Regensburg 2022 – scientific programme

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O: Fachverband Oberflächenphysik

O 46: New Methods and Developments 3: Theory

O 46.7: Talk

Wednesday, September 7, 2022, 16:30–16:45, H6

Accurate computation of chemical contrast in field ion microscopy — •Shalini Bhatt, Felipe F. Morgado, Shyam Katnagallu, Christoph Freysoldt, and Jörg Neugebauer — Max Planck Institut für Eisenforschung GmbH Düsseldorf Germany

Field ion microscopy (FIM) was the first microscopy technique to image individual atoms on a metal surface with near atomic spatial resolution. In short an imaging gas (e.g. He, Ne) is ionized above a surface subject of a few field 10¹⁰ V/m. The imaging contrast is dominated by the ionization probability at 5-10 Å above the surface. To simulate this within density-functional theory (DFT), we adapt the Tersoff-Hamann theory known from scanning tunneling microscopy (STM).

The gigantic electric field leads to very fast decay of wavefunctions into the vacuum. At the ionization height, they run into a regime that is dominated by numerical noise. To address this noise challenge inherent to any global-scale Kohn-Sham solver employed in DFT codes, wavefunction tails must be recomputed. To solve 3D Schrödinger equation at local scale we develop the extrapolated tail via reverse algorithm (EXTRA). The decaying tails are obtained by reverse integration (from outside in) using a Numerov-like algorithm. The starting conditions are then iteratively adapted to match the values of planewave DFT wavefunctions close to the surface. We demonstrate chemical contrast for Ta and W at Ni surface using this new technique.