Molecular dynamics simulations of thermal evaporation and critical electric field of copper nanotips

Due to the miniaturization of microelectromechanical systems, nanoelectromechanical systems and molecular devices, the problem of vacuum insulation becomes more and more prominent. The nanoscale thermal effects caused by electron emission and electric current Joule heat under high electric fields lead to gasification and migration of material in the device. In this work, a coupled molecular dynamics-electrodynamics method is used to simulate the thermal evaporation of nanotips under high electric field. Moreover, Cu nanotips with different initial geometries and different macroscopic electric fields are modelled. The deformation and damage mechanisms of nanotips under high electric field are discussed. Our simulations show that the aspect ratio of nanotips has a significant influence on the thermal evaporation of nanotips. The thermal runaway occurring in picosecond time-scale plays an important role for the initiation of the vacuum breakdown. An empirical relationship is obtained between the on-set breakdown time and the macroscopic electric field and the geometry of nanotips by analysing the numerical results.