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

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Abstract
Ab initiomolecular dynamics simulations have been used to study the subpicosecond chemistry and dynamics of hyperthermal O ( 3 P) collisions with single-walled carbon nanotubes, with a particular focus on insertion and substitutional doping. The barrier for inserting an O ( 3 P) 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 nanotubecarbon atom are observed to generate oxygen substitutionally dopednanotubes 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 ( 3 P) 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.