Resonant laser-induced formation of double-walled carbon nanotubes from peapods under ambient conditions

Abstract

The selective excitation of fullerenes encapsulated in single-walled carbon nanotubes (SWCNTs) is carried out by irradiating them using a UV laser, the wavelength of which corresponds exactly to their maximum of absorption. Under such conditions, fullerenes strongly absorb the laser energy, open, and break, while the containing SWCNT merely acts as both a nanoreactor and a mold which is only weakly heated by the laser. The containing tube confines the fullerene fragments, promotes their reconstruction into an inner tube, and protects them from air oxidation. This leads to the overall formation of double-walled carbon nanotubes (DWCNTs). The transformation is found to strongly depend on the laser irradiance and dose. This proves that the related mechanism is a multiphoton photolysis, different from the previous heat-induced transformation attempts found in the literature, whether the heat is produced by means of a thermostat, infrared laser, or nonresonant UV laser. The actual peapod-to-DWCNT transformation is monitored by Raman spectroscopy and high-resolution transmission electron microscopy.