Regensburg 2000 – wissenschaftliches Programm
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O: Oberflächenphysik
O 11: Postersession (Eröffnung)
O 11.40: Poster
Montag, 27. März 2000, 19:00–22:00, Bereich C
Photoelectron Spectroscopy of Conjugated Organic Materials: Surface Charging and Its Removal — •D. Pop1, R. Weber1, N. Böwering1, B. Winter1, N. Koch2, I. V. Hertel1, and G. Leising2 — 1Max-Born-Institut, Max-Born-Str. 2A, D-12489 Berlin — 2Institut für Festkörperphysik, TU Graz, Petersgasse 16, A-8010 Graz, Austria
Ultraviolet photoelectron spectroscopy (UPS) on conjugated
organic semiconductors is a key experimental approach to obtain
insight into basic physical properties of such materials, as well
as interfaces of these with other organic and inorganic materials.
In such UPS studies the binding energy of electrons (EB) relativ
to the Fermi-energy EF is very sensitive to impurities,
radiation-induced sample degradation or surface charging.
Especially the latter two mechanisms are expected to become
important when very intense light sources are used, as in our
case the U125 undulator at BESSY II. We have prepared thin films
of para-sexiphenyl (6P) in situ and have studied the dependence
of the 6P spectral features (lineshape and EB) on the
concentration of the radiation-induced defect centers in the
organic material. One striking observation was an increasing
surface charging for increasing damage of the 6P film. By
shining a laser of appropriate energy (3.1 eV, corresponding to
the energy-gap of 6P) onto the sample surface, it was possible
to reduce the surface charging, as judged from the shift of EB
relative to EF.