface. Two interface conditions, namely, infinitely strong and weakly bonded, are considered in the analysis. Both large displacement and plastic strain behavior for the matrix are considered to account for the geometric and material non-linearities. Investigations were carried out at three temperatures to compare the composite response obtained from mechanical tests at those temperatures. Stress-strain behavior and the local stress distributions at the fiber as well as at the matrix are presented, and their effects on the failure of the interface are discussed in the paper. The material under investigation was SiCf/Si3N4.
Evolution of Internal Stresses in Composites during Creep
Authors: Lara-Curzio Edgar , Ferber M. K. 
Published: April 2011

ABSTRACTThe redistribution of internal stresses in a composite with linear viscoelastic constituents was calculated when the composite is subjected to a constant stress at a temperature where the phases would exhibit time-dependent deformation. It was found for the case of an elastic fiber embedded in a matrix that behaves as a Burgers material under distortion and elastically under dilation, that the normal interfacial stress and the axial stress in the matrix undergo complete relaxation at long times. The implications of these findings are discussed in relation to the behavior of ceramic matrix composites.
Finite Element Analysis of the Fiber Twist Test
Authors: Gaudette F. , Ertürk T. , Robertson S. 
Published: April 2011

ABSTRACTInterface and torsional shear stresses in the fiber twist test (FTT) were computed using the ABAQUS finite element program. Interface stress singularities were compared with an elasticity solution for the torsion of a fiber embedded in an elastic half space [1]. Single fiber composite systems having perfectly bonded interfaces and fiber/matrix shear modulus ratios of Gf /Gm = 1 – 3 were considered. The decay rates and depths of the interface shear stress σrθ and the torsional shear stress σZθ in the fiber and matrix were evaluated for each Gf/Gm ratio.
Alpha-Si3N4 Precipitation in C/C-SiC Composites from inherent Fiber Impurity Sources
Authors: Pleger Roland , Braue Wolfgang 
Published: April 2011

ABSTRACTThe formation of crystalline α-Si3N4 filaments grown inside the pore channels of HT-carbon fibers from a 2D C/C-SiC composite is investigated by transmission electron microscopy. Precipitation of α-Si3N4 is promoted by a low carbonization heat treatment of the C/C material prior to liquid silicon infiltration and results from the interaction of a highly reactive nitrogen-rich vapor phase released from the fiber and silicon vapor diffusing ahead of the SiC reaction front into the porous microtexture of the fiber.
Temperature and Strain-Rate Effects on Deformation Mechanisms in Irradiated Stainless Steel
Authors: Brimhall J. L. , Cole J. I. , Vetrano J. S. , Bruemmer S. M. 
Published: April 2011

AbstractAnalysis of the deformation microstructures in ion-irradiated stainless steel shows twinning to be the predominant deformation mode at room temperature. Dislocation channelling also occurs under slow strain rate conditions. Stresses required for twinning were calculated by the model of Venables and are compatible with observed yield stresses in neutron-irradiated material if loops are the principal twin source. Computation of the expected radiation hardening from the defect structure, based on a simple model, is consistent with yield strengths measured on neutron-irradiated steels. Lower yield stresses and greater thermal energy at 288°C lessen the probability of twinning and dislocation channeling becomes the primary deformation mode at the higher temperature. However, preliminary results show that some twinning does occur in the irradiated stainless steel even at the higher temperature when higher strain rates are used.
Effect of Prior-Deformation on the Stability of the Intermetallic Precipitate in Zircaloy-2
Authors: Huang Peter Y , Adamson R.B. 
Published: April 2011

AbstractBoth stress-relieved (SR) and recrystallized (RX) samples irradiated near 300°C tofluences between 1 and 9 x 1021 n/;cm2 (E>IMeV) were examined using analytical scanning transmission electron microscopy (STEM). The aim was to extend our knowledge of irradiation effects on microstructure by examining the effect of prior-cold-work on the dissolution of intermetallic precipitates in Zircaloy-2. Resulting from prior mechanical deformation and fast neutron irradiation, SR samples contain a high density of <a>-component, mixed <a+> line dislocations and “black dot” damage. On the other hand, RX samples contain mostly “black dot” damage. Pure <c>-dislocations are detected in the high fluence samples in RX materials. For identical irradiation conditions, different degrees of amorphization and dissolution are observed in RX and SR samples. Also, preferential diffusion of solute is observed to occur along <c>-dislocations. These results are discussed in terms of possible interactions between irradiation produced defects, precipitates and solutes.
The Effect of Displacement Cascades on Small Helium Bubbles in Aluminum and Gold
Authors: Donnelly S E. , Birtcher R.C. , Templier C. , Valizadeh R. , Vishnyakov V. 
Published: April 2011

