Divacancies in carbon nanotubes and their influence on electron scattering

First-principles calculations are applied to study the formation energies of various divacancy defects in armchair and zigzag carbon nanotubes of varying diameter, and the transport properties for the corresponding structures. Our explicit ab initio calculations confirm that the lateral 585 divacancy is the most stable defect in small diameter tubes, with the 555 777 divacancy becoming more stable in armchair tubes larger than (30, 30). Evaluating the electron transmission as a function of diameter and chirality for a range of defects, the strongest scattering is found for the 555 777 divacancy configuration, which is observable in electrical spectroscopy experiments. Finally, validation of an approximation relating contributions from independent scattering sites enables the study of the characteristic localization length in large diameter tubes. Despite the fixed number of channels, localization lengths increase with increasing diameter and can exceed 100 nm for typical defect densities.