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O: Fachverband Oberflächenphysik

O 48: Scanning Probe Methods I

O 48.2: Talk

Wednesday, April 2, 2014, 10:45–11:00, GER 38

Detecting the Dipole Moment of a Molecule with Atomic Force Microscopy — •Alexander Schwarz, Arne Köhler, Josef Grenz, and Roland Wiesendanger — Institute of Applied Physics, University of Hamburg, Jungiusstrasse 11, 20355 Hamburg, Germany

Using non-contact atomic force microscopy (NC-AFM) in the constant Δ f mode with metallic tips enabled us to detect the permanent electrostatic dipole moment of single CO molecules adsorbed on three very different substrates, i.e., Cu(111), NiO(001) and Mn/W(001). The observed characteristic distance dependent contrast, which changes from a simple protrusion to a donut-shape for decreasing tip-sample separations, can be explained by an interplay between the attractive van der Waals interaction and a repulsive electrostatic interaction. The latter stems from antiparallel aligned dipoles present in CO as well as at the tip apex [1]. Our results suggest that the dipole-dipole interaction has to be considered when using metallic or CO functionalized tips to study polar molecules. They can also be responsible for complex and tip-dependent contrast patterns reported recently, which have been interpreted in terms of so-called subatomic features [2].

[1] G. Teobaldi, et al., Phys. Rev. Lett. 106, 216102 (2011).

[2] J. Welker and F. J. Giessibl, Science 336, 444, (2012).