A review of publications over the last years dealing with the development of gas and electrochemical sensors, including biosensors, on the basis of carbon nanotubes is provided. Results of the experimental and theoretical study of their principles and operation mechanisms are provided. The structure of carbon nanotubes has been described. The main regularities of the structure, energetic characteristics and sensor properties of the modified semiconducting systems on the basis of carbon nanotubes have been studied. Analysis of the mechanisms of the interaction between nanotubes and the functional groups (including carboxyl and amino ones), metal nanoparticles and polymers for the formation of chemically active sensors has been reported. The possibility of application of the boundary modified monolayer carbon nanotubes for the identification of metals is discussed. Results of simulation of the interaction between nanotubes boundary modified by —COOH and —NH2 groups with atoms and ions of potassium, sodium and lithium obtained using the molecular cluster model and the MNDO and DFT calculation methods are provided. The sensors synthesized in this way will be used for establishment of the existence and identification of metal atoms and their ions included in salts and alkalis.

An experimental and theoretical study of the process of the equal−channel angular pressing (ECAP) was performed to obtain a thermoelectric (TE) material based on bismuth telluride. A brief review of the mathematical modeling of the ECAP process is given. The influence of the ECAP design features and temperature modes on the process of plastic forming is considered. The results of calculations of the thermally stressed state of samples at different stages of the ECAP process are presented. The calculations of the ECAP process were carried out by means of Lagrangian finite element mesh, which adjusted adaptively during the process to the die geometry and became finer or coarser depending on the magnitude of the plastic deformation. It was required for the specified calculation accuracy and the convergence of iterative process. The results of an experimental study of the structure and properties of samples obtained by the ECAP using a set of measuring methods (X−ray diffractometry and electron microscopy) are discussed. The thermoelectric characteristics of the obtained materials were measured by Harman method. Comparative methodical calculations of the ECAP process for TE materials based on bismuth telluride have been made by adjusting parameters determining the grain formation (i.e. the critical plastic deformation as a function of temperature and power−law dependence of its rates). It made possible to adjust the ECAP model on the basis of the measured grain sizes for TE materials . The calculation results of grain creation during the plastic forming, which are compared with the measurement data, are presented. The practical result of this research was the improved geometry of the die and the validated technological regimes of plastic deformation, which allowed obtaining samples with the good TE efficiency.

The study of crystals of ZrO2 solid solutions (PSZ) stabilized with yttrium and cerium oxides was carried out by electron paramagnetic resonance (EPR) in the X and Q range. The presence of Zr3+ centers in annealed ZrO2 crystals stabilized only by yttrium oxide (2.8 mol.% Y2O3) is established. Another kind of paramagnetic O−centers appear when CeO2 is added to ZrO2 crystals in addition to yttrium oxide. To estimate the concentration of Ce3+ ions in PZS crystals, EPR spectra were recorded in the presence of a reference specimen at 7 K. Paramagnetic Ce3+ ions have been identified and their relative amounts in PSZ crystals before and after high−temperature heat treatment has been measured. The annealing in air leads to a decrease in the concentration of Ce3+ ions for all compositions and changes the color of the crystals from red to white. After annealing in the 2.0Y0.8Ce3Zr sample, the amount of paramagnetic Ce3+ ions decreased approximately twice. Paramagnetic centers from Ce3+ are not detected in a the sample with a low cerium content of 0.1 mol.% after annealing which indicates the complete transition of Ce3+ to the Ce4+ state. It is shown that the formed paramagnetic centers of cerium are bound by strong exchange interactions. No angular dependence of the EPR lines for the paramagnetic Ce3+ cations on the applied external magnetic field was observed. The probable reason for the absence of such angular dependence is that impurity rare−earth ions are located next to each other, forming impurity clusters with effective spin Seff = 1/2.

This work deals with elastically strained GeSiSn films and GeSiSn islands. Kinetic diagram of GeSiSn growth at different lattice mismatches between GeSiSn and Si has been established. Multilayer periodic structures with pseudomorphic GeSiSn layers and GeSiSn island array have been obtained. The density of the islands in the GeSiSn layer reaches 1.8 ⋅ 1012 cm−2 at an average island size of 4 nm. Analysis of the rocking curves showed that the structures contain smooth heterointerfaces, and strong changes of composition and thickness from period to period have not been found. Photoluminescence has been demonstrated and calculation of band diagram in the model solid theory approach has been carried out. Luminescence for the sample with pseudomorphic Ge0.315Si0.65Sn0.035 layers in narrow range of 0.71—0.82 eV is observed with the maximum intensity near 0.78 eV corresponding to a 1.59 µm wavelength. Based on a band diagram calculation for Si/ Ge0.315Si0.65Sn0.035/Si heterocomposition, one can conclud that luminescence with a photon energy of 0.78 eV corresponds to interband transitions between the X−valley in the Si and the heavy hole subband in the Ge0.315Si0.65Sn0.035 layer.

