Development of a method for quantitative comparison of the luminance of self-glowing crystals – the basic elements of a low current source

This work is devoted to the development of a method for the quantitative comparison of the luminosity of weakly luminous samples, such as self-glowing crystals. A self-glowing crystal is an efficient scintillator, whose self-luminescence is due to the decay of a radioactive isotope introduced into the crystal matrix during its growth. Such crystals can be used as low current sources with a service life of 50 years or more. This technique takes into account the luminescence spectra of the samples under study, the spectral functions of the spectrometer and photodetector. Information on the luminescence spectra of samples can be obtained based on their cathodoluminescence spectra. Thanks to the calculations performed according to this technique, it becomes possible to estimate the optical radiation power of a self-glowing crystal, which can be converted into an electric current using a photodiode. Also, the proposed technique can be applied to assess the luminosities of any materials under the influence of radioactive radiation.

Low-Frequency Admittance of Capacitor with Working Substance “Insulator–Partially Disordered Semiconductor– Insulator”

The study of the electrophysical characteristics of crystalline semiconductors with structural defects is of practical interest in the development of radiation-resistant varactors. The capacitance-voltage characteristics of a disordered semiconductor can be used to determine the concentration of point defects in its crystal matrix. The purpose of this work is to calculate the low-frequency admittance of a capacitor with the working substance “insulator–crystalline semiconductor with point t-defects in charge states (−1), (0) and (+1)–insulator”. A layer of a partially disordered semiconductor with a thickness of 150 μm is separated from the metal plates of the capacitor by insulating layers of polyimide with a thickness of 3 μm. The partially disordered semiconductor of the working substance of the capacitor can be, for example, a highly defective crystalline silicon containing point t-defects randomly (Poissonian) distributed over the crystal in charge states (−1), (0), and (+1), between which single electrons migrate in a hopping manner. It is assumed that the electron hops occur only from t-defects in the charge state (−1) to t-defects in the charge state (0) and from t-defects in the charge state (0) to t-defects in the charge state (+1).In this work, for the first time, the averaging of the hopping diffusion coefficients over all probable electron hopping lengths via t-defects in the charge states (−1), (0) and (0), (+1) in the covalent crystal matrix was carried out. For such an element, the low-frequency admittance and phase shift angle between current and voltage as the functions on the voltage applied to the capacitor electrodes were calculated at the t-defect concentration of 3∙1019 cm−3 for temperatures of 250, 300, and 350 K and at temperature of 300 K for the t-defect concentrations of 1∙1019, 3∙1019, and 1∙1020 cm−3.

Optical Properties of Monocrystalline Silicon Nanowires

The paper presents the results of a study of the optical reflection and transmission spectra of a silicon single crystal p-Si (100) with silicon nanowires grown on both sides and porous silicon p-Si (100) on a single crystal substrate in the spectral range 0.2 ÷ 1.7 μm. The layers of nanowires had a thickness of 5.5 µm, 20 µm, 50 µm and a porosity of 60 %. The porous silicon layers had a thickness of 5 μm, 50 μm and a porosity of 45 %, 55 % and 65 %. The change in the energy band structure in single-crystal silicon nanowires and in a single-crystal matrix of porous silicon is shown.

Sputtering rate of lead, tin and germanium tellurides with low energy argon ions

Sputtering of PbTe, SnTe, and GeTe crystal samples by low-energy Ar+ ions are investigated, and the sputtering rate vsp of the studied compounds, as well as its dependence on both the composition of crystal matrix and the sputtering energy are determined. It is found that under the same conditions the sputtering rate in the sequence of GeTe-SnTe-PbTe telluride compounds increases when their average atomic weight increases. This phenomenon is explained by changes in the surface binding energy of metal atoms in lead, tin and germanium tellurides. It is shown that for all compounds the sputtering rate also increases with the increase in the sputtering energy. In the energy range from 160 to 550 eV,this increase is almost linear. The coefficients of change in the sputtering rate with energy dvsp/dE are calculated. The surface density of Ar+ ion-induced structures and the relative area of the sputtered surface covered by these structures are determined for the natural lateral surfaces of a PbTe crystal grown from melt by the Bridgman method as a function of sputtering energy. It is shown that both studied parameters decrease exponentially with increasing the sputtering energy.

Optical, Structural and Spectroscopic Characterization of ZnS Nanocrystals Embedded in KBr Single Crystal Matrix Grown by Czochralski Method

ZnS nanocrystals were embedded in a KBr single crystal matrix using the Czochralski growth technique. The X-ray diffraction, FT-IR and optical spectroscopy revealed the incorporation of ZnS nanocrystals. A blue shift of the absorption edge of the obtained samples has been observed, indicating the quantum confinement effect. The optical band-gap is estimated to be about 4.67 eV. Two excitonic peaks appeared at 300.4 nm and 271 nm. The average nanocrystal size was derived from the optical spectra. Annealing led to a shift in the absorption edge towards longer wavelengths and an increasing of the emissions intensity. Raman lines of the nanoparticles are broader and frequency-shifted compared to those of the bulk crystals. These results show that KBr is a good matrix-host of ZnS nanocrystals, and that the elaborated samples can be used for important technological applications.

Ferromagnetic Ordering Theory of Colloidal Suspension of Magnetic Particles in Liquid Crystal

A molecular-statistical theory of colloidal suspension of spherical ferromagnetic particles in a nematic liquid crystal matrix is considered. A tensor expression of the suspension Hamiltonian is proposed, which contains contributions that make it possible to describe the ferromagnetic state of the studied system. Within the mean-field approximation, a system of equations is obtained that describes various orientational states of the suspension. Phase diagrams of the suspension are plotted. It is shown that depending on temperature and intensity of particles interaction with the liquid crystal matrix, the suspension can be in an ordered state with different magnetic properties, namely, in the ferromagnetic and superparamagnetic nematic phases, in addition to the isotropic phase.

Cotton Oil Shortenings And Optimal Parameters Of Their Temperature Process

The tempering properties of shortening of fats based on cottonseed oil and products of its processing were studied. It has been experimentally established that the tempering of hard shortening has several advantages. The tempering temperature is carefully selected to obtain the desired crystal matrix in shortening. In the absence of this step, the crystal structure in the product continues to change with time and temperature during storage and transportation. The consistency of the shortening changes at influence of high or low temperatures even with proper tempering. However, there is always some recovery of consistency when the product returns to its primary storage temperature. Properly tempered shortening shows plasticity over a wider temperature range, as well as storage temperature fluctuations.