Yu. A. Yurakov

SPECIFIC FEATURES OF ELECTRON STRUCTURES OF SOME THIN FILM D-SILICIDES

Abstract The Si L 2,3 -spectra of thin films of transition d-metal (TM) silicides (d-silicides) obtained by the ultrasoft X-ray emission spectroscopy (USXES) method have been analyzed on the basis of our d–s,p resonance model. Different stoichiometric composition silicides were obtained depending on the annealing conditions of heterostructures TM/Si mono TM/SiO 2 /Si mono. Compared with the spectra of the bulk samples, Si L 2,3 -spectra of thin film silicides demonstrate an increased intensity in the high energy range near the Fermi level. The unique sharp intensive peak of the Si s-state at the Fermi level is a consequence of the distinction of d–s resonance in NiSi 2 .

Electronic structure of rhenium disilicides

The valence band structure of amorphous and crystalline films of rhenium silicides has been studied by ultrasoft x-ray spectroscopy. A theoretical calculation of the electronic structure of bulk crystals and thin films of ReSi2 and ReSi1.75 was carried out. The experimental L2,3-spectra of silicon show the best correlation with the theoretical calculation for ReSi1.75. The decrease in the density of states at the Fermi level in ReSi1.75 in comparison with ReSi2 testifies that the phase with lack of silicon is more stable than the stoichiometric composition.

XANES and XPS investigations of surface defects in wire-like SnO2 crystals

Wire-like SnO2 micro- and nanocrystals prepared by gas-transport synthesis have been studied by X-ray photoelectron spectroscopy and X-ray absorption near edge structure spectroscopy with the use of synchrotron radiation. It has been found that the heat treatment in ultrahigh vacuum affects the surface state and the vacancy formation in surface layers of the wire-like crystals.

Composition and Reactivity of Porous Silicon Nanopowders

We have studied the chemical reactivity of silicon powders with distilled water. Nanopowders were prepared through electrochemical etching of silicon wafers, followed by grinding of the porous layer. The composition of the chemical bonds in the powders was determined by IR spectroscopy. The particle size of the powders was evaluated using transmission electron microscopy and nitrogen thermodesorption measurements. According to potentiometry data, the powders differ in their reactivity with water, which can be understood in terms of the particle composition and size.

Synchrotron studies of SnO2 wire-like crystals

Wire-like micro- and nanocrystals of SnO2 are obtained via gas-transport synthesis. The specifics of the atomic and electronic structure of an array of SnO2 wire-like crystals is revealed using near-edge X-ray absorption and X-ray photoelectron spectra. The method of photoemission electron microscopy with high-intensity synchrotron (undulator) radiation is used to study the morphology of SnO2 wire-like crystals for the first time.

The formation of tin oxides in thin-film Sn/C/KCl(100) structures

The formation of oxides upon the thermal annealing (both in air and vacuum) of island tin films grown on a KCl(100) substrate, which was coated by a thin layer of amorphous carbon, has been investigated by transmission electron microscopy. It is established that thermal annealing at temperatures below the tin melting point (Tm) does not lead to phase transitions with the formation of new crystalline oxide phases. At the same time, the films undergo structural changes: the average size of blocks in the substrate plane decreases compared to those in an as-deposited film. Thermal annealing in air at temperatures above the tin melting point leads to the formation of multiphase oxide structures and increases the average size of blocks and islands in the substrate plane. It is shown that preliminary thermal annealing in air at temperatures below Tm hinders oxidation upon subsequent heat treatment.

Kinetics of resistive response of SnO2 − x thin films in gas environment

Data on the gas sensitivity of SnO2 − x thin films in oxygen and hydrogen environment are obtained. The films were fabricated by oxidizing metallic tin layers in air at various temperatures. The nonmonotonic kinetics of the resistive response of SnO2 − x samples under gas-adsorption conditions is explained by the involvement of “biographic” electron states (determined by the manufacturing methods and machining of samples), whose density depends on the temperature conditions of manufacturing the SnO2 − x film in the adsorbate-semiconductor interaction.

Electronic structure of molybdenum disilicide

The electronic states of molybdenum disilicide in the body-centred tetragonal phase have been studied using the self-consistent linearized augmented plane wave method in the local density approximation. The total and local densities of electronic states, X-ray emission spectra of different series were calculated. The obtained results agree well with the known experiments.

X-ray Photoelectron Spectroscopy of Tin Oxide Nanolayers

X-ray photoelectron spectra of 30- and 100-nm nanolayers, recorded in the energy range 0–35 eV, show a strong dependence of both the distribution of the density of Sn 5s, p+ O2p valence states and the change in the intensity ratio for the Sn 4d and O 2s subvalence states on the annealing temperature and nanolayer thickness. In the nanolayers fabricated at an annealing temperature of 450°C, an unusually strong band of O 2s states of unbound oxygen is observed, which is retained for nanolayers doped with palladium and disappears for nanolayers doped with gold and silver.

Optical properties of SnO2−x nanolayers

Specific features in the optical absorption spectra and capacitance-voltage characteristics of SnO2−x nanolayers have been observed. These features are determined by the surface and intergranular states of Sn2+ ions, which appear due to the oxygen deficit and form localized states in the bandgap of SnO2−x. The observed dimensional effect in SnO2−x nanolayers is manifested by an increase in their bandgap width as compared to that in the bulk SnO2.