Submonolayer growth of CuPc on noble metal surfaces

The understanding of growth mechanisms and electronic properties is a key issue for improving the performance of small organic devices, in which the metal-organic interface and its properties play a crucial role. In this context we investigated the adsorption behavior and the electronic properties of copper-II-phthalocyanine (CuPc) within the first adsorbate layer on Au(111) and Cu(111). Together with recent results published for CuPc/Ag(111) [Kroger et al., New J. Phys. 12, 083038 (2010)] this leads to a comprehensive understanding of the adsorption of CuPc on noble metal surfaces: On Cu(111) the molecule-surface interaction is the strongest. The molecules chemisorb on the surface and form one-dimensional chains or two-dimensional islands, depending on coverage. This behavior indicates an attractive intermolecular interaction. In contrast, on Au(111) CuPc is only weakly physisorbed and behaves like a two-dimensional gas in a wide coverage regime. Only when densely packed do the molecules form ordered structures, which are scarcely influenced by the structure of the metallic surface. Molecule-molecule interaction is also very weak, but in contrast to CuPc on Ag(111) no clear indications for a repulsive interaction are found. Regarding the adsorption strength, this latter system represents an (possibly unique) intermediate case which enables the unusual intermolecular repulsion found recently. Our results highlight the special role of this model system, since the interaction of CuPc with the metal can be tuned in any order of the adsorption scenarios observed by selecting the right substrate material.