Orbital tomography for highly symmetric adsorbate systems

¹ Peter Grünberg Institut (PGI-3), Forschungszentrum Jülich - 52425 Jülich, Germany, EU
² Jülich Aachen Research Alliance (JARA)- Fundamentals of Future Information Technology 52425 Jülich, Germany, EU
³ Institut für Physik, Karl-Franzens-Universität Graz - 8010 Graz, Austria, EU

Received: 27 August 2012
Accepted: 8 October 2012

Abstract

Orbital tomography is a new and very powerful tool to analyze the angular distribution of a photoemission spectroscopy experiment. It was successfully used for organic adsorbate systems to identify (and consequently deconvolute) the contributions of specific molecular orbitals to the photoemission data. The technique was so far limited to surfaces with low symmetry like fcc(110) oriented surfaces, owing to the small number of rotational domains that occur on such surfaces. In this letter we overcome this limitation and present an orbital tomography study of a 3,4,9,10-perylene-tetra-carboxylic-dianhydride (PTCDA) monolayer film adsorbed on Ag(111). Although this system exhibits twelve differently oriented molecules, the angular resolved photoemission data still allow a meaningful analysis of the different local density of states and reveal different electronic structures for symmetrically inequivalent molecules. We also discuss the precision of the orbital tomography technique in terms of counting statistics and linear regression fitting algorithm. Our results demonstrate that orbital tomography is not limited to low-symmetry surfaces, a finding which makes a broad field of complex adsorbate systems accessible to this powerful technique.