Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 73: Surface dynamics: Reactions, elementary processes and phase transitions II

O 73.1: Vortrag

Mittwoch, 14. März 2018, 16:45–17:00, MA 043

Near-Field Enhanced Photochemistry of Single Molecules in an STM Junction — •Hannes Böckmann¹, Sylwester Gawinkowski², Jacek Waluk², Markus B. Raschke³, Martin Wolf¹, and Takashi Kumagai¹ — ¹Department of Physical Chemistry, FHI Berlin, Germany — ²Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland — ³Department of Physics, Department of Chemistry, University of Colorado, Boulder, USA

Optical near-field excitation of metallic nanostructures can be used to enhance photochemistry and promote photocatalysis. However, few studies have yet addressed near-field induced chemistry at the single-molecule level. Here we report the near-field enhanced tautomerization of porphycene on a Cu(111) surface in a scanning tunneling microscope (STM) junction. The light-induced tautomerization is mediated by photogenerated carriers in the Cu substrate. It is revealed that the reaction cross section is significantly enhanced in the presence of a Au tip compared to the far-field induced process. The strong enhancement occurs in the red and near-infrared spectral range for Au tips, whereas a W tip shows a much weaker enhancement, suggesting that excitation of the localized plasmon resonance contributes to the process. Additionally, the near-field enhanced tautomerization is examined in and out of the tunneling regime. Our results suggest that the enhancement is attributed to the increased carrier generation rate via decay of the excited near-field in the STM junction. Additionally, optically excited tunneling electrons also contribute to the process in the tunneling regime.