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The head and wake waves of filtration combustion of calcium hydride in a flow of a mixture of silicon tetrafluoride and hydrogen at silicon tetrafluoride weight fractions of 0.8, 0.85, 0.9, and 0.98 were studied. The spatial profiles of the combustion waves were constructed. With their aid, the thermal structure of the head and wake waves was found, and the width of each zone in the combustion wave for different compositions of the gas phase was determined. With increasing concentration of the reagent gas in the flow, the reaction zone width increases in the head wave and decreases in the wake wave. The structure of the head wave corresponds to the intermediate combustion wave, and the structure of the wake wave, to the normal combustion wave.

The dependence has been investigated of the maximum temperature in the reaction front, the linear velocity of the combustion wave of CaH2 in a mixture of gases SiF4 and H2 with the formation of SiH4, and the conversion of calcium hydride on the initial mass concentration of silicon tetrafluoride. The experimental data have been obtained in a vertical flow reactor with forced gas filtration in the range of SiF4 mass fractions of 0.7–0.98. The results of the experiment have been compared with the data of calculation according to the classical physical and mathematical model of the exothermic reaction wave propagation in a porous medium during gas blowing. The similarities and differences have been established between the experimental and calculated values of the maximum temperature in the reaction front, the linear velocity of the combustion wave propagation, and the conversion of the solid-phase reagent.

In order to study the isotopic effects in semiconductor materials, single crystals of high chemical and isotopic purity are required. The reliability of the obtained data on the magnitude and the direction of isotopic shifts depends on the accuracy of determining the concentration of all stable isotopes. In the isotopic analysis of enriched “silicon-28” with a high degree of enrichment ( 99.99%), it is necessary to determine the impurities of 29Si and 30Si isotopes at the level of 10-3 ¸ 10-5 at. %. At this concentration level, these isotopes can be considered as impurities. It is difficult to achieve high measurement accuracy with simultaneous registration of the main and “impurity” isotopes in such a wide range of concentrations. The registration of analytical signals of silicon isotopes must be carried out in the solutions with different matrix concentrations. The use of the solutions with the high concentration of the matrix element requires the introduction of corrections for matrix noise and the drift of the instrument sensitivity during the measurement. It is possible to reduce the influence of the irreversible non-spectral interference and sensitivity drift by using the method of internal standardization. The inconsistency of the literature data on the selection criteria for the internal standard required studying the behavior of the signals of the “candidates for the internal standard” for the ELEMENT 2 single-collector high-resolution inductively coupled plasma mass spectrometer on the matrix element concentration and the nature of the solvent, as well as on the solution nebulizing time. Accounting for the irreversible non-spectral matrix noise and instrumental drift in isotopic analysis of enriched “silicon-28” and initial 28SiF4 by inductively coupled plasma mass spectrometry had allowed us to reduce by 3-5 times the random component and by more than an order of magnitude the systematic component of the measurement error in comparison with the external standard method. This made it possible to carry out, with sufficient accuracy, the operational control of the isotopic composition of enriched “silicon-28”, both in the form of silicon tetrafluoride and polycrystalline silicon obtained from it, using a single serial device in the range of isotopic concentrations 0.0001–99.999%.Key words: high-resolution inductively coupled plasma mass spectrometry, isotope analysis, isotopically enriched silicon, internal standard DOI: http://dx.doi.org/10.15826/analitika.2021.25.2.009P.A. Otopkova, A.M. Potapov, A.I. Suchkov, A.D. Bulanov, A.Yu. Lashkov G.G. Devyatykh Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences (IChHPS RAS), 49 Tropinina St., Nizhny Novgorod, 603951, Russian Federation, Для изучения изотопических эффектов в полупроводниковых материалах требуются монокристаллы с высокой химической и изотопной чистотой. Надежность полученных данных о величине и направлении изотопических сдвигов зависит от точности определения концентрации всех стабильных изотопов. При изотопном анализе обогащенного “кремния-28” с высокой степенью обогащения (более 99.99 %) необходимо определять примеси изотопов 29Si и 30Si на уровне 10-3 ¸ 10-5 ат. %. На таком уровне концентраций указанные изотопы можно рассматривать как примеси. Достижение высокой точности измерений при одновременной регистрации основного и “примесных” изотопов в таком широком интервале концентраций затруднительно. Регистрацию аналитических сигналов изотопов кремния приходится проводить на растворах с разной концентрацией матрицы. Использование растворов с высокой концентрацией матричного элемента требует введения поправок на матричные помехи и дрейф чувствительности прибора в процессе измерения. Снизить влияние необратимых неспектральных помех и дрейфа чувствительности можно при использовании метода внутренней стандартизации. Противоречивость литературных данных о критериях выбора внутреннего стандарта потребовала исследования поведения сигналов элементов “кандидатов во внутренний стандарт“ для одноколлекторного масс-спектрометра высокого разрешения с индуктивно связанной плазмой ELEMENT 2 от концентрации матричного элемента и природы растворителя, а также от времени распыления раствора. Учет необратимых неспектральных матричных помех и аппаратного дрейфа при изотопном анализе обогащенного “кремния-28” и исходного 28SiF4 методом масс-спектрометрии с индуктивно связанной плазмой позволил снизить в 3-5 раз случайную составляющую и более чем на порядок систематическую составляющую погрешности измерения по сравнению с методом внешнего стандарта. Это позволило проводить с достаточной точностью оперативный контроль изотопного состава обогащенного “кремния-28”, как в виде тетрафторида кремния, так и получаемого из него поликристаллического кремния с помощью одного серийного прибора в интервале изотопных концентраций 0.0001–99.999 ат. %.Ключевые слова: масс-спектрометрия высокого разрешения с индуктивно связанной плазмой, изотопный анализ, изотопнообогащенный кремний, внутренний стандартDOI: http://dx.doi.org/10.15826/analitika.2021.25.2.009

