Berlin 2018 – scientific programme
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O: Fachverband Oberflächenphysik
O 73: Surface dynamics: Reactions, elementary processes and phase transitions II
O 73.1: Talk
Wednesday, March 14, 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.