Фотолюминесцентные исследования легированных кремнием эпитаксиальных пленок GaAs, выращенных на подложках GaAs с ориентациями (100) и (111)А при пониженных температурах

The electrical properties and photoluminescence features of uniformly Si-doped GaAs layers grown on GaAs substrates with the (100) and (111)A crystallographic orientations of the surface are studied. The samples are grown at the same As_4 pressure in the growth temperature range from 350 to 510°C. The samples grown on GaAs(100) substrates possess n -type conductivity in the entire growth temperature range, and the samples grown on GaAs(111)A substrates possess p -type conductivity in the growth temperature range from 430 to 510°C. The photoluminescence spectra of the samples exhibit an edge band and an impurity band. The edge photoluminescence band corresponds to the photoluminescence of degenerate GaAs with n - and p -type conductivity. The impurity photoluminescence band for samples on GaAs(100) substrates in the range 1.30–1.45 eV is attributed to V _As defects and Si_As– V _As defect complexes, whose concentration varies with sample growth temperature. Transformation of the impurity photoluminescence spectra of the samples on GaAs(111)A substrates is interpreted as being a result of changes in the V _As and V _Ga defect concentrations under variations in the growth temperature of the samples.

Insights into thermoadaptation and the evolution of mesophily from the bacterial phylum Thermotogae

Thermophiles are extremophiles that grow optimally at temperatures >45 °C. To survive and maintain function of their biological molecules, they have a suite of characteristics not found in organisms that grow at moderate temperature (mesophiles). At the cellular level, thermophiles have mechanisms for maintaining their membranes, nucleic acids, and other cellular structures. At the protein level, each of their proteins remains stable and retains activity at temperatures that would denature their mesophilic homologs. Conversely, cellular structures and proteins from thermophiles may not function optimally at moderate temperatures. These differences between thermophiles and mesophiles presumably present a barrier for evolutionary transitioning between the 2 lifestyles. Therefore, studying closely related thermophiles and mesophiles can help us determine how such lifestyle transitions may happen. The bacterial phylum Thermotogae contains hyperthermophiles, thermophiles, mesophiles, and organisms with temperature ranges wide enough to span both thermophilic and mesophilic temperatures. Genomic, proteomic, and physiological differences noted between other bacterial thermophiles and mesophiles are evident within the Thermotogae. We argue that the Thermotogae is an ideal group of organisms for understanding of the response to fluctuating temperature and of long-term evolutionary adaptation to a different growth temperature range.

Prolixibacter denitrificans sp. nov., an iron-corroding, facultatively aerobic, nitrate-reducing bacterium isolated from crude oil, and emended descriptions of the genus Prolixibacter and Prolixibacter bellariivorans

The facultatively aerobic, non-hydrogenotrophic, iron (Fe0)-corroding, nitrate-reducing Prolixibacter sp. strain MIC1-1T was characterized for representation of a novel species of the genus Prolixibacter. Strain MIC1-1T grew optimally at 35–37 °C, at pH 6.5 and with 2 % (w/v) NaCl. Strain MIC1-1T also grew fermentatively on some pentoses, hexoses, disaccharides and soluble starch. Succinic acid was the major end-product from d-glucose fermentation. Strain MIC1-1T was differentiated from the type strain of Prolixibacter bellariivorans by cell size, optimum growth temperature, range of temperature and NaCl for growth, and nitrate reduction. On the basis of phenotypic features and the phylogenetic position, a novel species of the genus Prolixibacter is proposed for strain MIC1-1T, to be named Prolixibacter denitrificans sp. nov. The type strain is MIC1-1T ( = JCM 18694T = NBRC 102688T = DSM 27267T). Emended descriptions of the genus Prolixibacter and Prolixibacter bellariivorans are also provided.

Aerobic Denitrification Characteristics Research of Pseudomonas Strains HFX08

In this report, a strains of nitrifying bacteria HFX08 with low temperature and low carbon nitrogen ratio is separated from the activated sludge which is domesticated of the northern city sewage plant in winter. The optimum carbon source for the growth of the strain is sodium acetate, the source of nitrogen is potassium nitrate and the optimum growth temperature range is 10-20°C correspondingly.

Nitrogen Incorporation and Growth Kinetics of GaAsN/GaAs Epilayers Grown by MOVPE

The nitrogen incorporation behavior in GaAs was investigated in the growth temperature range 500-600°C. It was observed that the temperature-dependence of the nitrogen incorporation exhibits two regimes. At 530°C, the nitrogen content x is a nonlinear function of the gas-phase composition indicating a surface-controlled reaction mechanism. The N composition varies slowly with 500°C < T < 560°C with an activation energy of 0.6 eV. For T < 560°C, N decreases exponentially with Ea= 3.7 eV, interpreted in terms of nitrogen desorption. In light of experimental results, we propose a surface kinetic model based on the competitive adsorption of group V precursors.

Use of Selective Media to Recover Salmonella and Vibrio cholerae after Growth in Reconditioned Pork-Processing Wastewater†

Selective plating media are used for the enumeration and isolation of bacterial pathogens from food and water samples. This study compared the quantitative recovery of Salmonella spp. and Vibrio cholerae grown in nutrient-limited, filter-sterilized, reconditioned wastewater over the temperature range of 4 to 45°C using nonselective and pathogen-specific selective media. Viable Salmonella were enumerated on tryptic soy agar (TSA) and XLT-4, and viable V. cholerae were enumerated on TSA and thiosulfate-citrate-bile-sucrose agar. There was a statistically significant (P &lt; 0.05) higher recovery of both pathogens over the growth temperature range on TSA compared to the selective media. Trehalose, a stress-induced metabolite of Salmonella, was isolated from the cells grown in the reconditioned wastewater, whereas, the V. cholerae exhibited a change in cellular morphology from rod to coccoid shape. These results suggest that growth in nutrient-limited water injured or stressed the individual pathogens. Care should be used in choosing the procedure and plating medium for quantitative recovery of pathogens from such a nutrient-limiting environment.

Selective Epitaxy of AlxGa1−x as and AlxGal−x as Based Structures

ABSTRACTSelective epitaxy of AlxGa1−x As by MOVPE was accomplished using diethyl gallium chloride and diethyl aluminum chloride as the metalorganic precursors. Selective epitaxy was achieved for Al containing compounds under certain growth conditions, but AlAs growth was not selective. Quantum wells were selectively grown on masked substrates and unpatterned GaAs wafers; QW luminescence was observed from all samples. Additionally, near gap luminescence was observed from AlxGa1−x, As heterostructures over the entire 550 °C - 850 °C growth temperature range. The ternary alloy composition was found to be a strong function of the gas phase composition and growth temperature. A simple thermodynamic model explained the dependence of growth rate and composition on these parameters.