The impurity composition of natural and isotopically enriched silane obtained from magnesium silicide and silicon tetrafluoride is studied by gas chromatography–mass-spectrometry. The impurities characteristic of silane with natural and isotopically enriched composition are atmospheric gases; carbon dioxide; hydrides; saturated, unsaturated, and aromatic hydrocarbons; halogenated hydrocarbons; alkyl derivatives and silane homologues, siloxanes. The impurity content of high-purity silane does not exceed 10–7–10–5 mol % After synthesis, the concentrations of impurities in the silane and fractions isolated by its distillation purification lie in the range n × 10–6 − n × 10 mol % The limits of detection for impurities are 1 × 10–8–9 × 10–4 mol %

High-purity isotopically enriched germanium has been prepared by a hydride method, and the main factors capable of reducing the germanium yield in the monogermane pyrolysis process have been identified. To raise the germanium yield, we have optimized pyrolysis conditions in a laboratory-scale flow apparatus. At a monogermane flow rate at the reactor inlet of 30 mL/min, the optimal monogermane decomposition temperature is 420–450°C. Such conditions ensure a decomposition rate of ~6 g/h and a high product yield and make it possible to obtain most of the germanium in polycrystalline form. Using isotopically enriched monogermane pyrolysis, we have obtained high-purity isotopically enriched germanium samples in the form of polycrystalline ingots with a yield above 95%. The ingots are n-type and range in resistivity from 25 to 50 Ω cm. The content of regulated impurities in the 72Ge-,73Ge-, 74Ge-, and 76Ge-enriched germanium ingots thus prepared does not exceed 0.01 to 1 ppm by weight.

A procedure is described for determining the isotopic composition of highly enriched silicon as elementary 28Si and initial 28SiF4 by a single collector double focusing sector field ICP MS over a wide range of isotope concentrations (more than 6 orders of magnitude). To expand the range of measured isotopic concentrations, the signals of the main and “impurity” isotopes were recorded in solutions of different concentrations. The determination of the matrix effects and mass discrimination factors was carried out using the isotopic dilution method. This procedure allowed us to reach the uncertainty of measuring the concentration of the main isotope of ten thousandths of a percent in enriching >99.999% on a high-resolution single-collector inductively coupled plasma mass spectrometer.

This paper presents a mathematical model for the ultrapurification of substances via distillation in a closed vaporization–condensation system, where vapor condenses on a flowing down liquid film. We jointly analyze the mechanisms behind vaporization, vapor transport, condensation, condensate motion, and impurity diffusion in vaporizing liquid. Examining the removal of cobalt impurities from iron pentacarbonyl as an example, we assess the degree of purification as a function of vaporization and condensation temperatures, vaporization area, the fraction of liquid vaporized, and the radius and height of the condensation tube. Using experimentally determined temperature-dependent effective separation coefficients and the mathematical model, we find diffusion coefficients and equilibrium separation coefficients of cobalt, tungsten, and chromium impurities in iron pentacarbonyl.