AbstractThe evolution of individual helium bubbles in thin foils of gold and aluminum irradiated with 400 keV Ar+ and 200 keV Xe+ has been followed with in-situ transmission electron microscopy for a comparison between the effects of dilute (Al) and dense (Au) collision cascades. Bubble shrinkage in Al has been attributed to direct displacement of the gas out of the bubbles. Effects in Au, include the disappearance and Brownian motion of bubbles under irradiation, and are consistent with thermal spike processes seen in molecular dynamics simulations.
Tem Investigation of Hydrogen Implanted and Laser Annealed Silicon
Authors: Zheng P. , Saint-Jacques R.G. , Terreault B. , Veilleux G. 
Published: April 2011

AbstractIn order to explain the relatively easy laser-induced desorption of hydrogen implanted in silicon, and particularly the lower temperature needed for desorption at higher implantation energy, the microstructural modifications produced by laser pulses were studied by means of transmission electron microscopy. The structural damage, such as defect clusters and hydrogen gas bubbles was observed. In the case of low dose implantation (H/Si ≤ 15&), most of the bubbles were produced during laser annealing rather than during implantation. This bubble formation in the course of desorption explains the higher temperature needed. When blisters are already present on the as-implanted surface, desorption starts at a lower temperature.
Control of Point Defects in Semiconductors
Authors: Loginov Yuri Y. , Brown Paul D. , Humphreys Colin J. 
Published: April 2011

AbstractThe prospects for localised point defect control within II-VI compound semiconductors are considered with reference to doping, thermal annealing, electron and ion beam irradiation and localised strain. Interstitials and vacancies generated within electron beam irradiated II-VI compounds interact and coalesce in a TEM foil to form voids decorated by metallic precipitates and the processes of CdTe chemical decomposition are examined. Ion beam and electron beam irradiated material show clear differences in behaviour following annealing of doped and un-doped CdTe. Controlled directional climb of dislocations within electron beam irradiated ZnSe is demonstrated. In view of the differential diffusion of interstitials and vacancies, the prospect of localised semiconductor type conversion is considered.
Thin Film Thermochromic Materials for Non-Linear Optical Devices.
Authors: Lewis Keith L , Pitt A M , Wyatt-Davies T , Milward J R 
Published: April 2011

AbstractA number of materials are available which exhibit thermochromic properties. These include the superionic materials (eg silver sulphide), phase transition materials (eg vanadium dioxide) and mixed valence materials (eg SmS). Such materials can be exploited as optical thin films and when incorporated into multilayer structures exhibit non-linear properties, particularly at wavelengths in the infra-red (1–12μm). The response of such devices is dependant on the degree of temperature rise produced in the active material, which in turn is dependant on the optical properties of the material and the heat sinking characteristics of the substrate. A summary is presented highlighting techniques for film deposition, multilayer device design and temporal response characteristics measured under conditions of pulsed irradiation.
Photorefractive Optical Limiters
Authors: Salamo Gregory J. , Duree Galen C. , Morin Matthew , Sharp Edward J. , Wood Gary L. , Neurgaonkar Ratnakar R. 
Published: April 2011

AbstractWe consider the application of photorefractive beam fanning as an optical limiter. Results indicate that by focusing the incident laser light into the photorefractive crystal and by applying electric fields that limiting is possible at the 10μJ range with an optical density or O. D. of 3. These results are independent of the incident optical pulse width.
New Self-Defocusing Materials: Synthesis, Structures and Nonlinear Optical Properties of Nest Shaped Clusters
Authors: Shi S. , Xin X. Q. , Ji W. , Xie W. 
Published: April 2011

