Free-standing Pd/Ag23 wt% membranes with five different thicknesses ranging from similar to 1.3 to similar to 5.0 mu m were prepared by magnetron sputtering. The hydrogen permeation was determined before and after a thermal treatment in air at 300 degrees C. For all membranes studied, the thermal treatment resulted in enhanced permeation, and for some membranes, the hydrogen flux more than doubled. A permeance of 1.7 x 10(-2) mol/m(2) s Pa-0.5 was observed for similar to 1.3 mu m thick membranes, which is one of the highest reported. Bulk diffusion was found to be the main rate-limiting step after thermal treatment in air. The permeability was quite similar for all membranes studied after this treatment, with a mean value of 2.1 x 10(-8)+/- 5 x 10(-10) mol m/m(2) s Pa-0.5. Topography studies by atomic force microscopy showed that the samples thermally treated in air had higher surface roughness, larger surface area and larger surface grains than samples not heat-treated in air. (c) 2007 Elsevier B.V. All rights reserved.