Effect of film thickness on hydrogen content in a-Si : H

The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness.     

Electrical passivation of the silicon surface by organic monolayers of 1-octadecene

The electrical properties of structures consisting of a monolayer of 1-octadecene deposited on the Si surface are investigated depending on the method of passivation of the surface prior to the deposition of the film (hydrogen and ion passivation) and the intensity of illumination which activates the addition reaction of molecules of 1-octadecene to the Si atoms. The monolayer of 1-octadecene on the Si surface is stable and provides the chemical passivation of the surface. Two types of traps are found, namely, traps for holes and electrons, whose density can be varied during deposition of the monolayer by the choice of intensity of illumination and by the method of passivation of the surface. In the case of a low level of illumination and/or the use of the iodine passivation of the surface, the electron traps prevail, and, in the case of high intensity of illumination and/or hydrogen passivation of the surface, the hole traps prevail. It is shown that the use of these films provides conductivity in thin near-surface layers of Si due to providing the mode of flat bands or accumulation of carriers near the surface.     

The effect of preventive vitamin supplementation on vitamin status and work productivity of conveyer belt workers in light industry

The authors have studied the ways of correcting the vitamin status and influence of vitaminization on working capacity in workwomen in light industry. Prophylactic polyvitaminization (1 dragee of "Undevitum"/day, during 2 months) proved to produce positive effect on the vitamin status parameters (vitamin content in the blood and urine, clinical microsymptoms of vitamin deficiency), and on the dynamics of the physiological parameters of working capacity of workwomen at modern conveyer shoe making industry. It is recommended that persons suffering from chronic diseases influencing vitamin metabolism, first of all those over 45 years, should receive increased doses of prophylactic polyvitamins, thiamine and ascorbic acid, in particular.     

Special characteristics of the filtration combustion of the system Ti?C?N in an audio-frequency sound field

The influence of sound fields on the filtration combustion of mixtures of titanium and carbon in nitrogen on the kinetics of self-propagating high-temperature synthesis and on the chemical and phase composition of the synthesis products is investigated. It is shown that filtration hindrances in a wide layer of the sample vanish if the charge material has an initial relative density of 0.2. The carbonitride component is formed most completely when the atomic fraction of carbon in the initial charge has values of 0.3 and 0.5. The optimum acoustic frequency stimulating the filtration of nitrogen deep within the briquette and yielding the most complete nitriding process is the resonance frequency of the acoustic system. Fast-framing photography exhibits the transient nature of the filtration combustion of titanium—carbon mixtures in nitrogen. Institute of Steel and Alloys, Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 5, pp. 44–51, September–October, 1995.     

Effect of gamma irradiation on the phase composition of ZrO<Subscript>2</Subscript>-based ceramic materials

We have studied the effect of gamma irradiation on the phase composition and crystallite size of ZrO₂ samples containing 0, 2, and 3 mol % Y₂O₃ as a stabilizer and heat-treated at 800°C. The results demonstrate that gamma irradiation leads to amorphization of the material and reduces the amount of the monoclinic phase. Irradiation had the strongest effect on the phase composition (increasing the percentage of the tetragonal phase and reducing that of the monoclinic phase) and caused the largest decrease in crystallite size in the case of the yttria-free samples.     

Alternative methods for production of alicyclic epoxides

The salient and peculiar features of the oxidation of dicyclopentene and unsaturated alicyclic hydrocarbons with a medium-sized carbon ring into the corresponding epoxides have been studied. Organic hydroperoxides, aqueous hydrogen peroxide, and peracids have been used as oxidizing agents. The reactivity of the substrates in each of the oxidation processes under consideration has been estimated, and conditions providing a high epoxide yield have been chosen. The advantages and disadvantages of each process taking into account the problems of isolation of the desired product are considered. The results obtained allow the peracid method to be recommended for the synthesis of dicyclopentene epoxide as an effective and convenient for practical implementation.     

Is it possible for dislocations to self-lock after high-pressure torsion?

The evolution of the dislocation structure of the intermetallic compound Ni₃Ge upon high-pressure torsion has been investigated. It has been determined that, under certain conditions, subsequent heating without loading leads to the self-locking of dislocations, while in other cases, this does not take place. The role played by the lattice distortions that arise under torsion is emphasized.     

Structure of the transition zone and its influence on the strength of copper-tantalum joint (Explosion welding)

The joint of copper and tantalum, metals without mutual solubility, formed by explosion welding is studied. The mechanism of the influence of mutual solubility on the structure of the transition zone is established. It is demonstrated that the interface contains heterogeneities, and their role in the strength of the materials joint is revealed. A microheterogeneous structure of the joint zones is detected.     

Effect of Heat Treatment on Dendritic Segregation and High-Temperature Strength of Single Crystals of Ni3Al-Base Rhenium-Alloyed Intermetallic Alloys

Metal Science and Heat Treatment - The nature of stability of dendritic microsegregation of rhenium in single crystals of intermetallic (γ′ + γ) alloys based on γ′-Ni3Al...