Quantitative surface analysis with elemental standards: Surface roughness limitations

The dependence of the detected Auger signal on crystal orientation and surface morphology has been investigated for a pure elemental standard of Mo. Two large adjacent grains with orientations close to (100) and (1, 4, 11) were used for this study. After polishing to a uniform surface topograpy the sample was sputtered with 2 keV argon ions at glancing incidence, typical of the conditions used in surface analysis. The initial line scan across both crystal surfaces showed an essentially constant detected Auger current. However, under continued ion bombardment up to a fluence of 5×10¹⁹ ions cm⁻², the Auger current changed until the (100) crystal showed an 18% larger signal than the high index grain. This large difference is attributed to changes in surface roughness that develop quite differently for different crystal orientations. The surface morphology changes have been characterized using scanning electron microscopy and surface profile measurements. The implications of these results for quantitative surface analysis are discussed.