June 7th, 10:00 CEST: Jascha Repp, University of Regensburg, Germany
Probing excited-state lifetimes by means of pump-probe atomic force microscopy
Scanning Tunneling Microscopy (STM) is a powerful tool for the investigation of individual molecules, being able to probe their orbitals with sub-molecular resolution. However, the requirement of a conductive substrate strongly limits the accessible electronic transitions. Conversely, atomic force microscopy (AFM) can be extended to insulating substrates, providing structural and electrostatic information. Recently, the single-electron sensitivity of AFM [1] in detecting electrostatic forces has been exploited to sense individual electron tunneling events between tip and investigated structure. Thereby, electronic states can be investigated with Angstrom resolution in absence of any conductance of the underlying substrate [2-4]. Beyond steady-state spectroscopy, all-electronic pump-probe techniques have opened the door to access dynamic properties on submolecular scales, as demonstrated by measurements of spin lifetimes of individual atoms [5]. Merging these developments, we probe the lifetime of the out-of-equilibrium triplet state of individual molecules by means of novel pump-probe AFM. Combining this with real-space atomic resolution, we observe the quenching of the triplet lifetime by surrounding oxygen molecules in atomistic details [6].
[1] J. Klein, C. C. Williams, Appl. Phys. Lett. 79, 1828 (2001).
[2] S. Fatayer et al., Nat. Nanotech. 13, 376 (2018).
[3] L. L. Patera et al., Nature 566, 245 (2019).
[4] S. Fatayer et al., Phys. Rev. Lett. 126, 176801 (2021).
[5] S. Loth et al., Science 329, 1628 (2010).
[6] J. Peng et al., unpublished (2021).