Volume 54, Nº 2 (2019)

The electromagnetic radiation on the eigenmodes of a dielectric waveguide is investigated for the charge rotating around a dielectric cylinder. A formula for radiation intensity at a given harmonic is obtained. The corresponding fields exponentially decay at distances from the surface of the cylinder larger than the radiation wavelength. A comparison is made for the intensities of the parts of the radiations propagating inside and outside the cylinder, as well as with the intensity of the radiation at large distances from the cylinder.

The problem of the radiation of a relativistic bunch of positrons channeled in densely packed nanotubes was solved. A model parabolic potential was used for the average nanotube field. The channeled positrons oscillate with the same frequency, but with different amplitudes equal to the distance from the point of entry of the positron in the nanotube to its axis. The polarization of the nanotube environment results in the appearance of a lower energy threshold for the formation of radiation. The boundaries of the frequency interval of radiation also depend on the amplitude of the oscillating positron. For the first time an analytical expression for the spectrum of the total radiation is obtained in the dipole approximation. At a zero angle, both hard (gamma) and soft (X-ray) photons are generated. Directed photon beams have important practical applications.

Based on the analysis of the forward current-voltage characteristics of the p-InSb–n-CdTe heterojunction fabricated by a method of pulsed laser deposition, the existence of two charge injection mechanisms was experimentally confirmed. At relatively small external bias voltages (0.03 V < U < 0.15 V), the current is in a satisfactory agreement with the expression I ~ exp(qU/ηkT) with the ideality factor η = 1. Above 0.18 V, the current-voltage characteristic obeys the law I ~ U^3/2 followed by an attainment to the linear section (the cut-off voltage of current is 0.47 V). A theoretical model of current transport is given taking into account the peculiarities of the heterojunction band discontinuity, leading to the origination of inversion layer near the interface.

In this work, the hydrogen-like impurity states in a strongly oblate ellipsoidal quantum dot have been investigated in the presence of the external hydrostatic pressure and temperature. Numerical computations were performed within the framework of the variational method. The dependences of the binding energy on the location of the donor impurity were obtained for various values of external pressure and temperature. At various values of external pressure, the dependence of the diamagnetic susceptibility on the impurity coordinate has been revealed. The dependence of the oscillator strength for the first two transitions from the impurity ground state to the conduction band has been computed. The three-dimensional dependence of the photoionization cross section on the frequency of the incident light and hydrostatic pressure is given.

The processes of heat propagation in a four-layer detection pixel of thermoelectric single-photon detector after the absorption of photon of the 0.8 eV energy are investigated by the computer simulation method. The design of the detection pixel consisting of successive layers on a sapphire substrate of heat sink (W), thermoelectric sensor (CeB₆), absorber (W) and the antireflection layer (LaB₆) is proposed. The temporal dependences of an intensity of the signal arising on the detection pixel, the values and the time to reach the maximum signal, the time of signal decreasing to the background value and the count rate of the detector for different thicknesses of the layers of the sensing element are determined. The computer modelling is carried out based on the equation of heat propagation from the limited volume by the use of three-dimensional matrix method for differential equations. It is shown that the thermoelectric detector with the four-layer detection pixel has a system detection efficiency on the level of 95%. It also provides a gigahertz count rate. A detector with such characteristics can be applied in various fields of science and modern technologies.

In this work, the impedance spectroscopy is presented as a promising method for the investigation of the sensitivity of gas semiconductor sensors. The sensor made of the ZnO nanosize film doped with the 1 at.% La was manufactured and its sensitivity investigated to the hydrogen peroxide vapors. The advantages of impedance spectroscopy compared with the studies of current-voltage characteristics are shown.

The influence of interdiffusion of heteromaterials on the diffraction focusing of spherical X-ray wave in a superlattice is investigated. It is shown that in case of dynamical diffraction of spherical X-ray wave in a short period superlattice, the focal lengths of satellites vary depending on the degree of interdiffusion of heteromaterials of the bilayer. The measurement of focal lengths of satellites allows the determination of structural factors of the superlattice and eventually the calculation of the thickness of transition diffuse layer.

A theoretical and experimental method is proposed to solve one of the important applied problems in hematology for development of an automated and inexpensive method to establish the size distribution curve of erythrocytes. Within the framework of two-wavelength model, a new method for the experimental data processing of laser diffractometry was suggested, which allows one to distinguish the anisocytoses with the various degrees of asymmetry. The advantages of the developed mathematical approach are discussed.