Sub-Phthalocyanine (SubPc), a dipole-bearing 3-fold symmetric phthalocyanine derivative with a delocalised π-electron system, shows at monolayer coverage very interesting complex, bi-stable molecular adsorption and 2D phase behaviour, as revealed by scanning tunnelling microscopy (STM) [1–3]. On Ag(111) a '2D-lattice-gas' phase, the 2D-condensed phases (e.g. honeycomb and hcp) with different densities have been associated to the delicate balance of intermolecular and molecule-surface interactions [1].
These STM studies have now been extended to higher coverages for the model system SubPc/Ag(111) and supported by X-Ray Photoelectron Spectroscopy (XPS) and Low Energy Electron Diffraction (LEED) studies. As a result we found new highly ordered adsorption phases (e.g. 'mixed orientation hexagonal' and an 'arabesque' pattern), with Cl-up and Cl-down oriented molecules, which are a direct consequence of the dipole interaction between the molecules [5]. To the best of our knowledge this is a new behaviour in the world of molecular self-assembly and has not been reported before.
The samples were prepared in UHV by in-situ sublimation of SubPc-molecules on an atomically clean Ag(111) single crystal at room temperature. Deposition and growth was monitored by a Quartz Crystal Microbalance (QCMB) during evaporation and by XPS after evaporation.
[1] S. Berner, et al., Phys. Rev. B 68, 115410 (2003).
[2] H. Yanagi, et al., Nano Letters 2, 951 (2002).
[3] S. Mannsfeld, et al., Surface Science 525, 215 (2003).
[4] M. de Wild, et al., ChemPhysChem 10, 881 (2002).
[5] R. Bertschinger, et al., (manuscript in preparation). |