Regensburg 2007 – scientific programme
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DS: Fachverband Dünne Schichten
DS 5: Organic Interfaces (SYOE 1)
DS 5.4: Talk
Monday, March 26, 2007, 15:15–15:30, H32
Charge Transfer Across Hexyl Layers Driven by Thermodynamics — •Steffen Duhm1, Hendrik Glowatzki1, Jürgen P. Rabe1, Robert L. Johnson2, and Norbert Koch1 — 1Institut für Physik, Humboldt-Universität zu Berlin, Newtonstr. 15, D-12489 Berlin, Germany — 2Institut für Experimentalphysik, Universität Hamburg, D-22761 Hamburg, Germany
The energy level alignment of α,ω-dihexylsexithienyl (DH6T) on tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) pre-covered Ag(111) and polycrystalline Au substrates was investigated with ultraviolet photoelectron spectroscopy (UPS). On both substrates DH6T exhibits a transition from flat lying molecules in the monolayer to inclined molecules in multilayers, accompanied by a shift of molecular levels. A transition from vacuum-level alignment to molecular level pinning - reminiscent of Fermi-level pinning - at the homo-interface between DH6T monolayer and multilayers was observed, which depended on the amount of pre-deposited F4-TCNQ. The measured shift in the vacuum level between monolayer and multilayer DH6T is direct evidence for interface dipoles and for thermodynamically driven charge transfer between molecular layers. The observed pinning behavior suggests that hexyl chains are not appropriate insulating layers for the use in molecular electronics, and longer chains may be needed.