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Tin dioxide is a large band gap semiconductor, crystallizing in the rutile structure with D4h space group symmetry. Its unit cell is tetragonal and contains two molecules. The calculation of energy bands from first principles for such a crystal of relatively low symmetry and with a large number of valence electrons per unit cell is complicated I 1 to 41. A general description of the band structure in accordance with existing experimental information is still an open problem.To interpret the electrical transport measurement data it is necessary to know the shape of the conduction band, as Sn02 especially in the form of thin film is mostly an n-type semiconductor. In Dlh crystal symmetry, according to the group theory, four energy band models are possible: Experimental investigations of Hall effect, magnetoresistance, and planar Hall effect made by Nagasawa and Shionoya / 5 / indicate that the results can be interpreted in terms of a single spheroidal conduction band model. In general, however, the conduction band being isotropic may not be parabolic. In the case of Sn02, the effective mass of conduction electrons, as will be discussed further, strongly depends on energy indicating the nonparabolicity of the band. The concentration of conduction electrons in the band is influenced by the native defects (oxygen vacancies and interstitial tin ions) and intentionally introduced dopants. For electron concentration greater than lo1' cm-3 Sn02 behaves like a degenerate semiconductor. In that case an impurity band may form. Merging of the impurity band with the parent conduction band can additionally influence the shape of the conduction band.For an energy band with spherical symmetry the energy is assumed to depend solely on the absolute value of the wave vector, the form of this dependence being arbitrary:Wkl, k2, k3) E(k) . .

Reduced graphene oxide and copper oxide multilayer structures were fabricated in a planar configuration by deposition on both ceramic and Si/SiO2 substrates with interdigitated Au electrodes by the spray method. SEM (scanning electron microscopy), TEM (transmission electron microscopy), XRD (X-ray diffraction), and elemental analysis investigations indicated that graphene oxide (GO) was obtained in a form of interconnected flakes consisting of 6–7 graphene layers for GO with the total thickness of ca. 6 nm and 2–3 layers for rGO with the total thickness of 1nm. The lateral size of one flake reached up to 10 micrometers. Copper oxide was obtained by the wet chemical method. The number of sequential layers of the sensing structure was optimized to obtain good sensitivity and acceptable response/recovery times in response to the oxidizing nitrogen dioxide atmosphere. Both semiconductor partners revealed p-type conductivity. Formation of isotype heterojunctions between both semiconductor partners was taken into account and their influence on electrical transport explained. Optimized sensor structures revealed relative sensitivities reaching several tens of percent and acceptable response and recovery times in NO2 concentration ranged from a few to 20 ppm. Possibility of manufacturing sensors working at room temperature was shown, but at the cost of prolonged response/recovery times.

The analytical expression for the reflectance of a weakly absorbing wedge shaped thin film supported on a thick transparent substrate has been obtained. The envelopes of reflectance maxima and minima derived from that expression together with known formulae for envelopes of transmission spectrum enable calculation of optical constants and thickness non-uniformity of the film. The calculations have been applied to thin films of amorphous silicon and the results obtained have been compared with those for films considered uniform.