Anisotropic electron-beam damage and the collapse of carbon nanotubes

Irradiation of multiwalled carbon nanotubes with the 800-keV electron beam of a transmission electron microscope induces anisotropic collapse of the nanotube. Tight-binding molecular-dynamics simulations of tube response following momentum transfer from large-angle electron-nuclear collisions reveal a strongly anisotropic threshold for atomic displacement. The theoretical displacement threshold for an impulse perpendicular to the local tangent plane of a single-walled tube is roughly half the damage threshold for impulses within the tangent plane. The electron beam preferentially damages the front and back of the nanotube, producing the observed anisotropic collapse perpendicular to the direction of the beam. The attraction of opposite faces of the inner wall then accelerates the collapse.