Electron-stimulated defect formation in single-walled carbon nanotubes studied by hydrogen thermal desorption spectroscopy

Defects in single-walled carbon nanotubes introduced by low-energy electron irradiation at 8 K were sensitively detected by cryogenic thermal desorption of hydrogen molecules H2 in the temperature range of 10-40 K. The thermal desorption spectrum was found to change significantly with sample annealing at temperatures as low as 40-70 K. Experimental results suggest that the H2 physisorption sites responsible for the 'defect' peak at 28 K are interstitial channel space between nanotubes closely packed in bundles which becomes more easily accessible on damage. It is also suggested that the disordering provides groove sites for H2 physisorption with smaller binding energy causing the damage-induced spectral component around 16 K, slightly lower than the desorption peak at 20 K that is observed in undamaged samples. The spectral change at 40-70 K could be interpreted by migration of adatoms at the low temperatures.