Formation and annihilation of nanocavities during keV ion irradiation of Ge

TL;DR

This study investigates the formation, growth, and annihilation of nanocavities in germanium during keV Xe ion irradiation, revealing size dynamics, internal gas pressure, and surface pit formation through microscopy techniques.

Contribution

It provides new insights into nanocavity behavior in Ge under ion irradiation, including size evolution, internal pressure estimates, and surface pit formation mechanisms.

Findings

Nanocavities nucleate near the surface and migrate thermally.

Nanocavities grow beyond equilibrium size at 773 K.

Surface pits form at ~ 523-578 K due to ion interactions.

Abstract

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 average diameter of 10 nm and areal density of 5.1 x 10-3 nm-2 are observed at 773 K, while nanocavities with average diameter of 2.9 nm and areal density of 3.1 x 10-3 nm-2 are observed at 673 K. The estimated Xe gas pressure inside the nanocavities is 0.035 GPa at 773 K, much smaller than the estimated equilibrium pressure 0.38 GPa. This result suggests that the nanocavities grow beyond equilibrium size at 773 K. 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 ~ 523-578 K by keV Xe ions even when less than a bilayer (monolayer) of surface material is removed.