Smooth and Vertical Facet Formation for AlGaN-Based Deep-UV Laser Diodes

Using a two-step method of plasma and wet chemical etching, we demonstrate smooth, vertical facets for use in Al _x Ga_1−x N-based deep-ultraviolet laser-diode heterostructures where x = 0 to 0.5. Optimization of plasma-etching conditions included increasing both temperature and radiofrequency (RF) power to achieve a facet angle of 5 deg from vertical. Subsequent etching in AZ400K developer was investigated to reduce the facet surface roughness and improve facet verticality. The resulting combined processes produced improved facet sidewalls with an average angle of 0.7 deg from vertical and less than 2-nm root-mean-square (RMS) roughness, yielding an estimated reflectivity greater than 95% of that of a perfectly smooth and vertical facet.     

New Diamond-Based Superhard Materials. Production and Properties. Review

The authors describe the processes that are integral to the production of diamond polycrystals and provide characterization of precursor materials. The methods of producing diamond-based polycrystalline and composite materials are outlined, and the factors that have an influence on the composition and properties of such materials are analyzed. Some new approaches to the production of diamond-based superhard materials of various functionalities are discussed.     

Development and trends of applications of the new types of turbogenerators with vector system of field control

The results of the application of asynchronized turbogenerators with vector control and biaxial excitation in the Russian electric power system are presented. Since 2003, five air-cooled asynchronized turbogenerators with powers of 110, 160, and 320 W have been in operation at heat electric power stations. The main results of their testing and operation are given.     

Liquid / liquid ion-transfer processes at the dioctylphosphoric acid (N,N-didodecyl-N',N'-diethylphenylenediamine) / water (electrolyte) interface at graphite and mesoporous TiO2 substrates

Biphasic electrode systems are studied for the case of the oxidation of the water-insoluble liquid N,N-didodecyl-N',N'-diethylphenylenediamine (DDPD) neat and dissolved in bis(2-ethylhexyl) phosphate (HDOP) and immersed in aqueous electrolyte media. The oxidation process in the absence of HDOP is accompanied by transfer of the anion (perchlorate or phosphate) from the water into the organic phase. However, in the presence of HDOP, oxidation is accompanied by proton exchange instead. This electrochemically driven proton exchange process occurs over a wide pH range. Organic microdroplet deposits of DDPD in HDOP at basal plane pyrolytic graphite electrodes are studied by voltammetric techniques and compared in their behavior to organic microphase deposits in mesoporous TiO2 thin films. The mesoporous TiO2 thin film acts as a host for the organic liquid and provides an alternative biphasic electrode system compared to the random microdroplet/graphite system. Two types of mesoporous TiO2 thin-film electrodes, (i) a 300-400-nm film on ITO and (ii) a 300-400-nm film on ITO sputter-coated with a 20-nm porous gold layer, are investigated.     

Determining permissible stresses in simple cyclic loading

Cyclic loading stress is examined for a limiting-state diagram which characterizes the fatigue resistance, the permissible stresses, the cyclic cracking resistance, and the limiting fatigue crack size. It has been found for 09G2 steel that the limiting crack size is dependent on the stress cycle asymmetry if the permissible stresses are determined for a given strength margin coefficient. One can construct a permissible-stress diagram for a given crack size. In that case, the strength margin coefficient is dependent on the stress cycle asymmetry, which enables one to make better use of the material. Translated from Problemy Prochnosti, No. 1, pp. 97–102, January–February, 1997.     

Solvent-free chemical functionalization of hydrogen-terminated boron-doped diamond electrodes with diazonium salts in ionic liquids

This paper reports on green chemical functionalization of hydrogen-terminated boron-doped diamond (BDD) surfaces with aryldiazonium salts in the presence of ionic liquids. The reaction takes place at room temperature in air without any external bias in either hydrophobic (1-butyl-3-methylimidazolium hexafluorophosphate) or hydrophilic (1-butyl-3-methylimidazolium methyl sulfate) ionic liquids. The resulting surfaces were characterized using X-ray photoelectron spectroscopy and electrochemical measurements.     

Benzene oxidation with hydrogen peroxide catalyzed by soluble and heterogenized copper compounds

Copper(II) salts (acetate, perchlorate, and chloride) catalyze the oxidation of benzene with hydrogen peroxide in an acetonitrile solution to give phenol and quinone. The initial rates, the yield of products, and the phenol: quinone ratio depend on the salt chosen and on the presence of 2,2′-dipyridyl as an additive. For example, catalysis by copper perchlorate in the presence of 2,2′-dipyridyl at 50°C results in the formation of phenol and quinone with a yield of 12.5 and 1.5%, respectively (the turnover number reaches 1900). Copper chloride coordinated to solid polymers, poly(4-vinylpyridine) or poly(4-methyl-4′-vinyl-2,2′-dipyridyl), also acts as a catalyst for benzene oxidation into phenol and quinone. It was shown that the catalysis is mediated by the copper ions on the surface of the solid support. The heterogenized catalyst may be reused with some loss of activity.     

Nondestructive diagnostics of microchannel (Macroporous) silicon by X-ray topography

It is demonstrated that X-ray topography can be used for imaging the boundary between a microchannel silicon layer and a substrate, evaluating the quality of this interface, determining the channel depth, and revealing mechanical stresses. This technique can be used for nondestructive monitoring of the structure of a microchannel layer at a spatial resolution of ≥5 μm.     

Synthesis and characterization of new functional poly(urethane‐imide) crosslinked networks

To synthesize new functional poly(urethane‐imide) crosslinked networks, soluble polyimide from 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride, 4,4′‐oxydianiline, and maleic anhydride and polyurethane prepolymer from polycaprolactone diol, tolylene 2,4‐diisocyanate and hydroxyl ethyl acrylate were prepared. Poly(urethane‐imide) thin films were finally prepared by the reaction between maleimide end‐capped soluble polyimide (PI) and acrylate end‐capped polyurethane (PU). The effect of polyurethane content on dielectric constant, residual stress, morphology, thermal property, and mechanical property was studied by FTIR, prism coupler, Thin Film Stress Analyzer (TFSA), XRD, TGA, DMTA, and Nano‐indentation. Dielectric constant of poly(urethane‐imide) thin films (2.39–2.45) was lower than that of pure polyimide (2.46). Especially, poly(urethane‐imide) thin films with 50% of PU showed lower dielectric constant than other poly(urethane‐imide) thin films did. Lower residual stress and slope in cooling curve were achieved in higher PU content. Compared to typical polyurethane, poly(urethane‐imide) thin films exhibited better thermal stability due to the presence of the imide groups. The glass transition temperature, modulus, and hardness decreased with increase in the flexible PU content even though elongation and thermal expansion coefficient increased. Finally, poly(urethane‐imide) thin films with low residual stress and dielectric constant, which are strongly affected by the morphological structure, chain mobility, and modulus, can be suggested to apply for electronic devices by variation of PU. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 113–123, 2006     

Electrical and thermomechanical properties of materials based on nonstoichiometric titanium carbide prepared by self-propagating high-temperature synthesis

This paper examines the effect of the chemical and phase compositions of nonstoichiometric titanium carbide prepared by self-propagating high-temperature synthesis on the electrical and thermophysical properties of polymer compounds. Doping of titanium carbide with trace amounts of nitrogen raises the conductivity of the polymer compounds. The addition of epoxy to the polymer matrix markedly reduces the thermal expansion of the material. The proposed materials can be used at temperatures of up to 300–350°C.