E. P. Domashevskaya

APPLICATION OF SEMICONDUCTOR GAS SENSORS FOR MEDICAL DIAGNOSTICS

Abstract The appearance of a small amount of acetone vapour (0.1–10 ppm) in the human expiration means exacerbation of diabetes. This form of disease requires special forms of medical treatment and thus the detection of acetone proves to be an actual problem. Moreover, for some sick persons this parameter correlates with the content of glucose in the blood. The aim of this work is to show the principal possibility of the application of semiconductor gas sensors in the diagnosis of diabetes and the development of the prototype of gas analytical instrument based on these sensors.

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.

Spinodal Decomposition of GaxIn1−xAsyP1−yQuaternary Alloys

Using X-ray structural analysis, scanning electron microscopy, atomic force microscopy, and photoluminescent spectroscopy, it is shown that it is possible to obtain a small-scale domain structure on the surface of liquid-phase epitaxial heterostructures. The domain structure emerges as a result of spinodal decomposition of the GaxIn1 − xAsyP1 − y quaternary alloy due to immiscibility of its components and relaxation of its lattice parameter to surrounding layers.

Spinodal Decomposition of Ga{sub x}In{sub 1-x}As{sub y}P{sub 1-y}Quaternary Alloys

Using X-ray structural analysis, scanning electron microscopy, atomic force microscopy, and photoluminescent spectroscopy, it is shown that it is possible to obtain a small-scale domain structure on the surface of liquid-phase epitaxial heterostructures. The domain structure emerges as a result of spinodal decomposition of the GaxIn1 − xAsyP1 − y quaternary alloy due to immiscibility of its components and relaxation of its lattice parameter to surrounding layers.

The substructure and luminescence of low-temperature AlGaAs/GaAs(100) heterostructures

The substructure and luminescence of low-temperature epitaxial AlGaAs alloys are studied by Raman spectroscopy and photoluminescence spectroscopy. It is shown that the experimental data obtained in the study are consistent with the results of the previous structural and optical study. The assumption that, at high concentrations of carbon acceptors, the acceptor atoms concentrate at lattice defects of the AlGaAs crystal alloys to form carbon nanocrystals is confirmed.

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

Effect of silicon on relaxation of the crystal lattice in MOCVD–hydride AlxGa1 − xAs:Si/GaAs(100) heterostructures

The X-ray diffraction and infrared spectroscopy data for MOCVD-hydride AlxGa1 − xAs:Si/GaAs(100) heterostructures and homoepitaxial GaAs:Si/GaAs(100) structures doped with Si to a content of up to ∼1 at % are reported. It is shown that, in the homoepitaxial heterostructures, the formation of alloys with Si yields a decrease in the crystal lattice parameters of the epitaxial layer and a negative lattice mismatch with the single-crystal substrate (Δa < 0). At the same time, the formation of quaternary alloys in the AlxGa1 − xAs:Si/GaAs(100) heterostructures is not accompanied by any pronounced strains in the crystal lattice. By introducing Si into the epitaxial layers of these heterostructures, it is possible to attain complete matching of crystal lattice parameters of the film and substrate in the appropriately chosen technological conditions of growth of the epitaxial layers.