Chromatography-mass-spectrometry was used to examine the stability of admixtures of C1−C7 hydrocarbons, fluorine and chlorinated derivatives of hydrocarbons, alkyl derivatives of silane, homologs of monosilane, and siloxanes in monosilane in its storage in molybdenum-glass ampules and stainless-steel cylinders. It was found that, in the case of storage in glass ampules, the concentration of ethylene and tetrafluoroethylene admixtures decreases and that of ethyl silane and disilane increases. When monosilane is stored in a stainless steel cylinder, the concentration of the acetylene admixture it contains changes.

It is for the first time that the method of gas chromatography was used for the determination of silicon fluoride-chlorides SiСl n F 4-n ( n = 0 ÷ 4) which are the initial, intermediate and final substances while producing silicon tetrachloride from silicon tetrachloride and aluminum chloride (III). The analysis of samples taken during this reaction was carried out using the "Tsvet - 800" gas chromatographer. The samples were injected into the instrument using a vacuum dosing system. To separate the components, a chromatographic column made of molybdenum glass with a length of 5 m and an internal diameter of 3 mm was used. It was filled with a Chromatone N-AW-HMDS (grain size 0.250-0.315 mm) with 15% methylsilicon elastoplastic E-301. The registration of silicon fluoride-chlorides was implemented using a thermal conductivity detector. The identification of SiF 4 and SiCl 4 in the mixture was conducted by comparing the times of holding the chromatographic peaks with the times of holding these individual substances. The times of holding not available for SiClF 3 , SiCl 2 F 2 , SiCl 3 F in the individual states were determined using the dependence of the logarithm of the corrected holding time on their molecular mass. The concentrations of silicon fluoride-chlorides were determined using the internal normalization method. The data were obtained on the changes in the concentrations of these substances during the synthesis of silicon tetrachloride. The confirmation of the correctness of the analysis results was made using the method of varying the size of the sample. Key words: silicon fluoride-chlorides, gas chromatography, identification, calibration factor, correctness (Russian) DOI: http://dx.doi.org/10.15826/analitika.2019.23.4.011 Т .G. Sorochkina, О .Yu. Chernova, О .Yu. Troshin, А .Yu. Sozin, А .D. Bulanov, А . А . Ermakov G.G. Devyatykh Institute of Chemistry of High-Purity Substances of the Russian Academy of Sciences, ul. Tropinina 49, Nizhny Novgorod, 603950, Russian Federation

The spectra of germane enriched up to 99.9 % of 73GeH4 were recorded with a high resolution (0.003 cm − 1 ) at different pressures with the Bruker IFS 125HR Fourier transform spectrometer (Nizhny Novgorod, Russia) in the region of 650–4400 cm − 1 and analyzed in the Dyad and Pentad region. The 9208 transitions belonging to the seven “cold” bands (6987 transitions) of the Dyad and Pentad and to the nine “hot” Dyad–Pentad bands (2221 transitions) were assigned and theoretically analysed in the frame of the effective Hamiltonian model. The obtained set of 68 fitted parameters reproduces the initial 9208 experimental line positions with the d r m s = 2.82 × 10 − 4 cm − 1 .

An international comparison study on the accurate determination of the molar mass M(Si) of silicon artificially enriched in 28Si (x(28Si) > 0.9999 mol mol−1) has been completed. The measurements were part of the high level CCQM-P160 pilot study assessing the ability of National Metrology Institutes (NMIs) and Designated Institutes (DIs) to make such measurements at the lowest possible levels of measurement uncertainty and to identify possible difficulties when measuring this kind of sample. This study supports the molar mass measurements critical to disseminating the silicon route to realizing the new definitions for the kilogram and the mole. Measurements were also made by one external research institute and an external company. The different institutes were free to choose their experimental (mass spectrometric) set-ups and equipment, thereby enabling also the comparison of different techniques. The investigated material was a chemically pure, polycrystalline silicon material. The subsequent modified single crystalline secondary product of this material was intended for the production of silicon which was used for two additional spheres in the context of the redetermination of the Avogadro constant NA, required for the revision of the International System of Units (SI) via fundamental constants which came into force from May 2019. The CCQM pilot study was organized by Physikalisch-Technische Bundesanstalt (PTB). Aqueous silicon solutions were shipped to all participating institutions. The data analysis as well as the uncertainty modelling and calculation of the results was predefined. The participants were provided with an uncertainty budget as a GUM Workbench® file as well as a free software license for the duration of the comparison. The agreement of the values of the molar mass (M(Si) = 27.976 942 577 g mol−1) was excellent with ten out of 11 results reported within the range of relative uncertainty of 1 × 10−8 required for the revision of the SI.

