Time-Resolved Two-Photon Photoemission Studies of Interface Electron and Exciton Dynamics

Summary

Time-resolved two-photon photoemission (2PPE) can measure the absolute energy position of occupied and unoccupied electronic states in the vicinity of the Fermi level and monitor electron transfer processes in the time domain. In the framework of the CRC, this unique capability is exploited for investigations of well-ordered organic layers on single-crystal metal surfaces. Of particular interest are metal/organic interface states, their energy position, their wavefunction overlap with both solids as well as the charge transfer between abrupt organic donor/acceptor interfaces such as those between phthalocyanines and PTCDA.

With a new experimental setup that uses probe photons above 20 eV from a high laser harmonic source it will be possible to photoemit electrons with large parallel momenta and thus access a much broader class of materials. This new capability will be exploited to investigate charge transfer excitations at van der Waals heterointerfaces of transition metal dichalcogenides and interfaces between organic semiconductors and these two-dimensional inorganic semiconductors.

Project-related publications

1. R. Wallauer, R. Perea-Causin, L. Münster, S. Zajusch, S. Brem, J. Güdde, K. Tanimura, K.-Q. Lin, R. Huber, E. Malic, U. Höfer
   Momentum-resolved observation of exciton formation dynamics in monolayer WS₂
   Nano Lett. 21, 5867 (2021).
2. R. Wallauer, M. Raths, K. Stallberg, L. Münster, D. Brandstetter, X. Yang, J. Güdde, P. Puschnig, S. Soubatch, C. Kumpf, F.C. Bocquet, F.S. Tautz, U. Höfer
   Tracing orbital images on ultrafast time scales
   Science 371, 1056 (2021).
3. K. Stallberg, M. Shibuta, U. Höfer
   Temperature effects on the formation and the relaxation dynamics of metal-organic interface states
   Phys. Rev. B 102, 121401(R) (2020).
4. R. Wallauer, P. Marauhn, J. Reimann, S. Zoerb, F. Kraus, J. Güdde, M. Rohlfing, U. Höfer
   Momentum-resolved observation of ultrafast interlayer transfer in MoS₂
   Phys. Rev. B 102, 125417 (2020) – editor’s suggestion.
5. N. Armbrust, F. Schiller, J. Güdde, U. Höfer
   Model potential for the description of metal/organic interface states
   Sci. Rep. 7, 46561 (2017).