NCAFM2023 Programme Booklet

Monday 1500 - 1520

EXPLORING IN PLANE INTERACTIONS BESIDE AN ADSORBED MOLECULE WITH LATERAL FORCE MICROSCOPY

Shinjae Nam 1 , Elisabeth Riegel 1 , Oliver Gretz 1 , Lukas Hörmann 2 , Oliver T. Hofmann 2 , Alfred J. Weymouth 1* , and Franz J. Giessibl 1 1 Faculty of Physics, University of Regensburg, 93053 Regensburg, Germany 2 Institute of Solid State Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria

Email: Shinjae.Nam@physik.uni-regensburg.de

One of the most important phenomena that hydrogen atoms take part in is hydrogen bonding. Many efforts have been made to directly observe hydrogen atoms, including by AFM [1], but it is an ongoing challenge to directly observe them in planar molecules. We use frequency modulation lateral force microscopy (LFM) [2], where the tip is oscillated laterally to directly measure short-range forces. We approached the side of the PTCDA molecule with a CO terminated tip [3] and found that we could directly observe the hydrogen atoms. One advantage of PTCDA is that it offers both H-terminated and O-terminated sides. Interestingly we did not observe a signature of hydrogen bonding between PTCDA and the CO at the tip apex. We explain our observations by including the electrostatic interaction of the large dipole of the metal apex via density functional theory calculations of the electrostatic field above the molecule.

Fig. Experimental observations of PTCDA on Cu(111). (a) Constant height Δf (LFM) image of the side of a PTCDA island probed with CO-terminated tip. Ball and stick models of two PTCDA molecules are shown with oxygen (red), hydrogen (white), and carbon (grey) atoms. The schematic figure of the tip heights is shown in (b). Force maps at the H-side and at the O-side (c) at z = 600 pm and (d) at z = 460 pm. References [1] S. Kawai, T. Nishiuchi, T. Kodama, P. Spijker, R. Pawlak, T. Meier, J. Tracey, T. Kubo, E. Meyer, A. S. Foster, Sci. Adv. 2017, 3, e1603258

[2] F.J. Giessibl, M. Herz, J. Mannhart, Proc. Natl. Acad. Sci. 2002, 99, 12006. [3] L. Gross, F. Mohn, N. Moll, P. Liljeroth, G. Meyer, Science, 2009, 325, 1110.

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