Images shown are mica surface irradiated with 150 KeV Ar ion taken
by using scanning force microscope (NanoScope III) operated under Tapping mode.(a)a single pit in top-view, (b)a pit in 3-D view and (c)a larger (1x1 micron) field view of 4 pits, each one of them has a satellite bump which are believed due to double tip effect. These pits are only 5 Angstroms in depth, about 80 Angstroms in diameter and 10^8 per cm^2 in density. The rims around pits are tens
Angstroms wide and 3 Angstroms high.