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Polymer films with small Ag-clusters and Ag-nanocrystals were obtained by the cocondensation of Ag and chloro-p-xylylene from the gaseous phase followed by low-temperature solid-state polymerization. UV-Vis spectroscopic data show that the annealing of films at ambient temperature and thereafter at 373 K leads to a sharp rise of the amount of Agnanocrystals by aggregation of small clusters, but the mean size iof the nanocrystals remains practically constant. According to X-ray data, the lattice of Ag-nanocrystals is close to that of metallic Ag and i i s equal to approximately 50 A.

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This paper reviews the important problems associated with the synthesis of metal-oxide nanocomposites, charge transfer phenomena in these composites, their conductive and sensory properties, modeling of sensory effect and the role on this sensory effect of the electronic structure of the metal oxide. The size of metal particles and temperature significantly influence the efficiency of such systems. However, the electronic interactions between the different components of the nanocomposite films play the dominant role in the exploitation of the properties of such sensory systems. Depending on the chemical nature of the analyzed gas and the electronic structure of the semiconducting metal oxides, such interactions can result in either an increase or a decrease of the sensory effect. Thus, by varying the electronic structure of the metal oxide composite sensors as well as the temperature and size of the metal-oxide nanoparticles, the inherent characteristics of the sensor can be changed and tailored for detection of various gases. Such findings clearly open up new opportunities for development of novel selective sensors.

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