Dresden 2017 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 75: Ultrafast Electron and Spin Dynamics
O 75.9: Vortrag
Mittwoch, 22. März 2017, 17:00–17:15, TRE Phy
Interplay between metal-organic interface state and donor-acceptor interface mediated charge separation on PTCDA/TiOPc/Ag(111) — •Alexander Lerch1, Frederik Schiller1, 2, and Ulrich Höfer1 — 1Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg — 2Centro de Física de Materiales, San Sebastian, Spain
Charge separation of excitons in the well ordered model system PTCDA on titanyl phthalocyanine (TiOPc) on Ag(111) was investigated by means of time-resolved two-photon photoemission (2PPE). An optical parametric oscillator provided pump pulses with photon energies ranging from 1.6 to 2.5 eV. This allowed for selective excitation of TiOPc or PTCDA. Between TiOPc and Ag(111) a shockley derived interface state (IS) approximately 0.3 eV above the Fermi energy forms. We observe a strong coupling of the first molecular layers to the IS and determine transfer times into the IS ranging from approximately 20 fs out of the second to 160 fs out of the third and fourth molecular layers. Systematic thickness-dependent measurements quantify the distance dependence of this coupling. Whereas the IS dominates the dynamics in the second layer, the PTCDA/TiOPc acceptor-donor interface (D/A) competes for electrons from excitons in the third to fourth layer. In the fifth to sixth layer no significant IS assisted separation on a timescale below 12 ns can be detected any longer. Our results highlight the competition between IS and D/A mediated charge separation of excitons in few-layer organic systems on metal substrates.