Electronic and vibration spectra of hydrogenated carbon single-wall nanotubes

Carbon single-wall nanotubes (SWNTs) were loaded with 5.4 wt.% H by exposing to a hydrogen pressure of 50kbar at 500 degrees C. Investigation of the optical transmission spectra showed that the hydrogenation significantly suppressed the high-frequency conductivity sigma of free carries in the SWNTs and also eliminated the hand-to-hand electronic transitions. Instead, a narrow line of the C-H stretching vibrational mode appeared at 2845cm(-1). A gradual removal of hydrogen from the hydrogenated SWNTs by vacuum annealing at T >= 500 degrees C resulted in an approximately linear decrease in the intensity of this line with decreasing hydrogen content. This evidenced that most H atoms in the hydrogenated SWNTs were covalently bonded to the carbon atoms. The complete removal of hydrogen by vacuum annealing at 700 degrees C partly restored sigma and the intensity of the electronic transitions characteristic of the initial SWNTs.