Ab-Initio Simulation of Field Evaporation

TL;DR

This paper introduces a physics-based ab-initio simulation method for field evaporation that explicitly calculates electric-field-induced forces on atoms, enabling more accurate predictions of evaporation phenomena without relying on thermal activation assumptions.

Contribution

The authors develop a novel simulation approach combining electrostatics with molecular dynamics that does not depend on empirical evaporation criteria, making it fully physics-based and ab-initio.

Findings

Successfully reproduces experimental field desorption patterns

Determines critical voltages and evaporation fields for metals

Highlights importance of interatomic potential selection

Abstract

A new simulation approach of field evaporation is presented. The model combines classical electrostatics with molecular dynamics (MD) simulations. Unlike previous atomic-level simulation approaches, our method does not rely on an evaporation criterion based on thermal activation theory, instead, electric-field-induced forces on atoms are explicitly calculated and added to the interatomic forces. Atoms then simply move according to the laws of classical molecular dynamics and are "evaporated" when the external force overcomes interatomic bonding. This approach thus makes no ad-hoc assumptions concerning evaporation fields and criteria, which makes the simulation fully physics-based and "ab-initio" apart from the interatomic potential. As proof of principle, we perform simulations to determine material dependent critical voltages which allow assessing the evaporation fields and the corresponding steady-state tip shapes in different metals. We also extract critical evaporation fields in elemental metals and sublimation energies in a high entropy alloy to have a more direct comparison with tabulated values. In contrast to previous approaches, we show that our method is able to successfully reproduce the enhanced zone lines observed in experimental field desorption patterns. We also demonstrate the need for careful selection of the interatomic potential by a comparative study for the example of Cu-Ni alloys.