Berlin 2008 – scientific programme

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DS: Fachverband Dünne Schichten

DS 4: Organic Thin Films

DS 4.1: Talk

Monday, February 25, 2008, 16:15–16:30, H 2013

PTCDA on an alkali-halogenide layer: adsorption or formation of a complex? — •Hatice Karacuban, Sascha Koch, Thorsten Wagner, and Rolf Möller — Universität Duisburg-Essen, Fachbereich Physik, Lotharstr. 1-21, 47057 Duisburg

The initial growth of 3,4,9,10 perylene tetracarboxylic dianhydride (PTCDA) on a thin layer of NaCl was studied by means of scanning tunnelling microscopy (STM) in ultra high vacuum. The alkali-halogenide layer with a average coverage of 1.5 monolayer was prepared by thermal evaporation while the Cu(111) substrate held was at 345K. The local height of NaCl varies between 0, 2 and 3 layers. This thin insulating layer on Cu(111) still allows to establish a tunnelling current without dipping the tip into the surface. PTCDA was adsorbed on this surface. At a mean coverage of 0.04 monolayer, it was possible to image individual molecules attached to <011> steps of the NaCl which are presumably sodium terminated. The alignment of the molecules at these steps can be explained by the partial charges of the molecules interacting with the steps. On terrasses which are not covered by NaCl and at a coverage of 0.4 monolayers, three phases are dominant where the molecules align parallel in rods. The rod phases contradict a simple Coulomb interaction between the molecules. However, this adsorption geometry can be explained by a complex formed between PTCDA molecules and sodium atoms.