This paper examines sources of carbon impurities in polycrystalline monoisotopic 28Si prepared by a hydride method. Analytical data on the concentrations of carbon-containing impurities in volatile silicon compounds (28SiH4 and 28SiH4), process gases (Ar and H2), and polycrystalline 28Si are used to identify the major sources of carbon in the polycrystalline 28Si prepared by the hydride method. These are the starting 28SiH4 and calcium hydride used in 28SiH4 conversion into 28SiH4. The rate of carbon intake into polycrystalline silicon from the apparatus material during the monosilane pyrolysis process does not exceed 9 × 1011 cm–2 h–1. Polycrystalline silicon has been precipitated from monosilane with different concentrations of hydrocarbon impurities. At hydrocarbon concentrations in the range 10–4 to 10–3 mol %, the carbon concentration in the monosilane correlates with that in the silicon obtained from it. High-purity monosilane has been used to prepare polycrystalline 28Si samples with concentrations of carbon impurities in the range (0.8–2.3) × 1015 cm–3. Based on calculations of the carbon impurity distribution along the length of a zone-refined ingot, we examine the effect of the initial carbon concentration in the starting polycrystal on the yield of single-crystal monoisotopic 28Si. Requirements are formulated for the carbon concentration in polycrystalline 28Si which ensure a high yield of single crystals with parameters suitable for metrological applications.

Using iron pentacarbonyl distillation as an example, we analyze the vaporization process in a closed vaporization–condensation system where vapor condenses on a flowing down liquid film. We jointly analyze the mechanisms behind vaporization, vapor transport, condensation, and flowing of the condensate on the inner surface of a vertical tube. We calculate the thickness of the flowing down liquid film, determine the vaporization coefficient for a closed system using experimentally determined temperature dependences of the vaporization rate and saturated vapor pressure, and present the vaporization rate as a function of the vaporization and condensation temperatures, the radius and height of the condensation tube, and the vaporization area of the still residue.

The vapor–liquid separation factors of SiCl4–A (A = SiCl4–nFn (n = 1–4) silicon fluorochloride impurities in silicon tetrachloride have been determined experimentally at 298 K by statically balancing phases. The values obtained for the SiCl4–SiCl3F, SiCl4–SiCl2F2, SiCl4–SiClF3, and SiCl4–SiF4 systems are 4.9 ± 0.8, 8.2 ± 1.2, 29.8 ± 6.1, and 42.0 ± 7.5, respectively. In the SiCl4–SiCl3F system, the vapor–liquid separation factor has also been determined by the Rayleigh distillation method: α = 5.0. The experimental data agree with the vapor–liquid separation factors estimated in conformal solution theory using parameters of the Lennard- Jones potential.

Some features of atmospheric-pressure radiofrequency (13.56 MHz) arc discharge and its use for obtaining bulk samples of isotope-enriched silicon carbide via the reaction between SiF4 and methane in a hydrogen medium have been considered. It has been shown that power in this type of discharge is released mainly in the near-electrode regions. The deposition of silicon and graphite occurs in a layer-by-layer mode, so that the product carbide contains up to 40% free carbon; therefore, the process requires optimization. At the same time, the proposed type of RF arc discharge with the product deposition zone localized at the ends of the electrodes makes it possible to avoid not only additional heating of the reactor space and walls, but also the loss of expensive isotope-enriched silicon fluoride.

The impurity composition of 28SiF4 has been studied for the first time by gas chromatography/mass spectrometry using gas-adsorption capillary columns. For identification and determination of impurity substances by gas chromatography/mass spectrometry, we have proposed using cryogenic preconcentration of the impurities from 28SiF4. The presence of C2–C4 hydrocarbon impurities and sulfur hexafluoride has been confirmed. We have identified 35 impurity substances in 28SiF4, including linear and branched C5–C8 saturated hydrocarbons, aromatic hydrocarbons, chlorine- and fluorine-containing hydrocarbons, and silicon- and sulfur-containing substances, of which 28 have been detected for the first time.

Volatile impurities have been removed from iron pentacarbonyl of natural isotopic composition by vacuum pumping. We have examined the behavior of impurities in the course of fractional distillation of iron pentacarbonyl. As a result of simple distillation, we have obtained an iron pentacarbonyl sample containing on the order of 10–4 mol % C3–C6 hydrocarbon impurities, 10–3 mol % C7–C8 hydrocarbons, and 10–8 to 10–6 wt % metallic impurities. We have estimated the effective separation factor at a distillation rate of 0.021 kg/(m2 s) for a number of impurities in Fe(CO)5.

