The origin of self-excited oscillation of double-walled carbon nanotubes

The mechanism of self-excited oscillation of the inner tube in a double-walled carbon nanotube (DWCNT) is investigated with the aid of the molecular dynamics (MD) simulation. In the simulation, the outer tube is fixed, and the inner tube is free in terms of axial displacement and rotation. The MD results indicate that a van der Walls (vdW) energy barrier to axial oscillation exists in both commensurate and incommensurate DWCNTs, and this vdW energy barrier can be broken through at sufficient high temperatures or with sufficiently large rotational excitations. The max amplitude of axial oscillation of the inner tube can reach larger than half distance of the difference between the length of the inner and outer tubes when the temperature exceeds around 10 ∼ 100 K for the incommensurate tubes and around 500 ∼ 700 K for the commensurate tubes. Above the critical temperature, the rotational excitation cannot increase the axial oscillation amplitude of the inner tube, but below the critical temperature, a sufficiently large rotational excitation can trigger an axial oscillation with large amplitude for incommensurate DWCNTs. Our findings are therefore helpful to both the understanding of oscillation mechanism and the design of nano-devices at ultralow temperature.