Hydrogen-induced unzipping of single-walled carbon nanotubes

The chemisorption of atomic hydrogen on the single-walled armchair and zigzag carbon nanotubes is studied with ab initio calculations. The binding energy of H adsorption at the exterior of the nanotubes is much greater than that at the interior. We predict that two rows of H atoms chemisorbed on selective sites exterior to the smaller armchair nanotubes can break the nearest-neighbor $\mathrm{C}—\mathrm{C}$ bonds of the nanotubes through the concerted formation of $\mathrm{C}—\mathrm{H}$ bonds, leading to the unzipping of the nanotube wall. On the other hand, the larger armchair and zigzag nanotubes are stable against unzipping. We provide insights into the underlying electronic mechanism for the H-induced unzipping, lending strong support to the recent experimental observations for the coalescence of single-walled nanotubes in the presence of atomic hydrogen. Interestingly, H atoms chemisorbed inside the nanotubes do not break the $\mathrm{C}—\mathrm{C}$ bonds.