Speaker
Description
Understanding how high electric fields influence metal surfaces is essential for advancing atomic-scale characterization techniques. In this talk, I will present our theoretical investigations into electric field effects on metals, using density functional theory (DFT) calculations to provide insights relevant to experimental observations.
Firstly, we investigate vacancy formation in Ni and Pt under high electric fields. While 3D field ion microscopy (FIM) allows imaging of vacancies and their interactions with other atoms, there is debate over whether the high electric fields used might introduce artificial vacancies. Our DFT simulations show that, contrary to conventional expectations, the reaction barrier for vacancy formation increases in the presence of an electric field compared to the field-free case. Furthermore, electric fields introduce kinetic barriers that inhibit mechanisms which would normally eliminate vacancies.
Secondly, we explore the challenges faced in atom probe tomography (APT) of Li. While APT can offer valuable atomic-scale insights into Li-containing materials, it often encounters evaporation artifacts that compromise data reliability. Our DFT studies reveal that at certain electric field strengths below the threshold for Li evaporation, the preferred adsorption sites for Li atoms shift. This shift leads to barrier-less diffusion of Li atoms across the surface, resulting in the “spotty” evaporation patterns observed experimentally.
Lastly, we address the computational challenges in modelling field evaporation and ionization. Traditional ab initio simulations are computationally intensive due to the shallow potential energy surfaces involved. To overcome this, we explore machine learning interatomic potentials with a charge equilibration scheme. We validate this approach using DFT reference data for Pt slabs under electric fields ranging from 1 to 4.5 V/Å.
By elucidating the mechanisms behind surface diffusion, field evaporation, and vacancy formation under electric fields, we aim to improve the interpretation of experimental data and the development of advanced materials characterization techniques.
