Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 25: Phase Transitions

O 25.3: Talk

Tuesday, March 27, 2007, 11:45–12:00, H41

Repulsive interaction between organic molecules upon adsorption: the case of Sn-phthalocyanine/Ag(111) — •Christoph Stadler, Sören Hansen, Christian Kumpf, and Eberhard Umbach — University of Würzburg, Experimental Physics II, 97074 Würzburg, Germany

The properties of organic thin films largely depend on the balance between molecule-molecule and molecule-substrate interactions and often can be tuned by changing the preparation conditions like temperature or coverage. This is also the case for the family of phthalocyanines (Pc), which are frequently studied as adsorbates on various surfaces. Here we present results on SnPc/Ag(111), a non-planar representative of this family. We used high resolution (SPA-)LEED to investigate the phase diagram of the monolayer regime.

At room temperature the adsorbed SnPc molecules show no long-range order in SPA-LEED up to a coverage of about 0.9. Above this coverage, the film forms incommensurate superstructures, the unit cell parameters of which change continuously with increasing coverage. This behavior can be explained by a repulsive intermolecular interaction of the SnPc molecules on the Ag surface. Interestingly, upon cooling below 230 K the film forms a commensurate superstructure between a coverage of 0.6 and 0.9 monolayer.