Damping Characteristics of Commensurate Double-Walled Carbon Nanotube Oscillators
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1057-II10-17
Damping Characteristics of Commensurate Double-Walled Carbon Nanotube Oscillators
Y. Ooi, and K. Shintani Department of Mechanical Engineering and Intelligent Systems, University of ElectroCommunications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan
ABSTRACT The intertube oscillations of double-walled carbon nanotubes (DWNTs) are investigated using molecular-dynamics (MD) simulation. The inner and outer tubes of model DWNTs have chiral indices of armchair type. The intertube oscillations are damped owing to energy dissipation. The logarithmic decrements and frequencies of the damped oscillations are calculated. The results show that the logarithmic decrement increases with increasing the tube diameter and decreases with increasing the tube length. INTRODUCTION Carbon nanotubes are applicable to functional mechanical devices such as bearings, actuators, sliders, oscillators, etc., in nanomechanical systems. Multi-walled carbon nanotubes (MWNTs) as oscillators especially attract researchers’ attention because it was reported that the inner and outer tubes can oscillate relatively and translationally in the axial direction, and the frequencies of such oscillations are of the order of several ten gigahertz. It was also found that the attenuation constant depends on the tube length and temperature. Cumings and Zettl [1] demonstrated controlled and reversible telescopic extensions of MWNTs. They suggested such a mechanism is applicable to ultralow-friction nanoscale linear bearing and constant-force nanospring. In their experimental setup, inner tubes of MWNTs were extracted in one-direction through an open end of the outer tubes. Stimulated by their demonstration, Zheng and Jiang [2] showed a possibility that inner tubes of MWNTs can oscillate in the frequencies of several gigahertz if the both ends of the outer tubes are open. By using MD simulations with a standard molecular force field, Legoas et al. [3] confirmed such nano-oscillators are dynamically stable if the differences between the radii of inner and outer tubes are of about 3.4Å. Guo et al. [4] also performed MD simulations, and showed the rate of energy dissipation depends on the commensuration of the MWNTs. Zhao et al. [5] investigated oscillations of DWNTs of various lengths and constructions. Their simulations showed a noncoaxial instability with resonance frequencies in the terahertz range. The MD simulations of Tangney et al. [6] showed the dynamical friction for relative sliding of DWNTs is virtually independent of the area of surface overlap between inner and outer tubes, and commensurate and incommensurate tubes dissipate energy at nearly the same rate. Zhao and Cummings [7] brought up the difference between the microcanonical and canonical ensembles under which MD simulations of DWNT oscillators are performed. It seems there are some contradictory results regarding the dependency of energy dissipation
Chiral indices (4,4)/(9,9) (5,5)/(10,10) (6,6)/(11,11) (7,7)/(12,12)
Table I. Dimensions of model DWNTs. Inner tube diameter (Å)
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