Effect of the growth parameters on the electron structure of quantum dots in InGaAs/GaAs heterostructures

The optical and structural properties of heterostructures with quantum dots (QDs) in the InAs/GaAs system overgrown with an InGaAs solid solution were studied. The QD layers were obtained using different molecular beam deposition techniques: molecular beam epitaxy versus submonolayer migration-stimulated epitaxy. The photoluminescence peaks in the spectra of samples with overgrown QD layers occur in the wavelength range from 1.18 to 1.32 μm. It was found that the growth conditions also influence the electronic structure of QDs.     

Definition of the remaining life of power-transmission lines with cross-linked polyethylene insulation

XLPE-insulated cables and wires are becoming more widespread. For this reason, it is becoming necessary to control the state of insulation over its total operating life. Online monitoring of the effects on the insulation and determination of its remaining life becomes possible using modern equipment. In this paper, a method of determining the remaining lifetime of the cross-linked polyethylene insulation of the powertransmission line is presented. An insulation-aging model developed at the previous stage of the research was used. It is proposed to control the destructive effects on the insulation and calculate the remaining life based on the obtained data. The results of the research showed that the probability of failure is subject to the normal character of distribution (Gaussian distribution) as the insulation in the process of operation is exposed to a large number of effects (partial discharges, thermal actions, effect of the environmental factors, etc.). The remaining lifetime is defined as a function of inverse failure probability. The proposed method can be used to develop a set of devices for determining the remaining life of polyethylene insulation.     

Self‐Assembly of Ferromagnetic Organic–Inorganic Perovskite‐Like Films

Perovskite‐based organic–inorganic hybrids hold great potential as active layers in electronics or optoelectronics or as components of biosensors. However, many of these applications require thin films grown with good control over structure and thickness—a major challenge that needs to be addressed. The work presented here is an effort towards this goal and concerns the layer‐by‐layer deposition at ambient conditions of ferromagnetic organic–inorganic hybrids consisting of alternating CuCl₄‐octahedra and organic layers. The Langmuir‐Blodgett technique used to assemble these structures provides intrinsic control over the molecular organization and film thickness down to the molecular level. Magnetic characterization reveals that the coercive field for these thin films is larger than that for solution‐grown layered bulk crystals. The strategy presented here suggests a promising cost effective route to facilitate the excellently controlled growth of sophisticated materials on a wide variety of substrates that have properties relevant for the high density storage media and spintronic devices.     

The effect of neutron irradiation and annealing temperature on the electrical properties and lattice constant of epitaxial gallium nitride layers

Effect of irradiation with high reactor-neutron fluences (Φ = 1.5 × 10¹⁷-8 × 10¹⁹ cm⁻²) and subsequent heat treatments in the temperature range 100–1000°C on the electrical properties and lattice constant of epitaxial GaN layers grown on an Al₂O₃ substrate is considered. It is shown that, with the neutron fluence increasing to (1–2) × 10¹⁸ cm⁻², the resistivity of the material grows to values of about 10¹⁰ Ω cm because of the formation of radiation defects, and, with the fluence raised further, the resistivity passes through a maximum and then decreases to 2 × 10⁶ Ω cm at 300 K, which is accounted for by the appearance of a hopping conductivity via deep defects in the overlapping outer parts of disordered regions. With the neutron fluence raised to 8 × 10¹⁹ cm⁻², the lattice constant c increases by 0.38% at a nearly unchanged parameter a. Heat treatment of irradiated samples at temperatures as high as 1000°C does not fully restore the lattice constant and the electrical parameters of the material.     

Study of processes of self-catalyzed growth of gaas crystal nanowires by molecular-beam epitaxy on modified Si (111) surfaces

The processes of growth of self-catalyzed GaAs crystal nanowires on Si (111) surfaces modified by three different methods are studied. For the technology of production of the GaAs nanowires, molecular-beam epitaxy is used. It is found that, in the range of substrate temperatures between 610 and 630°C, the surface density of nanowires and their diameter sharply increases, whereas the temperature dependence of the nanowire length exhibits a maximum at 610°C. An increase in the temperature to 640°C suppresses the formation of nanowires. The method that provides a means for the fabrication of purely cubic GaAs nanowires is described. A theoretical justification of the formation of the cubic phase in self-catalyzed GaAs nanowires is presented.     

Parameters of the positive column of glow discharge with dust particles

We calculate the measured nonlocal parameters of the plasma of the positive column of direct current glow discharge in the presence of dust structures with different dust particle concentrations. The calculations are performed for typical conditions of the positive column of low-pressure glow discharge in air at which a collisional regime of maintaining discharge is achieved. The discharge plasma is described using the diffusion approximation; the flows to the surface of the dust particles are described in the orbital motion limited approximation. Calculation is carried out for micron-size particles with concentrations of up to 10¹¹ m^?3. The distribution of the dust component is assumed to be independent of the discharge parameters. Radial distributions of the plasma components and of the electric field component are obtained. The charges of dust particles for various concentrations and discharge parameters are calculated. It is demonstrated that for a certain particle concentration, the absorption efficiency of plasma particles becomes comparable with diffusion losses at the tube walls. The influence of the dust cloud on the electric field configuration at different dust particle concentrations in the cloud is analyzed. The current-voltage characteristics of the positive column of glow discharge are calculated. A higher discharge stability toward the perturbative action of dust particles at high discharge current values is demonstrated.     

Optical properties of undoped n-AlGaN/GaN superlattices as affected by built-in and external-electric field and by ar-implantation-induced partial disordering

High-resolution x-ray diffraction patterns and 90 K microcathodoluminescence (MCL) spectra were taken for undoped, symmetric AlGaN/GaN superlattices (SLs) with GaN quantum-well (QW) widths of 35 Å and 80 Å. The short-period SL spectra were blue shifted by about 60 meV compared to the GaN substrate, and the magnitude of the blue shift was increased by about 20 meV by application of a reverse bias of ?3 V (electric field of about 4 · 10⁵ V/cm) to a Schottky diode prepared on this SL. A small red shift of about 40 meV compared to GaN was observed for the long-period SL. The two latter observations were interpreted as manifestations of the presence of a strong built-in piezoelectric field, giving rise to the quantum-confined Stark effect (QCSE). Partial disordering of the short-period SL was observed after Ar ion implantation (energy 150 keV, dose 8·10¹³ cm^?2 and 80 keV, 2·10¹³ cm^?2) and subsequent annealing at 1000°C for 3 h under the protective layer of Si₃N₄. However, it was observed that this partial disordering was accompanied by strain relaxation via formation of misfit dislocations or cracks.     

Increasing the service life of shafts of blast furnaces

Translated from Metallurg, Vol. 39, No. 10, p. 21, October, 1995.     

Reverse electric field in spherical striations

We have experimentally studied the floating potential distribution in a spherical stratified dc discharge. A nonmonotonic potential profile is observed in the region of striations, which is indicative of the existence of regions with a reverse electric field.