Low-temperature scanning tunneling microscopy study of double-decker DyPc2 on Pb Surface

Low-temperature scanning tunneling microscopy (STM), scanning tunneling spectroscopy and dI/dV mapping techniques have been applied to study double-decker DyPc₂ molecules on Pb(111) films grown on silicon wafers. The DyPc₂ molecules firstly self-assemble into a monolayer where two neighbouring molecules form an azimuthal angle of 6°. Scattered DyPc₂ molecules in the second layer can be stabilized on top of the first self-assembled monolayer, adopting a co-axial alignment with the underlying molecules. With the reference to the new layer assembled by Pc molecules generated by the cracking of DyPc₂ molecules on the substrate at or above room temperature, the molecular configuration can be directly deduced from STM imaging. The two Pc ligands in the same double-decker molecule rotate 45° with respect to each other. The dI/dV mapping of the individual DyPc₂ molecules in the second layer shows that they can appear as either four-lobed or eight-lobed features in the STM images depending on the bias voltage employed.