Berlin 2005 – scientific programme

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O: Oberflächenphysik

O 45: Organische Dünnschichten IV

O 45.6: Talk

Tuesday, March 8, 2005, 17:00–17:15, TU EB301

High resolution ARPES study of thin organic films on metallic substrates — •Azzedine Bendounan, Johannes Ziroff, Frank Foster, Felix Schmitt, Eberhard Umbach, Achim Schöll, and Friedrich Reinert — Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

We study by high energy and angular resolution photoemission (ARPES) the electronic properties of ultrathin organic films deposited on metal surfaces. Our interest is focused on large π-conjugated planar molecules like 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA). On noble metal surfaces, characterized by flat density of states close to the Fermi energy, these molecules form a highly ordered superstructure and grow in layer-by-layer mode. Ag(111), for example, is an ideal substrate since the molecule can diffuse over large distances and form ordered islands. After deposition of one monolayer of PTCDA, the Ag-Shockley surface state disappears and new spectrae features appear. One of these features is associated with the formation of a chemical bond suggesting an hybridization between the metal and the molecule which fills the lowest unoccupied molecular orbital (LUMO). The second feature is described as the highest occupied molecular orbital (HOMO) peak modified also by the bonding. Moreover, we observe an important modification in the photoelectron intensity as function of the emission angle. The observed structures are significantly narrower than in previously published investigations on similar systems.