Experiments on irradiated carbon nanotubes had provided evidence that ion bombardment gave rise to nanotube amorphization and marked dimensional changes. Using an empirical potential, together with molecular dynamics, a study was made of the structure and formation probabilities of atomic-scale defects produced by low-dose irradiation of nanotubes with Ar ions. For this purpose, impact events were simulated over a wide energy range of incident ions. It was shown that the maximum damage production occurred for a bombarding ion energy of about 600eV, and that the most common defects produced at all energies were vacancies, which at low temperatures were metastable but long-lived defects. Using the tight-binding Green’s function technique, scanning tunneling microscopic images of irradiated nanotubes were also calculated. It was demonstrated that irradiation-induced defects could be detected by scanning tunneling microscopy and that isolated vacancies could look like bright spots in atomically resolved scanning tunneling microscopic images of irradiated nanotubes.

Formation of Ion-Irradiation-Induced Atomic-Scale Defects on Walls of Carbon Nanotubes. A.V.Krasheninnikov, K.Nordlund, M.Sirviö, E.Salonen, J.Keinonen: Physical Review B, 2001, 63[24], 2454051-6