Molecular orientation and electronic states of vanadyl phthalocyanine on Si(111) and Ag(111) surfaces

We have investigated the molecular orientation and electronic structures of nonplanar vanadyl phthalocyanine (VOPc) on the Si(111)-(7 × 7) and Ag(111) surfaces by X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. The VOPc molecule adsorbs on Ag(111) in a parallel orientation to the surface with an oxygen-up configuration. A strong interaction between the N and C atoms of VOPc and surface Ag atoms is observed at the interface, although no marked change in the electronic state is observed for the V atom, similarly to the case for VOPc in a multilayer. On the other hand, the chemical interaction of the O atom of VOPc with the surface Si atoms favors the oxygen-down configuration. This chemical interaction causes the cleavage of the Vî-O π bond and facilitates electron charge transfer to the V-N-C molecular orbitals. Such intermediation of the oxygen atom between the V atom and Si surface suppresses the direct interaction between them, and the spin magnetic moment of V remains the same as that of bulk VOPc molecules.