Effect of heat-treatment on the hydrogen sensitivity of ZnO thin films loaded with palladium salts

Porous ZnO thin films were impregnated with palladium salts from their aqueous solutions, and the effects of heat-treatments on the appearence of the hydrogen sensitivity were investigated. In the course of the impregnation of PdCl₂, a ZnCl₂·4Zn(OH)₂ phase is formed in a surface region which retards the appearence of the hydrogen sensitivities. By heating the sample at 140–200 °C, this phase is decomposed but the impregnated PdCl₂ is not decomposed, and a remarkable hydrogen sensitivity appears even at room temperature. Similar situations hold in the loading of other kind of palladium salts, although the magnitude of the sensitivity is different between different kinds of loaded salts. The mechanisms of the appearence of the hydrogen sensitivity and of the loss of the sensitivity caused by the heat-treatment at higher temperatures are discussed.