No 10 (2023)

We studied the structure of thin films of various thicknesses made of benzotrifuroxan, triaminotrinitrobenzene, diaminodinitroethylene, obtained by crystallization from the gas phase on various substrates: polyethylene terephthalate, parchment, aluminum, quartz glass, polymer resin, silicon and sapphire. Preliminary preparation of gaseous products, which were obtained by the method of thermal vacuum sublimation, was carried out. It has been established that the molecular structure of the obtained thin films corresponds to the studied substances. The texture of the films has been determined. In the bulk, their morphology is determined by particles having a columnar shape, nonequilibrium faceting, and a developed surface. The measurements were carried out by X-ray powder diffraction, Raman spectroscopy, IR spectroscopy, spectrophotometry in the visible, ultraviolet, and near infrared regions, optical and electron microscopy. The surface topology and electronic properties of the obtained textured films were studied.

The influence of the electric field frequency in the range from 0.1 to 2.0 MHz during plasma-chemical deposition of diamond-like silicon-carbon films on their chemical composition, structure, and electrical properties has been studied. It is shown that the films obtained in the entire studied frequency range have an amorphous structure with a constant, within the measurement precision, chemical composition. At the same time, the morphology of the surface of the films and their electrophysical properties significantly depend on the frequency of the electric field during plasma-chemical deposition. This makes it possible to use the change in the field frequency in the preparation of films as a method of controlling their properties. The frequency range providing the most effective modification of electrophysical properties is determined.

A method for growing a hafnium oxide (HfO₂) protective coating on the surface of a tungsten–rhenium (W–Re) thermocouple is described, the structural and morphological properties and chemical composition of the coating are studied, and temperature tests of thermocouples with a protective coating are carried out. The optimal conditions for the formation of coatings resistant to oxidation and high temperatures (above 2000°C) are found. The tests confirmed the ability of the HfO₂ coating to slow down the processes of degradation and destruction of the thermocouple when operating in an aggressive oxidizing environment.

The development of most branches of lighting technology poses the challenge of developing advanced high-power white light-emitting diodes. Their design involves the combination of two basic elements – a high-power blue light-emitting diode or a laser diode with a yellow phosphor converter that can withstand high thermal loads. Recently, the development of solid-state (primarily ceramics) phosphors based on Ce:YAG, co-doped with the so-called “red” ions with high thermal conductivity and thermal stability, has been actively pursued. Additionally, the possibility of creating on their basis composite structures with a secondary thermostable phase of corundum α-Al₂O₃, which has many times higher thermal conductivity at a close coefficient of thermal expansion, is being considered. The development of a sintering map for complex systems based on solid ceramics solutions requires mandatory control of their structural-phase state by X-ray diffraction. However, laboratory equipment is not always sufficient to understand the processes occurring during sintering. Therefore, in this work, on the example of Al₂O₃–Ce:(Y,Gd)AG biphase ceramics, we optimized the trajectory of their sintering using diffraction of synchrotron radiation. The composites were synthesized by the method of reactive spark plasma sintering of powders of the initial oxides. It is shown that at the fixed applied pressure of 30 MPa and an isothermal holding for 15 min, a single phase of the Ce:(Y,Gd)AG solid solution is formed only at temperatures of at least 1450°C. At such high sintering temperatures, signs of recrystallization are observed due to the proximity of eutectic melting. Increasing the exposure time to 30 min makes it possible to lower the temperature of formation of the biphasic structure to 1425°C and prevent undesirable recrystallization. However, the subsequent increase in pressure to 90 MPa leads to the coexistence of several variations of the YAG-type phase in the system.

The intensity loss of transmitted beam due to parasitic diffraction (glitches) is an inherent property of single-crystal X-ray optics. This effect can lead to a weakening of the radiation, up to its complete disappearance. Therefore, understanding the effect of diffraction loss is essential for any experiments that use single-crystal optics. We present theory of glitch formation and demonstrate its application to experimental data to determine the orientation and cell parameters of optical elements made of the single-crystal diamond. A systematic error was found in determining the absolute energy of X-ray, which occurs due to the wrong monochromator tuning (an error in determining the absolute 2θ angle). The described error very often occurs during the experiment as a result of the fact that determining the absolute 2θ angle of the monochromator crystal is a technically difficult task. Simultaneous determination of the orientation and lattice parameters of the studied sample, together with the compensation of the systematic error in the monochromator tuning, made it possible to significantly improve the accuracy of processing the obtained data.

