Electron Beam Stimulated Molecular Motions of C$_{60}$s inside Single-Walled Carbon Nanotubes

Electron beam irradiation stimulated motions of carbon nanostructures from single C$_{60}$ to C$_{60}$s chain inside single-walled carbon nanotubes (CNTs) were investigated by low voltage and high resolution TEM. Single C$_{60}$'s jump in a defective zigzag C$_{60}$s molecular chain inside host CNT was observed. A cluster of C$_{60}$s inside an isolated partially filled CNT can translate back and forth within the hollow space for several times. Intermediate states of these translations were recorded as well, together with pickup of additional C$_ {60}$s when the moving cluster reached either end of the hollow space. Continuous rotation of a zigzag C$_{60}$ molecular chain inside an overloaded CNT resulted in alternate expansion and contraction of the projected width of the host CNT in the TEM images. The maximum expansion was up to 29\%. Potential calculation for the molecular motion was performed based on the van der Waals interaction among C$_{60}$s and CNT. Activation energies ranging from 0.3 eV to 0.7 eV were estimated. The molecular motion was attributed to momentum transfer during elastic scattering of electrons by the molecules, instead of thermal energy or thermal gradient. Our study demonstrates the potential of driving molecular motion by electron irradiation.