Investigation of polarization effects in organic thin films by surface core-level shifts

Abstract

We study charge delocalization and polarization effects in organic thin films by comparing surface- and bulk-sensitive, high-resolution $\mathrm{C}\phantom{\rule{0.2em}{0ex}}1\mathrm{s}$ photoemission data using tunable synchrotron radiation. In three cases, perylene-tetracarboxylicacid-dianhydride, coronene, and metal-free phthalocyanine, no surface core level shifts are observed (upper limit $100\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$). This unexpected finding shows that polarization effects, and hence polarization differences between surface and bulk, are rather small, and implies that the effective charge is not localized on the core-ionized molecule but delocalized over several neighboring molecules.