bluuebunny/crossref_metadata_2025_split huggingface dataset:
HgTe-CdTe Multiple Quantum Wells
Authors: Hoffman C. A. , Arnold D. J. , Meyer J. R. , Bartoli F. J. , Lansari Y. , Cook J. W. , Schetzina J. F. , Schulman J. N. 
Published: March 2011

ABSTRACTWe report a detailed magneto-transport investigation of HgTe-CdTe multiple quantum wells. The data yield the first experimental confirmation of a theoretically-predicted “negative-gap” semiconducting region in wide-well Hg-based heterostructures. Gaps of up to 19 meV are observed.
Quantum-Confined Stark Effect in II-VI Semiconductor Coupled Quantum Wells
Authors: Yang Z. , Schetzina J. F. 
Published: March 2011

ABSTRACTThe Quantum-Confined Stark Effect in II-VI semiconductor coupled quantum wells is studied theoretically. It is found that because of the difference in localization of the wavefunctions of the heavy hole and the electron subbands involved, large band gap shifts can be induced by an external electric field for quantum wells with zero-field band gaps in the spectrum region from 0.4 µm to 12 µm. Several potential device applications based on this effect are proposed.
Energy Level Spectra of Transition Metal Ions In Diluted Magnetic Semiconductors
Authors: Villeret Murielle , Rodriguez S. , Kartheuser E. 
Published: March 2011

ABSTRACTWe present a study of the low lying energy levels of Fe2+, Co2+, Ni2+ and Cu2+ in diluted magnetic semiconductors such as Cd1−xCoxTe and Cd1−xCoxSe and their counterparts. In the first of these compounds the magnetic ion sits on a site of symmetry Td while in the second the symmetry is trigonal (C3v). We develop a formulation that permits a continuous variation from Td to C3v symmetry. Comparison with experimental data in Cd1−xCoxSe shows that the C3v distortion amounts to about 10% of the crystal potential at the Co2+ site. Our study of the energy spectra of Fe2+ in Td and C3v crystal potentials reveals that, even in the cubic field, the levels exhibit an anisotropy which manifests it- self in an anisotropy of the magnetization, , in the regime in which is not a linear function of the magnetic field . The study includes all the levels in the lowest terms of the (3d)n (n=6,7,8,9) configurations. The calculations are carried out to second order in the spin-orbit interaction and in for the lowest orbital states and to first order in for the excited states. The g-factors of all the levels are obtained including their anisotropy for the Co2+ and Cu2+Γ8states.
Raman Spectroscopy of A Novel Diluted Magnetic Semiconductor: Cubic Cd1−xMnxSe.
Authors: Alonso R. G. , Suh E.-K. , Pascher H. , Oh E. , Ramdas A. K. , Samarth N. , Luo H. , Furdyna J. K. 
Published: March 2011

ABSTRACTIn contrast to the bulk diluted magnetic semiconductor (DMS) Cd1−xMnxSe which occurs with the wurtzite structure, its epilayers grown on (001) GaAs substrate by Molecular Beam Epitaxy exhibit the cubic zinc-blende structure. Raman spectroscopy and photoluminescence studies on this novel DMS show (1) a “two-mode” behavior of the zone center optical phonons, (2) the Raman line associated with the spin-flip in the Zeeman split S = 5/2 ground state of Mn2+, and (3) large Raman shifts associated with the spin-flip of donor-bound electrons. The large magnetic field dependence in (3) with saturation at high fields and low temperature shows that the s-d exchange interaction characteristic of DMS's is also manifested strikingly in the zinc-blende phase of Cd1−xMnxSe.
Free Exciton Magnetospectroscopy of CdFeSe Diluted Magnetic Semiconductor
Authors: A Twardowski , K Pakula , M Arciszewska , A Mycielski 
Published: March 2011

ABSTRACTThe magnetospectroscopy data of free exciton in hexagonal Cd1−xFexSe are presented for different magnetic field orientation. Combining exciton splitting data with magnetic susceptibility data we estimate p-d exchange integral for CdFeSe valence band.
High Resolution and Analytical Electron Microscopy of Multilayer Heteroepitaxial Semiconductors
Authors: Kleebe H.-J. , Hamilton W.J. , Ahlgren W.L. , Johnson S.M. , Rühle M. 
Published: March 2011

