Berlin 2015 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 55: Inorganic/Organic Interfaces: Electronic Properties II
O 55.11: Vortrag
Mittwoch, 18. März 2015, 17:45–18:00, HE 101
The Role of Pauli-Pushback fort he Electronic Properties of Self-Assembled Monolayers at Reduced Coverage — •Elisabeth Verwüster1, David A. Egger1,2, Oliver T. Hofmann1, and Egbert Zojer1 — 1Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16, 8010 Graz, Austria — 2Department of Materials and Interfaces, Weizmann Institute of Science, Rehovoth 76100, Israel
Using density-functional theory, advanced geometry optimization tools and accounting for van der Waals interactions we explain the coverage-dependent electronic structure of self-assembled monolayers (SAMs). As model systems for our calculations we choose acceptor- (-CN, -CF3) and donor- (-CH3, -NH2) substituted biphenylthiols on a Au(111) surface. Our focus lies on changes in the SAM-induced work-function modification, ΔΦ. Upon reducing the coverage the tilt angle of the molecules strongly increases. The latter significantly affects the molecular dipole perpendicular to the surface. The resulting changes in ΔΦ are, however, much more pronounced than one could expect on purely geometric grounds. For example, ΔΦ vanishes already at a coverage of 50% for the acceptor-substituted SAMs. This can only partly be explained by the tilt-angle dependence of the charge-rearrangements arising from the S-Au bond formation. Instead, we show that especially at low coverage the interaction-induced charge-rearrangements at the interface are dominated by Pauli-pushback, an effect well known for flat-lying adsorbates.