Electrodynamics—molecular dynamics simulations of the stability of Cu nanotips under high electric field

Abstract

The shape memory effect and pseudoelasticity in Cu nanowires is one possible pair of mechanisms that prevents high aspect ratio nanosized field electron emitters to be stable at room temperature and permits their growth under high electric field. By utilizing hybrid electrodynamicsmolecular dynamics simulations we show that a global electric field of 1 GV/m or more significantly increases the stability and critical temperature of spontaneous reorientation of nanosized <100> Cu field emitters. We also show that in the studied tips the stabilizing effect of an external applied electric field is an order of magnitude greater than the destabilization caused by the field emission current. We detect the critical temperature of spontaneous reorientation using the tool that spots the changes in crystal structure. The method is compatible with techniques that consider the change in potential energy, has a wider range of applicability and allows pinpointing different stages in the reorientation processes.

Dynamic coupling between particle-in-cell and atomistic simulations

“…The simulation geometry is motivated from the experimental observations that suggest the existence of field emitters with an aspect ratio of 20-100 [46] on flat Cu surfaces. The size of the tip is chosen to be large enough to prevent instability due to excess surface energy [47,48] and sufficiently small to result in a reasonable computational cost. In order to obtain results that are directly comparable to our previous work [12], we chose the dimensions of the thin system to be identical to the ones used in Ref.…”

“…For the MD simulations we used the interatomic EAM potential developed by Mishin et al [53]. This potential has been successfully used in our previous works [12,33,47] and has shown accurate reproduction of nonequilibrium system energetics [53]. The stochastic nature of the thermal effects were taken into account by running 50 independent simulations with different random seeds.…”

Atomistic behavior of metal surfaces under high electric fields

“…There are many indications in the literature that metal surfaces behave differently under the influence of a high electric field [2,5,[23][24][25][26][27][28][29][30]. For example, the surface diffusion of adatoms has been found both computationally [31][32][33] and experimentally [34][35][36] to vary depending on the magnitude of the applied field and even become biased when a non-uniform field is present [25,37].…”

Dynamic coupling of a finite element solver to large-scale atomistic simulations

“…The present work is the continuation of our previous attempt to include the electronic effects in atomistic simulations by solving the Laplace equation on a structured static mesh using FDM [5]. This method enabled us to investigate the behavior of Cu surface under high electric field when small-scale surface features are present [21]- [26]. However, the high computational cost and inflexible mesh limited the earlier simulations to specific crystal structures and orientations, few nm scale and very short times.…”