Regensburg 2022 – scientific programme

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O: Fachverband Oberflächenphysik

O 27: Electron-Driven Processes

O 27.2: Talk

Tuesday, September 6, 2022, 10:45–11:00, H6

Are vacancies in field ion microscopy artefacts? A DFT study — •Shyam Katnagallu, Jörg Neugebauer, and Christoph Freysoldt — Department of computational materials design, Max Planck Institut für Eisenforschung GmbH, Max-Planck- Str. 1, 40237, Düsseldorf, Germany.

Resolving the atomic structure of engineering materials in 3D continues to be an extensive research field. Field ion microscopy under evaporating conditions (3D-FIM) is one of the few techniques capable of delivering such atomic-scale information, allowing to even image vacancies and their interactions with solute atoms in alloys. However, the quantification of the observed vacancies and their origins are still a matter of debate. It was suggested that high electric fields (1-10 V/Å) used in FIM could introduce artefact vacancies. To investigate the possibility of this mechanism, we used density functional theory (DFT) simulations. Stepped Ni surfaces with kinks were modelled in the repeated slab approach with a (971) surface orientation. A field of up to 4 V/Å was introduced on one side of the slab using the generalized dipole correction. Contrary to conventional wisdom, we show that the reaction barrier to form vacancies on the electrified metal surface increases compared to the field-free case. We also find that the electric field can introduce kinetic barriers to a potential "vacancy-killing" mechanism. We compare these findings with field evaporation models proposed in the literature.