Cantilever miniaturization is crucial to realize highly sensitive force sensor based on resonant frequency shift of cantilevers. Carbon nanotubes (CNTs) are one of the promising candidates for this application because of their light weight, high aspect ratio, and extraordinary mechanical properties.[1,2] In contrast, low Q factors with high mechanical strength are also important for stabilizing parasitic vibration in the NEMS. Characterizing individual nanotubes should be necessary to ascertain their capability for the application of high performance NEMS. To open the way to clarification of these subjects, we investigated the mechanical properties of the vibrating cantilevered multiwall carbon nanotubes synthesized by chemical vapor deposition in terms of the energy loss of the vibration. Defect sites, which are a loss factor, are evaluated from the relation between Raman spectroscopic results and the mechanical strength. The loss factor derived from interlayer interaction corresponding to the van-der-Waals (vdW) interaction is also discussed based on the diameter-dependence of the Q factors.
Cantilevered CNTs were vibrated mechanically using a piezo device in the SEM at room temperature. The Young’s moduli of the nanotubes evaluated from the resonance frequency under the small deflection limit showed clear dependence of the perfection of the sp2 carbon hexagonal network, as determined from the G/D ratio of Raman spectroscopy. Under the linear elastic regime without large deformation, the energy loss for the vibration derived from the defects can be expected to have no diameter dependence, whereas the loss derived from the vdW interaction should depend on the diameter. Using results of experiments, we showed that the 1/Q corresponding to the energy loss for the vibration showed strong diameter dependence and weak strength dependence and that the energy loss increased with increasing tube diameter. These results suggest that the nanotube synthesized using CVD mainly dissipates its vibration energy through vdW interaction.
[1] M. Nishio, S. Akita and Y. Nakayama, Appl. Phys. Lett. 86, 133111(2005).
[2] M. Nishio, S. Sawaya, S. Akita and Y. Nakayama, J. Vac. Sci. Tech. B 23, 1975 (2005).
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