V. A. Moshnikov

XANES and IR spectroscopy study of the electronic structure and chemical composition of porous silicon on n- and p-type substrates

The differences in the electronic structure and composition of porous silicon samples obtained under identical conditions of electrochemical etching on the most commonly used n- and p-type substrates with different conductivities are demonstrated by X-ray absorption near-edge spectroscopy (XANES) and Fourier transform IR spectroscopy (FTIR) methods. It is shown that significantly higher oxidation and saturation with hydrogen is observed for the porous layer on n-type substrates.

Surface functional composition and sensor properties of ZnO, Fe2O3, and ZnFe2O4

Zinc and iron oxide (ZnO, Fe2O3) and zinc ferrite (ZnFe2O4) nanopowders are obtained by chemical co-precipitation. The gas-sensitive properties of materials upon exposure to acetone and ethanol vapors are analyzed. It is found that the sensitivity of ZnFe2O4 to ethanol and acetone is better than the sensitivity of simple oxides by one and two orders of magnitude, respectively. Analysis of the surface of the materials under study shows that the observed differences in their gas sensitivity are caused by a high concentration of Brönsted acid centers on the ZnFe2O4 surface, which can be involved in redox reactions and facilitate the selective adsorption of ethanol.

SnO2 based gas sensitive sensor

Abstract SnO2 films have been formed by the thermal vacuum deposition of Sn, pure Sn doped by Te and J2 has been formed and also Sn doped by Cu with post-treatment under controlled oxygen atmosphere has been formed. Iodium had been introduced into the initial mixture as a SnJ2 to form a better modified film surface for sensivity increase. The results of influence of annealing in dynamic vacuum conditions on SnO2 films properties are shown.

Study of the effect of the acid-base surface properties of ZnO, Fe2O3 and ZnFe2O4 oxides on their gas sensitivity to ethanol vapor

Binary (ZnO, Fe2O3) and ternary (ZnFe2O4) gas-sensitive oxide materials are synthesized, and the correlation between their sensitivity to ethanol vapor and the functional chemical composition of the surface is studied by X-ray photoelectron spectroscopy and by the technique of the adsorption of acid-base indicators. It is found that the sensitivity to ethanol increases with increasing content of Brönsted acid sites with the acidity index pKa ≈ 2.5 and with increasing percentage of surface oxygen involved in OH/CO3/C-O groups. This interrelation is attributed to the specific features of interaction between ethanol molecules and hydroxyl groups on the surface of the oxides.

Self-organization of polyaniline during oxidative polymerization: formation of granular structure

The paper is focused on oxidative polymerization of aniline proceeding in an acid medium with a strong oxidant; formation of polyaniline (PANI) granular structures in different steps of the synthesis was studied. The relationship between the processes of self-organization of the growing polymer into supramolecular structures and the steps of molecular synthesis has been revealed. It was shown that during the induction period (the initial synthesis step), insoluble non-conducting products are formed. They are characterized by the absorption band at 430 nm corresponding to the wavelength of the phenazinium cation radical peak. In the second step, the polymer chain growth, conducting PANI granules with the diameter of 50 nm were obtained. These granules consist of spherical particles with the diameter as small as several nanometers. Then, the granule dimensions increased to 200 nm due to the growth of the spheres; the sphere diameter reached 20 nm. The number of spheres in a granule remained constant. Both precipitate and PANI film consist of common structural elements, polymer spheres, organized into granules and larger structures. Suppression of the polymer chain growth leads to the formation of non-conducting aniline oligomers which are self-organized into large particles with fractal structure. To describe the self-organization processes of a growing polymer chain, the diffusion-limited aggregation mechanism was used.

Study of the morphological growth features and optical characteristics of multilayer porous silicon samples grown on n -type substrates with an epitaxially deposited p + -layer

This study is concerned with the growth features of multilayer porous silicon with layers of different porosity, obtained by electrochemical etching on an n-type single-crystal silicon (111) wafer with a p+-layer epitaxially deposited onto the surface. The possibility of obtaining a multilayer system of ordered pores of various sizes within a single technological cycle is demonstrated. The differences in the optical characteristics of separate layers of the grown structure are shown.

Net-like structured materials for gas sensors

Silicon dioxide-based fractal aggregates as an example of self-assembly in sol-gel processes were prepared. Main evolution stages of tin dioxide-silicon dioxide fractal systems were demonstrated by atomic force microscopy (AFM): diffusion-limited aggregation, cluster-cluster aggregation, formation of percolation net and 3D-net nanostructures. The formation possibilities of porous nanomaterials based on different metal oxides, including those based on tin dioxide, iron oxide and zinc oxide, were shown. New chemical etching method to obtain microreactors was developed. Specific surface area of nanostructures was investigated by thermal desorption of nitrogen and gas sensitive properties of tin dioxide nanocomposites were also studied.

Investigation of sol-gel derived nanomaterials with a hierarchical structure

The basic processes of self-assembly in sol-gel technologies during the formation of network nanomaterials with a hierarchical structure have been considered. The gas-sensitive fractal structures have been prepared in systems based on dioxides of tin and silicon. The formation of a structure of nanocomposites has been studied using atomic force microscopy and electron microscopy methods. The gas-sensitive properties of nanomaterials have been investigated. A method for diagnosing objects with a hierarchical structure based on metal oxides has been proposed.

Electron Microscopic Investigation of the Structure of Gas-Sensitive Nanocomposites Prepared by the Hydropyrolytic Method

Polycrystalline films in the SnO2–In2O3 and SnO2–ZnO systems, which are of interest for use in gas-sensitive sensors, are grown from metal chlorides on a 22-XC ceramic substrate by the hydropyrolytic method. The nanocomposites based on tin dioxide are studied. The structure of polycrystalline grains is investigated by electron spectroscopy and X-ray diffractometry. The distribution of components in the samples prepared is examined using electron probe X-ray microanalysis. It is established that homogeneous films in the SnO2–In2O3 system up to 10 mol % In2O3 in the initial solution can be grown by the hydropyrolytic method.

A computer-aided setup for gas-sensing measurements of sensors based on semiconductor nanocomposites

The design of the computer-aided setup for gas-sensing measurements of semiconductor sensors is described. The setup is intended to programmably control thetemperature and gas supply and measure the sensor resistances. The curves of the responses of the sensors manufactured by the sol-gel and hydropyrolysis methods to the gas-composition variations are obtained. They allow one to extend model concepts on the gas adsorption at these sensors.