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The fabrication and optical and electrical properties of a modulation-doped multiquantum-well (MD-MQW) AlGaInP light-emitting diode (LED), grown by low-pressure metal-organic vapor-phase epitaxy (LP-MOVPE), are analyzed. The n-type MD-MQW LEDs are better than conventional undoped-MQW LEDs, which are attributed to the presence of the large number of mobile electrons in the MD-MQW structure.

Proton implantation is used for fabricating AlGaN/GaN high electron mobility transistors (HEMTs) and the breakdown voltage of these HEMTs is increased without sacrificing dc characteristics. The increase of the breakdown voltage is because of the expansion of the depletion region under the two-dimensional (2-D) electron gas (2-DEG) channel.

The microstructural study of Al-Si-Mg alloy reinforced with stainless steel wires (Al-Si-Mg/S(S.sub.w)) has been investigated and focused on the both microstructures in the matrix and near to the interface and also the wetting condition at the interface. The wettability of solid metals by liquid metals is very important in determining the needed properties of the composite systems. In this study, the wetting conditions have been characterized using optical microscopy and scanning electron microscopy. Good wetting, incomplete wetting and very poor wetting associated with large voids are seen at the Al-Si-Mg/S[S.sub.w] interfaces. Heavily concentrated of needle shaped eutectic Si particles are found near to the single stainless steel wire as compared to double stainless steel wires. Key words: Interface, wetting conditions, needle shaped eutectic Si particles, INTRODUCTION The unique properties of the fiber reinforced composite materials are to a great extent dependent on the unique nature on the matrix-fiber interface which can be defined as the [...]

This paper presents a test program on aluminum alloy thin-walled square and rectangular hollow sections in combined axial compression and minor axis bending. A total of six series of tests was conducted that included 27 beam-column and 4 pure bending tests. The test specimens were manufactured by extrusion using 6061-T6 heat-treated aluminum alloy in three different cross sections having the clear width-to-thickness ratio ranged from 31.3 to 81.3. The beam-column specimens were compressed between pinned ends at different eccentricities in order to obtain an interaction curve for each series of tests. Pure bending tests were conducted for each test series to determine the bending capacities of the specimens. Local and overall initial geometric imperfections of the specimens were measured. Material properties were obtained from tensile coupon tests. The observed failure modes of the beam-column tests included local buckling, flexural buckling, interaction of local and flexural buckling, and material yielding in the heat-affected zone. The test strengths were compared with the design strengths calculated using the American, Australian/New Zealand, and European specifications for aluminum structures. Beam-column interaction curves were plotted for each test series. It is shown that the beam-column design strengths and bending capacities predicted by the three specifications are generally conservative. CE Database subject headings: Aluminum; Beam columns; Buckling; Experimentation; Structural design.

The shock response of the aluminum alloy 7010-T6, induced by the technique of plate impact, is investigated as a function of orientation to the loading axis to the rolling direction. A simulation using finite-element modeling has shown that while the model can reproduce the dependency of the Hugoniot elastic limit on orientation, the degree of success with the spall strength has not been so great.

Advanced transmission electron microscopy is combined with high-precision first-principles calculation to examine atomic-scale structures of the LaAl[O.sub.3]/Ti[O.sub.2] interface and bridge to their electronic property at the atomic level. The electronic structure is characterized and interfacial bonding is shown to be of a mixed covalent-ionic character.

Electrical spin-injection across the [Fe.sub.3][O.sub.4]:[Al.sub.0.1][Ga.sub.0.9]As interface is measured. The studies have shown the first step in the integration of molecular beam epitaxy-grown magnetic oxides into III-V semiconductor devices.

Reflection high-energy electron diffraction is used for analyzing the growth of AlInN alloys by molecular-beam epitaxy, where in-plane lattice constant and specular beam intensity oscillations are recorded for information of lattice misfit and growth rate as a function of source flux and temperature. The dependence of alloy growth rate on indium flux is observed, which has reflected the specific incorporation kinetics of indium in the alloy.

