Synthesis of New 10-R-1,8-Dinitro-3-oxa-5,10-diazatricyclo-[6.3.1.02,6]dodeca-2(6),4-diene Derivatives

Russian Journal of Organic Chemistry - A series of new 10-substituted 1,8-dinitro-3-oxa-5,10-diazatricyclo[6.3.1.02,6]dodeca-2(6),4-dienes have been synthesized by Mannich condensation of the...     

The Shortened Transition Metal–Tellurium Bonds in Organometallic Clusters

The shortening of partly multiple M–Te (M = Mn, Fe, Co, Cr or W) bonds is observed for two classes of organometallic compounds: (1) formally electron-deficient species with additional donor–acceptor interaction between Te lone pairs and half-occupied d-orbitals of M; (2) formally electron-saturated species having additional dative interaction between M lone pairs and LUMO of Te. These compounds could be prepared by two main methods: (a) interaction of [CpMn(CO)₂PhC(O)⁻]Li⁺ with Te proceeds via formation of intermediate {[CpMn(CO)₂]₂Te}²⁻ which is further transformed into binuclear complex [CpMn(CO)₂]₂Te(CH₂Ph)₂ or into trinuclear ditelluride cluster [CpMn(CO)₂]₃Te₂ on one hand or to mixed-metal monotelluride clusters [CpMn(CO)₂]₂TeM(CO)₅ on another hand. (b) treatment of Fe(CO)₅, CpMn(CO)₂(THF) or Me₄C₄Co(CO)₂I with [PhTeI]₄, PhTeI₃ or PhTeI₂HC = CPhI results in different PhTeI-containing complexes of Fe, Mn or Co. The molecular structures of all new compounds were studied by means of X-ray diffraction analyses and the mechanism of M–Te bond shortening is discussed. Proceeding of the international workshop on transition metal clusters, 3–5 July 2008, Université de Rennes 1, Campus de Beaulieu, Rennes, France.     

Wellposedness of a linearized problem of supersonic flow past a wedge in the case of arbitrary perturbations

The method of dissipative energy integrals is used in studying the wellposedness of the mixed problem on the flow past a wedge in the linear formulation.     

AlGaAs/GaAs photovoltaic cells with an array of InGaAs QDs

Specific features of the fabrication of AlGaAs/GaAs single-junction photovoltaic cells with an array of quantum dots (QDs) by molecular beam epitaxy have been studied. It was shown for the first time that, in principle, vertically coupled QDs can be incorporated, with no dislocations formed, into the structure of photovoltaic cells without any noticeable deterioration of the structural quality of the p-n junction. Owing to the additional absorption of the long-wavelength part of the solar spectrum in the QD medium and to the subsequent effective separation of photogenerated carriers, a ～1% increase in the short-circuit current density J _sc was demonstrated for the first time in the world for photovoltaic cells with QDs. The maximum efficiency of the photovoltaic cells was 18.3% in conversion of the unconcentrated ground level solar spectrum AM1.5G.     

Stresses in selectively oxidized GaAs/(AlGa)xOy structures

Raman scattering spectroscopy is used to study the process of selective oxidation of Al_0.97Ga_0.03As layers. Stresses arising in GaAs/(AlGa)_xO_y layers as a result of selective oxidation under different conditions are determined. The effects of local heating of the samples with laser radiation during measurements of the Raman signals, photoresist hardening resulting from the oxidation, and overoxidation are analyzed. The instrumentation and method of selective oxidation are optimized; as a result, arrays of vertical-cavity surface-emitting lasers are fabricated. The active region of these lasers is based on two InGaAs quantum wells with top oxidized and bottom semiconductor distributed Bragg reflectors.