Transport Properties of Carbon Nanotubes: Effects of Vacancy Clusters and Disorder

We investigate the effects of vacancy defects on the electronic and transport properties of carbon nanotubes through density functional calculations. In both cases, where vacancies aggregate into larger clusters and are disordered, conductance changes from metallic to insulating regime, while their origins are different. For small vacancy clusters, the suppression of conductance is led by the defect states associated with pi-topological and a-dangling bond defects, while the local gap opening plays a role for large vacancy clusters. In disordered tubes with various types of vacancy defects, conductance decreases exponentially due to the Anderson localization. The localization length not only depends on the type of vacancy defects but also the tube chirality.