Regensburg 2019 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 10: New Methods and Developments II: Scanning Probe, Spectroscopic, and Diffraction Techniques
O 10.2: Vortrag
Montag, 1. April 2019, 15:15–15:30, H3
DFT-based forces on a CO tip approaching Fe, Cu, Si adatoms on Cu(111) in an atomic force microscope — •Svitlana Polesya1, Sergiy Mankovsky1, Ferdinand Huber2, Franz Giessibl2, and Hubert Ebert1 — 1Dept. Chemistry, LMU Munich, D-81377 Munich, Germany — 2Inst. Expt./Appl. Physics, University of Regensburg, 93053 Regensburg, Germany
We present the results of a DFT-based investigation on the forces experienced by a CO tip approaching different types of atoms deposited on Cu(111) surface: Cu, Fe and Si. A similar behaviour has been found for the forces as function of distance of CO molecule from Cu and Fe adatoms: they show two attractive minima with a repulsive ’barrier’ in-between. In contrast to this, in case of a Si adatom the force on a CO tip is always repulsive at distances d ≤ 400 pm from the adatom. These findings are discussed using similar arguments as in the discussion of chemical and physical adsorption on a surface. In particular, attractive forces in the vicinity of Fe and Cu adatoms are explained by the formation of bonding states giving a significant energy gain in these cases, while charge redistribution in the vicinity of Si adatom is responsible for a strong Coulomb repulsion at these distances. Similar arguments are used to explain the variation of the force upon a lateral motion of the tip at constant distance from the surface, that was found in a good agreement with experiment. Based on these results we conclude about the crucial role of the quantum-mechanical contribution to the forces between the Fe and Cu adatoms and a CO tip responsible for experimentally observed AFM image.