AbstractMixed metal clusters (n-Bu4N)2[MoCu3OS3X3] (X = SCN, Cl and Br) were synthesized by solid state reactions. X-ray single crystal diffraction data show that the anionic clusters assume nest shaped structures. The clusters exhibit large self-defocusing effect as demonstrated by their Z-scan traces. The effective third-order polarizability of |γ| = 4.8 × 10−29 esu was determined for (n-Bu4N)2[MoCu3OS3(SCN)3] by a degenerate four-wave mixing technique with 7-ns laser pulses of 532 nm wavelength. An irradiance-dependent transmission measurement was conducted to assess the contribution of nonlinear absorption to the γ-value. These results in combination with the self-defocusing property of the cluster yielded a negative value for the real part of γ, Reγ = − 4.8 × 10−29 esu. These numerical values are in good agreement with those obtained in a Z-scan experiment. Even though the clusters absorb laser light at 532 nm significantly, the results of temporal profile analysis on transmitted pulses show that the solvent thermal effect makes little contribution to the observed nonlinear optical phenomenon.
A New Role for Bboron in Advanced Materials
Authors: Kaszynski Piotr , Lipiak Dariusz 
Published: April 2011

AbstractApplication of highly polar dative bonds of heteroatoms to boron atoms for the preparation of a new class of liquid crystals is discussed. Semiempirical calculations show that compounds incorporating polar bonds of tetra- and higher-coordinated boron centers are characterized by large coaxial dipole moments and relatively large first hyperpolarizabilities β. It is expected that these new liquid crystalline materials will be useful for electrooptical applications.
New Optical Limiting Materials: Synthesis, Structures and Nonlinear Absorption of Cubic Cage Shaped Clusters
Authors: Shi S. , Ji W. , Xin X. Q. 
Published: April 2011

AbstractMixed metal clusters (n-Bu4N)3[WCu3Br4S4] (I), (n-Bu4N)3[Wag3Br4S4] (II), (n-Bu4N)3[MoAg3BrCl3S4] (III) and (n-Bu4N)3[MoAg3BrI3S4] (IV) were synthesized by solid state reactions. The cluster anions assume cubic cage shaped structures and possess strong optical limiting capability. At very low fluences the molecules respond linearly to the incident light obeying Beer's law. As light fluence rises their molecular absorptivities increase rapidly exhibiting limiting effect with threshold and saturation fluence of 1.3 J/cm2 and 0.7 J/cm2 for compound I, 0.7 J/cm2 and 0.5 J/cm2 for compound II, 0.6 J/cm2 and 0.3 J/cm2 for compound III, and 0.5 J/cm2 and 0.3 J/cm2 for compound IV respectively. The threshold and saturation values of compound IV are about 3 and 2 times better than those of C60 measured under identical conditions. The optical limiting capability of the clusters is derived from excited state absorption, a process that turns on within nanoseconds and off over milliseconds.
On Fourier's Phase and Gradient Index Optical Design
Authors: Haaland Peter D. 
Published: April 2011

AbstractGradient index or rugate optical filters are continuous generalizations of the familiar quarterwave stack which find widespread applications in sensor hardening. In the design of a filter or mirror there are infinitely many refractive index profiles n(x) whose wavelength-dependent reflectance R(λ) is specified as a design objective. The relationship between R(λ) and n(x) is nearly that of a Fourier-transform pair. Exploiting this relationship, specifically the physically indeterminate phase of the Fourier transforms, permits constrained optimization of rugate designs. In this contribution we outline the approach of optimal phase modulation and indicate by examples its application to problems in optical limiting.
Study of the Microstructure of Amorphous Germanium Alloys Using AFM and SAXS
Authors: Moffitt Paul R. , Naseem Hameed A. , Ang Simon S. , Brown William D. 
Published: April 2011

