Periodic structures induced by normal-incidence sputtering on Ag(110) and Ag(001): flux and temperature dependence

The morphology generated on Ag(110) and Ag(001) by 1 keV Ar+ sputtering at normal incidence has been studied by scanning tunnelling microscopy as a fu nction of the substrate temperature T-S and the ion flux Phi. Since ion spu ttering is a non-equilibrium process in which erosion competes with diffusi on in determining the surface evolution, these macroscopic parameters can b e used to tune the final surface morphology. Flat or rough surfaces as well as periodic structures have been observed on both substrates. On Ag(110), ion sputtering at 230 K and 320 K produces two well defined ripple patterns whose wave vectors are parallel to <1 (1) over bar0 > and < 001 > respecti vely, while on Ag(001) a periodic pattern of square islands has been observ ed over a wide range of substrate temperatures (240 K less than or equal to T-S < 440 K), Similar to the results reported in growth experiments, a flu x increase produces a surface evolution qualitatively comparable with that obtained by lowering the temperature. The results are discussed in terms of a continuum model for the ion sputtering process.