Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 31: Organische Dünnschichten III

O 31.3: Vortrag

Montag, 7. März 2005, 11:15–11:30, TU EB420

New insight into the physics of organic materials by the absence of surface core level shifts — •M. B. Casu, Y. Zou, S. Kera, D. Batchelor, Th. Schmidt, and E. Umbach — EPII, Universität Würzburg, Am Hubland, 97074 Würzburg

We present highly resolved X-ray photoemission measurements on various different organic materials taken at different photon energies and at different take-off angles in order to investigate Surface Core Levels Shifts (SCLS). Thin films of perylenetetracarboxylic acid dianhydride, coronene, and metal free phthalocyanine were deposited on Ag(111). Photoemission spectra of the C1s core levels evidence the absence of SCLS in organic thin films. We explain these results in terms of very efficient screening. If the molecular interaction is sufficiently strong, the screening of the created charge by rapid delocalisation is quite efficient. This implies that the influence of polarization on the determination of orbitals and gaps and on the electronic and transport properties of organics must be reconsidered taking this delocalization process into account. The idea of the electronic polarisation playing a major role in their electronic properties has to be rediscuss: the usual values considered for the polarisation energy are too high and not supported by the present SCLS nvestigation. This has a strong implication on the characterisation of interfaces in electronic devices, where concepts like band offsets or charge injection should be reconsidered under these new aspect.