Dynamic friction force in a carbon peapod oscillator

We investigate a new generation of fullerene nano-oscillators: a single-walled carbon nanotube with one buckyball inside with an operating frequency in the tens-of-gigahertz range. A quantitative characterization of energy dissipation channels in the peapod pair has been performed via molecular dynamics simulation. Edge effects are found to be the dominant cause of dynamic friction in the carbon-peapod oscillators. A comparative study on the energy dissipation also reveals the significant impact of temperature and impulse velocity on the frictional force. (Some figures in this article are in colour only in the electronic version) Nanoscale fabrication technologies have had a pervasive impact over the past 20 years [1]. One of the manifestations has been in the area of nano-electro-mechanical-systems (NEMS) [2], which broadly refers to the application of nanofabrication technologies to construct sensors, actuators, and nano-scale integrated systems for a variety of applications. Very recently, Zettl’s group reported that frictional forces are very small, of the magnitude of about 10−14 N Å−2, during the controlled and reversible telescopic extension of multi-wall carbon nanotubes [3]. Furthermore, it has been proposed that the transit time for complete nanotube core retraction (on the order of 1–10 ns) implies the possibility of exceptionally fast electromechanical switches [4]. In fact, oscillating crystals have a long history, dating back to 1880 when the piezoelectric effect was discovered by the Curie brothers [5]. Quartz crystal oscillators are widely used to provide regular pulses to synchronize various parts of an electronic system. But a typical crystal is millimetres in size, which could not be integrated directly into a computer chip. Motivated by the observation of Zettl’s group, Zheng and Jiang [4] proposed a new type of nano-oscillator operating completely differently from conventional quartz oscillators. Since then, designing this type of nano-oscillator has been carried out actively. Legoas and collaborators [6] first simulated a 38 GHz nano-oscillator 4 Author to whom any correspondence should be addressed. consisting of a (9, 0) carbon nanotube (CNT) inside an (18, 0) CNT. Zhao et al [7] found that off-axial rocking motion of the inner nanotube and wavy deformation of the outer nanotube are responsible for energy dissipation in a double-walled nanotube oscillator. So far, no successful experimental realization of the bitube oscillators has been reported. This is probably due to the considerable amount of energy dissipation, and the difficulty of preparing a bi-tube type oscillator unit from multiwall carbon nanotubes with high quality. Fortunately, we have effective ways to place buckyballs inside nanotubes. For instance, single-walled carbon nanotube (SWNTs) can be synthesized by the pulsed-laser vaporization route, whereby the sublimation of solid C60 in the presence of open SWNTs causes the fullerenes to enter the SWNTs and self-assemble into one-dimensional (1D) chains [8]. Therefore, it is feasible for single C60 to enter a nanotube by van der Waals interactions. The peapod formation process has been widely studied [9–12]. Many studies also focused on the effect of the nanotube diameter on binding properties [9, 10]. Filling SWNTs with C60 is exothermic or endothermic, depending on the size of the nanotube. C60@(10, 10) is found to be stable (exothermic), while other peapods with smaller radius such as the (9, 9) and (8, 8) tubes are endoethermic [10]. Among many proposed interesting applications of peapod structures, one recent nanomechanical resonance study has been performed on 0957-4484/06/225691+05$30.00 © 2006 IOP Publishing Ltd Printed in the UK 5691