The surface structure of (111) gold films sputtered in the high voltage electron microscope A theoretical model

Thin (111) gold films irradiated in the high voltage electron microscope are transmission-sputtered by the ejection of single surface atoms, each removed atom thereby creating a single surface vacancy. In situ observations of sputtering at 1·0 MeV are described in which evaporated (111) gold foils developed a heavily pitted surface. The pit density varied with specimen temperature and sputtering rate but was reduced near pre-existing surface steps. Forbidden reflection electron microscopy (Cherns 1974) showed also that pitting developed on areas of an originally perfect (111) surface. A theoretical model is proposed in which pits form by the surface diffusion and agglomeration of surface vacancies produced by sputtering and it is shown that this model explains the experimental results in some detail. A value of Em = 0·45 ± 0·15 eV is derived for the migration energy of a surface vacancy on (111) gold. It is suggested that the surface diffusion model explains observations of surface roughening in other systems.