Absorption Spectra of Single Crystals of EuGa2S4 and EuGa2S4:Co

The optical properties of EuGa₂S₄ and EuGa₂S₄:Co single crystals in a range of temperatures from 77 to 300 K are investigated. The single crystals are obtained by the Bridgman method and are characterized by tetragonal syngony. The behavior of the optical transitions in the photon energy range 1.70–2.45 eV and the temperature range 77–300 K is determined. It is established that in the energy range 1.77–1.90 eV absorption is associated with transitions of the Co²⁺ ion, while in the range 2.20–2.40 eV, with indirect allowed optical transitions.     

Electron spin lifetimes in Hg0.78Cd0.22 Te and InSb

We have made direct pump–probe measurements of spin lifetimes in long wavelength narrow-gap semiconductors at wavelengths between 4 and 10 μm and from 4 to 300 K. In particular, we measure remarkably long spin lifetimes, τ_s300 ps, even at 300 K for epilayers of degenerate n-type InSb. In this material the mobility is approximately constant between 77 and 300 K, and we find that τ_s is approximately constant in this temperature range. In order to determine the dominant spin relaxation mechanism we have investigated the temperature dependence of τ_s in non-degenerate lightly n-type Hg_0.78Cd_0.22Te of approximately the same band gap as InSb, and find that τ_s varies from 356 ps at 150 K to 24 ps at 300 K. Our results, both in magnitude and temperature dependence of τ_s, imply that the Elliott–Yafet model dominates in these materials.     

Infrared and Raman spectra of M2Cu2O5 (M=Y,Ho)

We report both Raman and infrared reflectivity spectra of M₂Cu₂O₅ (M=Y, Ho) at room temperature in the spectral range of 30–1000 cm^–1.37 (31) ir and 18 (15) Raman active modes of Y₂Cu₂O₅ (Ho₂Cu₂O₅) are observed. A factor group analysis has been performed to identify the symmetries of the observed modes. Comparing the vibrational spectra of these compounds we conclude that the phonons above 300 cm^–1 originate from the Cu–O vibrations and those under 300 cm^–1 from M–O vibrations.Alexander von Humboldt Foundation fellow     

Electrophysical and photoelectric properties of (CdSe)1−x(CuInSe2)x solid solutions

The results are given of measurements of the electrophysical properties in the interval of temperatures 300–900°K and of the photoelectric properties at 300°K of (CdSe)_1–x–(CuInSe₂)_x solid solutions. It is shown that the electrophysical and photoelectric properties of the solid solutions depend on the composition and temperature. The forbidden-band widths calculated from the temperature dependence of the conductivity and from the photoconductivity spectrum, respectively, vary from 1.68 and 1.77 eV for initial compound CdSe to 1.25 and 1.18 eV for the solid solution Cu_0.1Cd_0.9In_0.1Se_1.1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 41–43, January, 1992.     

Mechanism for the optical absorption of cadmium sulfide

The optical transmission and reflection spectra of polycrystalline cadmium sulfide films heated in sulfur vapor have been measured at 77 and 300 °K. The absorption coefficient of the film is calculated for the range 2.25–3.5 eV. Analysis of the spectral dependence of the absorption coefficient shows indirect optical transitions of an electron from the upper valence band to the conduction band in the range 2.31–2.54 eV and direct substitutional transitions in the range 2.58–3.45 eV. Superimposed on this intrinsic absorption is selective absorption due to superstoichiometric atoms.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, Vol. 12, No. 4, pp. 97–103, April, 1969.     

Studies of divacancy in Si using positron lifetime measurement

The charge state dependence of positron lifetime and trapping at divacancy (V₂) in Si doped with phosphorus or boron has been studied after 15 McV electron irradiation up to a fluence of 8.0×10¹⁷ e/cm². The positron trapping cross sections for V ₂ ^2– , V ₂ ^– and V ₂ ⁰ at 300 K were about 6×10^–14, 3×10^–14 and 0.1–3×10^–14 cm², respectively. For V ₂ ⁺ , however, no positron trapping was observed. The marked difference in the cross sections comes from Coulomb interaction between the positron and the charged divacancy. The trapping rates for V ₂ ⁰ and V ₂ ^2– have been found to increase with decreasing temperature in the temperature range of 10–300 K. These results are well interpreted by a two-stage trapping model having shallow levels with energy of 9 meV (V ₂ ⁰ ) and 21 meV (V ₂ ^2– ). The appearance of a shallow level for V ₂ ⁰ can not be explained by a conventional Rydberg state model. The lifetime (290–300 ps) in V ₂ ⁰ is nearly constant in the temperature range from 10 to 300 K, while that in V ₂ ^2– increases from 260 ps at 10 K to 320 ps at 300 K. The lifetime (260 ps) in V ₂ ^2– is shorter than that in V ₂ ⁰ at low temperature, which is due to the excess electron density in V ₂ ^2– . At high temperature, however, the longer lifetime of V ₂ ^2– than that of V ₂ ⁰ is attributed to lattice relaxation around V ₂ ^2– .     

