Crystal orientation effects on the surface morphology produced by ion bombardment of a pure element: Implications for quantitative surface analysis

Abstract

The effect of crystal orientation and surface morphology on the detected Auger current was investigated using a polycrystalline Mo sample. The sample was initially polished to a uniform and featureless surface morphology. Two large grains were used in the study, with their crystal orientation determined as -(loo) for the low-index grain and -(l, 4, 11) for the high-index grain. Ion bombardment conditions used were typical for surface analysis, i.e. 2 keV Ar+ at glancing incidence. The initial Auger current measured from the cleaned as-polished surface was found to be essentially constant across both crystals. However, under continued ion bombardment, as the fluence was increased to -5 x 10'' ions cm-', gross differences of up to 18% were observed in the detected Auger current from the two crystal surfaces. This gross difference is attributed to the extent of surface roughness that evolved, which is in turn mainly dependent on the crystal orientation. It was found that, relative to the polished surface, the high-index grain developed considerable texture of macroscopic dimensions consisting mainly of 'hills and valleys' with a 'furrowed' fine structure in the direction of the ion beam, yielding a net decrease in the detected Auger current. The low-index grain became smoother, yielding a net increase in the detected Auger current. This latter effect was much larger than the decrease resulting from the increased roughening of the high-index grain. The implications for quantitative surface analysis are discussed.