ABSTRACTThin-film epitaxial layers on silicon substrates are being actively developed as an alternative to bulk substrates for infrared detectors. Success in this development is expected to yield improvements in size, strength, monolithic signal processing, and cost of the detector arrays. To provide feedback to the thin-film growth process, this study has investigated the structural and chemical properties of these films. CdTe or CdZnTe was grown on GaAs on Si wafers by metalorganic chemical vapor deposition (MOCVD) followed by the growth of HgCdTe by liquid-phase epitaxy (LPE). Development of TEM specimen preparation techniques permitted investigation of materials with up to four layers. Cross sectional TEM and AEM investigations resulted in the following observations: Selected area diffraction and CTEM show relations between the layers and structural defects. High resolution imaging of the multilayers reveals that most of the heteroepitaxial misfit is accomodated by misfit dislocations. Many, but not all, stacking faults and dislocations which propagate across the films appear to be related to structural interface defects. The evidence indicates that there is little, if any, contamination at MOCVD and LPE interfaces. Interface defects mainly appear to be extremely minute pits or hillocks. AEM investigations of interface regions have demonstrated a redistribution of material close to the CdZnTe / HgCdTe interface.
Thickness Measurement of Thin Films by X-Ray Absorption
Authors: Chaudhuri J. , Shah S. 
Published: March 2011

ABSTRACTAn x-ray diffraction method is described for determining thicknesses of thin films grown on single crystal substrates. The equations, based on the kinematical theory of x-ray diffraction and the mosaic crystal model, were developed. The thickness of the thin film was computed from the absorption of the integrated diffracted x-ray intensity from the single crystal substrate by the film. Since the diffracted intensity from the film is not required, the film does not have to be single crystal in nature. Thus, thicknesses of less ordered, polycrystalline or even amorphous films can be measured with high precision by this technique.
MOCVD Growth and Doping of ZnSe and Related II-VI Materials
Authors: Kukimoto Hiroshi 
Published: March 2011

ABSTRACTRecent progress in metalorganic chemical vapor deposition (MOCVD) of wide bandgap II-VI materials, especially of ZnSe, ZnS and their alloys, is discussed with emphasis on the general principles for obtaining uniform and high quality epitaxial layers and the current major issue of impurity doping for achieving conductivity control. The surface morphology and crystalline quality can be improved by a suitable choice of source materials and by lattice-matching the epitaxial layer to the substrate. By using appropriate sources, high conductivity n-type epitaxial layers of ZnSe and ZnS doped with impurities from group HI and VII of the periodic table have been successfully grown by low temperature MOCVD. We have also grown p-type ZnSe layers with carrier concentration ranging from low 1016 to high 1017 cm−3 using Li3N as the dopant. Extensive studies are now focussed on the better p-type control. High purity source materials, appropriate p-type dopants and low temperature growth are important keys.
A Ten Study of an Adhesive / Sheet Molding Compound Interface
Authors: Kamenetzky Eduardo A. , Farinato Raymond S. 
Published: March 2011

AbstractThe interface between an epoxy adhesive and sheet molding compound (SMC) was studied by TEM. The interface width is less than 20 nm where it is sharp, and on the order of 40 nm where it is more diffuse. The interfacial area in the TEM sample is located first by the difference between adhesive and SMC microstructures. Where there are no microstructural features we can investigate further the location of the interface by using the Mg Kx peak from magnesia thickener in the polyester matrix of the SMC. Calcium carbonate crystals in the SMC extend to within less than 25 nm of the interface. Measurements of interface extent and roughness indicate that there is intimate contact and good mechanical bonding between the adhesive and SMC. The surface and interfacial energetics of this epoxy-SMC system were evaluated using sessile drop advancing contact angles. Good mechanical bonding observed by TEM is consistent with a small advancing contact angle of 20°the epoxy adhesive on the SMC at 121 °C which shows a good thermodynamic driving force for the intimate contact during the bonding process.
The Influence of Water on the Epoxy-Resin-Glass Interphases
Authors: Marzi T. , Schröder U. , Heß M. , Kosfeld R. 
Published: March 2011

abstractThe absorption of water in glass fiber reinforced epoxy resins is a complex process. With dynamic-mechanical measurements it is possible to distinguish locations of water in the resin-glass interphase, in micro-cracks of the resin, and diluted in the bulk polymer. The dominant mechanism of incorporation depends on the resin/hardener system, the surface treatment of the glass fabrics, and the sorption temperature.
ACID/BASE Interactions with Silicon Carbide Fiber
Authors: Wesson Sheldon P. , Allred Ronald E. 
Published: March 2011

