Abstract

Adsorption of H2 and CO on Nb, Co, Ni and Pd films was monitored by changes of the film resistance during the exposure to the gases. Films with thicknesses varying from 6 to 400 nm were deposited onto mica or sapphire substrates. The increase in resistance was measured near room temperature during exposure to 1000 Langmuir of either H2 or CO. When the gas dosing was discontinued and the chamber was evacuated, the film resistance decreased until it reached its initial value. The change in resistance of very thin, rough Co and relatively thick, smooth Co, Nb and Ni films upon exposure to either H2 or CO are comparable in magnitude. There is a relationship between this effect and surface roughness. The change in resistace is related to weakly adsorbed states of these molecules close to the surface. On the other hand, the change in resistance of thin Pd films is related to the diffusion of atomic hydrogen into the bulk of the films.