A metrological challenge is currently underway to replace the present definition of the kilogram. One prerequisite for this is that the Avogadro constant, N A, which defines the number of atoms in a mole, needs to be determined with a relative uncertainty of better than 2 × 10−8. The method applied in this case is based on the x-ray crystal density experiment using silicon crystals. The first attempt, in which silicon of natural isotopic composition was used, failed. The solution chosen subsequently was the usage of silicon highly enriched in 28Si from Russia. First, this paper reviews previous efforts from the very first beginnings to an international collaboration with the goal of producing a 28Si single crystal with a mass of 5 kg, an enrichment greater than 0.9999 and of sufficient chemical purity. Then the paper describes the activities of a follow-up project, conducted by PTB, to produce a new generation of highly enriched silicon in order to demonstrate the quasi-industrial and reliable production of more than 12 kg of the 28Si material with enrichments of five nines. The intention of this project is also to show the availability of 28Si single crystals as a guarantee for the future realisation of the redefined kilogram.

The impurity composition of 28SiH4, 29SiH4, and 30SiH4 silanes and 72GeH4, 73GeH4, 74GeH4, and 76GeH4 germanes isotopically enriched to above 99.9 at % has been studied by gas chromatography/mass spectrometry using capillary adsorption columns. Impurities have been identified by comparing their mass spectra with NIST data and information available in the literature, and by inferring their structure from fragment ions and retention times. We have identified 53 impurity substances in silanes and 42 in germanes: permanent gases; saturated, unsaturated, halogen-containing, and aromatic C1–C9 hydrocarbons; their homologues; alkyl derivatives of silane and germane; chlorogermane; siloxanes; fluorosiloxanes; sulfur compounds; and dioxane. The silicon- and germanium-containing impurities have been shown to be isotopically enriched, as the major component. The detection limits of the impurities are 5 × 10–8 to 3 × 10–5 vol %, comparing well with the best results in the literature.

We have studied reaction between silicon tetrafluoride and calcium hydride in a vertical flow reactor, which proceeds as combustion in filtration mode. The principal kinetic characteristics of the reaction between SiF4 and CaH2 in a counterpropagating wave have been determined: reaction order n = 1, rate constant k = 0.38 ± 0.05 s–1, and activation energy Ea = 17 ± 2 kJ/mol.

A possibility of using inductively-coupled plasma high-resolution mass spectrometry for the isotope analysis of monogermanes enriched with isotopes 72, 73, 74, and 76 has been studied. The effects of isobaric and polyatomic interferences in the spectrum of germanium isotopes have been discussed. It has been shown that the signal intensities of i GeH+ ions formed in the inductively coupled plasma are 0.00001–0.0001 of the intensity of the i Ge+ signal. This can result in the overestimation of the found concentration of an isotope with a higher mass number next to the main isotope in recording spectra in the low and medium resolution mode. Approaches ensuring the determination of the isotope composition of highly-enriched monogermanes with the range of isotope concentrations extending five orders of magnitude have been proposed.

Silicon-based quantum bits with electron spins in quantum dots or nuclear spins on dopants are serious contenders in the race for quantum computation. Added to process integration maturity, the lack of nuclear spins in the most abundant $^{28}$silicon isotope host crystal for qubits is a major asset for this silicon quantum technology. We have grown $^{28}$silicon epitaxial layers (epilayers) with an isotopic purity greater than 99.992 % on 300mm natural abundance silicon crystals. The quality of the mono-crystalline isotopically purified epilayer conforms to the same drastic quality requirements as the natural epilayers used in our pre-industrial CMOS facility. The isotopically purified substrates are now ready for the fabrication of silicon qubits using a state-of-the-art 300 mm Si CMOS-foundries equipment and processes, Comment: 7 pages, 7 figures

The liquid–vapor separation factors in dilute solutions of methane, ethane, propane, n-butane, and isobutane in germanium tetrafluoride have been determined experimentally at 295 K by statically balancing phases. The measured temperature-dependent saturated vapor pressure over liquid germanium tetrafluoride in the range 260–300 K can be represented by the Antoine equation: log P (atm) = 5.2–1200/T. We have calculated the enthalpies of vaporization and fusion of germanium tetrafluoride:ΔH v 0= 22.9 kJ/mol and ΔH m 0(GeF4) = 8.0 kJ/mol.