Soft mode and far infrared spectra of ferroelectric lithium thallium tartrate at low temperatures

The far infrared spectra of lithium thallium tartrate single crystals have been studied for E//a and E//b at 300 K – 80 K and 5 K. A soft mode has been followed from 21 to 11 cm^–1 giving strong evidence that the transition is displacive. A large birefringence is observed.     

Behavior of block boundaries during ultrasonic vibration in alkali halide crystals at temperatures 20–300°C

The behavior of block boundaries was investigated in alkali halide crystals of various orientations deformed by ultrasound at frequencies 40–73 kHz in the temperature interval 20–300°C. The specimen orientation was defined by the angle between the fourfold axis and the propagation direction of the ultrasonic wave. The initial stage of plastic deformation at room temperature is due to the generation of sources at the block boundaries in KCl and KBr, and by the heterogeneous nucleation of dislocation in NaCl and LiF. In the temperature interval 200–300°C, in NaCl and LiF dislocation multiplication begins already with the generation of sources at the block boundaries. In 30° orientation specimens the beginning of multiplication is preceded by the motion initiated by the ultrasound of sections of the block boundaries in the {1 0 0} <110> secondary glide system.Translated from Izvestiya Vysshika Uchebnykh Zavedenii, Fizika, No. 1, pp. 49–53, January, 1986.     

Characterization of Submillimeter Wave Absorbers from 200–600 GHz

This paper presents measurements of both specular and non-specular scattering from several submillimeter wave absorber materials designed for antenna testing and from low-cost carpet materials. The frequency range is 200–600 GHz in specular scattering, and 300–400 GHz in non-specular scattering measurements. The constructed bistatic test bench allows testing of the full continuous angular range of 0°–90°. The measurement results show large differences in performance of different materials. It is shown that reflectivities below –50 dB over limited angular ranges are possible with a correct alignment of the material. Also, low-cost carpet materials have lower than –15 dB reflectivities in most angles, and may be useful in non-critical parts of the antenna test range. The results can be used to optimise the absorber placement inside an antenna range, concerning both best performance and lowest cost.     

Nitride-based photodetectors: from visible to X-ray monitoring

The performance of nitride-based photodetectors is investigated beyond the usual near-UV (400–300 nm) and mid-UV (300–200 nm) operation ranges. The responses of metal–semiconductor–metal (MSM) photodiodes were analyzed in the vacuum–UV and soft X-ray regions. To interpret the results, the absorption properties and the attributes of each of the photons with energies for producing multiple electron–hole pairs were considered. The soft X-ray characterization showed that in-plane MSMs worked efficiently up to photon energies of 600 eV. Above this value, the absorption decrease makes the diffusion length and layer thickness become critical parameters for the detector behavior. To perform detection in the violet and near-UV, InGaN-based photoconductors were fabricated and spectrally characterized. The devices presented abrupt wavelength cut-offs, demonstrating that the InGaN compositional fluctuations were tolerable up to In contents of 10% for fabricating selective photodetectors. Back-face illumination allowed us to obtain bandpass detectors for these spectral ranges.     

Dielectric losses in CVD diamonds in the millimeter-wave range at temperatures 300–900 K

We study losses in different CVD diamonds in the frequency range 50–210 GHz at temperatures 300– 900 K by using a high-Q open Fabry-Perot cavity. It is found that the effective activation energies determining a sharp increase in losses at high temperatures are distributed in the range 0.4–0.8 eV. We propose a formula which relates the frequency and temperature dependences of losses for different CVD-diamond specimens in the first approximation. Suggestions on the nature of these losses are put forward.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 12, pp. 1087–1095, December, 2004.     

Charge transport and accumulation in liquid crystals

Charge carrier formation mechanisms in liquid crystals and their contribution to conductivity in the voltage range 0.1–10 V and field action times of 0–300 sec are compared. Values of accumulated charge are calculated corresponding to the processes of carrier separation within the volume, injection from the electrode, and molecular dissociation under electric field action.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 9–12, July, 1989.     

Dielectric materials for gyrotron output windows

The dielectric parameters of materials for gyrotron output windows measured in the range 65–300 GHz are given. The special attention is paid to the spread of values of the refractive index and loss tangent of dielectrics produced by different firms. The refractive index and loss tangent are measured for sapphire at the cryogenic temperatures and for boron nitride and silica glass at the temperatures 300–1000K.     