Byline: T.J. Chen, J. Li, Y.D. Li, Y. Hao In situ Al3Ti-Al functionally graded composite rings were fabricated by centrifugal casting. The effects of processing parameters on the microstructures and hardness of the rings were mainly investigated. Simultaneously, the corrosion characteristics of the composites were discussed. The results indicated that not only the Al3Ti platelet concentration distributed with a gradient along the radial direction of the rings, but also their size appeared in a gradient distribution. The presence of Al3Ti platelets decreased the corrosion resistance of Al and the corrosion resistance of the rings also appeared in a graded manner.

Superconductor-normal metal-insulator-superconductor Nb/Al-Al[O.sub.x]/Nb Josephson junctions are developed with Al layer, which has resulted in nonhysteretic current-voltage characteristics for critical current densities. Stewart-McCumber parameters from 1 to 3 that is optimum for digital single-flux-quantum applications are obtained without external shunting, even though the specific capacitance is very high.

Several first-principles calculations are conducted to explain the saturation magnetization, as well as the magnetocrystalline anisotropy of the various MnAl permanent magnets. The maximum energy product of the magnet is also determined.

Electric field induced (Stark) shifts is studied in mid-infrared (IR) transitions that have occurred in type II AlSb/InAs/GaSb quantum wells. Low temperature current-voltage, capacitance-voltage and photocurrent measurements are used for characterizing a type II quantum well structure that has displayed a blueshift in the lowest energy transitions that is roughly linear with applied bias and is comparable to the potential drop across the structure.

Byline: P. Venkatachalam, B. Ravisankar, S. Kumaran The present work aims to investigate the microstructural evolution and mechanical behaviour of 2014 Al alloy upon equal channel angular pressing (ECAP) at ambient temperature. ECAP was carried using a 90° die through route A up to five passes. Microstructural and mechanical properties were compared for three different conditions namely: 1) as received; 2) homogenised at 768 K for 1 hr; 3) homogenised at 768 K for 1 hr + aged at 468 K for 5 hr. The improved strength and hardness of ECAPed 2014 Al homogenised at 768 K for 1 hr + aged at 468 K for 5 hr alloy was due to the precipitation hardening, grain refining and higher dislocation density. It was found that the grain size gradually decreased with number of passes and the average grain size was about 0.252 μm after five ECAP passes. The hardness and tensile strength of 2014 Al alloy remarkably increased up to 165 HV and 468 MPa, respectively. Correlation between tensile strength and hardness for the processing route A was also reported.

A study was conducted to examine the mechanisms that change the critical current density ([J.sub.c]) of Nb/Al[O.sub.x]/Al/Nb Josephson junctions due to the inclusion of hydrogen in the Nb electrodes. The results revealed that the [J.sub.c] change is caused by a Nb work function increase due to the hydrogen inclusion which result in an increase in barrier height.

The candidature of Fe-Si and Mg-Al alloys at millimeter-scale particle sizes for chemical degradation of disinfection byproducts (DBPs) in drinking water systems is substantiated by their increased corrosion resistance and catalytic effect on the degradation. The new method for chemical degradation of DBPs has the advantages of constant degradation performance, long-term durability, no secondary contamination and ease of handling, storage and maintenance in comparison with nanoparticle systems.

The synthesis and conformational analysis of a new type of conformationally restricted [alpha]-amino acid analogue of the amino acid antibiotic furanomycin is described. The synthetic strategy is based on a formal [2+2] cycloaddition between 2-(acylamino)acrylates as acceptor alkenes and 2,3-dihydrofuran as a donor alkene, which is promoted by bulky aluminum-derived Lewis acids, particularly by methylaluminoxane (MAO).

A study was conducted to mathematically analyze the effects of several parameters, including sample temperature, intensity of the ultraviolet (UV) light, wavelength, and intensity of the laser light on the charge status of surface states in an AlGaN/GaN heterostructure. The results obtained for the effect of the ambient illumination could be applied to achieve a higher sensitivity for an AlGaN/GaN sensor and discover their future applications.

