CVT法生长GaP多晶

阐述了CVT(化学气相输运)法生长GaP的基本反应和输运速度,采用CVT法生长出了GaP多晶.设计了石英管的结构以制造出一个局部的低温区域,防止了GaP在管壁的生长.生长出的GaP多晶相对密度为98;,红外透过率达到30;,努普硬度为611kg/mm2.散射颗粒测试表明主要的光散射颗粒为多晶中存在的孔隙.     

Synthesis of deuterium labelled L- and D-glutamate semialdehydes and their evaluation as substrates for carboxymethylproline synthase (CarB)--implications for carbapenem biosynthesis

Carboxymethylproline synthase was shown to condense L-glutamate semialdehyde with malonyl-coenzyme A to produce (2S,5S)-carboxymethylproline, while incubation of D-glutamate semialdehyde results only in uncoupled turnover of malonyl-CoA.     

Internally pumped subthreshold OPO

Received: 25 February 1998/Revised version: 27 March 1998     

A concise synthesis of the molecular framework of pleuromutilin

Two syntheses of the tricyclic carbon skeleton of pleuromutilin are reported. Diastereoselective 1,4-conjugate additions were used to elaborate bicyclic precursors at an early stage of each route, while ring-forming olefin metatheses were executed to complete the pleuromutilin carbon framework. The congeners prepared are appropriately functionalized to enable access to diverse pleuromutilin analogues.     

Concise, stereocontrolled synthesis of the citrinadin B core architecture

A concise, stereocontrolled synthesis of the citrinadin B core architecture from scalemic, readily available starting materials is disclosed. Highlights include ready access to both cyclic tryptophan tautomer and trans-2,6-disubstituted piperidine fragments, an efficient, stereoretentive mixed Claisen acylation for the coupling of these halves, and further diastereoselective carbonyl addition and oxidative rearrangement for assembly of the core.     

Negative and persistent photoconductivity in p-type Al0.5Ga0.5As/GaAs/Al0.5Ga0.5As heterostructures under uniaxial stress

Abstract

Illumination of a double p-Al_0.5Ga_0.5As/GaAs/Al_0.5Ga_0.5As heterostructure by a red light emitting diode results in a negative photoconductivity that, after the diode is switched off, slowly relaxes to a positive persistent photoconductivity, characterised by an approximately 1.5-fold increase of the two-dimensional hole concentration. This metastable state may be explained with a model in which deep electron traps are supposed to be located above the Fermi level on the inverted heterointerface. Under uni-axial compression the hole concentration in the persistent photoconductivity state, as well as in the dark state, demonstrates the same linear decrease.     

Selective hydrogen bond disruption in adenine monolayer films by reaction with water

High-resolution X-ray photoelectron spectroscopy of two-dimensional films of adenine on a highly oriented pyrolitic graphite [0 0 0 1] surface reveal bonding changes induced by exposure to water. The hydrogen-bond interactions between adenine molecules were replaced by adenine–water hydrogen bonds in a stepwise pattern. This reaction destroyed the film network and changed the chemical state of the nitrogen sites. The reaction with water molecules affected both the donor and acceptor states of the oxygen atoms, as compared to those in water.