Influence of helical rise on the self-excited oscillation behavior of zigzag @ zigzag double-wall carbon nanotubes

Abstract

Oscillation behaviors of oscillators consisting of defect-free multi-walled carbon nanotubes (MWCNTs) have been extensively studied, owing to the operating frequency of the nanotubes being able to reach up to gigahertz. However, there exist defects in most carbon nanotubes, which will affect the friction force between the walls of nanotubes. It is therefore critical to investigate the oscillation characteristics of the MWCNT-based oscillators containing a distorted or defective rotating tube, for the design of MWCNTs-based oscillators. Unlike the case in the armchair carbon nanotubes (Zeng Y H, et al. 2016 Nanotechnology 27 95705), the existence of the helical rise in the zigzag-type nanotubes can induce aberrant or defective shell structures. In this paper, the oscillatory behaviors of zigzag@zigzag double-wall carbon nanotubes containing a rotating inner tube with different helical rises are investigated using the molecular dynamics method. In all the simulation modes, the adaptive intermolecular reactive empirical bond order potential is used in this work for both the covalent bond between carbon atoms and the long-range van der Waals interaction of the force field. The perfect zigzag outer tube is assumed to be fixed while the zigzag inner tube is free after it has been rotated by a torque. At the beginning of the simulation, the whole system is heat bathed at a temperature around 300 K for 60 ps, to gently increase the whole system temperature to around 300 K after the energy minimization. The total number of particles, the system volume, and the absolute temperature are kept unchanged for 60 ps. Then we apply a torque of 30 eV to the inner tube under the constant temperature. After the rotation frequency of the inner tube reaches around 300 GHz, we remove the torque of inner tube and let the whole system be under a constant energy condition. The time steps for all simulations are all chosen to be 1 fs. The total time for the simulation is 3000 ps. It is found that the oscillatory behavior of the inner tube is dependent on the helical rise. The simulation results show that the oscillation frequency of the inner tube increases with the length of helical rise increasing. However, as the helical rise is further increased, the oscillation becomes awful because of the breakage of the inner tube with defects. Moreover, the zigzag@zigzag double-wall carbon nanotubes without any helical rise may be used as an ideal rotating actuator because the inner tube can rotate at an approximately constant rotational frequency. The influence of the system temperature on the oscillatory behavior of inner tube with a helical rise of 0.5 nm is also investigated. The results show that the oscillation amplitude of the inner tube increases with temperature increasing, but the oscillation of the inner tube is extremely unstable if the temperature is higher than a critical value.