Search

The aim of this work was to study the effect of the parameters of deposition process and subsequent annealing on the properties of vanadium oxide VO x films deposited by the pulsed reactive magnetron sputtering of a V target in an Ar/O 2 gas mixture. The dependences of the structure, phase, temperature coefficient of resistance (TCR), resistivity p , band gap Egof the films on the oxygen concentration in Ar/O 2 gas mixture during the deposition Г O2 , and the temperature of annealing in an O 2 atmosphere were obtained. The films were found to have an amorphous structure after deposition. Crystallization processes are observed at temperatures above 275 °C. In this case, depending on the temperature, polycrystalline films with a monoclinic, cubic or mixed crystal lattice are formed and a transition occurs from the intermediate oxide V 4 O 9 to the mixed phase VO 2 /VO x /V 2 O 5 and then to the higher oxide V 2 O 5 . The character of changes in p , TCR and Egof films coming from the change in the annealing temperature is complex and largely determined by Г O2 . It was established that with the view of using VO x films as thermosensitive layers, the following conditions of deposition and annealing would be preferable: films deposited at the oxygen concentration 25 % in Ar/O 2 gas mixture and annealed at a temperature of 250–275 °C in an O 2 atmosphere for 10 min. Under these conditions VO x films with the following properties were obtained: p = (1.0 – 3.0) . 10 -2 Ohm . m, TCR = 2.05 %/°C, and E g = 3.76–3.78 eV.

The influence of high-speed particle fluxes on changes in the structure and properties of materials has been widely studied currently. The effect exerted by particles moving at very high speeds can have both negative (in spacecrafts) and positive character (dynamic processing of tool steels). Therefore a task for studying an effect of high-speed particle flows on structure change in tool steels and improving their performance properties has been set in the paper. The study has used an explosive method for creation of a high-speed flow of SiC + Ni and Al2O3 particles. Samples after dynamic alloying have been subjected to diffusion nitriding. Microstructure of specimens made of X12M, R18, R6M5K5steel has been studied using optical and electron metallography. Wear resistance of the samples has been also tested on a friction machine. Theoretical and experimental results on a complex effect of high-speed microparticle flows and nitriding on a structure and properties of tool steels have been obtained during the research. It has been established that dynamic alloying by particles leads to formation of a specific structure in a composite material reinforced with channels. Central fiber (channel) zone with powder particles residues is surrounded by areas of amorphous state which is succeeded by a zone with a nanocrystalline fragmented cellular structure. Then we observe a zone with a microcrystalline structure that transits to a zone with crystalline structure which is characteristic for a matrix material of structural steel. The obtained data can expand and complement some ideas about mechanisms for dynamic loading of solids and condensed matter, plastic deformation, physical mechanics of structurally inhomogeneous media at different levels, a number of effects arising from collision and ultra-deep penetration of microparticles into metals. It has been shown that wear resistance of high-speed steel subjected to dynamic alloying in the quenched state is increased by 1.2 times in comparison with wear resistance of steel alloyed in the annealing state.

Triterpenoids from birch bark are valuable biologically active substances. They exhibit important biological properties. However, triterpenoids are insoluble in water due to their hydrophobicity. In order to increase their bioavailability we developed a technique for obtaining spherical amorphous nanoparticles (SANP) by their precipitation with water from a solution in THF. In the form of nanoparticles, triterpenoids show additional useful properties: they can be loaded with hydrophobic substances. SANP were also shown to be effective immunological adjuvants. This article is devoted to the study of conditions that could optimize their production. As a result, it was shown that among the three investigated solvents miscible with water - acetone, dioxane, THF -the latter gives the best results. Lowering temperature decreases the size of SANP. An increased temperature leads to the formation of betulin crystals. When the concentration of triterpenoids in THF is higher than 5 mg/ml, crystals of betulin also begin to form. The results of this study lead to the assumption that the main parameter of the process determining the formation of SANP is the rate of the solvent diffusion into water.

Mesoporous amorphous-nanocrystalline powders Gd2O3 — SiO2 (the specific surface area up to 177 m2/g, particle size less than 10 nm and large pore volume up to 1,19 cm3/g) were obtained by pulsed electron beam evaporation. Porous Gd2O3 — SiO2 nanoparticles are promising as nanocontainers for the drug delivery to cancer cells and contrast agents for the magnetic resonance imaging. Besides, they can used in catalysis and in other fields of nanotechnology.

Critical points of amorphous alloy of Fe-Si-Nb-Cu-Mo-B system was determined using the non-ambient x-ray diffraction method. The sample with amorphous structure was produced by planar flow casting process. Temperature range of alloy nanocrystalline state was established. © 2019, National University of Science and Technology MISIS. All rights reserved.

Transmission electron microscopy results are presented for as-deposited amorphous Ge 2 Sb 2 Te 5 thin films after theirs isothermal annealing and CW laser illumination. Obtained microphotographs suggested that the crystallization process was driven solely by heterogeneous nucleation on the film boundary. The simplified model of steady-state crystallization process was developed for the case of heterogeneous nucleation mechanism. The values of nucleation rate and growth rate for isothermal and CW laser crystallization are calculated. The calculated values are in reasonable agreement with both our experimental data and with results previously published by the other authors.

In this paper, we describe the results of the study of an MGA-95 semipermeable composite membrane with amorphous and crystalline regions, considering the effect of the three processes migration, diffusion and fluid convection of solute and solvent. It was found that during swelling the supramolecular structure of the membrane material undergoes changes caused by deformation of the crystalline and amorphous regions of the membrane sample. The data on the amorphous regions for air-dry, water-saturated and working semipermeable membrane samples were analyzed. The comparative analysis of the diffraction patterns of an MGA-95 membrane showed that the external impact does not change the intramolecular structure of the membrane. Using the experimental data and the method of small-angle X-ray scattering we calculated the size of pores for MGA-95 and ESPA composite membranes. The findings led to the conclusion about the relative uniformity of the pore distribution in the thickness of the active layer of the membrane, and made it possible to determine their configuration. The data on the pore structure morphology of semipermeable membranes indicated that sorption region of MGA-95 and ESPA membranes was formed by pores of different types with varied surface morphology; smaller radius pores had a smoother surface, while larger pores had a rough surface. The number of larger radius pores -12.9 and 16.8 nm were equal to 20 and 35.6 % for MGA-95 and ESPA, respectively. Specific surface values for MGA-95 was S sp = 9.15 × 107 m-1 and for ESPA it was S sp = 5.95 × 107 m-1.

We extend our method formerly suggested for structure refinement of the amorphous sp2 carbon, based on neutron or x-ray diffraction, and applied to amorphous fullerene and its derivatives produced by vacuum annealing. To diagnose heterogeneous media, the method uses the rigid body molecular dynamics simulations of the domain-like packing for a predefined set of structural blocks. Previously, the sensitivity of the results to the variability of mutual positions of these structural blocks was analyzed in two limiting cases: (A) any domain contains only identical structural blocks and (B) all domains are the identical mixtures of many different structural blocks with variable packing of the blocks. Here, we extend this analysis to intermediate cases which correspond to domains of the type “B” with the subdomains of the type “A”. Such a structuring corresponds to a partial destruction of the nanoscale structure of the sample (e.g. by low-temperature annealing).