Long-term stability of Cu surface nanotips

Abstract

Sharp nanoscale tips on the metal surfaces of electrodes enhance locally applied electric fields. Strongly enhanced electric fields trigger electron field emission and atom evaporation from the apexes of nanotips. Together, these processes may explain electric discharges in the form of small local arcs observed near metal surfaces in the presence of electric fields, even in ultra-high vacuum conditions. In the present work, we investigate the stability of nanoscale tips by means of computer simulations of surface diffusion processes on copper, the main material used in high-voltage electronics. We study the stability and lifetime of thin copper (Cu) surface nanotips at different temperatures in terms of diffusion processes. For this purpose we have developed a surface kinetic Monte Carlo (KMC) model where the jump processes are described by tabulated precalculated energy barriers. We show that tall surface features with high aspect ratios can be fairly stable at room temperature. However, the stability was found to depend strongly on the temperature: 13 nm nanotips with the major axes in the [Formula: see text] crystallographic directions were found to flatten down to half of the original height in less than 100 ns at temperatures close to the melting point, whereas no significant change in the height of these nanotips was observed after 10 [Formula: see text] at room temperature. Moreover, the nanotips built up along the [Formula: see text] crystallographic directions were found to be significantly more stable than those oriented in the [Formula: see text] or [Formula: see text] crystallographic directions. The proposed KMC model has been found to be well-suited for simulating atomic surface processes and was validated against molecular dynamics simulation results via the comparison of the flattening times obtained by both methods. We also note that the KMC simulations were two orders of magnitude computationally faster than the corresponding molecular dynamics calculations.

Au nanowire junction breakup through surface atom diffusion

“…For simulating the Au nanowires we use the Kinetic Monte Carlo for Surfaces code (Kimocs) [27]. Kimocs is an atomistic Kinetic Monte Carlo code for simulating single crystal structures.…”

“…To conduct a simulation, the attempt frequency and migration barriers for all possible transitions must be known in advance. Different transitions are characterized by the number of first and second nearest neighbors of the jumping atom in the initial and final positions (see [27] for details). For simplicity we do not take into account the positioning of the neighbors, only their number, thus drastically reducing the number of possible transitions.…”

Cu self-sputtering MD simulations for 0.1–5 keV ions at elevated temperatures

“…Two different cases were considered in these simulations. Surfaces with smaller roughness (R ≈ 1 nm) were generated with the Kinetic Monte Carlo (KMC) simulation code Kimocs [50]. The roughness was achieved by randomly removing surface atoms with an average rate of 10 27 s −1 m −2 at 300 K. The atoms were also allowed to diffuse, using a parameterization for surfaces, Cu Set 1, described in Refs.…”

“…The roughness was achieved by randomly removing surface atoms with an average rate of 10 27 s −1 m −2 at 300 K. The atoms were also allowed to diffuse, using a parameterization for surfaces, Cu Set 1, described in Refs. [50,51]. Three different surfaces, {100}, {110} and {111} were used.…”

Adatom diffusion in high electric fields

“…For simulating the surface diffusion of atoms, we use the KMC code Kimocs, which is described in detail in Ref. [7]. The code uses a rigid lattice, where the atom migration jumps are characterized by the number of first-and second-nearest neighbour atoms.…”