Yu. A. Sten’kin

Formation mechanisms of nanocomposite layers based on multiwalled carbon nanotubes and non-stoichiometric tin oxide

Nanocomposite layers based on multiwalled carbon nanotubes (MWCNTs) and non-stoichiometric tin oxide (SnOx) have been grown by magnetron deposition and CVD methods. In the case of the CVD method, the study of the structure and phase composition of obtained nanocomposite layers has shown that a tin oxide “superlattice” is formed in the MWCNT layer volume, fixed by SnOx islands on the MWCNT surface. During magnetron deposition, the MWCNT surface is uniformly coated with tin oxide islands, which causes a change in properties of individual nanotubes. Electrical measurements have revealed the sensitivity of nanocomposite layers to (NO2)− molecule adsorption, which is qualitatively explained by a change in the conductivity of the semiconductor fraction of p-type MWCNTs.

Fabrication of por-Si/SnOx nanocomposite layers for gas microsensors and nanosensors

Two-phase nanocomposite layers based on porous silicon and nonstoichiometric tin oxide were fabricated by various methods. The structure, as well as elemental and phase composition, of the obtained nanocomposites were studied using transmission and scanning electron microscopy, Raman spectroscopy, Auger electron spectroscopy, and X-ray photoelectron spectroscopy. The results obtained confirm the formation of nanocomposite layers with a thickness as large as 2 μm thick and SnOx stoichiometry coefficients x = 1.0–2.0. Significant tin diffusion into the porous silicon matrix with Deff ≈ 10−14 cm2 s−1 was observed upon annealing at 770 K. Test sensor structures based on por-Si/SnOx nanocomposite layers grown by magnetron deposition showed fairly high stability of properties and sensitivity to NO2.

Effect of ethanol on optical and electrical parameters of porous silicon

The effect of ethanol vapor adsorption on the properties of porous silicon-based structures was studied by Raman scattering, infrared spectroscopy, and I–V characteristics. A decrease in the resistance of porous silicon layers and a simultaneous increase in the intensity of the band of infrared absorption caused by the presence of (OH)−…x(OH)− (x = 1, 2, …) groups upon exposure to ethanol vapor and vice versa in the case of degassing were detected. The observed effect is attributed to a change in the depletion region in por-Si skeleton elements due to the electrostatic interaction of (OH)− groups with positively charged surface defects. The effect of hydrogen-bonded Si-OH…OH-C2H5 centers on the increase in the silicon conductivity is discussed.

Origin of the low-frequency band in Raman spectra of multi-walled carbon nanotubes synthesized by the CVD method

The origin of the low-frequency band (250–300 cm−1) in the Raman spectra of multi-walled carbon nanotubes (MWCNTs) produced by the CVD method has been studied. The studies performed by Raman spectroscopy, transmission electron microscopy, Auger spectroscopy, and X-ray photoelectron spectroscopy after chemical and thermal treatments allow the assumption that this band belongs to radial vibrations of carbon atoms in internal walls of MWCNTs.

Formation of por-Si/SnOx nanocomposite by high-power ion beams of nanosecond duration

Layers of por-Si/SnOx nanocomposite formed by high-power ion beam irradiation with nanosecond duration have been studied. The results of structural and elemental analyses of these layers are presented. The high sensitivity of this nanocomposite to low NO2 concentrations at room temperature has been revealed.

Electrical and gas sensing properties of por-Si/SnO x nanocomposite layers

The electrical characteristics and chemical reactant sensitivity of layers of heterogeneous nanocomposites based on porous silicon and nonstoichiometric tin oxide por-Si/SnOx, fabricated by the magnetron sputtering of tin with subsequent oxidation, are studied. It is shown that, in the nanocomposite layers, a system of distributed heterojunctions (Si/SnOx nanocrystals) forms, which determine the electrical characteristics of such structures. The sensitivity of test sensor structures based on por-Si/SnOx nanocomposites to NO2 is determined. A mechanism for the effect of the adsorption of NO2 molecules on the current-voltage characteristics of the por-Si(p)/SnOx(n) heterojunctions is suggested.

Spectroscopic ellipsometry study of porous silicon-tin oxide nanocomposite layers

The layer-by-layer distribution of components in a porous silicon-tin oxide nanocomposite produced by the following three methods is studied by spectroscopic ellipsometry: chemical vapor deposition, atomic layer deposition, and magnetron sputtering. It is shown that, in the nanocomposites fabricated by these methods, SnOx penetrates to a depth more than 400 nm and is nonuniformly distributed over the porous layer thickness. The nanocomposite prepared by magnetron sputtering followed by heat treatment has the maximum penetration depth and the maximum uniformity of layer-by-layer SnOx distribution.

Effect of halogens on the formation and properties of the porous silicon layers

The method of atomic-force microscopy is used to study the morphology of the surface of porous silicon layers formed on the p-Si substrate and obtained by anodic etching in an electrolyte with addition of free halogens (bromine, iodine) and potassium halogenides (KCl, KI). It is established that the presence of halogens in the electrolyte is conducive to formation of large pores with the diameter as large as 150 nm. The mechanism of an increase in the pore sizes with involvement of halogens is related to an increase in the concentration of free holes due to formation of donor-acceptor pairs in the case of adsorption of halogens on the silicon surface.

Investigation of the hemoglobin adsorption in porous silicon by the ellipsometry method

The hemoglobin adsorption in porous silicon is studied by the method of spectroscopic ellipsometry. The layer-by-layer component distribution in the porous silicon-hemoglobin system shows that hemoglobin molecules penetrate through the porous layer with a slight gradient of the protein volume fraction.

Adsorption of hemoglobin molecules on porous silicon

It is established that hemoglobin can be immobilized in pores and on the surface of porous silicon. This is confirmed by the data of atomic force microscopy and Fourier-transform IR spectroscopy.