SKM 2023 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 76: Plasmonics and Nanooptics III: Light-Matter Interaction and Spectroscopy II

O 76.4: Vortrag

Donnerstag, 30. März 2023, 11:15–11:30, WIL A317

Plasmon-Induced Molecular Switching of PTCDA on Si(111) Studied by STM-TERS — •Youngwook Park¹, Adnan Hammud¹, Martin Wolf¹, Takashi Kumagai², and Akitoshi Shiotari¹ — ¹Fritz Haber Institute of the Max Planck Society, Berlin, Germany — ²Institute for Molecular Science, Okazaki, Japan

We studied a unique plasmon-induced molecular motion of perylenetetracarboxylic dianhydride (PTCDA) single molecules on the Si(111)-7x7 surface by means of the atomic point contact (APC) tip-enhanced Raman spectroscopy (TERS) with a low temperature scanning tunneling microscope (STM) under an ultrahigh vacuum condition. In our APC-TERS scheme, a silver tip approaches close to the surface until the tip makes an atomic point contact with its counterpart. It was reported by our previous study that at the point contact with Si(111) the TERS signal was significantly enhanced. The PTCDA on the Si(111), fixed on the surface by four oxygen-silicon bonds, showed a distinctive APC-TERS pattern where the Raman intensity was dramatically enhanced at a certain gap distance during the tip approach, and then was attenuated at shorter tip-molecule distances. At the TERS "sweet spot", the STM current rapidly switched between two states, implying a fluctuative motion of PTCDA molecule between the tip and the surface. On the contrary to PTCDA, perylenetetracarboxylic diimide (PTCDI) did not show such TERS "sweet spot" nor STM current switching. We believe this unique system could provide a better understanding on the plasmon-molecule interaction, as well as their implication on the enhancement mechanism in TERS.