Novel gas sensors based on multilayer structures of metallic thin films (Pt, Au, Ni, Mo) and tin oxide were fabricated and investigated. Surface chemical composition of the sensors before and after the interaction with gases was analysed by using X-ray photoelectron spectroscopy (XPS). The XPS depth profiles of the samples were acquired by using low energy Ar~+ etching. The temperature dependencies of the dc electrical resistance and the resistance response to CO, H_2 and NO_x gases tested, while the single metal layers were practically insensitive. The addition of the metal interlayer modified drastically the resistance response to gas. The results of surface analysis and depth profiling are compared with the data of electrical measurements. Gas sensitivity is explained by reversible processes of gas adsorption-desorption, which cause the changes of electron transport in very thin films of metal.
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