Pattern transition from nanohoneycomb to nanograss on germanium by gallium ion bombardment

During the irradiation of Ge surface with Ga⁺ ions up to 10¹⁷ ions·cm^-2, various patterns from ordered honeycomb to nanograss structure appear to be decided by the ion beam energy. The resulting surface morphologies have been studied by scanning electron microscopy and atomic force microscopy. For high energy Ga⁺ irradiation (16-30 keV), by controlling the ion fluence, we have captured that the equilibrium nanograss morphology also originates from the ordered honeycomb structure. When honeycomb holes are formed by ion erosion, heterogeneous distribution of the deposited energy along the holes leads to viscous flow from the bottom to the plateau. Redistribution of target atoms results in the growth of protuberances on the plateau, and finally the pattern evolution from honeycomb to nanograss with an equilibrium condition.