Nanomechanical resonance studies of carbon nanotube peapod bundles

Filled carbon nanotubes represent a class of tunable nanoscale materials that could provide both high-quality resonance and sensing specificity for nanoresonator-based devices. We have studied the mechanical properties of C60-filled single-walled carbon nanotube bundles through observation of their mechanical resonances in a transmission electron microscope. X-ray diffraction was used to qualitatively study the filling of C60 in the bulk material. Electron diffraction was used to confirm the filling of each bundle prior to the measurement of individual mechanical resonance frequencies. The electron-diffraction pattern revealed a C60 spacing periodicity of 9.97 Å within the lumen of the nanotubes, which is close to the theoretical equilibrium spacing of R0=10.05Å in bulk C60. An average ratio of (Eb∕ρ)1∕2=13230±3187m∕s was observed for the unfilled bundles, compared with a ratio of (Eb∕ρ)1∕2=19002±2307m∕s for C60-filled bundles. Such values indicate an increase of the average bending modulus by as much as 170% in C60-filled bundles. A dependence of this ratio on the diameter of the structures was also observed. This dependence is explained by the increased importance of intertube slipping in bundles of larger diameter.