The adsorption process of hydrogen on Gd(0001)

The development of the adsorption processes of hydrogen on Gd(0001) was studied by means of photoelectron spectroscopy in combination with scanning tunneling microscopy and spectroscopy, respectively. Due to its high spatial resolution the visualization of the adsorption process is obtained. It was found that the adsorption occurs in two steps. It starts at crystallographic surface imperfections. From these nucleation centers, a domain-like spreading is present which is strongly hindered at surface steps. A short duration high exposure dose results in a different behavior; areas on the surface without imperfections now become affected. These areas with adsorbed hydrogen are not connected to each other. (C) 1999 Elsevier Science B.V. All rights reserved.