Molecular Arrangements in the First Monolayer of Cu-Phthalocyanine on In2O3(111)
Abstract
Well-ordered organic molecular layers on oxide surfaces are key for organic electronics. Using a combination of scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM) we probe the structures of copper phthalocyanine (CuPc) on In2O3, a model for a prototypical transparent conductive oxide (TCO). These scanning-probe images allow the direct determination of the adsorption site and distortions of the molecules, which are corroborated by DFT calculations. Isolated CuPc molecules adsorb in a flat, slightly tilted geometry in three symmetry-equivalent configurations on the stoichiometric In2O3(111) surface. Increasing the coverage leads to densely packed 1D chains oriented along 〈1-10〉 directions, which dissolve into a highly ordered (2 × 2) superstructure upon increasing the CuPc density to ¾ per surface unit cell. At a coverage of one CuPc per surface unit cell, a densely packed (1 × 1) superstructure fully covers the surface. The molecules still assume the same site and orientation as before, but they partially overlap to accommodate the high packing density, leading to a bending of the molecules. These results are compared to the behavior of CoPc on In2O3(111). In summary, we demonstrate that a uniform first layer of metal-phthalocyanine molecules can be realized on the In2O3(111) surface when using the proper metal atom in the molecule.
- This article is part of the themed collection: Honorary collection for Professor Dr. Petra Rudolf