Dresden 2020 – wissenschaftliches Programm
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CPP 93.2: Vortrag
Donnerstag, 19. März 2020, 10:45–11:00, WIL C107
Atomic Force Microscopy study of the complex surface unit cell of CaF2(111) with a CO-terminated tip — •Alexander Liebig1, Prokop Hapala2, Alfred J. Weymouth1, and Franz J. Giessibl1 — 1Institute of Experimental and Applied Physics, University of Regensburg, Universitätsstraße 31, D-93053 Regensburg, Germany — 2Department of Applied Physics, Aalto University, 00076 Aalto, Espoo, Finland
A chemically inert tip apex of an atomic force microscope (AFM), such as a carbon-monoxide (CO) molecule, allows to enter the repulsive interaction regime without destroying tip or sample. Imaging in a gentle repulsive regime has led to unprecedented spatial resolution of organic molecules  and opened the way for numerous results on different sample systems [2,3]. Here, we probe the ionic CaF2 (111) surface with a CO-terminated tip over a range of distances, starting from a regime, where short-range electrostatics dominate the AFM contrast, down to distances, where Pauli repulsion and CO bending lead to a complete reversal of the atomic-scale contrast. By comparing the data to simulations, we demonstrate that a mechanical model using the overlap of electron densities  as well as the Lennard-Jones potential  is reproducing experimental AFM images even at tip-sample distances, where strong lateral forces cause strong lateral deflection of the CO molecule at the tip apex.  L. Gross et al., Science 325, 1110 (2009).  P. Jelínek, J. Phys.: Condens. Matter 29, 343002 (2017).  F. Huber et al., Science 366, 235 (2019).  M. Ellner et al., ACS Nano 13, 786 (2019).  P. Hapala et al., PRB 90, 085421 (2014).