Calculation of the electrical resistance and power distribution in a glass-melting furnace with two pencil electrodes

A method of calculating the electrical resistance of a furnace and power distribution in the bulk of the melt was examined for different mutual positions and lengths of two pencil electrodes. The electrical characteristics of a rectangular furnace with internal dimensions of 1.5×3 X 1.5 m and pencil electrodes 0.025 m in diameter were calculated.Translated from Steklo i Keramika, Nos. 5–6, pp. 24–26, May–June, 1994.     

Various Scale Levels of the Gel-to-Glass Transformation

The gel-to-glass transition in SiO₂ xerogels prepared by inorganic sol-gel synthesis was studied. The evolution of the molecular structure is traced using the infrared and lowfrequency Raman spectroscopy methods. The elastic moduli of the samples as well as the pore wall moduli at various stages of heat treatment are determined from the data on Brillouin scattering. The formation of monolithic glass on the macroscopic level manifests itself within a narrow temperature range by the dramatic increase of Young's modulus to the accepted value for fused silica. This phenomenon coincides with structural transformations on the molecular scale: (i) the definite correlation radius (the long-range order sphere) appears; (ii) local distortions of the silica network relax. The presence of structural defects influences the kinetics of vitreous SiO₂ formation during xerogel heat treatment.     

The nature of the deep levels responsible for photoelectric memory in GaAs/AlGaAs multilayer quantum-well structures

The electron capture parameters and photoionization cross section of the unintentional deep levels, which are responsible for photoelectrical memory in GaAs/AlGaAs multilayer quantum-well structures, have been found from an analysis of the kinetics of the excess current during and after optical illumination of these structures. The dependence of the photoionization cross section on the photon energy, the capture cross section, and the energy barrier for capture of an electron from the bottom of the conduction band indicate that the unintentional deep levels are DX centers formed by the silicon impurity. These DX centers probably appear during growth of the structures as a result of silicon diffusion from the quantum wells along as-grown defects. Fiz. Tekh. Poluprovodn. 32, 1213–1218 (October 1998)     

The temperature dependence of internal optical losses in semiconductor lasers (λ = 900–920 nm)

The temperature dependences of radiative characteristics of semiconductor lasers based on asymmetric heterostructures of the separate confinement with an extended waveguide fabricated by MOCVD epitaxy (the emission wavelength λ = 900–920 nm) are studied. It is established that the threshold concentration in the active region and waveguide layers of the laser heterostructure of the separate confinement increases in the CW lasing mode as the pumping current and temperature of the active region are increased. It is established experimentally that, in the temperature range of 20–140°C, the stimulated quantum yield remains unchanged. It is shown that the temperature delocalization of charge carriers leads to an increase in the carrier concentration in the waveguide layers of the laser heterostructure. The total increase in internal optical losses due to scattering by free charge carriers in the layers of the active region and waveguide layers of the laser heterostructure leads to a decrease in the differential quantum efficiency and to saturation of the watt-ampere characteristic of semiconductor lasers in the continuous lasing mode.     

In-situ investigations as a basis for development of a procedure for calculation of the stress-strain state of a soil mass during installation of substructures

Results of field observations of the settlements of buildings and structures and deformations of pit enclosures are analyzed. The results are subjected to computational analysis using a viscoelastoplastic model of the soil medium. Practical recommendations are given for design of pit enclosures and underground structures with consideration of soil deformation over time.     

Effect of Bound Water on the Fractal Geometry of Nanosized Cracks in Glasses Prepared by Vacuum Pressure-Assisted Sintering

The vibrational properties of fractal nanocracks in vitreous SiO₂samples prepared by vacuum pressure-assisted sintering are investigated by low-frequency Raman scattering spectroscopy. In the Raman spectrum, nanosized discontinuities with a fractal geometry manifest themselves in a specific frequency dependence of the scattering intensity: a monotonic decrease in the intensity according to the law of light scattering by acoustic vibrations localized on fractals is observed instead of the boson peak. The frequency dependence of the low-frequency Raman scattering intensity is analyzed for samples of different origins. A smoothing of the nanocrack profile with a decrease in the amount of bound water in the material is revealed.     

Isotope-modified silicon layers obtained by plasma enhanced chemical vapor deposition from gaseous silicon tetrafluoride

Layers of silicon with an isotope composition that differs from the native composition have been obtained by the method of plasma enhanced chemical vapor deposition from gaseous silicon tetrafluoride. The deposited layers possess an amorphous structure and high oxygen content. The Raman spectra and the spectra of optical transmission in the IR range are presented. The in-depth distribution of Si isotopes has been determined using the second ion mass spectrometry techniques.     

Electroluminescent properties of heterostructures with GaInNas quantum wells

GaInNAs quantum wells were grown by metal-organic vapor-phase epitaxy. In order to improve the optical properties, the GaNAs barriers were incorporated on both sides of the quantum well; these barriers compensated the elastic stresses. Characteristics of the optical transitions were assessed from the measurements of photoluminescence and photocurrent. In order to fabricate light-emitting diodes, nonalloyed ohmic contacts based on heavily δ-doped layers were used. Electroluminescence was observed at a wavelength of ～1.2 μm at temperatures of 77 and 300 K; the electroluminescence intensity depended linearly on the injection current if the latter exceeded a certain threshold value.