The Response of Work Function of Thin Metal Films to Interaction with Hydrogen

The aim of this paper is to summarize the results of experiments carried out at our laboratory on the response of the work function of several thin films of transition metals and rare earth metals to interaction with molecular hydrogen. The main focus concerns the description of surface phenomena accompanying the reaction of hydride formation as a result of the adsorbate’s incorporation into the bulk of the thin films. Work function changes ∆Φ caused by adsorption and reaction concern the surface, hence this experimental method is appropriate for solving the aforementioned problem. A differentiation is made between the work function changes ∆Φ due to creation of specific adsorption states characteristic of hydrides, and ∆Φ arising as a result of surface defects and protrusions induced in the course of the reaction. The topography of thin metal films and thin hydride films with defects and protrusions was illustrated by means of atomic force microscopy. For comparison, the paper discusses work function changes caused by H2 interaction with thin films of metals which do not form hydrides (for example platinum), or when this interaction is performed under conditions excluding hydride formation for thermodynamic reasons. Almost complete diminishing of ∆Φ was observed, in spite of significant hydrogen uptake on some rare earth metals, caused by formation of the ordered H–Y–H surface phase.