ABSTRACTMany researchers have found the photoresponse of germanium-based films to be directly related to the homogeneity of the film's microstructure, with more homogeneous films having better photoresponse. Transmission electron microscopy (TEM) gives the resolution needed for studying microstructure, but is typically limited to imaging films with a thickness of less than 200 nm. Surface measurement by atomic force microscopy (AFM) gives a three-dimensional representation of the film surface and can be used for measuring any thickness film. A more complete idea of the microstructure can be gained by combining AFM with small-angle x-ray scattering (SAXS) measurements. SAXS measurements yield the size of internal voids or less dense regions and indicate whether the inhomogeneities have a preferred orientation, such as might be associated with columnar growth. Films of amorphous germanium and germanium carbon alloy were grown by the PECVD method from SiH4, GeF4, H2 and CH4 source gases. The films were then characterized using AFM, SAXS, and FTIR. The effect that various growth conditions had on the microstructure and photoresponse will be reported.
Nonlinear Optical Defect Absorption in Hydrogenated Amorphous Silicon
Authors: Rjeger W. , Lanz M. , Graeff C. F. O. , Nebel C. E. , Stutzmann M. 
Published: April 2011

ABSTRACTBy using a Nd: YAG-pumped optical parametric oscillator (OPO) as excitation light source (8 ns pulse width), the dynamic range of photothermal deflection spectroseopy (PDS) is increased by a factor up to 1000. This enables the study of nonlinear defect absorption in intrinsic, phosphorus and boron doped a-Si:H. To probe nonlinear absorption of defects, the intensity of the fundamental emission of the Nd:YAG (1064 nm) has been varied over three orders of magnitude. For intensities greater than 1024 photons/ (cm2s), a significant increase of a by a factor 1.4 in p-, 1.2 in i-, and 1.15 in n-a-Si:H is detected. From electron spin resonance (ESR) and transient photoconductivity experiments on intrinsic a-Si:H, a bleaching of the defect density by electron excitation into the conduction band is measured. A hole-like signature in the ESR spectra indicates that electrons from the valence band are excited into the defect band as well. The data are interpreted based on a model for IR-induced nonlinear optical effects.
Stress and the Goal of Improved Amorphous Silicon Stability
Authors: Fortmann C. M. 
Published: April 2011

ABSTRACTThe stability of amorphous silicon-based solar cells is related to the i-layer carrier mobilities as these determine the carrier densities under illumination. Materials with high mobilities quickly diffuse the carriers to high recombination regions such as the contacts and interface regions. The quick out diffusion of carriers lowers the i-layer carrier densities and therefore the driving force for defect generation. Increased compressive stress appears to be correlated to increased electron mobility and is related to the hydrogen content. Solar cell configurations also play a role in the i-layer carrier density. For example, factors that increase the V∝ tend to decrease the stability because the associated decrease in interface recombination results in increased i-layer carrier densities. Factors that reduce the blue response such as increased interface recombination tend to increase the stability as these results in reduced i-layer carrier densities.
Measurement of Two Deep H Bonding Levels in Device Quality Glow Discharge a-SI:H
Authors: Mahan A. H. , Johnson E. J. , Crandall R. S. , Branz H. M. 
Published: April 2011

ABSTRACTWe present the results of H effusion studies on device-quality glow discharge deposited hydrogenated amorphous silicon (a-Si:H) films. We measure the decrease in the amount of Si-H infrared absorption as pieces of an a-Si:H sample are annealed isothermally at temperatures from 425°C to 500°C, until more than 95% of the initial H is evolved. We use the rate equation for loss of H due to annealing to calculate the activation energy for H effusion. For anneals below 500°C we observe two distinct rate processes, a fast process corresponding to release of ∼ 70% of the total H (∼10 at. %) contained in the sample, and a slower process corresponding to effusion of the remainder. The fast loss process yields an activation energy of ∼1.4 eV; this is the energy level widely observed in diffusion coefficient measurements. A similar analysis for the slow loss process yields an activation energy of ∼2.1 eV and a diffusion constant prefactor higher than that for the fast loss process. We suggest that this slow component represents the first determination of the energy depth of the “isolated” H component commonly observed in nuclear magnetic resonance experiments.
Amorphous Silicon Three Color Detector
Authors: Stiebig H. , Giehl J. , Knipp D. , Rieve P. , Böhm M. 
Published: April 2011

