Determining adsorption geometry of individual tin-phthalocyanine molecules on Ag(111) - a STM study at submonolayer coverage

Adsorption of the non-planar molecule tin-phthalocyanine (SnPc) on a Ag(111) single crystalline surface was studied by means of VT-STM under UHV conditions. For coverage less than one monolayer and deposition on a substrate held at room temperature, a disordered and an ordered phase were found. The disordered phase showed short range ordering in terms of molecular chains and agglomerates. For the ordered phase a rectangular unit cell with a two-molecular base was found. Submolecularly resolved images allow to distinguish between two different adsorption states of the shuttlecock shaped molecule. In these states the central Sn-atom was pointing either towards or off the surface. In case of the densely packed phase an azimuthal rotation of the "up" and "down" adsorbed molecules enables a high packing density. (C) 2002 Elsevier Science B.V. All rights reserved.