The Response of Work Function of Thin Metal Films to Interaction with Hydrogen
E. Nowicka and R. Nowakowski
Institute of Physical Chemistry, Polish Academy of Sciences
Kasprzaka 44/52, 01-224 Warszawa, Poland
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.