The spectra of germane 72GeH4 and 73GeH4 enriched up to 99.9 % were recorded with high resolution (0.003 cm − 1 ) at different pressures with the Bruker IFS 125HR Fourier transform spectrometer (Nizhny Novgorod, Russia). The region of 4020–4260 cm − 1 , where the 2ν1(A1) and ν 1 + ν 3 ( F 2 ) bands are located, was theoretically analyzed. The 2025 and 1774 transitions with J max = 21 were assigned to these bands of the 72GeH4 and 73GeH4 species. Rotational, centrifugal distortion, tetrahedral splitting, and interaction parameters of the (2000, A1) and (1010, F2) vibrational states were determined from the fit of experimental line positions of both isotopologues. The obtained sets of 13/13 fitted parameters reproduce the initial 2025/1774 experimental line positions with a d rms = 2.9 × 10 − 4 cm − 1 and d rms = 2.7 × 10 − 4 cm − 1 (for 72GeH4 and 73GeH4, respectively).

The results of the precise measurement of the refractive index of stable germanium isotopes Ge72, Ge73, Ge74, and Ge76 single crystals with high enrichment and a germanium single-crystal Genat of natural isotopic composition with the Fourier-transform interference refractometry method from 1.94 to 20 μm with 0.1 cm−1 resolution and accuracy of 2×10−5 to 1×10−4 are shown. The content of 72 impurities measured by the mass spectrometric method was below 10−5–10−6 wt. %. Oxygen and carbon concentrations measured by IR spectroscopy in all crystals are within 5×1015 cm−3. All germanium crystals have a hole conductivity with specific electric resistivity of 45–50 Ohm×cm. The coefficients of the generalized Cauchy dispersion function approximating the experimental refractive index values all over the measuring range are given. The transmission and Raman spectra are also given.

We presented the results on the preparation of high-purity monoisotopic varieties of silicon and germanium. The process involves the separation of isotopes in the form of SiF4 and GeH4 by centrifugation, ultrapurification of volatile compounds, and preparation of poly and single crystals. The attained degree of isotopic and chemical purities of single crystals obtained was shown. The content of the main isotope in the single crystals of 28Si is >99.99% and those in the single crystals of 29Si and 30Si are >99.9%. The specific resistivity of the 28Si single crystals is ∼1 kOhm cm and those of 29Si and 30Si are about 100–150 Ohm cm. The samples of the 76Ge single crystals have the main isotope content of >88 at.% and the difference concentration of electrochemically active impurities of 5·1010 cm−3. The main isotope content in the 74Ge polycrystal is 99.93 at.%. The optical and thermophysical properties of the isotope-enriched silicon and germanium single crystals were measured, which suggest a significant effect of the isopotic composition on thermal capacity, thermal conductivity, luminiscence, and light absorption.

IR absorption spectra of monoisotopic 28SiH4 and 76GeH4 are studied in Ar and N2 matrices at 10 K. It is shown that the absorption spectra of silane and germane are similar in the regions of the stretching ν3 and bending ν4 vibrations. Four groups of bands can be separated out in the spectra of each molecule: (1) narrow bands characteristic of the matrix isolation studies, (2) broad bands, (3) diffuse absorption with a large value of the spectral moment M 2 * the intensity of which increases upon annealing, and (4) bands of dimers the intensity of which increases quadratically with concentration. The spectra of 28SiH4 and 76GeH4 in nitrogen matrices contain a triplet in the stretching region and a doublet in the bending region, which is explained by the change in the molecular symmetry from T d to C 3V on passage from the gas phase to solid nitrogen.

Using high-resolution Fourier-transform IR spectroscopy and gas chromatography, we have identified more than 20 impurity species, in concentrations from 10−1 to 10−5 vol %, in GeF4 samples of different isotopic compositions. The germanium tetrafluoride samples are shown to contain C1–C4 hydrocarbons; hydrogen, carbon, silicon, and sulfur fluorides; fluorogermanes; fluorosilanes; and carbon and nitrogen oxides.

Possibility of performing a mechanically activated synthesis of pure monosilane by the reaction of calcium hydride with silicon tetrafluoride in a rotating flow-through reactor containing milling bodies was analyzed. A number of operation parameters of the grinding reactor were theoretically evaluated and experimentally determined.

