Pattern formation on ion-irradiated Si surface at energies where sputtering is negligible

Abstract

The effect of low energy irradiation, where the sputtering is imperceptible, has not been deeply studied in the pattern formation. In this work, we want to address this question by analyzing the nanoscale topography formation on a Si surface, which is irradiated at room temperature by Ar+ ions near the displacement threshold energy, for incidence angles ranging from 0° to 85°. The transition from the smooth to ripple patterned surface, i.e., the stability/instability bifurcation angle is observed at 55°, whereas the ripples with their wave-vector is parallel to the ion beam projection in the angular window of 60°–70°, and with 90° rotation with respect to the ion beam projection at the grazing angles of incidence. A similar irradiation setup has been simulated by means of molecular dynamics, which made it possible, first, to quantify the effect of the irradiation in terms of erosion and redistribution using sequential irradiation and, second, to evaluate the ripple wavelength using the crater function formalism. The ripple formation results can be solely attributed to the mass redistribution based mechanism, as erosion due to ion sputtering near or above the threshold energy is practically negligible.