Surfactant-driven self-organized surface patterns by ion beam erosion

In this paper, we report on the self-organized pattern formation on Si surfaces driven by Fe surfactant atoms. Si substrates were irradiated with 5 keV Xe ions at normal incidence and ion fluences up to 5 x 10(17) Xe+ cm(-2) under continuous deposition of Fe surfactant atoms. In the absence of Fe deposition, uniform flat surfaces were obtained. With Fe surfactants, pronounced patterns, such as dots, combinations of dots and ripples and ripples with about 100 nm wavelength, were generated. The Fe coverage and deposition direction determine the pattern type and the pattern orientation, respectively. A critical Fe steady-state coverage for onset of dot formation and onset of ripple formation ranges between 2 x 10(15) and 6 x 10(15) Fe cm(-2). With increasing ion fluence, the pattern contrast increases but the pattern type remains unchanged. The surface region consists of a thin amorphous FexSi layer with x approximate to 0.2 in the ripple and dot regions and x approximate to 0.03 in the intermediate regions. Pattern formation is explained by ion-induced diffusion and phase separation of the initially flat amorphous FexSi layer and subsequent ion beam erosion with composition-dependent sputter yield. Directed deposition of Fe causes preferential deposition and shadowing and determines the final pattern orientation and morphology.