Project B6: Time-Resolved Two-Photon Photoemission Studies of Interface Electron and Exciton Dynamics

Principle Investigator: Prof. Dr. Ulrich Höfer, Dr. Robert Wallauer (Marburg, Dept. of Physics)

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. C. M. Heyl, J. Güdde, A. L’Hullier, U. Höfer High-order harmonic generation with μJ laser pulses at high repetition rates J. Phys. B – At. Mol. Opt. 45, 074020 (2012).
2. U. Höfer and P. M. Echenique Resolubility of image-potential resonances Surf. Sci. 643, 203 (2016).
3. N. Armbrust, J. Güdde, U. Höfer, S. Kossler, P. Feulner Spectroscopy and dynamics of a two-dimensional electron gas on ultrathin helium films on Cu(111) Phys. Rev. Lett. 116, 256801 (2016).
4. R. Wallauer, N. Armbrust, J. Reimann, J. Güdde, U. Höfer Intervalley scattering in MoS₂ imaged by two-photon photoemission with a high-harmonic probe Appl. Phys. Lett. 109, 162102 (2016).