Fine Purification of Monoisotopic Silanes 28SiH4 , 29SiH4 , and 30SiH4 via Distillation

High-purity isotopically enriched (99.98% ²⁸Si, 99.57% ²⁹Si, and 99.83% ³⁰Si) silane samples are prepared for the first time. The total hydrocarbon content of the samples is no higher than 0.1–0.3 ppm. The concentration of electroactive impurities in the silicon prepared from the purified monoisotopic silane is below 10¹⁵ cm^–3.     

Hydrocarbon impurities in SiF<Subscript>4</Subscript> and SiH<Subscript>4</Subscript> prepared from it

Using gas chromatography and high-resolution Fourier-transform IR spectroscopy, we have determined the concentrations of C₁–C₄ hydrocarbon impurities in isotopically unmodified silicon tetrafluoride before and after fine purification and in ²⁸Si-enriched SiF₄. The concentrations of C₁–C₄ hydrocarbon impurities in silicon tetrafluoride for SiH₄ synthesis have been shown to correlate with those in the synthesized silane.     

Effect of spontaneous polarization on the energy levels in quantum wells formed at the contact between cubic and noncubic silicon carbide polytypes

We have studied the effect of spontaneous polarization, which is inherent in noncubic silicon carbide (SiC) polytypes, on the characteristics of quantum wells (QWs) formed in the cubic region at the heterojunction. The analysis is performed for various QW models, including triangular, parabolic, and exponential. Conditions for the appearance of a two-dimensional electron gas at the interface are briefly discussed.     

Consideration of spontaneous polarization in the problem of NH-SiC/3C-SiC/NH-SiC heterostructures formed by cubic (3C) and hexagonal (NH) silicon carbide polytypes

The problem of three-layer NH-SiC/3C-SiC/NH-SiC heterostructures was considered within the model previously proposed for describing the heterojunction between NH-SiC/3C-SiC silicon carbide polytypes, taking into account spontaneous polarization of hexagonal regions. The potential in the cubic 3C region was approximated by a model function constructed from physical considerations. Much attention was paid to the study of the effect of spontaneous polarization and the 3C region thickness on energy characteristics of quantum wells formed near heterojunctions. Original Russian Text ? S.Yu. Davydov, A.V. Troshin, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 10, pp. 1211–1217.     

Improving the safety of aluminum press molds by protecting them from wear and corrosion by the microarc oxidation method

The results of an increase of wear and corrosion resistance of the working surfaces of transfer press molds by means of the development and use of the microarc oxidation method are given. The protective coatings obtained enabled an increase their service life mainly within the most stressed area of the junction (closing area) and its sharp edges. Taking into account the processes occurring in the transfer press molds, the best properties of the coating and their operation modes are specified. The laboratory tests of coatings for bending, compression with shear, wear and thermal resistance, as well as tests on the structure of the transfer press mold in full-scale production proved their safe operation over 10⁵ cycles without any damage.     

Ultrapurification of <Superscript>76</Superscript>Ge-enriched GeH<Subscript>4</Subscript> by distillation

⁷⁶Ge-enriched germane has been ultrapurified by low-temperature distillation. The nature and concentration of molecular impurities in the germane samples were determined by gas chromatography/mass spectrometry, high-resolution Fourier transform IR spectroscopy, and gas chromatography. The distillate contains no more than 10⁻⁵ mol % hydrocarbons, 10⁻⁴ mol % carbon dioxide, 10⁻³ to 10⁻¹ mol % digermane and trigermane, and <3 × 10⁻⁵ mol % other impurities. A distinctive feature of the impurity composition of the isotopically enriched germane samples is the presence of silicon tetrafluoride and sulfur hexafluoride impurities.     

Minimal brain dysfunction in childhood

Minimal (minor) dysfunction of brain (MDB) is the peculiar form among other consequences of perinatal damages of nervous system. The problems of organization of medical care for children with MDB at preschool age are very important. 106 patients with MDB aged 3-8 years were examined. Detailed clinical-neurological, neuropsychological, instrumental and some other forms of examinations were performed including data about postnatal development. It is demonstrated that MDB may be considered as a diffuse cerebral dysregulation, conditioned by a delay of maturation of some connections between different CNS regions. Leading levels of maximal dysregulation are identified. A necessity was emphasized of early revelation, prolonged follow-up and purposeful rehabilitation of such patients.     

Influence of stress concentrators on the stressed-strained state of a tubular elastic element in a tensoresistor force sensor

Translated from Izmeritel'naya Tekhnika, No. 1, pp. 25–26, January, 1991.     

THE REACTION OF C60F20 WITH ANTHRACENE: FORMATION OF AN OXIDISED-ANTHRACENE 1 : 1 COMPLEX

The reaction of C₆₀F₂₀ (“Saturnene”) with anthracene yields a white 1 : 1 cycloadduct (1) in which two oxygen atoms have inserted into the anthracene framework due to fullerene-catalysed oxidation; the ¹⁹F NMR spectrum of the product shows evidence of through-cage homoconjugation.