Resistance change of cobalt and niobium films when exposed to hydrogen and carbon monoxide

The resistance of thin cobalt and niobium films was monitored during 1000 s exposures to hydrogen or carbon monoxide at a fixed pressure (${10}^{\mathrm{-}6}$ torr) and also during their removal. Upon an adsorption-desorption cycle the resistivity changed in a ``sawtooth'' fashion, similar to the changes previously observed in niobium foils. The resistivity increase by the adsorbed gas seems to be directly related to weakly adsorbed states on the surface. The magnitude of the resistivity changes due to gas adsorption is related to the surface roughness of the film.