Quantitative deuterium analysis is developed by using the neodymium doped yttrium aluminum garnet laser-induced breakdown spectroscopy (LIBS) with atmospheric pressure surrounding He gas by studying the appropriate experimental condition and special sample cleaning method. The results have shown the achievement of a full resolution between the D and H emission lines from zircaloy-4 samples and a linear calibration line with zero intercept is obtained for the emission intensity of deuterium from zircaloy samples.

The parallel arrays of superconducting Nb/Al[O.sub.x]/Nb tunnel junctions nonevenly distributed in a superconducting Nb/SiO/Nb microstrip transmission line are examined to understand the discretized Josephson transmission lines (DJTLs) and magnetic flux quanta ('fluxons') in the device which could travel as solitonic waves. The results suggested that nonuniform DJTLs could be applied as a promising type of Josephson device for submillimeter-wave oscillators and fast fluxon-based electronics.

A newly designed chemical vapor deposition (CVD) reactor is used to grow a nonpolar GaN crystal on lattice-matched [100] [gamma]-LiAl[O.sub.2] substrate. The enhanced quality of the as-grown GaN {1010} epilayer on [100] [gamma]-LiAl[O.sub.2] substrate is demonstrated by using the modified inner structure of the CVD reactor.

The composition of [beta]- precipitates in an Al-Mg-Si alloy is examined by using atom probe tomography, ab initio density functional calculations and quantitative electron diffraction. Ab initio calculations have shown that replacing the [Si.sub.3]-site by aluminum has led to energetically favorable compositions consistent with the other phases in the precipitation sequence.

The preparation of metal/interlayer/semiconductor (MIS) diodes formed by coating of an organic film to p-Si semiconductor substrate is reported. Modification of the interfacial potential barrier of Al/p-Si diode achieved by using a thin interlayer of the PSP organic material is attributed to the PSP organic interlayer which increased the effective barrier height by influencing the space-charge region of Si.

A study about the short term oxidation behavior of [gamma]-TiAl treated in low-concentration phosphoric acid solution at 900 degree [Celsius] in air is reported. The transformation of the pyrophosphate film into a Ti[O.sub.2] solid solution containing phosphorus during the initial course of oxidation at 900 degree [Celsius] is found to impede the usual oxides external growing mechanisms and leads to an internal development of the oxide scale with an associated reduced oxidation rate.

A criterion is proposed for evaluating the glass-forming ability of alloy systems. Regression analysis between the logarithm of the critical cooling rate In [R.sub.c] and [theta] has produced value of [alpha] = 0.0728 and a fine linear relationship is present between criterion [theta] and In [R.sub.c] with a coefficient of determination [R.sup.2] = 0.942.

The intrinsic high-frequency (HF) behavior of three-terminal junctions based on InGaAs/InAlAs heterostructures is examined by using a well-calibrated three-dimensional semiclassical ensemble Monte Carlo simulation model. The studies have shown the important role played by surface charge effects in the frequency regime.

Rutherford backscattering spectrometry and x-ray diffraction has shown good correlations between the [Eu.sup.2+] emission linewidth and key structural parameters of [In.sub.x][Al.sub.1-x]N films on GaN in the composition range near lattice matching. [Eu.sup.3+] emission from [In.sub.0.13][Al.sub.0.87]N:Eu has shown less thermal quenching than GaN:Eu and InAlN films are superior to GaN for rear earth (RE) optical doping.

A general approach is developed for preparing 3,5-diarylcyclopentenones, where the key aspects have included the intramolecular Friedel-Crafts-type cyclization of vinyl chlorides and subsequent Pd-catalyzed cross-coupled reactions. The vinyl chloride-bearing arylacetic acid precursors are available by straightforward alkylation of arylacetic acid esters and have undergone cyclization to produce 3-chloro-5-aryl-2-cyclopentenones when treated with Al[Cl.sub.3].

