Effect of a modified cover layer on the properties of hydrogen-sensitive Pd/GaAs/InGaAs diode heterostructures with quantum wells

The influence of a developed surface relief of an overgrowth (cover) layer modified by anodic oxidation and/or etching on the characteristics of hydrogen-sensitive Pd/GaAs/InGaAs diode heterostructures with quantum wells has been studied. The modified structures exhibit a significant increase in sensitivity and response speed, which is related for the most part to a decrease in the effective distance from the surface, on which atomic hydrogen is chemisorbed, to an elastically strained layer of the InGaAs quantum well. This layer retards the diffusion of hydrogen, which leads to an increase in the hydrogen concentration at the interface.     

Capacitors with nonlinear characteristics based on stabilized zirconia with built-in gold nanoparticles

It is shown that capacitors based on stabilized zirconia with gold nanoparticles exhibit nonlinear properties: the admittance of these capacitors depends on the amplitude of the control voltage, test-signal frequency, and temperature. The nonlinearity is due to electron capture by traps generated during nanoparticle formation. The possibility of determining the trap parameters by measuring the capacitor admittance has been established.     

Design of composite porous cermets synthesized by hydrothermal treatment of CrAl powder followed by calcination

The microstructure of the porous Cr–Al metal–oxide cermet was studied by means of XRD, SEM, EDX as well as IR and Raman spectroscopy. This cermet was synthesized by mechanical alloying of Cr–Al powders in an AGO-2 planetary ball mill followed by hydrothermal treatment in a special stainless steel die and calcination in air. As a result, a highly porous monolith comprised of metal-like particles randomly distributed in the oxide matrix (Cr₂O₃ and Al₂O₃) was formed. Two types of the composite cores were found in cermets. The first one consisted of chromium phase containing nanoparticles sized from 50 to 140 nm and Al-enriched phase at the interfaces. The second one consisted of new chromium oxide phases with hexagonal Cr₂N-like and fcc CrN-like structures probably with Cr₂O and CrO stoichiometry. These new phases were stabilized within aggregates of the nanocomposite particles containing inclusions of alumina. The relations between different preparation stages and the cermet microstructure are discussed.     

Modification of the structural,textural, and mechanical properties of an Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al composite on the addition of an Al-SBA-15-type mesoporous phase

The formation of the pore structure of metal–ceramic materials based on Al₂O₃/Al composites has been studied in detail by modifying them via the incorporation of SBA-15-type mesoporous materials. The composition, pore structure, pore size, and morphology of the composite particles have been studied using nitrogen adsorption/desorption isotherms, scanning electron microscopy, and X-ray diffraction. We have produced Al-SBA-15/Al₂O₃/Al monoliths that combine properties of both adsorbents and permeable materials, but the incorporation of Al-SBA-15 into an Al₂O₃/Al matrix reduces the permeability and mechanical strength of the composites.     

Tuning the energy spectrum of InAs/GaAs quantum dots by varying the thickness and composition of the thin double GaAs/InGaAs cladding layer

It is shown that the ground state transition energy in quantum dots in heterostructures grown by atmospheric-pressure MOCVD can be tuned in the range covering both transparence windows of the optical fiber at wavelengths of 1.3 and 1.55 μm by varying the thickness and composition of the thin GaAs/In_xGa_1−x As double cladding layer. These structures also exhibit a red shift of the ground state transition energy of the In_xGa_1−x As quantum well (QW) as a result of the formation of a hybrid QW In_xGa_1−x As/InAs (wetting layer) between the quantum dots (QDs). The Schottky diodes based on these structures are characterized by an increased reverse current, which is attributed to thermally activated tunneling of electrons from the metal contact to QD levels. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 4, 2004, pp. 448–454. Original Russian Text Copyright ? 2004 by Karpovich, Zvonkov, Levichev, Baidus, Tikhov, Filatov, Gorshkov, Ermakov.     

A method for determining the state of the silicon-sapphire boundary in thin silicon-on-sapphire layers

A simple method for determining the state of the silicon-sapphire boundary in thin silicon-on-sapphire layers, which is based on measuring a saturation photo-emf and volt-ampere characteristics in Au/Si diode structures is proposed. It is shown that in silicon-on-sapphire layers that are obtained by the low-temperature molecular beam epitaxy a p-type conduction layer is formed at the silicon-sapphire boundary.     

Kernel quantile estimators in the dose-effect dependence

Nonparametric quantile estimators in the dose-effect dependence are considered. It is shown that these estimators are consistent and asymptotically normal. Limiting variances of the constructed estimators are given.     

Plasmon Resonance Induced Photoconductivity in the Yttria Stabilized Zirconia Films with Embedded Au Nanoclusters

We report on the investigation of the photoconductivity (PC) in the yttria stabilized zirconia (YSZ) films with embedded Au nanoclusters (NCs). A peak in the PC spectrum corresponding to the plasmon optical absorption resonance in the Au NCs was observed. The temperature dependence of PC near 300 K obeyed Mott law. In this case, the PC was attributed to the heating of the YSZ matrix due to the plasmon optical absorption in the Au NCs (bolometric effect). Near 77 K, the PC did not depend on temperature and was attributed to plasmon-assisted electron transport between the NCs via the vacancy α-band in YSZ.     

Bromine-promoted PtZn is very effective for the chemoselective hydrogenation of crotonaldehyde

The phase pure, unsupported intermetallic compound PtZn is intrinsically active and selective for chemoselective hydrogenation of crotonaldehyde to crotyl alcohol in the absence of any support effects or auxiliary phases. During un-promoted reaction conditions, the PtZn surface becomes platinum enriched within the XPS sampling depth with respect to the 1:1 bulk stoichiometry. Catalyst modification by co-feeding ppm levels of bromoethane results in (i) surface enrichment by zinc, (ii) pronounced formation of a chemically distinct Zn^δ+ species and (iii) substantial improvements in selectivity toward crotyl alcohol (up to 88% at 10% reactant conversion). Bromoethane promotion acts both by suppressing formation of the undesired products and by enhancing crotyl alcohol formation, likely due to activation of the CO bond by coordination to the Zn^δ+ sites. Haloalkanes containing F, Cl or I do not induce any significant effects in either surface composition or electronic structure, serving only to poison the system.     

Features of Fermi-level pinning at the interface of Al0.3Ga0.7As with anodic oxide and stabilized zirconia

In the metal-oxide-semiconductor structures based on the Al_0.3Ga_0.7As films prepared by metal-organic epitaxy, Fermi-level pinning at the Al_0.3Ga_0.7As/oxide interface at a distance of 1.1 eV from the top of the Al_0.3Ga_0.7As conduction band was observed. In these structures, a long-term memory phenomenon was found that was caused by the inflow of electrons from Al_0.3Ga_0.7As to the anodic oxide and their capture by deep traps. The reversible change in the states of the structures due to this memory effect under the action of an electric field or light was observed.