We have recently shown that the dramatic reduction in linewidth of many deep luminescence centers in highly enriched 28 Si can lead to the observation of isotopic fingerprints, revealing not only that a specific element is involved in the defect complex, but also the number of atoms of that element. This has led to many surprises regarding the actual constituents of supposedly well known luminescence centers, as well as the discovery of new members of a family of four-atom centers where the constituents can be chosen from Cu, Ag, Au and Li. Obtaining the isotopic fingerprint of Au is problematic, since only 197 Au is stable, but we have now used the relatively long-lived 195 Au to reveal the presence, and the number, of Au atoms in several of these centers. We find a series of four-atom centers containing one Au plus Cu and/or Li. Surprisingly, the Au isotopic fingerprint also reveals a series of five-atom centers containing a single Au plus Cu and/or Li. Further evidence for the ubiquity of these four- and five-atom defects is provided by two previously observed Pt-related centers, with luminescence at 884 and 777 meV, which are present in these samples due to the decay of 195 Au to 195 Pt. In addition to Pt, these centers are found to contain three and four Cu atoms, respectively.

The current status of the problem of obtaining high-purity silicon isotopes 28Si, 29Si, and 30Si is analyzed. The scheme of obtaining monoisotopic silicon includes the stages of isotope separation in the form SiF4, synthesis and deep purification of isotopically enriched silane, obtaining polycrystalline silicon-28,-29, and-30, and growing monocrystals. The basic problems and methods of their solution in the synthesis and deep purification of silane and obtaining poly-and monocrystals of isotopically enriched silicon are discussed. Data characterizing the achieved level of chemical and isotopic purity of high-purity monocrystals of silicon-28 with a main isotope content of more than 99.99% and silicon-29 and silicon-30 with isotopic purity higher than 99% are presented. In monocrystalline 28Si, the boron content was 4.5 × 1013, the phosphorus content was 5 × 1011, the carbon and oxygen contents were

The synthesis of silane by reacting silicon tetrafluoride and calcium hydride is shown to proceed as a propagating wave. The main parameters of the process, namely, the propagation velocity, the reaction front temperature, and calcium conversion, are determined. The mathematical model of wave propagation for an exothermic reaction in a porous medium with purging a gaseous oxidant describes qualitatively the major laws of the process.

We present a study of excitons bound to sulphur- and copper-related isoelectronic centres in highly enriched 28Si. The S-related centre, which has been shown to have two configurations, SA and SB, was believed to consist of a substitutional sulphur atom paired with an interstitial copper atom. High resolution photoluminescence (PL) emissions from the no-phonon S B 0 transition reveal fine structure not observable in natural silicon. In both 28Si:natS and 28Si:34S, low temperature PL reveals at least 18 distinct components of the S B 0 system, including a triplet splitting seen in natSi:natS by optical detection of magnetic resonance. Investigation of the effect of copper isotopic composition on the S B 0 system shows that the centre contains at least three copper atoms. We also present results of the copper isotope effect on the 943.7 meV *Cu00 system in 28Si and show that three Cu atoms contribute to the Cu isotope shift of *Cu00.

The chalcogen deep double donor sulfur (S) has been studied extensively with optical methods in natural silicon ( Si nat ) . Recently, it was shown that the spectroscopic linewidths of absorption transitions from shallow impurities like boron and phosphorus is limited by inhomogeneous broadening due to a Si isotope effect which is removed with the use of highly enriched 28Si. In this work we extend these results to deep centers and show that the true homogeneous linewidths of many transitions can only be revealed in isotopically enriched Si. The S + 1 s ( T 2 ) Γ 7 transition exhibits a full width at half maximum (FWHM) of only 0.008 cm - 1 in 28Si—more than one order of magnitude sharper than in Si nat , and substantially narrower than the sharpest transitions of B and P in 28Si. Hence, it is the narrowest absorption line ever seen for impurity states in semiconductors. We also report dramatically narrower absorption transitions for the neutral S 0 center, together with higher excited states than previously observed. The isotope shifts of S absorption transitions between Si nat , 28Si and 30Si are also reported.

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.

Electron spin resonance (ESR) is used to study the neutron transmutation doping of silicon crystals enriched with 30Si isotope: phosphorus donors and radiation defects produced in the course of transmutational doping are observed. The ESR signals related to the phosphorus uncontrolled impurity in 30Si before transmutational doping (the P concentration is ∼1015 cm−3) and phosphorus introduced by neutron irradiation with doses ∼1 × 1019 cm−2 and ∼1 × 1020 cm−2 (the P concentrations are ∼5 × 1016 and ∼7 × 1017 cm−3, respectively) are studied. As a result of drastic narrowing of the phosphorus ESR lines in 30Si, the intensity of lines increased appreciably, which made it possible to measure the phosphorus concentration in the samples with a small volume (down to 10−6 mm−3). The methods for determining the concentration of P donors from hyperfine structure in the ESR spectra of isolated P atoms, exchange-related pairs, and clusters that consist of three, four, and more P donors are developed. In the region of high concentrations of P donors, in which case the hyperfine structure disappears, the concentration of P donors was estimated from the exchange-narrowed ESR line.

