Mechanical properties of carbon nanotubes with vacancies and related defects

Although as-grown carbon nanotubes have relatively few defects, defects can appear at the purification stage or be deliberately introduced by irradiation with energetic particles or by chemical treatment when aiming at the desired functionality. The defects, especially vacancies, give also rise to a deleterious effect-deterioration of axial mechanical properties of nanotubes. By employing molecular dynamics simulations and continuum theory we study how the Young's modulus and tensile strength of nanotubes with vacancy-related defects depend on the concentration of defects and defect characteristics. We derive an analytical expression, with coefficients parametrized from atomistic computer simulations, which relates the Young's modulus and defect density in carbon nanotubes. We further show that the tensile strength and critical strain of single-walled nanotubes decrease by nearly a factor of 2 if an unreconstructed vacancy is present. However, this deterioration in the mechanical characteristics is partly alleviated by the ability of nanotubes to heal vacancies in the atomic network by saturating dangling bonds.