Resistivity ρ, magnetoresistance Δρ_xx/ρ₀(P) and Hall constant R_H were measured in (Cd_{1 – x}Zn_x)₃As₂ sample with х = 0.31 under the action of all-round pressure and at various temperatures in the range (80–400) K. These samples were obtained by the modified Bridgman method. The composition of the samples and their homogeneity were controlled by X-ray phase analysis and energy-dispersive X-ray spectroscopy. The results of energy dispersive X-ray spectroscopy showed that the distribution of elements in the sample is uniform. It was found that the resistivity increases with increasing temperature, and the change in ρ(T) has a metallic character. The Hall constant R_H in the field decreases slightly with increasing temperature and retains a negative sign throughout the entire range under study. With increasing pressure, anomalies were observed in the baric dependences of the electrical resistivity ρ(Р), magnetoresistance Δρ_xx/ρ₀(Р) and the Hall coefficient R_H(Р). Increasing the confining pressure leads to suppression of the positive magnetoresistance. In the phase transition region, the negative magnetoresistance at a pressure Р (2.4–2.7) GPa in a field of 5 kOe is the maximum value of 1.7.

The absorption spectra of infrared radiation by membranes of the AMN-P and OPMN-P brands are analyzed. In the spectra of the surface layer of the AMN-P membrane, there is a decrease in the relative intensity of the frequencies of the carbonyl group (1724, 3392 cm^–1 for air dry). For the cellulose acetate AMN-P membrane, the number of hydrophilic OH groups increases, which changes its molecular structure and transport characteristics. In the infrared radiation spectra of the surface layer of the OPMN-P membrane, the 1650–1670 cm^–1 band characteristic of C=O group shows changes in the frequency of the spectrum: for air-dry and water-saturated samples, it shifts from 1652 to 1666 cm^–1, respectively. Interactions of carbonyl (C=O) and amide (H–N) groups form the supramolecular structure of polyamides. Changes in the infrared radiation spectrum of the water-saturated sample of the OPMN-P membrane can be explained by the fact that the C=O…–…H–N bonds of the amide fragment do not break. Therefore, membrane swelling partially affects the structural rearrangement of the polyamide at the supramolecular level. In the electron nanofiltration separation of an aqueous solution of ammonium chloride, two intervals of change in the specific output flux are noted at fixed transmembrane pressure and experiment time. The first period occurs at a current density of 12.82 to 15.38 A/m² and is associated with the penetration of the solvent with a slight gas formation on the electrodes. The second period is observed from 15.38 to 25.64 A/m² and is associated with membrane degradation and intense gas formation, especially chlorine. It is noted that in the intermembrane channels the migration of cations and anions is affected by the processes of throttling, heat release, when operating in the limiting mode (when current carriers – H⁺ and OH^–) appear, which is confirmed by the data of studies of the electrochemical parameters of the membrane system.

The results of an experimental study of the surface morphology of zinc oxide films and the electrical properties of structures based on the monocrystalline Si/microcrystalline ZnO heterojunction are presented. The structure of zinc oxide films grown in an atmosphere of argon and oxygen is analyzed, and the size distribution of nanoscale fibers grown on its surface is obtained. The capacitance-voltage characteristics of the In/ZnO/n-Si/Al and Au/ ZnO/n-Si/Al heterostructures have been simulated. Based on the calculations and comparison of experimental and model dependences, the concentration of free charge carriers in the sample and the position of the Fermi level were determined, the presence of a fixed charge in the structure was revealed, the density of surface states was found based on the ratio of the voltage applied to the structure and the surface potential at the interface of the materials of the layers of structures. The value of the built-in surface charge is calculated. The interrelation of the upper contact material with the volt-farad and volt-ampere characteristics of the structure is investigated. The resistance of the formed zinc oxide films is calculated. The prevailing charge transfer mechanisms are discussed. The influence of technological modes of obtaining zinc oxide films obtained by spray pyrolysis on the structure of the surface, the effective capacity of the structure, the density of electronic states, the processes of charge carrier transfer in samples under the action of an electric field is analyzed.