Development of the surface topography on polycrystalline metals by ion bombardment investigated by scanning electron microscopy

Polycrystalline Cu and Ag surfaces were bombarded by a monoenergetic parallel beam of 10 keV Ar+ ions from various directions of incidence. The relief formation at grain boundaries has been studied by means of a scanning electron microscope. In a large range of angles of incidence only single slopes are observed at the great majority of grain boundaries. The formation of slopes has been studied quantitatively with stereo pairs. The change of the direction of incidence causes the formation of new areas starting from the grain boundaries. With grazing incidence only a small part of grain boundaries will be visible. Including the special cases the formation of the areas observed can be described with a simple model based on the influence of geometrical parameters, especially the beam direction (channelling effect), on the sputtering rate.