Dresden 2014 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 69: Focussed Session: Towards a Quantitative Understanding of Complex Adsorption Structures: Surface Science goes Organic II

O 69.2: Vortrag

Donnerstag, 3. April 2014, 11:00–11:15, HSZ 01

Charge Localization at Inorganic/Organic Interfaces — •Oliver T. Hofmann, Patrick Rinke, and Matthias Scheffler — Fritz Haber Institute of the Max Planck Society, Berlin, Germany

Understanding the mechanism behind level alignment at heterointerfaces is of fundamental importance for a variety of fields, including organicelectronics. Using density functional theory, we investigate the atomistic details of the level alignment of organic acceptors adsorbed on different surfaces. For adsorbates in direct contact with an Ag(111) surface, we observe the formation of hybrid states. This induces density of states at the Fermi energy and all molecules in the layer become partially and uniformly charged. Preventing the hybridization by inserting an NaCl layer between the adsorbate and the metal leads to a drastic change in the charge transfer behaviour. While semi-local density functionals still predict a fractional electron transfer, more sophisticated hybrid functionals break the translational symmetry and result in the integer charging of only a fraction of the molecules. The associated molecular states are found several tenth of an eV below the Fermi energy. This charge localization is accompanied by a distortion of the molecular geometry and can be interpreted as polaron. It affects several observables including core-level shifts or the electrostatic potential in the vicinity of the surface. Furthermore, a qualitatively different dependence of the adsorption-induced work-function change on the coverage is found.