Formation and annihilation of nanocavities during keV ion irradiation of Ge

Nanocavities in Ge(111) created by 5 keV Xe ion irradiation are characterized by ex situ transmission electron microscopy and Rutherford backscattering spectrometry. Nanocavities nucleate near the surface and then undergo thermal migration. Nanocavities with an average diameter of 10 nm and areal density of 5.1×10^-3nm^-2 are observed at 500°C, while nanocavities with an average diameter of 2.9 nm and areal density of 3.1×10^-3nm^-2 are observed at 400°C. The estimated Xe gas pressure inside the nanocavities is 0.035 GPa at 500°C, much smaller than the estimated equilibrium pressure 0.38 GPa. This result suggests that the nanocavities grow beyond equilibrium size at 500°C. The nanocavities are annihilated at the surface to form surface pits by the interaction of displacement cascades of keV Xe ions with the nanocavities. These pits are characterized by in situ scanning tunneling microscopy. Pits are created on Ge(111) and Ge(001) at temperatures ∼250–305°C by keV Xe ions even when less than a bilayer (monolayer) of surface material is removed.