North-Holland Bo8m Internotions with Yatortatr & Atoms The angular dependence of sputtering yields of Ge and Ag

30 keV Ar+ and Kr+ ion bombardment. It is found that Ag exhibits a weaker angular dependence, though its sputtering yield is higher than that of Ge. The results are compared to the existing theoretical and empirical formulas. The variation of the sputtering yield Y with angle of ion incidence 8, measured with respect to the surface normal, shows that Y(0) first increas:s monotonically with 8, passes through a maximum at B typically 60-80” and then decreases harply as 0 approaches 90”. Such a variation is typical for amorphous and polyc~stalline materials. For single-kn~kon sputtering, the yield is expected to rise as (cos f?-‘, simply because of the longer pathlength close to the surface. For high energy sputtering (say E> 10 keV), however, the sputtering phenomenon is of a multiple-scattering character as described by Sigmund [l]. He showed that for not-too-oblique incidence, the (cos 8)- ” law holds only for large target-to-projectile-mass ratios (M2/M1> 7). For smaller mass ratios (M2/M1 < 31, a faster variation with angle like (cos 0)- 5/3 should be expected. The compilation of Y(0) data by Andersen and Bay [2] reveals that few yield data follow the theoretical pre-dictions of Sigmund [I]. Quite recently, Frijhlich et al. [31 found a (co