AlGaN-based quantum-well heterostructures for deep ultraviolet light-emitting diodes grown by submonolayer discrete plasma-assisted molecular-beam epitaxy

Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al _x Ga_{1 ? x} N/Al _y Ga_{1 ? y} N quantum wells. Structural and optical properties of the Al _x Ga_{1 ? x} N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al₂O₃ substrates, heterostructures for light-emitting diodes with Al _x Ga_{1 ? x} N/Al _y Ga_{1 ? y} N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm.     

Effect of the properties of the water sorbent on the heat generation in the Fe-C-NaCl-H<Subscript>2</Subscript>O-O<Subscript>2</Subscript> system

The water adsorption and retention behaviors of vermiculite, silica gel, activated carbon, and a zeolite are analyzed in relation to their pore structures, and their effects on the dynamics of heat generation in Fe-C-NaCl-H₂O-O₂-water sorbent systems are investigated.     

Geoecological estimation of land and water use in the ural natural and technogeneous mineral resource exploitation areas

The paper focuses on the geoecological estimation of the mining impact on land and water resources in the Ural. The present ecological exploration are prompted by the current situation dealing with the abundance of natural and technogeneous mineral resources and natural zonal geographical peculiarities in the Ural.     

Growth of GaN by molecular-beam epitaxy with activation of the nitrogen by a capacitive rf magnetron discharge

It is shown that GaN films can be grown by molecular-beam epitaxy with plasma activation of the nitrogen by a magnetron rf discharge in a specially constructed coaxial source with capacitive coupling. A growth rate of ∼0.1 μm/h is obtained on GaAs and sapphire substrates, and ways are found for optimizing the design of the plasma source in order to increase the growth rate. The electrophysical and luminescence properties of undoped epitaxial films are investigated at temperatures ranging all the way to room temperature. Pis’ma Zh. Tekh. Fiz. 24, 30–35 (June 26, 1998)     

Low-temperature anti-Stokes photoluminescence in CdSe/ZnSe nanostructures

Intense anti-Stokes photoluminescence was observed at low temperatures in CdSe/ZnSe nanostructures with separate CdSe inserts in a ZnSe matrix; the nominal thickness of these inserts amounted to 1.5 and 0.6 monolayers. It is shown that the intensity of an anti-Stokes band excited by the photons of energies considerably lower than the band’s peak is quadratic in the excitation power; in the case of resonance excitation, a weaker dependence is obtained. A mechanism behind the excitation of anti-Stokes photoluminescence is suggested on the basis of nonlinear two-step two-photon absorption via the deep states of the defect centers including cation vacancies localized at the barrier-nanoisland interface.     

Composition and structure of resins in lube distillates from west siberian crudes

Translated from Khimiya i Tekhnologiya Topliv i Masel, No. 2, pp. 27–30, February, 1994.     

Diverse world of unconventional hydrogen bonds

This Account presents our view of unconventional intermolecular hydrogen bonds (HBs) for organometallic complexes and transition-metal or main-group hydrides. Over the past decade, low-temperature spectroscopic (IR, UV, and NMR) studies combined with theoretical calculations have disclosed the static and dynamic features of different HBs. Their guiding role in the proton-transfer processes was determined, as well as the energetic characteristics of HB intermediates and the activation barriers. Nevertheless, there is still much to explore in terms of the prediction of HB properties and control of protonation/deprotonation processes.