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We present studies of the catalytic-adsorption properties of the layered semiconductor structures metal - isolator-semiconductor (MIS) with Pd, bimetal Cu/Pd films and thin nanoporous silicon layers. Auger electron spectroscopy (AES) was used for elemental analysis of the metal electrodes and nanoporous layers. It was found that the using of thin bimetal films of d- and sp- metals (Cu/Pd) lead to the enhanced adsorption activity and stability to oxidation and ageing process. Moreover, a spillover gives rise to an additional mechanism of increasing of the gas adsorption activity related to the absorption gas by the Pd film and the suppression of desorption process. Porous silicon layers are known to be very active in gas adsorption. However, there are some problems that prevent the widely using of the porous silicon in the gas sensors. First, this is a large instability of its electrophysical parameters. Second, it is the change of its physical properties during ageing process. It was shown that the thermal treatment of the nanoporous silicon layers at 400-600°C for 30-60 min in O2-Ar gas mixture is one way of producing stable oxide at nanoporous silicon surface. The enhanced adsorption properties of MIS structures based on oxidized nanoporous silicon appear as a result. Moreover, palladium and composite CuxPd top electrodes play an important role in gas sensitivity of MIS structures based on nanoporous silicon layers upon hydrogen containing gas molecule action. Experiment shows that the adsorption isotherms depend on the type and state of catalytic metal surface. It can be seen that three types of the isotherms for fresh, aged or regenerated Pd films may be distinguished. Finally, we have studied the gas sensitivity of MIS structures based on nanoporous silicon films and catalytic active palladium/composite electrodes at room temperature upon the low H2S, H2 and H2O concentration (5–100 ppm) in air. The kinetic characteristics of the response signals of MIS structures with the different types of catalytic active top electrodes have been studied. The main conclusion is that the thin bimetal films (Cu/Pd) and oxidized nanoporous silicon give rise the enhanced gas sensitivity. The physical model has been proposed for explanation of the observed phenomena. |