V. M. Astashynski

Erosion of materials under the effect of compression plasma flows

Erosion of the surface of St3-type steel and BrB2-type bronze samples as well as bronze and copper samples with zirconium coating under the effect of compression plasma flows is studied. The results show the increase in mass removed from the surface of samples with the growth of energy absorbed by the surface layer and with the growth of the number of pulses. Probable mechanisms of erosion have been discussed. Erosion leads to the decrease in the coating element concentration in the alloyed layer in the case of the coating/substrate system treatment. This effect depends on thermal characteristics of the treated material.

Thermal stability of silicon photovoltaic structures produced using compression plasma flows

Thermal stability investigations of photovoltaic structures synthesized by the compression-plasma-flow treatment of doped silicon are performed. The samples are annealed in an atmosphere of nitrogen, in air or in vacuum in a temperature range of 100–900°C for 30 min or 3 h. The photovoltaic effect does not change after annealing at temperatures up to 600–700°C. It decreases 1.3–1.7 times after thermal annealing at a temperature of 900°C. The structure-phase changes of silicon treated with compression plasma flows are studied using X-ray diffraction and scanning electron microscopy methods. It is established that a recrystallized pre-surface layer with a thickness of 10–20 μm and modified (but not melted) layer with a thickness of up to 50–60 μm localized below the recrystallized layer are formed.

Structural and phase changes in single-crystalline silicon treated with compression plasma flows

The structural-phase changes in p-type single-crystalline silicon treated with compression plasma flows (CPFs) with an energy density of 5–12 J/cm2 are investigated by the X-ray diffraction method depending on the crystallographic orientation of the silicon and the plasma energy density. In addition, the conductivity type on the treated silicon surface is determined by means of measuring the sign of the thermopower.; the surface morphology, by scanning electron microscopy; and the open-circuit voltage, upon illumination of the treated silicon surface (AM1.5 spectrum). It is found that treatment with CPFs results in the occurrence of the photovoltaic effect conditioned by the formation of an n-type modified surface layer. Depending on the crystallographic orientation, the modified layer either remains single crystalline (for the initial orientation (111)) or is subjected to amorphization (for the initial orientation (100)). At an energy density of ∼8–9 J/cm2 the action of CPFs leads to texture formation on the silicon surface.

On features of the magnetic structure of spherical iron nanoparticles

The results of research into the behavior of the magnetic structure inherent to spherical ferromagnetic nanoparticles with radii of 5–30 nm are presented. The behavioral features are investigated in an external magnetic field by means of computer modeling. The hysteresis loops and formation of the vortex structure of magnetization are analyzed using particles with different sizes. The size effect of changes in the magnetization symmetry, which is analogous to phase transitions of the second kind, is established. The magnetic moments of spherical iron nanoparticles with radii of 5–30 nm are calculated. Calculations are performed by means of the Nmag micromagnetic simulation package.

Thermal Stability of the Structure and Phase Composition of Titanium Treated with Compression Plasma Flows

The results of studying the structure and phase composition of the surface layer of commercial pure VT1-0 titanium treated with compression plasma flows in nitrogen atmosphere and annealed in the temperature range of 400–900°C for 1 h are presented. Using the X-ray diffraction method, the α-Ti(O) solid solution is found to form in the titanium surface layer at 500°C, without pretreatment with plasma, and to transform into the titanium oxide TiO2 (rutile) phase at 600°C. Pretreatment of titanium with compression plasma flows promotes the formation of α-Ti(N) solid solution decreasing the rate of surface oxidation and increasing the initial temperature of rutile formation to 700°C, which indicates enhancement of the thermal stability of this structure.

NANO-SIZED SPHERICAL CLUSTERS OF TANTALUM SILICIDE FORMED BY COMPRESSION PLASMA FLOW

A pre-deposited tantalum thin film on a Si(100) substrate was treated by compression pulsed plasma flow. SEM images demonstrated the formation of spherical clusters with multi-level structures. Formation of crystalline metal rich tantalum silicides is confirmed by X-ray diffraction and EDX elemental map analysis. The results show great potential application of compression plasma flow for the development of novel nanostructured metal-silicide materials.