Nanotip Shape Evolution Under High Electric Fields Based on Molecular Dynamics

The insulation of micro/nano electronic devices under high electric fields determines the life and reliability of electronic components. Research on vacuum discharge in nanoscale and subsequent thermal damage effect of electrode materials during the breakdown process still lacks of systematic research. In this work, tip morphological evolution and crystal shape changes caused by thermal-field emission and field evaporation in high electric fields is studied. The whole tip morphological dynamic evolution process under electric field is modeled and calculated by a recently developed model FEMOCS which couples finite element method (FEM) with classical molecular dynamics (MD). Monocrystalline cooper nanotips was modeled with the applied electric field which was about the critical electric field of nanoscale pre-breakdown. At lower electric fields, the results showed that shape memory effect (SME) occurred when the tip temperature exceed its critical temperature, and it resulted in a larger radius and shorter tip length, which caused the electric field to be smaller than the initial electric field, and eventually the breakdown would not occur. And when the electric field is greater than the critical electric field, the breakdown occurred quickly and with a large amount of atomic evaporation. The results showed that the critical electric field not only determines whether the breakdown will occur, but also influences the tip morphological evolution in different ways and whether atomic evaporation takes place.