Coverage-Dependent Architectures of Iron Phthalocyanine on Ag(110): a Comprehensive STM/DFT Study

Iron(II) phthalocyanine (FePc) self-assembly on Ag(110) has been studied in ultrahigh-vacuum conditions at room temperature by means of scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. For submonolayer to monolayer coverage, FePc molecules lie parallel to the Ag(110) surface, arranged in rows running along the [001] direction. Two similar yet distinct ordered phases are formed, the c(10 x 4) and p(10 x 4) superstructures. The latter is characterized by two equivalent equilibrium configurations of the constituent FePc units, that interconvert by means of a concerted transformation wherein molecules belonging to adjacent rows collectively rotate in opposite directions around the molecular axis perpendicular to the surface. The FePc adsorption site for both Superstructures and the transition mechanism between the two configurations in the p(10 x 4) phase have been inferred from high resolution STM images and rationalized by means of DFT calculations. In the case of multilayer films a (1 +/- 4, 4 -/+ 3) phase is observed, whose stacking geometry has been revealed by STM analysis. The p(10 x 4)/c(10 x 4) -> (1 +/- 4, 4 -/+ 3) coverage-dependent transformation is analyzed by DFT calculations, and shown to be driven by the overlayer-substrate interaction. The inclusion of the dispersion contribution to this interaction is found to be essential to correctly reproduce the observed phenomenon.