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O: Fachverband Oberflächenphysik
O 15: Scanning Probe Techniques: STM/AFM
O 15.11: Talk
Monday, March 16, 2015, 17:30–17:45, MA 043
Intermolecular Contrast in Atomic Force Microscopy Images without Intermolecular Bonds — Sampsa K. Hämäläinen1, Nadine van der Heijden2, Joost van der Lit2, Stephan Hartog2, Peter Liljeroth2, and •Ingmar Swart1 — 1Department of Applied Physics, Aalto University School of Science, Finland — 2Debye Institute for Nanomaterials Science, Utrecht University, The Netherlands
Atomic force microscopy (AFM) finds increasing use in the study of molecules on surfaces. This development started with the demonstration of imaging the chemical structure of organic molecules with atomic resolution.[1] Recently, features described to hydrogen bonds have also been reported. [2] These intermolecular bonds primarily have an electrostatic origin and may include some covalent character and other attractive interactions. However, it is not clear why these should yield significant repulsive contrast in AFM.
A recent theoretical study showed that the intermolecular features can be explained by the flexibility of molecule-terminated tips.[3] We probed this effect by carrying out atomic force microscopy experiments on a model system that contains regions where intermolecular bonds should and should not exist between close-by molecules. Intermolecular features are observed in both regions, demonstrating that intermolecular contrast cannot be directly interpreted as
intermolecular bonds.[4]
[1] L. Gross et al. Science, 325, 1110 (2009).
[2] J. Zhang et al. Science 342, 611 (2013).
[3] P. Hapala et al., Phys. Rev. B 90, 085421 (2014).
[4] S.K. Hämäläinen et al., Phys. Rev. Lett. 113, 186102 (2014).