Electrical resistance and thermophysical properties of solid solutions of germanium in iron

Temperature dependence of thermal diffusivity, thermal conductivity, and electrical resistance is studied in solid solutions of germanium in iron at impurity concentrations of 0.49–18.0 at.% Ge over the temperature range 300–1300K. The results obtained are evaluated and compared to similar dependences for the system Fe-Si.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 36–41, June, 1984.     

Choice of the informative parts of the rotational raman spectrum when measuring gas temperatures in the range 300–1200°K

The question of choosing the most informative parts of the rotational Raman spectrum for purposes of temperature measurements is considered, and to this end relationships for calculating the theoretical accuracy of temperature determination are derived. The results of some practical calculations relating to the measurements of air temperature at 300–1200°K are presented.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 116–119, January, 1977.     

Experimental results on muon-catalyzed dt fusion

A comprehensive experimental study of the kinetics of muon-catalyzed dt fusion has been conducted at PSI, based on the measurement of the 14 MeV neutrons from the fusion process. The target conditions included densities from 1–150% of the atomic density of liquid hydrogen, relative tritium concentrations of 2–95%, and temperatures of 13–300 K. Information about the dt cycle has been obtained from the measured neutron time distributions by different methods: Monte Carlo simulations primarily aimed at investigating epithermal effects in molecular formation and the determination and interpretation of cycling rates describing the steady state regime.     

A study of the fine structure of steel 110G13L after high-velocity deformation

The fine structure of austenitic manganese steel after high-velocity deformation was studied by the methods of metallographic analysis, x-ray structural analysis, and transmission electron microscopic examination of foils. As the result of these investigations it was established that apart from the highly developed fine structure (the magnitude of the regions of coherent scattering reduced to 200–300 å, microdeformation increased to 3 ·10^–3–5 ·10^–3, density of dislocations increased to 10¹¹ g/cm²) a large number of deformation twins is formed in the structure which, by blocking the dislocations, increases the energy of strain hardening of that steel.Translated from Izvestiya Vysshihkh Uchebnykh Zavedenii, Fizika, Vol. 16, No. 7, pp. 72–77, July, 1973.     

Laser-fluorescence diagnostics for condensation in laser-ablated copper plasmas

We are investigating the thermodynamic conditions under which condensation occurs in laser ablated copper plasma plumes. The plasma is created by XeCl excimer laser ablation (308 nm, 300 mJ/pulse) at power densities from 500–1000 MW/cm² into backing pressures of helium in the range 0–50 torr. We use laser-induced fluorescence (LIF) to probe velocity and relative density of both atomic copper and the copper dimer molecule, Cu₂, which is formed during condensation onset. At low pressure (10 mtorr), the atomic Cu velocity peaks at approximately 2×10⁶ cm/s. Copper dimer time-of-flight data suggest that condensation onset occurs after the Cu atoms have slowed very significantly. Excitation scans of the Cu₂A-X (0,0) and (1,1) bands yield a rotational and vibrational temperature in the neighborhood of 300 K for all conditions studied. Such low temperatures support the theory that Cu₂ is formed under thermally and translationally cold conditions. Direct laser beam absorption is used to determine the number density of atomic copper. Typical densities attained with 5 torr of helium backing gas are 6–8×10¹³ cm^–3. Rayleigh scattering from particulate is easily observable under conditions favorable to particulate production.     

Effect of maceoscopic structure on the thermal expansion of synthetic graphite

The predominant-orientation parameters and grain defectiveness (microscopic cracks and pores) have been evaluated for extruded coke-pitch samples subjected to various types of heat treatment (220–2770 °K). The calculations are based on a previously reported theoretical model and experimental thermal-expansion coefficients for temperatures in the range 300–1070 °K. The results are used in a discussion of the effect of macroscopic structure on thermal expansion.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 8, pp. 52–56, August, 1969.     

Twin refinement below room temperature in the 1-2-3 highT c superconductors

Thea–b microtwinning in the 90 K superconductors of the Y(1)Ba(2)Cu(3)O(7–) family of perovscites is studied by transmission electron microscopy betwen 300 and 85 K. Thermally stable twin spacings of order 300 Å are observed in dense polycrystalline material. In grains with free surfaces of sufficiently regular shape, the twin pattern is observed to refine at low temperature, either spontaneously or by low temperature thermal cycling, from a spacing of about 1000 Å to about 300 Å. In grains with free surfaces of less regular shape, the twins can be brought to disappear at low temperature after a sufficient electron dosis, and to reappear reversibly. A correlation between transition temperature and twin spacing is discussed.