Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 60: Post Deadline Session followed by Surface Science "get-together"
O 60.1: Vortrag
Donnerstag, 26. März 2009, 20:00–20:15, HSZ 02
Can molecular orbitals be simply reconstructed from photoemission data? — •Peter Puschnig1, Claudia Ambrosch-Draxl1, Thomas Seyller2, Stephen Berkebile3, Georg Koller3, Falko P. Netzer3, and Michael G. Ramsey3 — 1Chair for Atomistic Modelling and Design of Materials, University Leoben — 2Institut für Technische Physik II, Universität Erlangen-Nürnberg — 3Surface Science Group, Institute of Physics, University Graz
We present a new and simple approach with the aim to determine the shape of molecular orbitals by means of angle-resolved photoemission (PE) experiments. It applies to molecular films ranging from monolayers up to multilayers and leads to images of individual molecular states with a spatial resolution of about 1 Å, thereby competing with state-of-the-art scanning probe techniques. We demonstrate how the PE intensity recorded over a hemispherical region generates reciprocal space maps of the initial state. This data provides unambiguous fingerprints of individual molecular orbitals and is used to reconstruct real space images of the frontier molecular orbitals in good agreement with density functional (DFT) calculations. With k-space maps obtained using the toroidal analyser at BESSY II we demonstrate the viability of the proposed method even for the strongly bound monolayer of para-sexiphenyl adsorbed on Cu(110). Here the reconstructed HOMO and ex-LUMO orbital can both be clearly recognized and compare well to the DFT results. The generality of the approach is then illustrated with examples from molecular films ranging from the small rod-like pentacene to the plate-like tetraphenylporphyrin.