he scanning electron microscopy (SEM) combined with electron probe microanalyzer(EPMA) technique was used to measure the composition difference between the convex and concave regions of the sputtered surface. The experimental results show that the "surface element localized enrichment" phenomenon occurs in a single-phase Cu-12at.% An alloy after 30keV Ar+ ions bombardment to a dose of 1.4×1018ions/cm2 as in multi-phase alloys. A model considering the effects of both the initial stage of the localized enrichment and the capillary pressure (Laplace pressure) producing a selective drift force was proposed for explaining these results.