Peculiarities of growing Ga1–xInxAs solid solutions on GaAs substrates in the field of a temperature gradient through a thin gas zone

Solid solution Ga1–xInxAs is widely used in modern optoelectronics as a material for p-i-n photodetectors, lasers emitting in the spectral range 1.3–1.55 μm. In this paper, the features of obtaining Ga1–xInxAs films by the method of zone recrystallization with a temperature gradient, the essence of which is the sequential recrystallization of parts of the source melt moving under the action of a temperature gradient, are studied. Ga1–xInxAs films on GaAs substrates were obtained in a temperature gradient field through a thin gas zone in a specially designed graphite cassette. The films were prepared at a temperature of 1123 K with a temperature gradient of 30 K/cm. A 1:1 mixture of nitrogen and hydrogen was used as the carrier gas. The thickness of the gas zone between the source and the substrate was 1 mm. The deposition time for all films was 10 min. The growth kinetics, morphology, and structure of the chemical bonds of the obtained films have been studied. Based on the results of theoretical calculations, it was found that an increase in the concentration of indium leads to a decrease in the film growth rate to 0.3137 μm/min. A comparison of the results of theoretical calculations with experimental results showed a discrepancy between the growth rates for films with an indium concentration in the growth source of more than 20 %, which is primarily due to the segregation of indium on the film surface. The films have an RMS roughness from 9.1 to 24.2 nm. It is shown that the content of indium in the growth source significantly affects the properties of the grown films and leads to a decrease in the growth rate, an increase in the elastic stresses in the layer, and a nonstoichiometric composition of the film. It has been established that with an increase in the indium concentration in the film, a significant shift in the frequency of the LO and TO phonon modes of GaAs to the left by 13 and 16 cm–1, respectively, is observed due to the influence of elastic mechanical stresses. The presented results show that Ga1–xInxAs solid solution films with short-range order of chemical bonds were obtained by the method of zone recrystallization in a temperature gradient

2D Molybdenum Carbide MXenes for Enhanced Selective Detection of Humidity in Air

2D transition metal carbides and nitrides (MXenes) open up novel opportunities in gas sensing with high sensitivity at room temperature. Herein, 2D Mo2CTx flakes with high aspect ratio are successfully synthesized. The chemiresistive effect in a sub-mu m MXene multilayer for different organic vapors and humidity at 10(1)-10(4) ppm in dry air is studied. Reasonably, the low-noise resistance signal allows the detection of H2O down to 10 ppm. Moreover, humidity suppresses the response of Mo2CTx to organic analytes due to the blocking of adsorption active sites. By measuring the impedance of MXene layers as a function of ac frequency in the 10(-2)-10(6) Hz range, it is shown that operation principle of the sensor is dominated by resistance change rather than capacitance variations. The sensor transfer function allows to conclude that the Mo2CTx chemiresistance is mainly originating from electron transport through interflake potential barriers with heights up to 0.2 eV. Density functional theory calculations, elucidating the Mo2C surface interaction with organic analytes and H2O, explain the experimental data as an energy shift of the density of states under the analyte's adsorption which induces increasing electrical resistance

The small spacecraft with a magnetic sail on high-temperature superconductors

It is proposed to develop a small spacecraft for an experiment using high-temperature superconductors (HTS) and shape memory materials. The purpose of the experiment is to test a technological capability of creating a strong magnetic field on the small spacecraft using HTS and shape memory materials for deployed large-area structures, and study the magnetic field interaction with the solar wind plasma and the resulting force impact on the small spacecraft. This article is of a polemical character and makes it possible to take a fresh look at the applicability of new technologies in space-system engineering.</jats:p

Monitoring of the technical condition of structures and building materials of an elevator silo housing

The results of assessing the technical condition of the elevator silo housing, obtained on the basis of a visual instrumental examination using the non-destructive testing method, are considered. Existing defects and damages in the building materials and structures of the building, which adversely affect its performance, were identified. An assessment was made of the state of foundations, walls, floors of the silo and columns installed at the corners of the silo at the height of the silo. The results of the assessment of individual results of the performed instrumental studies of structures and building materials at the object under study are presented. The technical condition of the building as a whole is assessed as a limited operational technical condition. The phase of the period of operation of the building was determined. Recommendations have been developed to ensure the safe operation of the building under study. It has been established that it is necessary to strengthen the structural elements of the building for further safety during the operation of the elevator. It is proposed to introduce the necessary measures to improve the reliability and strength properties of individual structural elements after a period of their long-term operation

Rabbit models of ischemic stroke in biomedical research

The development of experimental models of ischemic stroke allowing for effective translation of results from animal studies to humans is an important task of modern neuropharmacology. Due to the fact that new drugs with neuroprotective properties that have shown activity in rodents most often turn out to be not effective enough in humans, the use of larger laboratory animals may become a viable solution. Among the latter, rabbits are the most accessible species for laboratories. Since they have gyrencephalic brains and a significant amount of white matter, they can be considered to be highly similar to humans. In the present review, we discussed the main methods of ischemic stroke modelling in rabbits. The breed, age and sex of the animals, anesthesia methods as well as criteria for functional state assessment after cerebral ischemia are the issues that should be addressed before the start of the study.</jats:p