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O: Fachverband Oberflächenphysik
O 103: Focus Session: Molecular Nanostructures on Surfaces: On-Surface Synthesis and Single-Molecule Manipulation IV
O 103.9: Vortrag
Freitag, 22. März 2024, 12:45–13:00, HE 101
Exploring in-plane interactions beside an adsorbed molecule with lateral force microscopy — Shinjae Nam1, Elisabeth Riegel1, Lukas Hörmann2, 3, Oliver T. Hofmann2, Oliver Gretz1, •Alfred J. Weymouth1, and Franz J. Giessibl1 — 1Universität Regensburg, Deutschland — 2TU Graz, Österreich — 3University of Warwick, UK
Atomic force microscopy (AFM) with a CO-tip can directly image the internal structure of a planar molecule. However, H-atoms usually cannot be directly observed due to their small size. At the same time, H-atoms are highly important, since they can direct on-surface chemical reactions. Measuring in-plane interactions at the sides of PTCDA molecules with lateral force microscopy allowed us to directly identify hydrogen atoms via their repulsive signature. Additional features in the force data could not be explained by H-bonding of the CO tip with the PTCDA sides. Instead, they are caused by electrostatic interaction of the large dipole of the metal apex. DFT calculations allowed us to estimate the strength of the dipole at the metal tip apex. To confirm that this dipole generally affects measurements on weakly-polarized systems, we investigated the a single CO molecule. We determined the radially-symmetric atomic interaction to be valid over a large solid angle of 5.4 sr, corresponding to 82°. Therefore in both the PTCDA and CO systems, the underlying interaction preventing direct observations of H-bonding and causing a collapse of the radially-symmetric model is the dipole at the metal apex, which plays a significant role when approaching closer than standard imaging heights.
Keywords: Lateral force microscopy; On-surface reactions; Atomic force microscopy