AbstractSilicon carbide fiber surfaces were analyzed by programmed thermal desorption and inverse gas chromatography, using Lewis acids and bases as probe adsorbates to compare the effect of RF glow discharge plasma and thermal treatment on surface energetics. Changes in surface acid/base character were correlated with wetting data, surface titrations, and surface chemical composition deduced from x-ray photoelectron spectroscopy. Thermal treatment did not alter fiber surface energetics significantly. Plasma treatment rendered the surface more acidic and more basic. XPS and thermal desorption analysis indicate that the plasma removed: strongly adsorbed organic contaminants, exposing and activating the underlying glassy surface.
Interfacial Reactions of Refractory Metals Niobium and Tantalum with Ceramics Silicon Carbide and Alumina
Authors: Joshl A. , Hu H. S. , Wadsworth J. 
Published: March 2011

AbstractRecent interest in the development of advanced metal matrix composites has prompted research on interfacial reactions of Nb and Ta with candidate reinforcements such as silicon carbide and alumina. Formation of reaction layers as small as 0.1 μm can be detrimental to composite strength and ductility and in some instances to the corrosion behavior, which suggests the importance of understanding the early stages of interfacial reactions. Thin films of Nb and Ta were sputter deposited on single crystal and polycrystalline silicon carbide and on sapphire substrates, and the nature and extent of reaction evahiated using Auger depth profiling and electron microscopy. In the Nb/SiC system, NbCX is the first reaction product to form, but the overall extent of the reaction is dominated by the formation of the more stable NbCXSiY ternary phase. Little or no interfacial reaction was observed in the Nb/Al2O3 system for up to 4 hburs at 1100°C, which also suggests that Al2O3 may be a potential diffusion barrier to minimize reactions in the Nb/SiC system. Similar interesting observations were made in the Ta/SiC and Ta/Al2O3 systems.
Chemical Interactions in the Aluminum-Carbon and Aluminum-Silicon Carbide Systems
Authors: Maruyama Benji , Ohuchi Fumio S. , Rabenberg L. 
Published: March 2011

AbstractX-ray Photoelectron Spectroscopy (XPS) was used to investigate the influence of O2 and H2O on the formation of aluminum carbide at aluminum-carbon and aluminumsilicon carbide interfaces. It was determined that dosing the interfaces with H2O catalyzed the formation of aluminum carbide in both the aluminum-carbon and aluminum-silicon carbide systems. This result is consistent with the oxidation model of carbide formation [1], previously developed to understand the kinetics of aluminum carbide formation at graphite-aluminum interfaces. These results imply that the formation of aluminum carbide in graphite and silicon carbide reinforced metal matrix composites, which severely degrades the composite mechanical properties by degrading the fiber and interface strength [2], is catalyzed.
Improved Performance in Monofilament Fiber Reinforced Glass Matrix Composites Through the Use of Fiber Coatings
Authors: Tredway William K. , Prewo Karl M. 
Published: March 2011

AbstractThe mechanical performance of glass matrix composites reinforced with large diameter (140 µm) monofilaments has been investigated. Strong interfacial adhesion between uncoated boron monofilaments and the borosilicate glass matrix resulted in composites exhibiting low failure strain and brittle fracture. The use of coated monofilaments improved composite performance considerably by reducing fiber-matrix interfacial adhesion. Auger analysis of the interface indicated that a carbon-rich layer had formed between the monofilament coating and the matrix during composite fabrication
Creep Properties and Interfacial Microstructure of SiC Whisker Reinforced Si3N4
Authors: Swan Håkan A. , O'meara Colette 
Published: March 2011

AbstractPreliminary creep tests were performed on SiC whisker reinforced and matrix Si3N4 material fabricated by the NPS technique. The material was extensively crystallised in the as received material, leaving only thin amorphous films surrounding the grains. No improvement in the creep resistance could be detected for the whisker reinforced material. The deformation mechanisms were found to be that of cavitation in the form of microcracks, predominantly at the whisker/matrix interfaces, and the formation of larger cracks. Extensive oxidation of the samples, as a result of high temperature exposure to air, was observed for the materials tested at 1375°C.
R-Curve Behavior of SiC Whisker / Al2O3 Matrix Composites
Authors: Homeny Joseph , Mangin Christophe 
Published: March 2011

