Pressure-induced phenomena in single-walled carbon nanotubes: Structural phase transitions and the role of pressure transmitting medium

We studied the effect of pressure on the electronic properties of bundled single-walled carbon nanotubes by infrared transmission measurements. Different pressure transmitting media were employed to verify their influence on the observed pressure dependence. A redshift of the optical absorption bands is observed under pressure. Irrespective of the pressure transmitting medium, the pressure-induced frequency shifts of the optical transitions show an anomaly at a critical pressure P-c=2-3 GPa, which can be attributed to the predicted circular-to-elliptical structural phase transition. We find a second anomaly in the frequency shifts of the optical transitions at 5 6 GPa which we interpret in terms of the change of the nanotubes cross-section from to race-track or peanut type, in agreement with earlier reports. (c) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim