Institute of Solid State Physics


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Adsorption behavior of nonplanar GaCl-phthalocyanine on Cu(111): Geometric and electronic properties
E. Wruss
Institute of Solid State Physics, Graz University of Technology
15:00 - 17:00 Monday 28 September 2015 Foyer Alte Technik

The geometric and electronic properties of nonplanar chlorogallium-phthalocyanine GaClPc upon adsorption on Cu(111) are investigated, building on a study by Gerlach et al. [1]. There, X-ray standing wave (XSW) and ultraviolet photon spectroscopy (UPS) experiments in combination with quantum-mechanical DFT simulations were used to study the properties of that interface. These investigations suggested an orientation with the molecule standing on the Cl atom in a spinning-top manner (Cl-down) rather than a flipped orientation with the Cl atom pointing away from the surface (Cl-up). The development of new computational tools over the past few years which integrate long-range van der Waals interactions into approximate DFT prompted us to revisit this particularly interesting system, for the first time allowing a full and unconstrained optimization of the geometric structure of the interface. The method of choice was vdWsurf by Ruiz et al. [2], which has been shown to give geometries in excellent agreement with experimental results. Our simulations point towards a previously unconsidered possibility for the interfacial structure in addition to Cl-up and Cl-down, namely a dissociation of the molecule associated with the loss of the Cl atom. Interestingly, for this structure we find a calculated adsorption geometry that is clearly in better agreement with the experimental XSW results than the now fully optimized Cl-up and Cl-down conformations. Even more surprisingly, the quantitative agreement between measured and calculated work-function shifts that has been obtained for the Cl-down case [1] prevails for this dissociated structure, in spite of the massively different geometry. This observation can be explained by Fermi-level pinning. Our findings indicate that the adsorption process and interfacial structure of chlorinated phthalocyanines and related molecules could very well be considerably more complex than previously assumed.
[1] A. Gerlach et al., Phys. Rev. Lett. 106, 156102 (2011).
[2] V. G. Ruiz et al., Phys. Rev. Lett. 108, 146103 (2012).