Theoretical STM images of carbon nanotubes with atomic vacancies: A systematic tight-binding study

We calculated STM images of both metallic and semiconducting single-wall carbon nanotubes with atomic vacancies. In our simulations, we employed the tight-binding Green's function technique and the recursion method. We predict that at small bias voltages (of about 0.1 V) vacancies will result in the formation of hillock-like features in STM-images of metallic nanotubes. An enhancement in the tunneling current is due to the vacancy-induced states at the Fermi energy, which are spatially localized on the atoms surrounding the vacancies. Electronic superstructures analogous to those in graphite near point defects are observed near the vacancy. For semiconducting nanotubes, vacancies do not give rise. to hillock-like features at low bias voltages. However, at bias voltages exceeding half of the semiconductor gap, hillocks and superstructures are visible. Our results for nanotubes, if confirmed experimentally, may shed light on the nature of similar hillock-like features and superstructures in STM images of graphite surfaces with point defects.