PREPARATION OF ATOMICALLY SMOOTH SURFACES VIA SPUTTERING UNDER GLANCING INCIDENCE CONDITIONS

The surface topographies of thin films of 60 nm Cr on highly polished BK7 glass substrates were characterised using scanning tunnelling microscopy both before and after irradiation with 3 keV Arf beams at glancing angles of 3 degrees and 5 degrees. Before irradiation the films have an rms roughness of 9.2 +/- 2.5 nm and an autocovariance length of 56 +/- 2 nm. After irradiation the rms roughness was reduced by a factor of 5-8 with little change in the autocovariance length being observed. The films appear to consist of small, three-dimensional crystallites. A sequential binary collision computer simulation suggests that erosion of such crystallites occurs in the vicinity of step edges and preferentially from the upper layer from which the step is formed. We conclude that this selectivity leads to the preferential removal of protruding features.