MOVPE of InP Using Trimethylindium – Trimethylamine Adduct

Growth of InP layers by MOVPE using trimethylindium-trimethylamine (TMIn–TMN) is described. Low temperature photoluminescence results reveal the high crystal quality indicated by the well resolved excitonic spectra and high internal quantum efficiency. A strong near-gap luminescence degradation with decreasing substrate temperature during the growth corresponds with the increasing deep level concentration estimated by the DLTS-investigations. In the specimens prepared at higher temperatures carbon and zinc are believed to be the main residual acceptors. From C–V data free carrier concentrations of 10¹⁵ cm⁻³ were obtained.     

Influence of micromixing on the free-radical polymerization in a discontinuous process

With the help of a simple reaction-diffusion model with constant striation thickness the influence of micromixing on free-radical polymerization was investigated for several test reactions with discontinuous prepolymerization and jerky addition of selected reactants. Monomer conversion or mean values of molar mass and chemical composition cannot be expected to be very sensitive to micromixing effects. If molar mass distributions are to be used, problems will arise from the fact that the distribution of the polymer accumulated during prepolymerization covers mixing influences occurring after reactant feed. The instantaneous molar mass distribution would be more suitable. Time-integral distributions of chemical composition or sequence length in combination with appropriate test reactions proved to be feasible indicators for the effects of micromixing as it becomes possible to separate the distribution of the prepolymer from that of the polymer which is formed after addition when micromixing is to be investigated.     

Growth mechanisms in GaAs-VPE at low deposition temperature

The VPE growth of GaAs in the system GaAs AsCl₃ with either H₂ or He as the Carrier gas was studied in the range of low deposition temperatures. Down to about 670 °C the growth in the H₂-system is limited by the kinetics of chlorine desorption by molecular hydrogen. The increase in growth rate at lower temperatures results from the onset of GaCl₃-desorption (disproportionation mechanism). The addition of NH₃ to the vapour phase enhances this effect. Below about 700 °C the growth rate in the GaAs AsCl₃ H₂ NH₃ system becomes comparable to that in the GaAs AsCl₃ He-system, where the GaCl₃ desorption mechanism is the only possible growth mechanism.     

A correlation between concentration of deep levels and growth conditions for VPE?GaP

A minimum in deep level concentration in VPE-GaP is found which corresponds to exceptional growth conditions near a relative maximum of the growth rate r in dependence on the GaCl input pressure pG̊aCL. The minimum occurs at the cross-over between mass flow controlled growth (at low pG̊aCL.) and surface reaction controlled growth (at high pG̊aCL.).     

Isolation of ent-labdane (+)-12,15-epoxylabda-8(17), 12,14-trien-16-yl acetate from the seeds of Turraeanthus africanus and its cytostatic/cytotoxic effect on the growth of cancer cells in vitro

(+)-12,15-Epoxylabda-8(17),12,14-trien-16-yl acetate has been isolated from the seed kernels of Turraeanthus africanus (Nelw. ex DC). The stereo structure was confirmed by 1D-and 2D-NMR spectroscopy. Cytostatic/cytotoxic test of (I) on the growth of cancer cells in vitro gave positive results. Published in Khimiya Prirodnykh Soedinenii, No. 1, pp. 38–39, January–February, 2006.     

Suzuki–Miyaura reactions in PEG–water solutions using Pd/BaSO4 as catalytic source

Suzuki–Miyaura reactions between halobenzenes and other substituted (hetero)arenes and boronic acids were carried out in PEG–water solution using Pd/BaSO₄ as catalytic source in a ligand‐free system. High to moderate yields were generally obtained. The catalytic system could be recycled up to six times, showing a slight decrease in activity after each cycle. Copyright © 2008 John Wiley & Sons, Ltd.