S. P. Bardakhanov

Structure and mechanism of the formation of core-shell nanoparticles obtained through a one-step gas-phase synthesis by electron beam evaporation.

Summary The structure of core–shell Cu@silica and Ag@Si nanoparticles obtained in one-step through evaporation of elemental precursors by a high-powered electron beam are investigated. The structure of the core and shell of the particles are investigated in order to elucidate their mechanisms of formation and factors affecting the synthesis. It is proposed that the formation of Cu@silica particles is mainly driven by surface tension differences between Cu and Si while the formation of Ag@Si particles is mainly driven by differences in the vapour concentration of the two components.

Visible photoluminescence from silicon nanopowders produced by silicon evaporation in a high-power electron beam

Silicon nanopowders produced by electron-beam-induced evaporation of a bulk silicon sample in an argon atmosphere are studied by the photoluminescence technique and Raman scattering spectroscopy. A photoluminescence peak in the visible region of the spectrum has been detected at room temperature in powders consisting of silicon nanocrystals. The strong short-wavelength shift of the photoluminescence peak can be attributed to the quantum size effect of electrons and holes in small silicon nanocrystals (about 2 nm). The size of silicon nanocrystals is determined by analyzing Raman spectra, and it is consistent with estimates obtained from photoluminescence data.

Properties of ceramics prepared from nanopowders

Fine-grained (on the order of several microns in grain size) ceramics have been produced from various nano- and submicron-sized powders (silica, alumina, titania, aluminum nitride, and tungsten carbide). The compaction and sintering behaviors of various powder mixtures and the properties of the resultant ceramics have been studied. For a number of compositions, fine-grained, dense, high-strength ceramics have been obtained with a microhardness of up to 16–18 GPa.

High Volume Synthesis of Silicon Nanopowder by Electron Beam Ablation of Silicon Ingot at Atmospheric Pressure

The evaporation of high purity silicon ingot was performed in Ar, N2, and air atmospheres using a power electron accelerator. The obtained powders with primary particle sizes of 10–500 nm were investigated using Brunauer–Emmett–Teller analysis (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence measurement, and Raman spectroscopy. The structure and photoluminescence properties of Si(Ar) nanopowder obtained at a large quenching rate differ substantially from those of Si(Ar) and Si(N2) obtained at a smaller quenching rate. Photoluminescence peaks in the visible region of the spectrum are detected at room temperature for the Si(Ar) nanopowders.

Synthesis of copper nanopowders using electron-beam evaporation at atmospheric pressure of inert gas

This work is devoted to the description and analysis of the technique used to obtain copper nanopowder by substance evaporation with the help of a powerful electron beam. The method possesses the following features: high yield, the possibility of obtaining nonoxidized copper, it works at atmospheric pressure, and the possibility of varying the parameters of the powders to be obtained directly in the process of synthesis. The possibility of efficiently obtaining nonoxidized copper using a closed cycle of inert gas circulation has been implemented. Copper nanopowders of a spherical shape with a diameter from 15 to 700 nm have been obtained. The dependences of the performance and specific surface area of the powders on the parameters of the production process for various evaporation modes are obtained. The factors affecting the size of the particles to be obtained (modes of boiling and cooling and configuration of the vaporization region) are analyzed. The peculiarities of the process used to obtain copper nanopowders are revealed. This allowed us to create a system for monitoring and controlling the parameters of the process, which made it possible to increase its performance and broaden the range of varying nanopowder properties.

Polymer-liquid crystal composites doped by inorganic oxide nanopowders

This paper investigates the impact of nanoscale additives on electro-optical properties of films of polymer-liquid crystal composites (PLCC). It has been shown that the nanoparticles doping in the polymer matrix leads to a change in the parameters of the film produced therefrom, in particular, the coefficient of refraction and the dielectric constant. The absence of a chemical interaction between the nanoparticles and droplets of liquid crystals (LCs) was noted. The dependence of the light transmission of the composition on the nanoparticles size and their concentration were obtained. It is noted that the presence of ionic impurities in silica distorted the photosignal shape and degraded the relaxation time. It is shown that the nanopowders decreased the threshold voltage of LC reordering and reduced the LC response time at both threshold levels and at the saturation level of the control field. This shows the good potency of nanomodifiers in the PLCC.

Synthesis, Characterization, and Mechanism of Formation of Janus-Like Nanoparticles of Tantalum Silicide-Silicon (TaSi2/Si)

Metal-semiconductor Janus-like nanoparticles with the composition tantalum silicide-silicon (TaSi2/Si) were synthesized for the first time by means of an evaporation method utilizing a high-power electron beam. The composition of the synthesized particles were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), selective area electron diffraction (SAED), and energy dispersive X-ray fluorescence (EDX) analysis. The system is compared to previously synthesized core-shell type particles in order to show possible differences responsible for the Janus-like structure forming instead of a core-shell architecture. It is proposed that the production of Janus-like as opposed to core-shell or monophase particles occurs due to the ability of Ta and Si to form compounds and the relative content of Ta and Si atoms in the produced vapour. Based on the results, a potential mechanism of formation for the TaSi2/Si nanoparticles is discussed.

Preparation and properties of ceramics from a zirconia nanopowder

The possibilities of preparing ceramics from a zirconia nanopowder have been investigated. A ceramic material with a fine-grained (of the order of 2–3 µm) structure is synthesized. A ceramic material with zircon predominant is produced using a silica nanopowder (tarkosil). The properties of the initial nanopowder and the ceramic material synthesized are investigated using transmission electron and scanning electron microscopies. The microhardness and strength of the ceramics are determined.

Ceramics prepared from silicon dioxide nanopowders

The possibilities for preparing ceramics from silicon dioxide nanopowders are analyzed. A ceramic material with a fine-grained structure (with grain sizes of the order of 10–20 μm) is synthesized, and its optical properties are investigated.

Use of hot-wire anemometry for measuring the nanopowder flow velocity

A new technique for measuring the flow velocity of nano-scale powders is used. The hot-wire anemometry method widely used in gas flows is employed for investigating nanopowder flows. By way of illustration, the flows of nanopowders of aluminum oxide C and silicon dioxide aerosil A-90 and A-380 in a vertical channel are studied. The results obtained show that nanoscale powder flow investigation by means of the hot-wire anemometry is promising.