| Abstract | The recent development of hybrid carbon nanotube materials, such as supramolecular self-assembled arrays of C60 molecules encapsulated within single-wall carbon nanotubes (C60@@SWNT), has opened new possibilities for the development of nanomechanical devices of tunable properties. We studied the mechanical properties of C60-filled SWNT bundles through analysis of their resonance in a transmission electron microscope (TEM). X-Ray diffraction was used to qualitatively study the filling of C60 in the bulk material. The intensity of the (1,0) bundle peak, located at Q = 0.45 A^-1, was reduced after filling of the tubes with C60. Electron diffraction analysis revealed a C60 spacing periodicity of 9.97 Ã. within the lumen of the SWNTs. Mechanical resonance measurements were conducted in a TEM by selecting bundles whose extremities were appropriately affixed. An average ratio of (E*/rho)^1/2 = 19002 ± 2307 m/s was extracted from the resonance analysis of the C60-filled bundles, compared to a ratio of (E*/rho)^1/2 = 13230 ± 3187 for the unfilled material. These values correspond to an effective average Young's modulus of E* = 240 ± 105 GPa for empty bundles, and of up to E* = 650 ± 156 GPa for the C60-filled materials. These moduli are significantly lower than the ~ 1 TPa usually reported for individual SWNTs due to the weak interaction and sliding effect that are known to exist between tube surfaces. However, the significant increase of stiffness upon filling is believed to be related to an increase of strain energy of the individual SWNTs within the bundle. A dependence of this modulus on bundle diameter was also observed. This dependence is explained by the increased importance of inter-tube slipping in bundles of larger diameter. We will also present recent results on the mechanical resonance properties of single-crystalline GaN nanowires. Preliminary resonant analysis of 30-160 nm wide wires suggest an average effective Young's modulus of E* = 120 ± 20 GPa. |
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