Structural, electronic and magnetic properties of vacancies in single-walled carbon nanotubes

The monovacancy and the divacancy in single-walled carbon nanotubes (CNTs) are addressed by spin-density functional calculations. We study these defects in four nanotubes, the armchair (6, 6) and (8, 8) and the zigzag (10, 0) and (14, 0), which have diameters of about 8 and 11 Å, respectively. We also consider different defect concentrations along the tube axis. Our results show that CNTs with a monovacancy exhibit ferromagnetism with magnetic moments ranging from 0.3 to 0.8 μ_B. Whereas, CNTs with a divacancy do not exhibit magnetism due to the full reconstruction around the defect where all C atoms are three fold coordinated. We observe that the monovacancy does not change drastically the CNT electronic properties, preserving their corresponding metallic or semiconducting character. However, both armchair and zigzag CNTs with a divacancy become small-gap semiconductors with an energy gap of about 0.15 eV.