Large asymmetric Stark shift in GaxIn1–xAs/InP/InAsyP1–y composite quantum wells

Strong asymmetric Stark shift in excess of 115 meV of the lowest energy transition has been experimentally observed in composite Ga/sub x/In/sub 1-x/As/InP/InAs/sub y/P/sub 1-y/ quantum-well system. In this structure, we can independently control the confinement of electrons and holes by controlling the strain. The photoexcited electrons and holes are confined in spatially separated regions without the application of an electric field. Due to the large asymmetry in the structure, we observed large blueshifts and redshifts of the absorption edge with an applied electric field. All our measurements agree with the calculations within the framework of the Bir-Pikus strain Hamiltonia

Heterogeneous hydride pyrolysis in a chemical beam epitaxy cracker cell and growth of high quality InP

The decomposition of phosphine and arsine in a chemical beam epitaxy cracker cell was investigated with a quadrupole mass spectrometer. We have determined the kinetical parameters for a unimolecular reaction of the first order, i.e. the activation energy and frequency factor, from the decomposition efficiency as a function of temperature. These results are compared with data from literature. We find the lowest activation energies ever reported for the hydride pyrolysis, namely 72 and 48 kJ/mol for phosphine and arsine, respectively. This is due to the heterogeneous decomposition on catalytic molybdenum baffles inside the cracker cell. Additionally, we have studied the impurity incorporation in epitaxially grown bulk InP layers in relation to the efficiency of this particular molybdenum containing cracker cell. Impurity levels were determined by fitting calculated Hall values to experimental data. The best quality is achieved for the cracker temperature at which the efficiency starts to saturate. At this cracker temperature, optimized mass flow rates resulted in InP layers with a maximum mobility of 186¿000 cm2/V¿s and impurity concentrations in the low 1014 cm-3 range

Vegetatietypen in Nederlandse naaldhoutbossen

Vegetatieonderzoek Stibok

DNA barcoding of euryglossine bees and the description of new species of Euhesma Michener (Hymenoptera, Colletidae, Euryglossinae)

This paper launches an open access DNA barcoding project "AUSBS" under the Barcoding of Life Datasystems (BOLD). The aims of the project are to help scientists who lack the necessary morphological knowledge to identify known species using molecular markers, to aid native bee specialists with the recognition of species groups that morphologically are difficult to define, and, eventually, to assist with the recognition of new species among known species. Using integrative taxonomy, i.e. morphological comparison to type specimens in Australian museum collections combined with phylogenetic analysis of a fragment of the mitochondrial DNA cytochrome c oxidase subunit I (mtCOI) gene sequences led to the recognition of four new species of Euhesma Michener (Hymenoptera: Colletidae: Euryglossini) collected during intensive surveys in remote Australian conservation areas, which are described. The new species are Euhesma micans, Euhesma lyngouriae, and Euhesma aulaca in a species group associated with Eremophila flowers, and Euhesma albamala in the walkeriana species group.Katja Hogendoorn, Mark Stevens, Remko Leij

Exposure source for skin sensitizing hydroperoxides of limonene and linalool remains elusive: an analytical market surveillance

International audienc