AbstractThe R-curve behavior of SiC whisker / Al2O3 matrix composites was evaluated. Composites were fabricated with Silar SC-9 and Tateho SCW-1-S SiC whiskers. The properties of the two SiC whiskers were similar in all aspects, except for significant differences in surface chemistry. These differences were found to be a key factor in determining the R-curve behavior
Mechanical Properties and Grain Growth Inhibition in The System Al2O3 : c-ZrO2
Authors: French J. D. , Chan H. M. , Harmer M. P. , Miller G. A. 
Published: March 2011

AbstractThe grain coarsening in a 50:50 volume percent Al2 O3 : c-ZrO2 composite is shown to be severely limited even after long heat treatments at high temperatures (100 hours at 1650°C). The strength behavior, measured by an indentation-strength-inbending (ISIB) method, shows a “rule-of-mixtures” type behavior. The microstructural stability at high temperatures yields reliability in the mechanical properties which has important implications with regard to fiber-reinforcement technology.
Improved Interfacial Adhesion in Metal Matrix/Metallic Glass Composites
Authors: Köster Uwe , Blank-Bewersdorff Margret 
Published: March 2011

AbstractInterfacial adhesion in metal matrix/metallic glass composites can be improved by two methods: either by shifting the original interface into the glassy material by interface induced crystallization or by creating new crystalline/amorphous interfaces during glass formation by solid state reactions between two crystalline materials.
Intrinsic Material Limitations in Using Interphase Modification to Alter Fiber-Matrix Adhesion in Composite Materials.
Authors: Drzal Lawrence T. 
Published: March 2011

AbstractA very large percentage of studies seeking to improve fiber-matrix adhesion to alter composite properties are directed at the formation of primary chemical bonds between the reinforcement surface and the matrix. The dynamic events that occur when the fiber-matrix interface is formed lead to the creation of an interphase which can have properties quite different from the matrix in addition to any chemical bond formation.This study has been directed at elucidating the role of these interphase properties themselves on fiber-matrix adhesion. A reinforcement (AS-4 carbon fiber) with a quantifiable surface chemistry and an epoxy matrix have been kept constant through a series of experiments in which the distance between crosslinks of the matrix has been changed. The wettability of the fiber and the degree of chemical bonding to the fiber have not changed but the interfacial shear strength measured for each of these systems has decreased with decreasing matrix modulus. It will be shown that the properties of the matrix and the residual stresses created during processing limit the maximum interfacial shear stress that can be supported by the fiber-matrix interphase.
Elastic Modulus of the Interphase in Organic Matrix Composites
Authors: Williams J. G. , Donnellan M. E. , James M. R. , Morris W. L. 
Published: March 2011

AbstractIn organic matrix composites the properties of the matrix in the vicinity of the reinforcing fiber are of interest [1]. It has been suggested that a volume of material surrounding the fiber is significantly different from the bulk matrix [2–6]. Recent work has indicated that the interphase layer may be softer than the normal matrix material [6]. For a model composite with a single fiber embedded in an epoxy/amine matrix this layer was observed to be about 500nm thick and the material had an average elastic modulus of about 1/4 of that of the normal matrix material. The objective of the present work is to observe the effect of fiber treatment on the elastic properties of the interphase.
Thermomechanical Stability of Interphases in Glass Reinforced Composites
Authors: Dibenedetto A. T. , Gomez Jaime A. , Schilling C. , Osterholtz F. , Haddad G. 
Published: March 2011

AbstractThe thermomechanical stability of organosilane surface treatments for E-glass fibers used in fiber reinforced composites was evaluated. The effect of molecular structure of 40 to 80 namometer coatings on the force transmission across the fiber/matrix interface was measured as a function of temperature and exposure to water using a fiber fragmentation test. It was found that phenyl-substituted amino silanes exhibited better thermal stability, but were less resistant to boiling water, than the commierically available γ-amino propyl silanes. A bis-trimethoxy γ-amino propyl silane showed an increase in both the hydrolytic and thermal stability when compared to the commiercial product. A good balance of thermal and hydrolytic stability was also obtained with a methylaminopropyltrimethoxy silane coating.The strain energy released from the glass fibers upon decoupling from the poxy matrix or silane coating was found to be in the range of 145 to 186 g/m2 and varied no more than 20 percent over a temperature range of 25 to 75°C or when exposed to boiling water and then redried. It also varied very little with the silane coating used. In addition, the average shear stress attained at the fiber-matrix interface in an imbedded single fiber test at 25°C was as much as two times higher than the shear strength of the epoxy matrix and as much as five times higher at elevated temperature. These data lead one to the conclusion that the interphase failure in these composites is controlled by a plane strain fracture in the constrained region of the organic phase, near the fiber surface, rather than by the maximum shear strength in the interphase.
Effect of Ti+, Ar+, N+ and He+ Ion Implantation on Aramid Fiber Adhesive Properties
Authors: Kalantar J. , Grummon D. S. , Drzal L. T. , Loh I. H. , Moody R. A. 
Published: March 2011

