Berlin 2024 – scientific programme

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O: Fachverband Oberflächenphysik

O 106: Scanning Probe Microscopy: Light Matter Interaction at Atomic Scales IV

O 106.5: Talk

Friday, March 22, 2024, 11:45–12:00, MA 041

Excited-state spectroscopy of individual molecules with atomic force microscopy — •Lisanne Sellies, Jakob Eckrich, and Jascha Repp — University of Regensburg, Regensburg, Germany

The combination of scanning probe microscopy with an increasing number of spectroscopic techniques, such as Raman and luminescence, provides unprecedented microscopic understanding. Despite its very direct access to well-defined single-molecule model systems, the unambiguous assignment of observations to specific quantum transitions is not always straightforward [1,2], and typically only a small fraction of all transitions can be studied.

Here, we propose a novel type of single-molecule spectroscopy that enables access to many quantum transitions of different types, including radiative, non-radiative and charge-related transitions. The molecules of interest are deposited on thick insulating films, preventing tunneling of charges to and from the underlying support. By controlled charge exchange between the conductive tip of an atomic force microscope and the molecule, we bring a molecule into different electronic configurations. The detection proceeds via the force acting on the tip. Thereby, quantum transitions can be mapped out in energy, enabling access to the energies of the lower-lying electronic states of individual molecules, including out-of-equilibrium states. We demonstrate our technique by applying it on pentacene and PTCDA, shedding light on the recent STM luminescence experiments on PTCDA [1,2].

References: [1] K. Kimura et al., Nature 570, 210-213 (2019) [2] J. Dolezal et al., ACS Nano 16, 1082-1088 (2022)

Keywords: Atomic force microscopy; Excited-state spectroscopy; Single molecules