Berlin 2015 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 69: Ultrafast Electron and Spin Dynamics

O 69.7: Poster

Mittwoch, 18. März 2015, 18:15–21:00, Poster A

Electronic Structure and Excitation Dynamics of the CuPc/PTCDA/Ag(111) Heterointerface — •Jonas Zimmermann, Andreas Namgalies, Nico Armbrust, and Ulrich Höfer — Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg

We grow well-defined monolayers of copper(II)phthalocyanine (CuPc) on top of monolayers of perylene-tetracarboxylic acid dianhydride (PTCDA) on Ag(111) as model systems for organic donor-acceptor heterointerfaces. We employ time-resolved two-photon photoemission (2PPE) to examine the dynamics of charge transfer processes at these interfaces. An optical parametric oscillator (OPO) enables us to tune the pump photon energy to the HOMO-LUMO transition of CuPc. The time-resolved 2PPE spectra reveal the subsequent decay of the excitation. In case of the PTCDA monolayer the excited electron cannot be transferred from the LUMO of CuPc to unoccupied PTCDA orbitals because the former LUMO of PTCDA is shifted below the Fermi level by chemisorption. Instead, we observe an electron transfer into the interface state of PCTDA/Ag(111). This metal-organic hybrid state arises from the Shockley surface state of clean Ag(111) and is located at 0.6 eV above the Fermi level. The electron transfer from CuPc shows up as resonantly enhanced and temporarily delayed 2PPE intensity of the interface state when the pump photon energy is tuned through the CuPc HOMO-LUMO transition at 1.8 eV.