Unusual pattern formation on Si(1 0 0) due to low energy ion bombardment

In this paper evolution of silicon surface topography, under low energy ion bombardment, is investigated at higher oblique incident angles in the range of 63–83°. Si(1 0 0) substrates were exposed to 500 eV argon ions. Different surface morphologies evolve with increasing angle of incidence. Parallel-mode ripples are observed up to 67° which undergo a transition to perpendicular-mode ripples at 80°. However, this transition is not a sharp one since it undergoes a series of unusual pattern formation at intermediate angles. For instance, mounds, cone-, and needle-like structures appear at intermediate angles, viz. in the angular range of 70–78°. Complete smoothening of the silicon surface is observed at incident angles beyond 80°. The observed patterns are attributed to surface confined viscous flow and sputter erosion under ion bombardment.