In order to obtain a large movement with high power and responsiveness, a hydrogenation operated bimetal device made of La-Ni alloy film deposited on a thin copper (Cu) substrate foil, has been successfully developed. The sample of La-Ni film deposited on the Cu thin foil exhibits about 50% larger bending displacement than that on a thick sheet of polyimide substrate within 50 s. The influence of load on bending motion has also been investigated. The moving yield of the La-Ni film deposited on the Cu thin foil is larger than that on a polyimide thick sheet.

In this study, the effect of the palladium surface treatment was investigated on the mechanical response of the LaNi 5 thin film actuator deposited on polyimide substrates. Since controlling the hydrogen concentration in film by changing the pressure may reversibly drive this actuator, this film actuator can be expected as a sensor and/or a controller of hydrogen gas flux in various hydrogen related devices. In the present experiments, it was shown that the initiating time for the actuation to be measured after hydrogen gas exposure was reduced from 100 s to 1 s by the palladium surface treatment. This significantly improved mechanical response was attributed to the switching of the reactions in the rate determining steps. The rate determining reaction after the palladium treatment was no longer the dissociation of hydrogen gas molecules on the sample surface, but the hydrogen permeation or diffusion in the film. Furthermore, it was found that the high responsiveness induced by the palladium treatment was also caused by the high permeability of hydrogen in palladium film at room temperature.

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