Monte Carlo simulations were applied to study two different narrow band gap semiconductors, InAs and InSb, and their associated heterostructures, AlSb/InAs and AlInSb/InSb. The results suggested that the experimentally mobile values for the model could be correctly reproduced by optimizing the bulk simulation parameters of the heterostructures and adjusting the strength of roughness scattering.

The synthesis of [Nd.sub.25][Fe.sub.40][Co.sub.20][Al.sub.10][B.sub.5] by high-energy milling and melt-spinning techniques followed by subsequently annealed temperature range from 400 to 1100 degree Celsius for 20 min, is described. The findings from x-ray diffraction combined with high-resolution transmission microscopy for the annealed samples showed the presence of ferromagnetic [Nd.sub.2][(Fe,Co,Al).sub.14]B crystallites coexisting with antiferromagnetic [Nd.sub.6][(Fe,Co,Al).sub.14] ones, among an amorphous matrix.

A current-sensing atomic force microscopy is used for measuring the nanoscale capacitance spectroscopy of the two-dimensional electron gas (2DEG) of AlGaN/GaN heterostructures. The current-sensing method has detected the change in Schottky barriers of the probe-sample contact, which has affected the measurement of the threshold voltage of 2DEG.

Deep level transient spectroscopy (DLTS) measurements are used for studying GaN/AlGaN/SiC heterostructures prepared by low-pressure metalorganic vapor phase epitaxy. The energy of the deep level has decreased with increasing electrical field due to Poole-Frenkel effect and the carrier capture kinetics have shown interacting point defects arranged along a line, probably a threading dislocation.

A heterostructure with three AlGaN layers with successively increasing Ga contents and compressive strains was grown on an AlN template layer to examine the strain relaxation produced by inclined threading dislocations in AlGaN. The study evidence indicated that local strain inhomogeneities due to neighboring dislocations influenced the specific bend angles of individual dislocations in AlGaN and the lattice-mismatch strain also influenced the average bend angle.

Magneto-optic measurements are used for studying the polarization of the mobile electrons in [La.sub.0.7][Sr.sub.0.3]Mn[O.sub.3] strained thin films grown epitaxially on single crystalline (001) LaAl[O.sub.3] (LAO) and (001) [La.sub.0.3][Sr.sub.0.7][Al.sub.0.65][Ta.sub.0.35][O.sub.9] substrates. The magnetic circular dichroism (MCD) spectra of both the films have shown a peak at the band gap at around 3 eV and the peak is shifted toward lower energy side with the increase in temperature.

The analysis of two series of [Co.sub.2]MnAl (CMA) and [Co.sub.2]MnAlO (CMAO) thin films deposited on Si (100) coated with thermo-Si[O.sub.2] by using two CoMnAl targets is presented. The oxygen impurity has increased the thickness of magnetic dead layer, weakened the magnetic anisotropy and decreased the spin polarization in CMA film.

The space layer thickness dependence of interlayer exchange coupling is examined in the fully epitaxial trilayers of the [Co.sub.2]MnAl (CMA)/Cr/CMA structure. The comparison of the results of the experiments and the simulations of magnetization curves have disclosed novel behavior, dominating the 90[degree] coupling and the absence of 180[degree] coupling.

The in-plane effective mass in the two-dimensional electron gas of nominally undoped AlGaN/GaN heterostructures with a different degree of quantum confinement is examined. The contribution of the wave-function hybridization has played the dominant role and the band edge effective mass value is deduced.

The structural properties of AlGaN/GaN heterostructures grown by metal organic chemical vapor deposition on sapphire substrate with different thicknesses are examined by using high-resolution x-ray diffraction and Raman scattering methods. The studies have shown that the increase in substrate thickness has led to a reduction in dislocation density in the layers and an increase in the elastic deformations.

High quality GaSb layers are grown on semi-insulating (001) GaAs substrates by molecular-beam epitaxy by using AlSb and GaSb buffer layers and strong photoluminescence is observed for temperatures higher than 100 K. The increase in the excitation power has shown increase in the ratio of the acceptor-bound exciton with respect to the donor-acceptor pair transition due to the saturation of the donor-acceptor pair transitions.