Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 44: Metal substrates: Adsorption of organic / bio molecules VI
O 44.6: Talk
Thursday, March 26, 2009, 11:45–12:00, SCH A118
Interface states investigated by PES, IPES and 2PPE: the example of PTCDA/Ag — •Achim Schöll1, Stefan Krause1, Sönke Sachs1, Johannes Ziroff1, Christian Schwalb2, Manuel Marks2, Ulrich Höfer2, Eberhard Umbach3, and Friedrich Reinert1 — 1Uni Würzburg, Experimentelle Physik II, D-97074 Würzburg — 2Philipps-Uni Marburg, Physik und Materialwissenschaften, D-35032 Marburg — 3FZ Karlsruhe, D-76021 Karlsruhe
We have studied the occupied and unoccupied states at the PTCDA/Ag interface, enabling us to draw a comprehensive picture of the interfacial electronic structure [1]. The strong, unambiguously covalent, interaction leads to hybrid orbitals (interface states), involving at least LUMO, HOMO, and HOMO-1, and Ag 5s- and 4d-states. The LUMO is pulled below EF resulting in a new occupied state. High-resolution photoemission (PES) data reveal that on Ag(111) this state is partially filled leading to a "metallic" phase. Inverse PES (IPES) and two-photon photoemission (2PPE) reveal a new unoccupied state 0.6 eV above EF, which disperses with an effective mass of 0.39 me at the Γ-point. The short lifetime (54 fs) indicates a large penetration into the metal. This state is interpreted as predominantly due to an adsorption induced upshift of the Ag(111) Shockley state[2].
These interface states are expected to have notable influence on the charge carrier injection properties at an interface, particularly if their wave function penetrates the metal as well as the molecular layer.
[1] Y. Zou et al., Surf. Science, 2006. 600(6)1240.
[2] C.H. Schwalb et al., Phys. Rev. Lett., 2008. 101(14).