Formation of bug-like micro-structures on silica surface by MeV ion implantation at early stages

The evolution of surface pattern induced by 1.8 MeV Au ion implantation on fused silica glass is studied in the fluence range of ions cm -2 . The surface characterization was performed by optical microscopy, SEM, AFM-Raman, and EDS. The Au ion implanted depth distribution was measured by RBS. At early fluences, the formation of bug-like structures on a flat surface was observed. The creation of similar structures has previously been reported only on silicon and they are not predicted by classical models for pattern formation. Their origin suggest that bugs grow by differential sputtering on regions with high residual stress. Due to a shadowing effect, the prominent features of the bugs are richer in Au. A surrounding ripple pattern begins to emerge at a threshold fluence of ions cm -2 . As fluence increases, bugs-like structures are progressively surrounded by the ripples, eventually merging into a single pattern. Finally, at the highest ion fluences, the ripples evolved into a wrinkle-like pattern.