Resonant Raman spectroscopy of single-wall carbon nanotubes under pressure

Abstract

We performed high pressure resonant Raman experiments on well characterized purified single-wall carbon nanotubes up to $40\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ using argon as pressure transmitting medium. We used two different excitating wavelengths, at $632.8\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ and $514.5\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$. In contrast with other studies no clear sign of phase transformation is observed up to the highest studied pressure of $40\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Our results suggest that the progressive disappearance of the radial breathing modes observed while increasing pressure should not be interpreted as the sign of a structural phase transition. Moreover, a progressive change of profile of the tangential modes is observed. For pressures higher than $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ the profile of those modes is the same for both laser excitations. We conclude that a progressive loss of resonance of single-wall carbon nanotubes under pressure might occur. In addition, after high pressure cycle we observed a decrease of intensity of the radial breathing and tangential modes and a strong increase of the $D$ band.