Growth mechanism for nanotips in high electric fields

TL;DR

This paper uses atomistic simulations to reveal how high electric fields induce nanotip growth from surface asperities through biased diffusion, enhancing understanding of field-induced surface modifications.

Contribution

The study introduces a physically motivated Kinetic Monte Carlo model that explains nanotip growth mechanisms under electric fields without fitting parameters.

Findings

Growth of nanotips is enhanced by higher electric fields.

Temperature increases accelerate nanotip formation.

Model reproduces experimental faceting patterns of tungsten surfaces.

Abstract

In this work we show using atomistic simulations that the biased diffusion in high electric field gradients creates a mechanism whereby nanotips may start growing from small surface asperities. It has long been known that atoms on a metallic surface have biased diffusion if electric fields are applied and that microscopic tips may be sharpened using fields, but the exact mechanisms have not been well understood. Our Kinetic Monte Carlo simulation model uses a recently developed theory for how the migration barriers are affected by the presence of an electric field. All parameters of the model are physically motivated and no fitting parameters are used. The model has been validated by reproducing characteristic faceting patterns of tungsten surfaces that have in previous experiments been observed to only appear in the presence of strong electric fields. The growth effect is found to be enhanced by increasing fields and temperatures.