Contributions of the interior and surface states of charge carriers to the emission spectra of CdS quantum dots in borosilicate glasses

The photoluminescence spectra of CdS quantum dots grown in a borosilicate glass by sol-gel technology are recorded and analyzed. It is shown that the photoluminescence spectra of the samples are related to annihilation of free (interior) excitons in the ground state and excited state. Emission associated with the surface states of the quantum dots is detected in the region around 2.7 eV for the first time. The emission is due to recombination of electrons localized at the surface with heavy holes in the free states of the quantum dots. Resonance excitation of the structures makes it possible to reveal the specific features of the localized surface states responsible for the photoluminescence band. The properties of the band are, to a large extent, similar to the properties of the emission bands of both three-dimensional media (amorphous semiconductors and substitution alloys) and two-dimensional systems (quantum wells and superlattices).     

Inside Front Cover: Homeotropic Alignment of Columnar Liquid Crystals in Open Films by Means of Surface Nanopatterning (Adv. Mater. 6/2007)

Columnar liquid crystals (LCs) are found to spontaneously form homeotropically‐aligned films when deposited on surfaces fabricated via friction transfer of polytetrafluoroethylene. The inside cover schematically shows the film structure of a phthalocyanine derivative together with the corresponding X‐ray diffraction pattern (inset). The results, reported on p. 815 by Dmitri Ivanov and co‐workers, indicate that not only are the columns homeotropically oriented but also that they form a single monodomain of macroscopic size. These findings can have an important impact for fabrication of LC‐based organic solar cells.     

Physicochemical materials research

For alloys in the range Os-OsAl₂-IrAl_2.7-Ir, as-cast and annealed at 1400 °C (Os-OsAl-IrAl-Ir) and 1250°C (OsAl-OsAl₂-IrAl_2.7-IrAl), phase equilibria are studied by powder x-ray diffraction (PXRD), differential thermal analysis (DTA), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDX). Between isostructural aluminides OsAl and IrAl there exists a continuous solid solution (Os,Ir)Al. Other unary and binary phases form terminal solid solutions: (Os), (Ir), (OsAl₂), and (IrAl_2.7).     

Direct simulation of rarefied high-enthalpy flow around the RAM C-II capsule

An ionized flow around the RAM C-II space vehicle is studied by the direct simulation Monte Carlo method in the range of altitudes of 73 to 81 km. It is shown that the predicted value of the plasma density in the shock layer essentially depends on the approach to simulation of high-temperature nonequilibrium dissociation. Good agreement of the results of numerical simulation with flight experiment data is obtained.     

Determination of 90Sr, 238Pu, 239,240Pu, 241Pu, and 241Am in soils of chernobyl region using various sample preparation techniques

Radiochemical analysis is made of soddy-podzolic sandy and peaty gley soils collected from the Chernobyl zone. Radionuclides were separated by extraction chromatography or ion exchange, and then determined using an α-ray spectrometer and liquid scintillation and proportional gas counters. Leaching from the preliminarily calcined sample with 8 M HNO₃ does not ensure 100% recovery of radionuclides from peaty gley soil.     

System analysis of the efficiency and competitiveness of chroming technologies

The scientifically based selection of efficient chemical technologies is related to the integrated assessment of indicators of their energy and resource efficiency and environmental safety, as well as indicators of the quality of products. The authors conducted systematic analysis of the efficiency and competitiveness of two electrochemical technologies of chroming from the solutions based on chromium salts of different valences. The strengths and weaknesses of each technology have been defined using the methodology of SWOT analysis, and the defined qualitative indicators of the efficiency of technologies have been determined using the methods of nonparametric statistics.     

Heaven on Earth

‘By 2050 we will have probed the universe even further, peeling back time as we strive for some sense of creation and meaning.’ The world's first neurologist in space, Roberta L Bondar , who conducted international experiments on space mission STS 42 and has subsequently undertaken neurological research with NASA, urges us to look up and into space, which is set to remain a rich area of exploration, scientific investigation and wonder, with the discovery of new planets, light, patterns and materials on the not-so-distant horizon.