Metastable defect formation at microvoids identified as a source of light-induced degradation in a-Si:H.

Light-induced degradation of hydrogenated amorphous silicon (a-Si:H), known as the Staebler-Wronski effect, has been studied by time-domain pulsed electron-paramagnetic resonance. Electron-spin echo relaxation measurements in the annealed and light-soaked state revealed two types of defects (termed type I and II), which can be discerned by their electron-spin echo relaxation. Type I exhibits a monoexponential decay related to indirect flip-flop processes between dipolar coupled electron spins in defect clusters, while the phase relaxation of type II is dominated by 1H nuclear spin dynamics and is indicative for isolated spins. We propose that defects are either located at internal surfaces of microvoids (type I) or are isolated and uniformly distributed in the bulk (type II). The concentration of both defect type I and II is significantly higher in the light-soaked state compared to the annealed state. Our results indicate that in addition to isolated defects, defects on internal surfaces of microvoids play a role in light-induced degradation of device-quality a-Si:H.

The relationship between hydrogen and paramagnetic defects in thin film silicon irradiated with 2 MeV electrons.

After irradiation of hydrogenated amorphous and microcrystalline silicon (a-Si:H and µc-Si:H) with 2 MeV electrons at 100 K, we observe satellite-like components close to the dominating electron spin resonance (ESR) signal of these materials. The satellites overlap with the commonly observed dangling bond resonance and are proposed to originate from a hyperfine interaction with the nuclear magnetic moment of hydrogen atoms in a-Si:H and µc-Si:H. Our present study is focused on the verification of this hypothesis. Equivalent hydrogenated and deuterated a-/µc-Si:H/D materials have been investigated with ESR before and after 2 MeV electron bombardment. From the difference between ESR spectra of hydrogenated and deuterated samples we identify the doublet structure in the ESR spectra as a hyperfine pattern of hydrogen-related paramagnetic centers. The observations of H-related paramagnetic centers in a-/µc-Si:H are of particular interest in view of metastability models of a-Si:H, which include H-related complexes as precursors for the stabilization of the metastable Si dangling bonds. The nature of the observed center is discussed in the light of known H-related complexes in crystalline Si and suggested H-related dangling bonds in a-Si:H.

[Morphometric characterization of hepatocytes during adaptation to extreme Antarctic factors].

The dynamics of ultrastructural changes in the hepatocytes of albino rats after prolonged influence of extreme Antarctic factors had been studied using the morphometric method. It was found that at the early stage of the experiment (7-45 days) the intracellular homeostasis in the hepatocytes was disturbed owing to a pronounced decrease in energy sources and plastic reserves (the decrease in numerical and volume density of the mitochondria, the reduction of the rough endoplasmic reticulum volume and the dilatation of its cisterns, the increase in the volume of the smooth endoplasmic reticulum). The following stages (up to 180 days) were characterized by a practically complete restoration of energy-plastic potential of the hepatocytes; at the conclusive stage of the experiment (270 days) the exhaustion of energy and, especially, of plastic reserves of the hepatocytes was noted (the significant decline in numerical density of the mitochondria and the relative volume of the rough endoplasmic reticulum).

[Dynamics of morphometric indicators of rat testes during adaptation to high-altitude in the Antarctic regions with subsequent dysadaptation]. / Dinamika morfometricheskikh pokazatelei semennikov u krys v khode adaptatsii k vysokogor'iu Antarktidy i posleduiushchei deadaptatsii.

In the experiments performed on 100 white non-inbred male rats (some of them have been kept at the altitude of 3.488 m in the station Vostok, and others--at the coastal level in the station Mirny) testes have been studied, as well as morphometric analysis of convoluted seminiferous tubules and estimation of spermatogenesis activity. During the first month of living at the altitude the section area of the convoluted seminiferous tubules decreases, while the area of their lumen increases. During subsequent periods in the animals, living at the altitude, differences in the parameters, in comparison with the control, disappear. During the first 6 months of their living at the altitude a sharp decrease in spermatogenesis activity is observed. A month of life at the coastal level (after 10 months of hypoxic effect) does not result in normalization of the spermatogenesis activity.

[Features of the capillarization of the skeletal muscles of the white rat during adaptation to high altitude in the Pamir Mountains and the Antarctic]. / Osobennosti kapilliarizatsii skeletnoi myshtsy belykh krys v khode adaptatsii k usloviiam vysokogor'ia Pamira i Antarktidy.

The capillary-myofiber quantitative relations were examined morphometrically in 180 white male rats exposed for 1.5 month to altitudes of 3488-4000 m above sea level (Antarctic and Pamir highlands). During the first three weeks of adaptation drastic changes in the parameter were seen. It is suggested that one of the factors responsible for them is a shift in the functional status of muscles produced by the method of transportation of the animals to the high altitude environment.

[Capillarization of the myocardium of the yak]. / Kapilliarizatsiia miokarda iaka.

Organometric and histometric characteristics of various parts of the heart have been performed in the yak, a permanent inhabitant at altitudes of 3,000-5,000 m above the sea level. Forty hearts of mature animals have been studied. Morphometric investigations of capillaries in the muscle fibers have been carried out in the atrial walls, in the right and left auriculae. in the ventricles and in the papillary muscles. The data are presented for each cardiac part: they describe diameters, density and volume of the capillary network and muscle fibers. In order to estimate the degree of capillarization of the cardiac muscle tissue, a new parameter is suggested to be used, when analyzing the morphometric data. It characterizes ratio of capillaries volume. According to the criterion given, a significant difference is stated between the degree of capillarization in the myocardium of the right and left ventricles. We suppose that this adequately reflects an increased loading experienced by the right cardiac parts under a long-lasting effect of altitude factors.