Sputtering in the high-voltage electron microscope

The 1.0 MeV electron microscope has been used to observe and analyse transmission sputtering caused by the electrons in the incident beam. The method, reviewed here, is particularly suitable for investigating low energy collision events. Total sputtering yields and angular distributions of sputtered atoms have been measured for (111) gold films to within a few eV of the sputtering threshold energy. It is shown that the results can be explained by the sputtering of surface atoms either directly by electrons, or indirectly by collision sequences generated down 〈110〉 directions. The necessity of using a many-body collision model to interpret the results is stressed. High resolution electron microscopy has been used to study the surface structure of (111) gold films during sputtering on a near-atomic level. It is shown how the results confirm a model where surface roughness develops due to the migration and agglomeration of surface vacancies produced during sputtering. The future scope of the 1.0 MeV electron microscope as an analytical tool for sputtering is also discussed. It is suggested that the rôle of long range focussed collision sequences in sputtering may be determined for materials of medium atomic number. A need for further high resolution studies of sputtered surfaces is identified; such studies are seen as complementary to those by other surface analysis techniques.