  For hydrogen sensor and storage applications, films of Au and Pd were (i)
co-sputtered at different rates or (ii) deposited in a sequential
layer-by-layer fashion on a cover glass. Peculiarities of hydrogen uptake and
release were optically monitored using 1.3 micrometers wavelength light.
Increase of optical transmission was observed for hydrogenated Pd-rich films of
10-30 nm thickness. Up to a three times slower hydrogen release took place as
compared with the hydrogen uptake. Composition ratio of Au:Pd and thermal
treatment of films provided control over the optical extinction changes and
hydrogen uptake/release time constants. Higher uptake and release rates were
observed in the annealed Au:Pd films as compared to those deposited at room
temperature and were faster for the Au-richer films. Three main parameters
relevant for sensors: sensitivity, selectivity, stability (reproducibility) are
discussed together with the hydrogenation mechanism in Au:Pd alloys.
