In situ Raman investigations of single-wall carbon nanotubes pressurized in diamond anvil cell

Raman spectra of single-wall carbon nanotubes produced by arc-discharge and laser ablation techniques have been registered in a diamond anvil cell under hydrostatic pressure up to 10 GPa. The pressure-induced high-frequency shifting and broadening of the tangential and "breathing" modes have been observed. The intensity of the "breathing" mode decreased substantially with the pressure. The mode has disappeared completely at 2,6 GPa. Such type of the mode behavior was predicted by modeling with empirical Brenner's potential. A comparison of the Raman and HRTEM data allows to interpret a chain of the pressure-induced transformations as a facetting of individual tubes in ropes followed by their merging and formation of graphitic needles. A possibility of a pressure-induced bulk polymerization is discussed.