Substrate-induced symmetry reduction of CuPc on Cu(1Â 1Â 1): An LT-STM study

The adsorption of copper phthalocyanine (CuPc) on Cu(1 1 1) was studied by means of low-temperature scanning microscopy. At very low coverage, individual molecules are randomly distributed over the surface. Increasing the coverage, the molecules align in chains before forming ordered domains with a rectangular unit cell. The molecules are centered on top of a copper atom aligning two opposite lobes with a principal axis of the substrate. The topographic images of the molecules show a reduction of the fourfold to a twofold symmetry. At negative sample bias, a switching between two states at a typical rate of 500 Hz is observed for isolated molecules, which are neither adsorbed at defects nor forming chains or domains.