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MM: Fachverband Metall- und Materialphysik

MM 23: Methods in Computational Materials Modelling (methodological aspects, numerics)

MM 23.2: Vortrag

Mittwoch, 3. April 2019, 10:30–10:45, H44

Evaporation Mechanisms for Field-Ionized Surface Atoms — •Michael Ashton, Christoph Freysoldt, and Joerg Neugebauer — Max Planck Institut für Eisenforschung GmbH, Max-Planck-Str. 1 40273 Düsseldorf

Detailed information regarding the atomic-scale mechanisms of field evaporation has long eluded the theoretical community, in part due to the challenge of applying finite electric fields in density functional theory (DFT) models that require periodic boundary conditions. We explain how our recent advances in the treatment of electric fields in DFT have enabled fundamental insights into the near-surface mechanisms of field evaporation for atoms on Tungsten surfaces. These insights are obtained from static calculations of the energy landscapes for low-coordinated atoms departing from a charged surface. They show that even for very strong fields a two-stage rollover mechanism - in which an evaporating kink atom rolls into the hollow site above the neighboring step and then proceeds to evaporate - is the minimum energy path. We find that this two-stage rollover mechanism is circumvented at fields very close to the critical evaporation field, resulting in a much simpler single barrier trajectory. The origin of this change in mechanism will be discussed along with some of its implications for experimental evaporation procedures. Finally, we discuss the similarities and differences between our DFT results and those obtained using classical models to describe field evaporation.