Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 5: Adsorption on semiconductors, oxides and insulators I

O 5.1: Talk

Monday, March 26, 2012, 10:30–10:45, MA 042

Tailoring Hybrid States at Inorganic/Organic Interfaces: Pyridine/ZnO(10-10) — •Oliver T. Hofmann, Yong Xu, Patrick Rinke und Matthias Scheffler — FHI, Berlin

Hybrid inorganic/organic systems (HIOS) have opened up new opportunities for the development of optoelectronics due to their potential of achieving synergy beyond simply combining the best features of two distinct material classes. Even new physics and thus added value could be achieved if new quantum mechanical states occur at the interface, provided their energetic position is readily controllable. Theory and experiment indicate that such states can be found for a pyridine monolayer adsorbed on the transparent conductive oxide ZnO. We employ density functional theory, augmented with the electron-density dependent vdW-TS scheme, to investigate the nature of these states and the factors governing their energetic position. We find that conventional semi-local functionals give the wrong ordering of the pyridine orbitals and underestimate the bond strength between adsorbate and substrate, favoring an incorrect morphology. Both issues are ameliorated by incorporating exact exchange. The hybrid states, found approximately 1eV above the valence band edge and within the conduction band, originate from the ZnO conduction band and the pyridine LUMO. The large adsorption-induced interface dipole responsible for the energetic alignment is attributed to strong charge rearrangement within the subsystems. Having identified the interaction mechanism, we propose tailoring the energetic position of the interface state by controlling the interface dipole, e.g. by pre-covering ZnO with small molecules.