V. A. Terekhov

A study by XPS and XRS of the participation in chemical bonding of the 3d electrons of copper, zinc and gallium

Abstract The participation of 3d electrons in chemical bonds and their part in the formation of valence bands was studied by X-ray photoelectron- and X-ray-spectroscopy for Cu, Zn and Ga phosphides, sulphides and oxides. Incomplete screening of ( n + 1)s,p electrons through the n d shell leads to non-systematic changes of orbital energies and radii of the valence electrons in the first, second and third Group elements. It is reflected in the electronic structure of the respective compounds. A qualitative interpretation of XPS and XRS data for Cu, Zn, Ga phosphides is given. Possible reasons for phosphorus s band splitting for zinc and copper phosphides are considered. The interaction of 3d metal states and 3s, p third Period element states considerably affects the valence band of compounds, and this interaction should be taken into account when considering electronic structures of Cu, Zn and Ga compounds.

XPS and XES emission investigations of d–p resonance in some copper chalcogenides

Abstract Investigations of binary and ternary copper tellurides and selenides electron energy spectra are of interest because of the considerable sensitivity of their electrophysical and optical properties to the stoichiometry of these compounds. Ab initio theoretical calculations for these non-stoichiometric AI2−xBVI compounds are difficult due to the existence of 3d-electrons in copper. Thus investigations of their band structure and electron density by means of X-ray photoelectron (XPS) and X-ray emission (XES) spectroscopy are important. In this work XPS of binary Cu2Se, Cu1.84Se, Cu1.82Se, Cu2Te, Cu1.95Te, Cu1.9Te, Cu1.7Te, and ternary CuInSe2 are obtained and matched on a common binding energy scale with the corresponding XES. The results of this matching show that copper 3d-states appear to be in the center of the tellurium or selenium p-band, splitting it into two components nearly symmetrically relatively to the d-bands. The splitting value is proportional to the content of copper in all compounds and inversely proportional to the gaps in binary chalcogenides, which corresponds with the d–s, p-resonance model. Comparative analysis of the electronic structure of binary and ternary compounds raises questions about the role of indium in determining the optical properties of CuInSe2.

Determination of the phase composition of surface layers of porous silicon by ultrasoft X-ray spectroscopy and X-ray photoelectron spectroscopy techniques

Abstract The phase composition of the surface layers in porous silicon (por-Si) is determined by analysis of the density of states in the valence band using ultrasoft X-ray emission spectroscopy (USXES) and X-ray photoelectron spectroscopy (XPS) of the core levels. Since porous silicon demonstrates instability of its properties the investigations of the changes in its phase composition under atmosphere exposure (e.g. low-temperature anneals in an oxygen flow) have been made. Phase analysis by USXES is performed with the help of a specially elaborated mathematical technique using expansion of the experimental spectrum by the spectra of some standard samples. c-Si and c-SiO 2 as well as disordered phases of these species (by USXES) and low-oxidized defect silicon (by USXES and XPS) have been detected in the surface layers of por-Si. Some changes in the composition were found in the samples annealed in oxygen at various temperatures.

Valence-level structure of phosphides of 3d-metals on the basis of XRS and ESCA data

Abstract For the first time, comprehensive X-ray spectroscopic and X-ray photoelectron data have been obtained on the energy spectra of valence electrons in phosphides of the transition metal series: TiP, CrP, MnP, FeP, NiP. Analysis of the experimental data on the electronic structure of phosphides of 3 d -metals in the TiPNiP series indicates that the mechanism of interaction of the M 3 d -states occurring near the top of the valence band with the s,p -states of phosphorus in the following sub-bands resides in the latter being induced near the d -sub-band as a result of the M 3 d —P 3 s,p interaction with the density maximum of the nearest P 3 p -states being oppositely shifted as the number of d -electrons of the metal increases. Analysis of X-ray spectroscopic and X-ray photoelectron data on phosphides of transition metals along with those of metals of groups I(Cu, Ag) and II(Zn, Cd), and comparison of these data with the results of similar studies involving sulphides and silicides of the same metals indicate that the occupancy and the associated position of the d -shell of the metal within the valence band are the determining factors as far as the mutual arrangement of energy sub-bands and the symmetry of respective states are concerned.

Participation of d-electrons of metals of groups I, II, and III in chemical bonding with sulphur

Abstract X-ray photoelectron and X-ray spectroscopic data have been used to study the participation of the d-electrons in chemical bonding and their role in the With increasing metal atomic number within one group the d sub-band increases by ca. 2 eV in group I and by ca. 1 eV in group II. In the sulphur compou

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.

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.

Density of states and photoconductivity in hydrogenated amorphous silicon

Changes in the electron structure of a-Si:H films subjected to thermal annealing in vacuum has been investigated by ultrasoft X-ray emission spectroscopy. It is shown that the density of localized states (DOLS) in various regions of the pseudogap varies differently with the annealing temperature. Two maxima in the DOLS were detected at a distance of ~1 eV and ~1.4 eV from the top of the valence band.

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 study of the formation of nanoclusters in Al2O3/SiOx/Al2O3/SiOx/…/Si(100) multilayer nanostructures

Al2O3/SiOx/Al2O3/SiOx/…/Si(100) multilayer nanoperiodic structures (MNS) are studied by X-ray absorption near-edge structure spectroscopy (XANES). Experimental XANES spectroscopy spectra are obtained using synchrotron radiation. The formation of Si nanoclusters in the surface layers of the structures during their high-temperature annealing is observed. The structures featured intense size-dependent photoluminescence in the wavelength region near 800 nm. At the same time, it is shown that the formation of aluminum silicates is possible. The inversion effect of the intensity of the XANES spectra during the interaction of synchrotron radiation with MNSs is revealed.