Ab initio simulations of oxygen atom insertion and substitutional doping of carbon nanotubes

Abstract

Ab initio molecular dynamics simulations have been used to study the subpicosecond chemistry and dynamics of hyperthermal O(3P) collisions with single-walled carbon nanotubes, with a particular focus on insertion and substitutional doping. The barrier for inserting an O(3P) atom through the center of a hexagonal carbon ring was determined to be 13.7 eV, compared to an estimated dynamic effective barrier of 15.9 eV and a threshold energy on the order of 15–20 eV. Under similar conditions, collisions with a nanotube carbon atom are observed to generate oxygen substitutionally doped nanotubes and heptagonal carbon ring defects. At incident energies above the insertion threshold, an oxygen atom that passes through the center of a hexagonal carbon ring has the tendency to become accelerated and pass completely through the nanotube. Under thermal conditions the O(3P) atom binds to the nanotube without a barrier, leading to one of two products: an epoxide, and an adatom oxygenated nanotube. Tube curvature effects result in an increase of the epoxide binding energy with a decrease in tube diameter. However, no noticeable effects of tube diameter on insertion were established from the simulations.