Articles in "Physics and astronomy"

Summary: The dielectric properties and power dissipation of PtSi/n-Si Schottky diodes of small area (8x10-6 cm2) were studied when the bias voltage varied in the range -2V ÷ 4V at room temperature. The amplitude of the alternating signal (Vac) varied from 5 mV to 1x103 mV. Studies based on impedance measurements revealed the dependence of dielectric parameters (ε', ε″), ac-conductivity (σac) and power dissipation (P) only at Vac = 200 mV. The obtained result is explained by the inhomogeneity of polarization and surface states.

Summary: In this paper, the magnetization of diluted magnetic semiconductor superlattices with a magnetic impurity of manganese is studied. It was found that the magnetization of a quasi-two-dimensional electron gas, depending on the degree of filling of the miniband superlattices, the molar concentration of the impurity, the exchange interaction constant and the spin splitting factor, changes sign and in a strictly two-dimensional case becomes positive. In a magnetic field, magnetization oscillates, and in strong magnetic fields the oscillations weaken, and their amplitude and frequency decrease. The contribution of the impurity to the magnetization is calculated. In a relatively weak magnetic field the magnetization associated with the impurity increases linearly and at a certain condition to the depending on the magnitude of the exchange constant and the impurity concentration changes its sign.

Summary: In this work have been presented the result of investigation of K0,945Ag0,055NO3 and K0,945Cs0,055NO3 single crystals were grown from aqueous solution of KNO3, AgNO3 and CsNO3 using isothermal crystallization method. Then, structural and phase transformations in samples were studied by X-ray and optical microscopy methods. It has been determined that in K0,945Ag0,055NO3 monocrystal at T393K temperature, in K0,945Cs0,055NO3 monokrystal at T455K temperature the rhombic (II)  hexagonal (III) transformation occurs with the formation and growth of the III - modification crystal embryo within II – modification. The results obtained from the kinetic studies were determined that the temperature dependence of the conversion rate of II  III in K0,945Ag0,055NO3 and K0,945Cs0,055NO3 single crystals can be expressed by an empirical formula of υ=(aΔT+bΔT^2+cΔT^3)⋅10^(-2) cm/sec. ΔT=T_t-T_0 is temperature delay, T_t- is transformation temperature and is equilibrium temperature between interconverting modification crystals. Based on the results of velocity measurements, the activation energy of IIIII polymorphic transformations were calculated.

Summary: Doping effects on the electronic and magnetic properties of Zn1−x(Co,Cr)xO systems are investigated within Local Spin Density Approximation and Hubbard U methods. Based on Density Functional Theory the spin-polarization band structures, density of states for investigated systems are calculated. Systematic analysis of the electronic properties shows that TM-doped ZnO has generated new energy levels in the vicinity of Fermi energy level. From first-principle calculations we obtained Cr-ZnO and Co-ZnO systems are metallic and half-metallic ferromagnetic materials, respectively. The obtained results for Cr-doped ZnO 128- and 192-atom supercell systems show magnetic properties with higher Curie temperature than room temperature. There are large local moments, ∼2.9 and ∼4.2 for Co and Cr dopants, respectively. Magnetic moments are related with two electron defects in the supercell structure and unpaired electrons of transition metal. The ferromagnetic and antiferromagnetic phases and the total energy are obtained for x = 2.08%, 3.125%, 4.16%, 6.25%, 8.3%, 12.5%, and 25% impurity concentrations for doped ZnO.

Summary: The electrical and photoelectric properties of anisotype n-Si−p-GaSe heterojunctions obtained as a result of the deposition of a GaSe thin layer on a cold n-Si single crystal substrate by the thermal evaporation method were studied. It was determined that the height of the potential barrier in thermal annealing structures at T = 200°C during t = 3 hours occurs due to the decrease in the density of states of local levels located near the Fermi level in the amorphous layer. The mechanism of photosensitivity in an isotype heterostructures was analyzed and it was found that the photosensitivity of the heterojunction increases as a result of a decrease in the surface density of state at the contact boundary of the components, by thermal means. The spectral distribution of the quantum efficiency in the n-Si – p-GaSe heterojunction was studied and their perspective was determined.

Summary: The radiation oxidation of Be in water at room temperature in the absorbed dose range Dγ = 0.5…180 kGy was studied by radiothermoluminescence (RTL), infrared reflection-adsorption spectroscopy (IRRAS), and electrical conductivity. The participation and role of surface relaxing intermediate-active particles in the dynamics of changes in the oxidation process are considered. Using the RTL method, the role of surface oxygen hole centers generated by γ-irradiation and chemisorbed oxygen in the formation of nanooxide films was experimentally established. The formation of nanooxide films on the surface of Be in water was traced in the IR reflection spectra. The kinetics of radiation oxidation of beryllium has been studied and its radiation passivation has been established. According to the logarithmic dose dependence of the surface resistivity Be, two stages of the oxidation process were revealed. It is shown that the formation of nano oxide films leads to a decrease in the surface electrical conductivity of beryllium by 2 orders of magnitude and an increase in the thickness of oxide films by 1.6 times.