Phosphorus-doped silicon 30Si monoisotope samples with a highly homogeneous impurity distribution at a concentration of 5 × 1016 cm−3 were obtained for the first time by means of neutron transmutation doping.

The medical-preventive administration of ginseng and eleutherococcus was studied on sub-acute carbon tetrachloride-induced mice liver injury under exhaustive physical activity. The ability of these drugs to reduce CCL4-induced decrease in health expectancy indicator of swimming mice with 7% of the cargo was identified. In this study eleutherococcus and ginseng mostly showed protective effect against a physical endurance than the comparison drug, karsil. To assess the content of glycogen in the liver tissue was carried out histo-chemical study by PAS-reaction. The ranges of reduced glycogen have pale pink color on micrographs, unlike hepatocytes with normal glycogen having deeply stained reddish color that the more intensively, the greater the amount of glycogen contained in the hepatocyte. In all groups of experimental animals treated with CCL4, is uneven loss of glycogen by hepatocytes, which correlates with the data on the mechanism of hepatotoxicity of carbon tetrachloride. There was a significant effect of the phytoadaptogens of the distribution of glycogen under these experimental conditions. This effect may be related to the hepato-protective effect of the drugs, as well as the previously identified ability phyto-adaptogens optimize bioenergetic processes during physical exercises.

The impurity contents of different silicon tetrafluoride samples (isotopically unmodified and enriched) are determined by optical emission spectroscopy with the preconcentration of nonvolatile impurities by distilling off SiF4 .

We report the successful isotope separation and bulk single crystal growth of 29Si and 30Si stable isotopes. The isotopic enrichments of the 29Si and 30Si single crystals determined by mass spectrometry are 99.23% and 99.74%, respectively. Both crystals have the electrically active net-impurity concentration less than 1015 cm-3. Thanks to the result of this work and the 28Si crystals we grew previously, high quality single crystals of every stable Si isotope (28Si, 29Si, and 30Si) have been made available for a wide variety of basic research and industrial applications.

Silicon tetrafluoride was obtained by the thermal decomposition of pure-grade sodium hexafluorosilicate and purified by low-temperature distillation. Next, SiF4 was 28Si-enriched by centrifugation and converted to silane by calcium hydride reduction. To remove hydrocarbons, the silane was distilled.

Hydrocarbon impurities in silicon tetrafluoride originate from the sodium hexafluorosilicate used as a precursor for the preparation of SiF4 through the thermal decomposition of Na2SiF6. We have studied the fraction of C1–C4 hydrocarbons released as a function of temperature during the thermal decomposition of sodium hexafluorosilicate. The lighter hydrocarbons—methane, ethane, and ethylene—are shown to be released at lower temperatures. One source of hydrocarbon impurities in sodium hexafluorosilicate is the sodium carbonate used to prepare it.

The possibility of the reduction of hexafluorodisiloxane by calcium hydride in the synthesis of silane from silicon tetrafluoride has been studied. This reaction is shown to be not decisive for oxygen contamination of silane. The most likely reason for the appearance of impurity Si2OH6 in “fluoride” silane is the Ca(OH)2-catalyzed reaction of silane with trace water. The concentration of impurity Si2OH6 in silane at the stage of synthesis may be efficiently decreased by the preliminary purging of calcium hydride with a hydrogen (grade A) flow.

We presented the results on the preparation of high-purity monoisotopic varieties of silicon and germanium. The process involves the separation of isotopes in the form of SiF4 and GeH4 by centrifugation, ultrapurification of volatile compounds, and preparation of poly and single crystals. The attained degree of isotopic and chemical purities of single crystals obtained was shown. The content of the main isotope in the single crystals of 28Si is >99.99% and those in the single crystals of 29Si and 30Si are >99.9%. The specific resistivity of the 28Si single crystals is ∼1 kOhm cm and those of 29Si and 30Si are about 100–150 Ohm cm. The samples of the 76Ge single crystals have the main isotope content of >88 at.% and the difference concentration of electrochemically active impurities of 5·1010 cm−3. The main isotope content in the 74Ge polycrystal is 99.93 at.%. The optical and thermophysical properties of the isotope-enriched silicon and germanium single crystals were measured, which suggest a significant effect of the isopotic composition on thermal capacity, thermal conductivity, luminiscence, and light absorption.