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The results of theoretical and experimental studies into the effect of water vapor on the electrical conductance of a gas sensor and the sensor response to hydrogen action are discussed. A relation describing the dependence of electrical conductance G 0 on absolute humidity in the pure air is derived using a hypothesis of the presence of space-charge regions depleted of electrons between the SnO 2 grains in a polycrystalline tin dioxide film. Due to dissociative chemisorption of water molecules, the energy-band bending at the SnO 2 grain interfaces decreases and the oxygen-vacancy concentration in the grains increases, resuling in an increase in G 0 . An equation for the sensor response to hydrogen action is derived (the G 1 /G 0 , ratio, where G 1 is the sensor conductance in a gas mixture containing molecular hydrogen). The expression describes the dependence of G 1 /G 0 on the hydrogen concentration n H 2 in the interval 50-6·10 3 ppm, band bending at the SnO 2 grain interface, and sensor temperature. The dependences of the sensor conductance, highest possible conductance, and energy-band bending on temperature and absolute humidity resulting from processing of the experimental data are in good agreement with the theoretical predictions.

The growth of MnF2 and ZnF2 layers on Si(001) and Si(111) substrates was studied by molecular-beam epitaxy. Calcium fluoride buffer layers with (001), (110), and (111) orientations were used to prevent chemical interaction of MnF2 and ZnF2 molecules with the Si substrate. The analysis of x-ray and reflection high-energy electron-diffraction (RHEED) patterns showed that MnF2 layers grow on all of these planes in the orthorhombic α-PbO2-type crystal phase observed earlier only at high pressures and temperatures. Atomic force microscopy revealed a strong dependence of the surface morphology on the buffer orientation and growth temperature. The best-ordered MnF2 growth occurred at 500 °C on a CaF2 (110) buffer layer. The diffraction analysis enabled us to find the epitaxial relations at the MnF2∕CaF2 interface. A careful analysis of the RHEED patterns of the films grown on CaF2(001) showed a similarity in the structure and growth modes between MnF2 and ZnF2 layers, with ZnF2 tending to form multiphase layers. These findings are in agreement with the x-ray diffraction measurements.

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