The diffusive behavior of small hydrocarbon radicals (-CH, -CH2 and -CH3) on the outer wall of a (9,0) carbon nanotube was investigated by performing tight-binding potential calculations. It was found that -CH or -CH2 preferentially zig-zagged on the wall of the tube, whereas -CH3 hopped from the top of a carbon atom to its nearest one, by overcoming energy barriers of less than 1.3eV. If the 5-1DB defect, a type of monovacancy, existed in the tube, it appeared to be a trap for radicals diffusing nearby. Two typical pathways of the radicals migrating into a 5-1DB defect were revealed here. Along one pathway, -CH and -CH2 diffused from the defect-free region to the dangling-bond atom in the 5-1DB defect by crossing the hexagon directly. Along the other one, the radicals diffused to the pentagon, where either -CH or -CH2 converted the original 5-1DB defect into an overturned one (by breaking and re-bonding of C-C bonds); with -CH or -CH2 attached on the new dangling-bond atom. It was also found that -CH or -CH2 bonding at the dangling-bond atom could ultimately convert the 5-1DB defect into a three-fold coordinated or bridge-like structure only at an energy cost of 0.5eV; improving the local structure of the monovacancy. A -CH3 radical could not improve the structure of the 5-1DB defect in any case.

Diffusion of Small Hydrocarbon Radicals on the Outer Wall of a (9,0) Carbon Nanotube. H.Y.He, B.C.Pan: Physica E, 2008, 40[3], 542-9