AbstractComposites made with high performance polymer fibers can achieve axial properties comparable to those which use inorganic reinforcements, but with somewhat inferior interfacial properties. A high degree of chain alignment in polyaramids, such as Kevlar, produces weak interactions between adjacent polymers, resulting in poor transverse strength in the fiber, and low interfacial shear strength in composite systems. The latter controls many composite properties, such as transverse, shear and flexural strengths. Also, by reducing the tendency to form weak interfacial boundary layers, good fiber-matrix adhesion can enhance environmental stability. For these reasons, modifications to reinforcement fiber surfaces that promote fiber-matrix adhesion are frequently used to improve the performance of composites.
Toughening of Intermetallics by Coated Ductile Reinforcements
Authors: Deve H. E. , Evans A. G. , Mehrabian R. 
Published: March 2011

AbstractThe effects of reinforcement debonding and work hardening on ductile reinforcement toughening of γ-TiAl have been examined. Debonding has been varied by either the development of a brittle reaction product layer or by depositing a thin oxide coating between the reinforcement and matrix. The role of work hardening has been explored by comparing Nb reinforcements that exhibits high work hardening with solution hardened Ti-Nb alloy that exhibits negligible work hardening. It is demonstrated that a high work of rupture is encouraged by extensive debonding when the reinforcement exhibits high work hardening. Conversely, debonding is not beneficial when the reinforcement exhibits low work hardening.
Determination of Flexible Interlayer Thickness for Fiber Reinforced Composites
Authors: Lo King H. , Schmitz Robert W. , Gottenberg William G. 
Published: March 2011

AbstractThe influence of flexible interlayers/interphases on the performance of unidirectional fiber reinforced composites is studied. Micromechanical analysis based on the embedded composite cylinders model is used to study the stiffness as well as the internal stress distributions within the matrix phase of composites. Based on the results of the analysis, a criterion is proposed for the selection of optimal interlayer thickness for fiber composites. The proposed criterion gives results which seem to correlate well with the experimental data published in the literature.
Effects of a Frictional Interface on the Load Diffusion from a Broken Filament in a Fibrous Composite
Authors: Aksel Bulent , Lagoudas Dimitris C. , Hui Chung-Yuen 
Published: March 2011

AbstractThe effects of a frictional interface on the load diffusion from a broken fiber to the surrounding matrix material and the extent of debonding near the fiber break in a single-fiber reinforced composite of infinite extent are studied by using the finite element method. The normal and shear stresses on the interface, the extent of the slip zone and the axial load of the fiber are evaluated for different frictional coefficients and material parameters for both the fiber and the matrix. A shear-lag analysis is also carried out to obtain a closed form approximate solution of the fiber load diffusion problem. The extent of the slip zone and the stresses predicted by the shear-lag model are compared with the finite element method results.
Filament Fragmentation Phenomena
Authors: Figueroa Juan C. , Schadler Linda S. , Laird Campbell 
Published: March 2011

AbstractThe effect of fiber surface treatments on the relationship between the tensile strength of a filament and the shear strength of its interphase is one of the central issues facing composite materials technologists today. We demonstrate here that analysis of fragmentation phenomena in monofilament composites can simultaneously yield information about these two parameters. Characterization of shear stress transfer zones in non-critical fragments has led us to the determination of interphase strength.A phenomenological treatment that highlights the role of the matrix in the fragmentation process is presented here. This analysis considers issues such as the strain energy exchange between a failing fiber and the matrix, as well as interphase relaxation due to the viscoelastic nature of the matrix. Our observations of the fragmentation phenomena in AU4/polycarbonate monofilament composites indicate that the fiber/matrix interaction in this system is governed by micromechanical locking.