The adsorption process of hydrogen on Gd(0001)

The development of the adsorption processes of hydrogen on Gd(0001) was stu died by means of photoelectron spectroscopy in combination with scanning tu nneling 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 crystallographi c surface imperfections. From these nucleation centers, a domain-like sprea ding is present which is strongly hindered at surface steps. A short durati on high exposure dose results in a different behavior; areas on the surface without imperfections now become affected. These areas with adsorbed hydro gen are not connected to each other. (C) 1999 Elsevier Science B.V. All rig hts reserved.