A. V. Gusev

Refractive index spectral dependence, Raman spectra, and transmission spectra of high-purity Si28, Si29, Si30, and Sinat single crystals

Precise measurement of the refractive index of stable silicon isotopes Si, Si, Si single crystals with enrichments above 99.9 at.% and a silicon single crystal Si of natural isotopic composition is performed with the Fourier-transform interference refractometry method from 1.06 to more than 80 μm with 0.1 cm resolution and accuracy of 2 × 10 . . . 1 × 10. The oxygen and carbon concentrations in all crystals are within 5 × 10 cm and the content of metal impurities is 10 . . . 10 at.%. The peculiar changes of the refractive index in the phonon absorption region of all silicon single crystals are shown. The coefficients of generalized Cauchy dispersion function approximating the experimental refractive index values all over the measuring range are given. The transmission and Raman spectra are also studied.We performed precise measurement of the refractive index of stable silicon isotopes 28Si, 29Si, and 30Si single crystals with enrichments above 99.9u2009at.% and a silicon single-crystal natSi of natural isotopic composition with the Fourier-transform interference refractometry method from 1.06 to more than 80u2009μm with 0.1u2009cm(-1) resolution and accuracy of 2×10(-5)…1×10(-4). The oxygen and carbon concentrations in all crystals are within 5×10(15)u2009cm(-3), and the content of the metal impurities is 10(-5)…10(-6)u2009at.%. The peculiar changes of the refractive index in the phonon absorption region of all silicon single crystals are shown. 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 studied.

Preparation of single-crystal 29Si

A process has been developed for the preparation of single-crystal 29Si from 29Si-enriched silane. A silicon single crystal has been grown with a 29Si content over 99.9 at %. The oxygen and carbon concentrations in the crystal are under 1 × 1016 cm−3, and its resistivity exceeds 1 kΩ cm.

Monoisotopic varieties of silicon and germanium with a high chemical and isotopic purity

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.

Determination of oxygen and carbon impurities in polycrystalline silicon by IR spectrometry

The possibility of using infrared spectrometry for the determination of the total oxygen and carbon impurity in polycrystalline silicon of the natural isotope composition and that enriched with the 28Si isotope was studied for samples synthesized by different methods. The results of determining these impurities by the optical method are compared to those obtained by independent methods of analysis. The conditions of IR spectrometric analysis of the silicon synthesized by deposition from the gas phase are determined. It is shown that, for IR spectrometry, the upper boundaries of the analytical range of oxygen and carbon in polycrystalline silicon are 1 × 1018 and 2 × 1018 cm−3; and the limits of their detection are 8 × 1015 and 5 × 1015 cm−3 at a sample thickness of 0.5 and 0.2 cm, respectively.

Multi-Decadal Oscillations of the Ocean Active Upper-Layer Heat Content

Spatial patterns in multi-decadal variability in upper ocean heat content for the last 60xa0years are examined using a numerical model developed at the Institute of Numerical Mathematics of Russia (INM Model) and sea water temperature-salinity data from the World Ocean Database (in: Levitus, NOAA Atlas NESDIS 66, U.S. Wash.: Gov. Printing Office, 2009). Both the model and the observational data show that the heat content of the Active Upper Layer (AUL) in particular regions of the Atlantic, Pacific and Southern oceans have experienced prominent simultaneous variations on multi-decadal (25–35xa0years) time scales. These variations are compared earlier revealed climatic alternations in the Northern Atlantic region during the last century (Byshev et al. in Doklady Earth Sci 438(2):887–892, 2011). We found that from the middle of 1970s to the end of 1990s the AUL heat content decreased in several oceanic regions, while the mean surface temperature increased on Northern Hemisphere continents according to IPCC (in: Stocker et al. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change, Cambridge University Press, Cambridge, 2013). This means that the climate-forcing effect of the ocean–atmosphere interaction in certain energy-active areas determines not only local climatic processes, but also have an influence on global-scale climate phenomena. Here we show that specific regional features of the AUL thermal structure are in a good agreement with climatic conditions on the adjacent continents. Further, the ocean AUL in the five distinctive regions identified in our study have resumed warming in the first decade of this century. By analogy inference from previous climate scenarios, this may signal the onset of more continental climate over mainlands.

Heat capacity of high-purity isotope-enriched germanium-76 in the temperature range of 2–15 K

The heat capacity of high-purity isotopically-enriched germanium Ge-76 has been measured in the range of 2.5–15 K. In this range, the heat capacity of Ge-76 is 6–15% higher than the heat capacity of germanium of the natural isotopic composition, which is determined by a change in the average mass.

Isotopic effects in the infrared absorption spectra of electrically active impurities in silicon 28, 29, and 30 with high isotopic enrichment

The results of studying the IR absorption spectra of shallow donors and acceptors in high-purity stable 28Si(99.99%), 29Si(99.92%), and 30Si(99.97%) isotope single crystals grown by the method of float zone melting were reported. The content of residual boron, phosphorus, and arsenic impurities in the studied single crystals was determined with a detection limit of 1 × 1012, 4 × 1011, and 1 × 1012 at./cm3, respectively. The results of the IR spectroscopic estimation of the content of shallow donors and acceptors were in good agreement with the data obtained from the Hall effect measurements for the concentration of free charge carriers. The parameters of the absorption lines of boron and phosphorus impurities in the single crystal of silicon isotopes were studied. The change in the isotope composition of silicon was shown to lead to the shift of the energy spectrum of shallow impurity sites towards higher energies with an increase in the atomic weight of an isotope.

Crucibles for Czochralski growth of isotopically enriched silicon single crystals

We have assessed isotope dilution during Czochralski growth of single crystals of stable silicon isotopes from crucibles of quartz glass of natural isotopic composition. A procedure has been developed for applying protective coatings from isotopically enriched silicon dioxide to crucibles. Comparison of the isotopic compositions of isotopically enriched polycrystalline silicon and 28Si, 29Si, and 30Si single crystals grown from it demonstrates that the use of protective coatings makes it possible to preclude isotope dilution in the crystal growth step.