ABSTRACTBand gap and defect engineered amorphous silicon based nipin photo diodes with bias controlled spectral response have been fabricated successfully. The devices exhibit good linearity over a wide illumination range and linearly independent spectral response curves which are required to generate a standard RGB-signal. In the bias range from -1.5 V to 1.5 V a dynamic range exceeding 90 dB for two color sensors and 80 dB for three color sensors has been observed. The general operation principle of the multispectral photo diode is discussed using a numerical simulation program. The model describes the defect state distribution of dangling bonds according to the defect-pool model and uses coherent wave propagation in the device to calculate the profile of photo generated carriers. Additionally, an analytical model has been developed to be included into standard circuit simulation programs like SPICE (Simulation Program with Integrated Circuit Emphasis). The analytical model uses linear field approximations in both i-layers of the device.
Effect of Plasma Damage on Interface State Density Between a-Si:H and Insulating Films
Authors: Umezu Ikurou , Kuwamura Takahiro , Maeda Keiji 
Published: April 2011

ABSTRACTThe interface state density between a-Si:H and insulating film is very important in characteristics of a-Si:H thin film transistors. In this study, the interface state density was measured by photothermal deflection spectroscopy (PDS). Layered structures of a-SiN, 1.7:H on a-Si:H and a-SiO2.0 on a-Si:H were deposited by P-CVD method. The a-SiN1.7:H layer was grown from a gas mixture of SiH4 and NH3 and the a-SiO2.0 layer was grown from a gas mixture of SiH4 and N2O. While the interface state density of a-SiN1.7:H on a-Si:H structure was smaller than the free surface state density of a-Si:H, that of a-SiO2.0 on a-Si:H structure was larger than the free surface state density of a-Si:H. The difference in the surface state density between these specimens is discussed in terms of plasma damage of a-Si:H surface by the source gases during deposition of insulating layer. Surface of the a-Si:H was treated by plasma of NH3 or N2o gas which is dominant constituent of source gases of insulating layer. Although the surface state density of the N2o plasma-treated sample increases, that of NH3 plasma treated sample does not increase. The shape and intensity of the spectra of N2o plasma-treated sample is similar to that of the a-Sio2.0 on a-Si:H structure. These results indicate that the interface defect between a-Sio2.0and a-Si:H layer was induced by plasma damage of the a-Si:H surface.
Deposition of Amorphous Hydrogenated Silicon Films by VUV Laser CVD: Influence of Substrate Temperature
Authors: Karstens H. , Hess P. 
Published: April 2011

ABSTRACTAmorphous hydrogenated silicon (a-Si:H) films were deposited from disilane at substrate temperatures between 180 and 390 °C using a F2-laser (157 nm) in a parallel configuration. Material properties such as hydrogen content, SiH and SiH2 group concentration, photo-and dark conductivity, band-gap energy and the Urbach parameter were determined as a function of the deposition temperature. The material with the best optical and electronical properties was found for a substrate temperature of 260 °C. Using argon as the buffer gas instead of helium results in films of poor quality.
Low Energy Ion Implantation of as During Si-MBE
Authors: Collart E. J. H. , Gravesteijn D. J. , Lathouwers E. G. C. , Kersten W. J. 
Published: April 2011

AbstractAs-doped Si layers were grown using Molecular Beam Epitaxy (MBE) together with simultaneous Low Energy Ion Implantation (LEII). The influence of growth conditions such as Si-substrate temperature, ion energy and ion dose was investigated using structural and electrical characterization techniques. Below the As solid solubility limit, well defined and 100 % electrically active As-doped layers were grown. Above solid solubility segregation occured, with broadened profiles and less than 100 % activation.
The Ultrafast Carrier Dynamics in Semiconductors: The Role of Defects
Authors: Fauchet P. M. , Wicks G. W. , Kostoulas Y. , Lobad A. I. , Ucer K. B. 
Published: April 2011

AbstractThe presence of point defects is expected to influence the properties of free carrier in semiconductors. We have used the techniques of ultrafast laser spectroscopy to characterize the dynamics of photoinjected carriers in several III–V semiconductors grown at low temperature. The initial scattering time and the lifetime of the carriers become very short at low growth temperatures. Results obtained with low-temperature grown III–Vs are compared to those obtained with III–Vs grown at normal temperatures and amorphous silicon.