Diameter dependent wall deformations during the compression of a carbon nanotube bundle

Raman scattering is used to study the pressure-dependence of the radial (R) bands of bundled single-walled carbon nanotubes (SWNT) produced by the HiPCO process. We find that the normalized pressure derivative of the R-band frequency, $\Phi =d\left(\ln {\omega }_{\mathrm{R}}\right)/dP,$ increases with increasing nanotube diameter D as $\Phi \sim D^2.$ Using results from elastic theory, we show that the contribution to Φ from isolated SWNT, $(={\Phi }_0),$ is small, which agrees with previous model calculations. We show here that ${\Phi }_0$ is independent of D. We conclude that most of the pressure dependence observed for the R bands in SWNT bundles may be identified with tube wall deformations mediated via tube-tube interactions within a bundle and not with the compression of an individual tube.