S. Yu. Turishchev

Effect of Natural Aging on Photoluminescence of Porous Silicon

The influence of natural aging on the intensity and position of the photoluminescence (PL) peak in n-type porous silicon (por-Si) has been studied. Changes in the phase composition and relative content of the amorphous and oxide phases in por-Si during aging were determined by simulating the spectra of Si L2,3 ultrasoft X-ray emission based on the reference spectra of the corresponding phases.

Influence of natural aging on photoluminescence from porous silicon

The influence of natural aging on the photoluminescence intensity and the position of a photolu-minescence peak in n-type por-Si (por-Si) is studied. The variation of the phase composition and the relative content of the amorphous and oxide phases of silicon in por-Si during aging is determined by fitting simulated spectra to experimental ultrasoft Si L2,3 X-ray emission spectra using reference spectra.

XANES investigations of interatomic interactions in multilayered nanostructures (Co 45 Fe 45 Zr 10 / a -Si) 40 and (Co 45 Fe 45 Zr 10 /SiO 2 ) 32

The electronic structure and phase composition of amorphous multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32 have been investigated by means of the X-ray absorption near-edge structure (XANES) technique, which is the most sensitive and useful in investigation of the chemical environment of elements in multicomponent nanostructures. The fact of interatomic interactions leading to the formation of composite “nanoferrite”-like FeO · Fe2O3 · ZrO2(CoO) was established. Also it was shown that in the mentioned nanoferrite there is an exchange interaction which involves not only two- and three-charged ions of iron (Fe2+ and Fe3+) but also ions like Zr4+ and, partially, Co2+. The transformation of the thin structure of L2,3-ranges for the iron component of multilayered nanostructures in XANES spectra reflects on the change of the ratio of di- and trivalent ions in iron oxides as a part of the composite “nanoferrite.”

Preparation of porous silicon nanocomposites with iron and cobalt and investigation of their electron structure by X-ray spectroscopy techniques

A method for the galvanic deposition of iron-group metals onto porous silicon (por-Si) substrates has been developed. The morphology and phase composition of por-Si nanocomposites containing galvanically deposited particles of Fe, Co, and their mixtures have been studied by scanning electron microscopy (SEM), ultrasoft X-ray emission spectroscopy (USXES), and X-ray absorption near-edge structure spectroscopy (XANES) techniques. It is established that iron uniformly covers the surface of porous silicon, whereas cobalt penetrates deep into pores in the form of nanoparticles. During the galvanic codeposition of both metals from a mixed solution of their salts, cobalt favors the penetration of iron in depth of the pores.

Synchrotron investigations of the specific features in the electron energy spectrum of silicon nanostructures

The Si L2, 3 x-ray absorption near-edge structure (XANES) spectra of porous silicon nanomaterials and nanostructures with epitaxial silicon layers doped by erbium or containing germanium quantum dots are measured using synchrotron radiation for the first time. A model of photoluminescence in porous silicon is proposed on the basis of the results obtained. According to this model, the photoluminescence is caused by interband transitions between the energy levels of the crystalline phase and oxide phases covering silicon nanocrystals. The stresses generated in surface silicon nanolayers by Ge quantum dots or clusters with incorporated Er atoms are responsible for the fine structure of the spectra in the energy range of the conduction band edge and can stimulate luminescence in these nanostructures.

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.

A study of the local electronic and atomic structure in a-SixC1−x amorphous alloys using ultrasoft X-ray emission spectroscopy

X-ray spectroscopy has been used to obtain data on the local electronic and atomic structure of a-SixC1−x:H(Er) alloys produced by plasma-enhanced chemical vapor deposition (PECVD) with various relative amounts of silane and methane in the gas mixture (x=0.3–0.9). It is shown that the alloys contain silicon and carbon atoms in different coordination environments. Silicon is observed as elementary amorphous silicon and silicon carbide, and the relative amounts of these phases in the films depend on the composition of the gas mixture. Carbon atoms can form bonds with silicon in a coordination close to that found in crystalline silicon carbide, with a noticeable amount of C-H bonds also appearing. In addition, carbon can form an elementary carbon phase with various coordination numbers characteristic of graphite and diamond in the film.

X-Ray photoelectron spectroscopy investigations of atomic interactions in surface layers of multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32

The interatomic interaction and chemical state of elements in amorphous multilayered (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32 nanostructures with different interlayers have been investigated by X-ray photoelectron spectroscopy using synchrotron radiation. The results of X-ray photoelectron spectroscopy investigations have demonstrated that, in surface layers of all the studied multilayered structures, the metallic layer components Co, Fe, and Zr are in the oxidized state. The silicon state is found to be identical and close to the state of nonstoichiometric silicon oxide, regardless of the presumed compositions of SiO2 and a-Si interlayers. After the removal of surface layers of the multilayered structures in the sample preparation chamber by ion etching, the metallic layer components Co, Fe, and Zr are predominantly in the elemental state.

Interatomic interactions at interfaces of multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32

The interatomic interaction and phase formation at interfaces between the metallic layers Co45Fe45Zr10 and nonmetallic interlayers of amorphous silicon or silicon dioxide in multilayered nanostructures (Co45Fe45Zr10/a-Si)40 and (Co45Fe45Zr10/SiO2)32 have been investigated using ultrasoft X-ray emission spectroscopy (USXES) and X-ray diffractometry. The multilayered nanostructures have been fabricated by ion-beam sputtering of two targets onto the surface of a rotating glass-ceramic substrate. The investigations have demonstrated that, regardless of the expected composition of the interlayer (amorphous silicon or silicon dioxide), d-metal silicides, predominantly lower cobalt silicides, are formed at the metallic layer/interlayer interface. However, in this case, the thickness of silicide interfaces in the multilayered nanostructures with oxide interlayers (series O) has a significantly lower value of ∼0.1 nm, and, therefore, the central layer of the interlayers remains oxide. In the multilayered nanostructures with amorphous silicon interlayers almost all silicon is consumed in the formation of nonmagnetic silicide phases. When the thickness of this interlayer exceeds the thickness of the metallic layer, the multilayered nanostructures become nonmagnetic.

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.