Berlin 2018 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 12: Ultrafast Electron and spin dynamics at interfaces II

O 12.5: Vortrag

Montag, 12. März 2018, 16:00–16:15, MA 005

The Unoccupied Electronic Structure of CuPc/PTCDA/Ag(111) Probed with Two-Photon Photoemission — •Klaus Stallberg, Jonas Zimmermann, Alexander Lerch, Andreas Namgalies, and Ulrich Höfer — Fachbereich Physik, Philipps-Universität, D-35032 Marburg

Stacked layers of copper-phthalocyanine (CuPc) and PTCDA on Ag(111) represent a structurally well-defined model for an organic donor-acceptor interface above a metal substrate. The unoccupied electronic structure of this model system is investigated by means of time-resolved two-photon photoemission (2PPE). The 2PPE spectra comprise several photoemission bands which originate from both occupied and unoccupied electronic states. More specifically, we observe direct 2PPE from the CuPc HOMO as well as photoemission involving the n=1 and n=2 image potential states (IPS), a Shockley-derived interface state (IS) at the PTCDA/Ag(111) interface, and excitonic states in the organic heterolayer as intermediate states. Photoemission from the IS is measured for pump photon energies ranging from 1.6 eV to 2.5 eV and is found to follow the optical absorption of CuPc. This indicates efficient transfer of photoexcited electrons from the CuPc layer to the IS at the PTCDA/silver interface which takes place on a timescale of 40 fs. Moreover, we discuss the origin of excitonic bands in the 2PPE spectra and investigate the relaxation dynamics of excitonic states in the CuPc/PTCDA donor-acceptor type heterosystem.