Adsorption behavior of iron phthalocyanine on Au(111) surface at submonolayer coverage

Adsorption behavior of iron(II) phthalocyanine (FePc) on Au(111) surface at submonolayer coverage has been investigated using low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. At the initial adsorption stage, FePc molecules prefer to adsorb on terrace dispersedly as isolated adsorbates because of the stronger molecule-substrate interaction than the lateral intermolecular interaction. Two different configurations of FePc on Au(111) surface are resolved on the basis of STM image analysis and are further identified by DFT calculations. When increasing molecule coverage, the intermolecular interaction becomes more important. The FePc molecules assemble to dimers, trimers, and short chains and even peculiar porous hexamers with two configurations. At a saturated coverage, highly ordered FePc monolayer with only one configuration of FePc is observed. The results indicate that the adsorption behavior of FePc on Au(111) is governed by a coverage-dependent competition between molecule-substrate and intermolecular interactions.