Eur. Phys. J. B 75, 23-30 (2010)
https://doi.org/10.1140/epjb/e2010-00106-6

Time-resolved measurements of electron transfer processes at the PTCDA/Ag(111) interface

¹ Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, 35032 Marburg, Germany
² Universität Würzburg, Experimentelle Physik VII, Am Hubland, D-97074 Würzburg, Germany
³ Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany

Corresponding author: chris.schwalb@physik.uni-marburg.de

Received: 31 October 2009
Revised: 18 December 2009
Published online: 24 March 2010

Abstract

The electron transfer processes at the interface between 3,4,9,10-perylene-tetracarboxylic acid dianhydride (PTCDA) and Ag(111) have been studied using time- and angle-resolved two-photon photo-emission (2PPE). For this system a dispersing unoccupied interface state can be identified that is located 0.6 eV above the Fermi level with an effective electron mass of 0.39 m_e at the -point. The lifetime of 54 fs for the interface state is relatively short indicating a large penetration of the wavefunction into the metal. Supported by model calculations this interface state is interpreted as predominantly arising from an upshift of the occupied Shockley surface state of the clean metal substrate due to the interaction with the PTCDA overlayer. Coverage dependent measurements show a second long-lived component in the time-resolved measurements for higher PTCDA coverages that can be associated to charge transfer processes from the PTCDA multilayers into the metal substrate. Additionally the influence of the PTCDA adlayers on the image-potential states is studied indicating that the n = 1 image-potential state is localized in the first two monolayers of the PTCDA film.