Berlin 2005 – wissenschaftliches Programm

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O: Oberflächenphysik

O 54: Adsorption an Oberfl
ächen VI

O 54.7: Vortrag

Mittwoch, 9. März 2005, 12:15–12:30, TU EB202

STM and STS studies of planar and non-planar Naphthalocyanines (Nc) on Graphite (0001) — •T. G. Gopakumar and M. Hietschold — Chemnitz University of Technology, Institute of Physics, Solid Surfaces Analysis Group, D-09107 Chemnitz, Germany.

Adsorption of base free naphthalocyanine (Nc), planar molecule and tin-naphthalocyanine (SnNc), non-planar molecule were studied using a STM on freshly cleaved highly oriented pyrolytic graphite (HOPG) surface at low temperature (50 K) in UHV conditions. Planar Nc molecules form large areas of defect free ordered superstructure [1] with larger molecular packing density (0.3 molecule/nm2) while the non-planar molecules show different phases of adsorption with comparatively less molecular packing density (0.18 molecule/nm2). Tip-sample distance dependent current voltage spectroscopy has been conducted and its normalized differential conductivities have been characterized. The general current voltage curves show an asymmetrical diode like nature. A distant dependent HOMO-LUMO gap shrinking have been observed in the case of Nc, in which it is shown that the HOMOs of the molecules are pinned and the LOMOs are moving towards the Fermi energy. But there is no subsequent HOMO-LUMO gap shrinking in the case of SnNc but an increased current of almost one order of magnitude has been observed in the current voltage characteristics.

[1]. M. Lackinger, T. Müller, T. G. Gopakumar, F. Müller, M. Hietschold, G. W. Flynn, J. Phys. Chem. B. 2004, 108, 2279-2284.