Optical and Photoelectric Inhomogeneity of CdTe:V Crystals

The optical and photoelectric properties of CdTe:V crystals with the doping impurity concentration N _V = 5·10¹⁸–5·10¹⁹ cm^–3 are investigated and the possibility of their use as a photorefractive material is considered. As is seen from the spectra of optical transmission, the crystals of both types possess high transparency (50–65%), which for CdTe:V specimens with N _V = 5·10¹⁹ cm^–3 decreases sharply and in the range 12–14 m does not exceed 5%, whereas for CdTe:V crystals with vanadium concentration of 5·10¹⁸ cm^–3 such a value of transmission remains unchanged up to 25 m, implying a good optical quality of the latter crystals and their possible application in the spectral range 1.06–1.25 m in modern fiber-optic communication lines.     

Best trigonometric approximations for some classes of periodic functions of several variables in the uniform metric

We study best M-term trigonometric approximations and best orthogonal trigonometric approximations for the classes B _pθ ^r and W _pα ^r of periodic functions of several variables in the uniform metric.     

Effect of uniaxial pressure on the infrared spectra of (NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript> crystals

The infrared reflectance spectra of a mechanically free or uniaxial-pressure-confined (NH₄)₂SO₄ crystal were studied for the first time in the spectral range 800–1700 cm^?1 in three crystallographic directions. Using the Kramers-Kronig relations, the dispersion and pressure dependences of the following quantities are obtained: the index of refraction n, the real (?₁) and imaginary (?₂) parts of the permittivity, the frequencies of longitudinal (ω_LO) and transverse (ω_TO) optical vibrations, the damping constant γ, and the oscillator strength f of the mechanically free or clamped (NH₄)₂SO₄ crystal. A considerable change in the main reflection bands with pressure was observed, which is due to the effect of uniaxial pressure on the NH₄ and SO₄ tetrahedral frames.     

Approximating Characteristics of the Classes of Periodic Multivariate Functions in the Space B∞,1

Ukrainian Mathematical Journal - We obtain the exact-order estimates of the Kolmogorov widths and entropy numbers for the classes $$ {\mathbbm{W}}_{p,\alpha}^r $$ and $$ {\mathbbm{B}}_{p,\theta}^r...     

Thermal conductivity of thermoelectric Al‐substituted ZnO thin films

ZnO:Al thin films with a low electrical resistivity were grown by magnetron sputtering on sapphire substrates. The cross‐plane thermal conductivity (κ = 4.5 ± 1.3 W/mK) at room temperature is almost one order of magnitude lower than for bulk materials. The thermoelectric figure of merit ZT at elevated temperatures was estimated from in‐plane power factor and the cross‐plane thermal conductivity at room temperature. It is expected that the thermal conductivity drops with increasing temperature and is lower in‐plane than cross‐plane. Consequently, the thin film ZT is at least three times higher than for bulk samples at intermediate temperatures. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of dislocations on the shape of islands during silicon growth on the oxidized Si(111) surface

The formation of dislocation-rich and dislocation-free silicon islands during growth in the absence of mechanical stresses has been studied by scanning tunneling microscopy. The rounded shape of islands obtained at growth temperatures of 400–500°C on the oxidized Si(111) surface is associated with the presence of dislocations within them. The transfer of atoms from the oxidized surface to the islands occurs due to the barrier of the potential energy at the SiO₂/Si boundary. The {111} and {311} facets dominate in the shape of the islands grown at 500–550°C. Their appearance indicates the absence of the threading dislocations in the islands and that the growth is limited by the stage of the nucleation of a new atomic layer.     

Trigonometric widths of the classes B p,θ r of functions of many variables in the space L q

We obtain estimates exact in order for the trigonometric widths of the Besov classes B _p,θ^r of periodic functions of many variables in the space L _q for 1 ≤ p ≤ 2 < q < p/(p - 1). Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 8, pp. 1089–1097, August, 1998.     

Swelling of a sulfamide polymer in alcohols

Swelling of a sulfamide polymer of UPM brand in a series of alcohols was studied gravimetrically. Correlation analysis with multiparameter equations showed that solvation processes exert a decisive effect on the swelling.     

Growth of thin silver films on silicon oxide pretreated by low temperature argon plasma

In the present study, we investigate the influence of low energy ion bombardment on nucleation and growth of thin silver films on silicon oxide by in situ photoelectron spectroscopy (PES) combined with specific resistivity measurements. Thermally grown thin silicon oxide films were exposed to a low temperature argon plasma for different time intervals resulting in changes in surface chemical composition as monitored by angle-resolved X-ray photoelectron spectroscopy (ARXPS). We demonstrate that irradiation of the oxide surface with low energy ions results in substantially changed nucleation of silver. Furthermore, silver films deposited on plasma treated oxide tend to have lower resistivity which is attributed to the effect of reduced grain boundary and surface roughness.