Hydrogen absorption in Pd/Al multilayers

Hydrogen absorption in Al thin films coated with Pd is studied as a functio n of Al film thickness. For the thicker films, more than 70 nm, only small concentrations are achieved at all hydrogen pressures tested. For thinner f ilms, less than 55 nm, concentrations of up to 120 at.% are achieved. The c oncentration in Pd/Al multilayers, with modulation length of 60 nm, is simi lar to that of the thinner bilayers. The Pd layer thickness is 12 +/- 3 nm in all multilayers. Each multilayer is exposed to a hydrogen atmosphere of up to 80 Torr. The hydrogen concentration is determined from the frequency change in a quartz crystal microbalance. This absorption is confirmed by th e electrical resistance change of the Pd/Al multilayers.