Predicted scanning tunneling microscopy images of carbon nanotubes with atomic vacancies

We calculated STM images of both metallic and semiconducting single-wall carbon nanotubes with atomic vacancies. In our simulations, we employed the tight-binding Greenʹs function technique and the recursion method. We predict that vacancies should result in the formation of hillock-like features in STM images of metallic nanotubes, which are especially appreciable at small bias voltages (of about 0.1–0.4 V). An enhancement in the tunneling current is due to vacancy-induced states at the Fermi energy, and these states 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, hillocks and superstructures are also visible at those bias voltages when band edges contribute to the tunneling current.