Regensburg 2010 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 74: Nanostructures at surfaces: Other
O 74.10: Vortrag
Donnerstag, 25. März 2010, 17:15–17:30, H34
Excitonic luminescence of pentacene nanocrystals induced by STM — •Klaus Kuhnke1, Alexander Kabakchiev1, Theresa Lutz1, and Klaus Kern1,2 — 1Max-Planck Institut für Festkörperforschung, D-70569 Stuttgart — 2Institut de physique de la matiere condensee, EPFL, CH-1015 Lausanne
The local injection of charge carriers by scanning tunneling microscopy (STM) can be employed to excite luminescence from nanostructures. We study the luminescene of pentacene nanocrystals grown on a thin insulating KCl layer on different metals. The observed electroluminescence spectrum at liquid He temperature exhibits up to 3 features and is dominated by the emission of the self-trapped singlet exciton at 1.60 eV. It compares well to low temperature spectra reported for photoluminescence on macroscopic single crystals. We find the onset bias of light emission at 1.8 eV - close to the energy of the free exciton and still below the transport gap in bulk pentacene. The charge injection conditions for luminescence involve a high electric field between STM tip and metallic substrate. The field results in a Stark shift of the dominating emission line of about 20meV. This strong shift may indicate a charge-transfer (CT) contribution to the Frenkel exciton.