Nanometer-scale patterning of alkali halide surfaces by ion bombardment

Structural properties of alkali halide surfaces (KBr, KI, and RbI) have been modified by low energy Ar+ ion beam bombardment. The morphology developed on the irradiated surfaces was investigated by the atomic-force microscopy (contact mode) under UHV conditions. The results indicate that for the incidence angles between 30° and 40° a periodic ripple morphology is developed with the ripple vector parallel to the beam direction, whereas for the angles larger than 60° the vector is perpendicular to the beam. The average surface roughness and the wavelength of the ion-induced periodic structures were measured as a function of the ion fluence (1013-1018 ions/cm2), the beam energy (1-5 keV), and the sample temperature (from 300 K to 600 K). The results are explained in terms of a new atomic-scale model taking into account the fact that ion sputtering of alkali halides in the investigated energy range is dominated by electronic processes rather than ballistic collisions.