Dresden 2009 – scientific programme

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DS: Fachverband Dünne Schichten

DS 21: Organic Thin Films I

DS 21.5: Talk

Wednesday, March 25, 2009, 10:30–10:45, GER 38

Contacts for spin injection into organic semiconductors: Energy level alignment and interactions — •Mandy Grobosch, Katrin Dörr, Ramesh B. Gangineni, and Knupfer Martin — IFW Dresden, D-01069 Dresden, Germany

The energy level alignment at interfaces between La_0.7Sr_0.3MnO₃ (LSMO) and two archetype organic semiconductors, copper-phthalocyanine (CuPc) and sexithiophene (6T) has been studied by combined X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). La_0.7Sr_0.3MnO₃ is a ferromagnetic metal and can be used to inject spin-polarized current into organic semiconductors. Thin films of this material have been grown using pulsed laser deposition. Prior to the deposition of the organic semiconductors the LSMO has been cleaned by either an ex-situ treatment only, or by annealing in an oxygen atmosphere. The former results in surfaces that are covered by a thin contamination layer while the latter yields atomically clean surfaces. All interfaces are characterized by a rather large interface dipole and substantial charge injection barriers. Moreover, at the interfaces between clean La_0.7Sr_0.3MnO₃ and the two organic semiconductors there is a chemical reaction resulting in a partial oxidation of the organic molecules. At such interfaces the energy level alignment considerably depends on the LSMO cleaning procedure prior the deposition, i.e. whether there is still a contamination layer present.