Molecular dynamics of carbon nanobearings
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Molecular dynamics of carbon nanobearings K. Sato, N. Arai, and K. Shintani Department of Mechanical Engineering and Intelligent Systems, University of ElectroCommunications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan ABSTRACT A concept of nanoscale bearing structures utilizing nanocarbon materials is presented based on the prediction via molecular dynamics simulations. The proposed mechanism consists of a graphene layer, intercalated single walled carbon nanotubes (SWNTs), and substrate graphenes. It is found that the friction against the movement of the uppermost graphene is smallest for the 1 SWNT model. INTRODUCTION Nanoscale bearings are an essential part of nano-electro-mechanical systems (NEMS). Rotational actuators based on multi-walled carbon nanotubes (MWNTs) were proposed by Fennimore et al. [1]. Their actuator consists of a metal plate rotor and a MWNT which acts as a support shaft. Imposing a voltage between the rotor and a gate stator generates a torque to rotate the rotor. If large voltages between the rotor and the stator were successively applied, the initially pristine MWNT was fatigued, and the rotor became free to rotate. However, they could not make it clear how the MWNT was modified and how its shells could move. Bourlon et al. [2] suggested that a short section of the outer shell of Fennimore et al.'s MWNT was removed in the region between the rotor and the anchors, and the outer shell could slide around the inner ones. Based on such an idea, they fabricated a rotational actuator of a new layout. Their rotor attaches to an inner MWNT shell which can rotate around outer shells fixed to two anchor pads. The static friction against rotational sliding was estimated to be about 0.85MPa, which agrees with the values obtained for intershell friction in the direction of the tube axis. Miura et al. [3] investigated ultralow friction of a graphite/C60/graphite interface using molecular dynamics (MD) simulation. They concluded that the atomic-scale friction coefficient of the graphite/C60/graphite interface is about 30% of that of a graphite/graphite/graphite interface, which is partly due to the three-dimensional degree of freedom of intercalated C60 motion. On the other hand, Falvo et al. [4] manipulated MWNTs on a highly oriented pyrolytic graphite substrate with atomic force microscopy. They found certain discrete orientations in which the lateral force for manipulation increases during the rotation of the MWNTs. They suggested these discrete orientations correspond to commensurate contact between the MWNTs and the substrate surface. Based on the results of the above works, we investigate by MD simulation whether a graphene/SWNTs/graphene interface can work as a nanobearing. A graphene/SWNTs/graphene interface is expected to have friction coefficients lower than those of a graphite/graphite/graphite interface and higher than those of a graphite/C60/graphite interface. The sliding direction of the graphene/SWNTs/graphene interface will be limited to one direction; the friction coeffic
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