Features of solid−phase synthesis and a research technique of the perovskit structure of calcium stannat activated by three ions of the rare−earth elements Yb3+, Er3+, Ho3+ are described. It is established that for the formation of luminescent structure of CaSnO3 : Yb3+, Er3+, to Ho3+ the following conditions of synthesis are required: calcination temperature 1250 °C and duration at least 18 h. the luminescent properties of the samples for excitation were probed by a semiconductor laser diode with a 960 nm wavelength. Luminescence emission bands in the visible and IR−regions were recorded. We show that Yb3+ ions preferentially act as sensitizers and are capable to transfer part of the absorbed energy to Er3+ ions and Ho3+, causing a luminescence gain in the bands corresponding to them. Er3+ ions also transfer part of the absorbed energy to Ho3+ ions, and therefore an intensity gain of IR luminescence in the bands at 1194 and 1950 nm is observed. The diagram of energetic transitions is provided for the CaSnO3 : Yb3+, Er3+, Ho3+ system for excitation by a laser with a 960 nm wavelength, and the mechanism of energy transmission between ions of Yb3+, Er3+, Ho3+ is explicitly described. The dependence of the luminescence intensity of the studied phosphor in the area 994, 1194, 1550, 1950 nm on the concentration of Ho3+ ions is studied. The intensity maxima for the emission bands at 1194 and 1950 nm are observed for Ho3+ ion concentration of 0.007 atomic shares. It is suggested to use the CaSnO3 : Yb3+, Er3+, Ho3+ luminescent structure as the source of radiation capable to transform IR radiation in the 960 nm region to IR radiation with a wavelength of about 2000 nm.

The aim of this work is to find out the possibility to reduce the laboriousness and cost of high−power silicon transistors manufacturing with retention of their low thermal resistance. To this end we carried out experimental research of replacement soldering silicon chips in the housing transistors of Au—Si solder for lead−silver solder and some other solders. This will reduce the consumption of gold and increase the productivity of the high−power transistors silicon chips installation due to the collective technology application. At the same time it was found that different treatments of the reverse side of the silicon wafer and their thinning influence the thermal resistance. To improve the quality of soldering we used preliminary metallization of the reverse side of the silicon wafer — Ti—Ni coating. We performed experimental evaluation of the influence of the outer layer materials of the housings and the back side metallization of the chips. When one utilizes soldering silicon chips with lead−silver solder, the housing with a nickel outer layer has the advantage, rather than the gold−plated one, as far as the resulting thermal resistance was lower and the absence of gold made the technology cheaper. We obtained a thermal resistance of 0.6 K/W for a chip area of 24 mm2.

A noncontact method for the determination of recombination parameters of p(n) layer local ranges of silicon n+−p(n)−p+ structures is considered. The method is based on local illumination of the investigated structure by two different absorbed light beams. Initially both beams illuminate simultaneously one side of the local range of this structure and then another side. The intensities оf the light beams are modulated at one frequency so the alternative photo−voltage becomes equal to zero. In this case the short current regime is established for its alternating component. As a consequence the nonilluminated parts of the structure do not shunt its illuminated part. The ratios of the light beam intensities are measured under these conditions. In this work we calculated nomograms for separate determination of the nonequilibrium charge carrier lifetime of the illuminated p(n) local space and its surface recombination velocity using the measured intensity ratios. The calculations were performed at low injection level for one dimensional case. The nomograms were calculated at wave lengths of 1064 and 808 nm for various thicknesses of the n+−p(n)−p+ structures and various modulation frequencies. It was found that the nomograms almost do not depend on the modulation frequency if the live time of the nonequilibrium charge carriers is less than the modulation period. Furthermore, we observed that the nomograms shift substantially and change their shape for thin structures if the diffusion time of nonquilibrium charge carriers from the rear side of the structure to its face side becomes less than their lifetime. In this case the nomograms may be only used for the determination of the surface recombination velocity of the nonquilibrium charge carriers at the rear side of the structure.

The features and changes in the microstructure of the negative electrode material of a lead−acid battery appearing after adding of carbon black and hybrid carbon were investigated. As shown by X−ray phase analysis and scanning electron microscopy, carbon black and hybrid carbon additives influence the electrode material structure causing changes in soaking and formation processes. In accordance with the structural research, hybrid carbon increases the dispersity of the negative active material and impedes sulfate ions diffusion into its internal layers. Electrical tests of lead−acid batteries including high rate partial state of charge cycling were conducted and the roles of each kinds of carbon additives were estimated. It was shown that the addition of hybrid carbon increases the cycle life of the batteries at high rate partial state of charge operation, improving charge acceptance approximately by 9 % and deep discharge stability. Capacity loss after deep discharge is less than 4.4 % if hybrid carbon is used as an additive and 7.2 % in case of carbon black.