Composition control and hydrogen permeation characteristics of sputter deposited palladium-silver membranes

Submicron thick continuous palladium-silver films were deposited by sputtering on mesoporous gamma-alumina substrates from a target composed of 75% Pd and 25% Ag. These membranes were tested in a multigas permeation system for hydrogen permeance and hydrogen selectivity over helium. Hydrogen permeance for the membrane used in the study was found to be in the range of 3 x 10(-8) to 1 x 10(-7) mol/m(2)s Pa and H-2/He selectivities were in the range of 4-4000, depending mainly on Ag concentration and microstructure of the Pd-Ag films. A simple model based on the material balance concept has been developed to describe the transient composition behavior of the multicomponent sputter deposition process. The model is compared with experimental data over a range of deposition powers and target equilibration times. The results of the model agree well with experimental data. Both theoretical and experimental data show that deposition power and target equilibration are the most important variables affecting membrane composition. (C) 1999 Elsevier Science B.V. All rights reserved.