Unique Near-Zero Friction Regime of C60 Molecular Bearings Along [123-bar 0] Direction

We numerically analyzed unique near-zero friction regime of the C60 molecular bearings, graphite/C60/graphite interface, for the lateral scan along the [123-bar 0] direction under the relatively low loading condition. Here the C60 molecule slides, facing its six-membered ring nearly parallel to both the upper and lower graphene sheets. The sinusoidal motion of the C60 molecule along the carbon bond is continuous and reversible during the forward and backward scans. As a result, the hysteresis loop of the lateral force curve nearly disappears, which leads to a mean frictional force of nearly zero, (FL)≅ 0. The mechanism of this conservative motion is clarified by comparing the structural optimization of the C60 molecular bearing system with the direct calculation of the local minimum position located on the total potential energy surface Vtotal. The energy barrier between the neighboring minimum positions always exists, which prevents the C60 molecule from taking stick-slip motion.