Formation of ion-irradiation-induced atomic-scale defects on walls of carbon nanotubes

Recent experiments on irradiated carbon nanotubes provide evidence that ion bombardment gives rise to nanotube amorphization and dramatic dimensional changes. Using an empirical potential along with molecular dynamics, we study structure and formation probabilities of atomic-scale defects produced by low-dose irradiation of nanotubes with Ar ions. For this, we simulate impact events over a wide energy range of incident ions. We show that the maximum damage production occurs for a bombarding ion energy of about 600 eV, and that the most common defects produced at all energies are vacancies, which at low temperatures are metastable but long-lived defects. Employing the tight-binding Green's function technique, we also calculate scanning tunneling microscopy (STM) images of irradiated nanotubes. We demonstrate that irradiation-induced defects may be detected by STM and that isolated vacancies may look like bright spots in atomically resolved STM images of irradiated nanotubes