Raman characterization of carbon materials under non-hydrostatic conditions

Raman spectroscopy experiments on double-wall carbon nanotube and highly oriented pyrolytic graphite (HOPG) samples subjected to non-hydrostatic conditions have been conducted in anvil cells to study the effect of the pressure/stress on the bands assigned to defects. Typical diamond anvils used in high pressure experiments have been substituted by moissanite (6H-SiC) and sapphire (Al2O3) anvils to allow the observation of the D band (around 1350 cm(-1)) and the second-order Raman scattering without interference. We demonstrate that Raman experiments at high pressure provide unique information to probe the mechanical behaviour of carbon materials (CMs). We also show that this can be also a powerful technique to assign controversial spectral features such as those appearing in the second order region of the spectra of CMs. In HOPG samples we find that the D'/D band intensity ratio is independent of stress. The results indicate that an increase of non-hydrostatic stresses on HOPG generates graphitic domains with sizes around 20-30 nm when the sample is recovered to room conditions. (C) 2010 Elsevier Ltd. All rights reserved.