Molecular Orientation and Electronic States of Vanadyl Phthalocyanine on Si(111) and Ag(111) Surfaces

Abstract

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 V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.

Surface chemistry of porphyrins and phthalocyanines

“…The elements Ti and V form M(IV) oxo phthalocyanine complexes, (O)TiPc (Ti 3d 0 ) and (O)VPc (V 3d 1 ). On Ag (1 1 1), the reported absence of significant V-Ag interactions was found to be in agreement with the preservation of the spin (S¼ 1/2) at the V center [212]; this decoupling of the metal center from the substrate was attributed to the surface trans effect [20] of the oxo ligand (cf. Section 7.2) [212].…”

“…On Ag (1 1 1), the reported absence of significant V-Ag interactions was found to be in agreement with the preservation of the spin (S¼ 1/2) at the V center [212]; this decoupling of the metal center from the substrate was attributed to the surface trans effect [20] of the oxo ligand (cf. Section 7.2) [212]. However, there were indications for substantial interactions between the Pc ligand and the substrate [212].…”

“…Pure (O)TiPc↑ island were found on Cu(1 1 1) above 0.8 ML [213]. On Ag(1 1 1), the orientation seemed to depend on the preparation conditions, as indicated by reports of oxygen-up orientation [212], mixed orientation [213], and tilted molecules [208]. Oxygen-up orientation was also reported for (O)VPc on Fe, Co and Ni films on Cu (0 0 1) [214], while an oxygen-down orientation was found on Si (1 1 1)-(7 Â 7) [212].…”

“…Section 7.2) [212]. However, there were indications for substantial interactions between the Pc ligand and the substrate [212]. For (O)VPc on HOPG and the (1 1 1) surfaces of Cu, Ag and Au, weak physisorptive interactions were reported for HOPG and Au, while strong chemisorptive interactions resulting in a commensurate adsorbate structure was found for Cu.…”

“…(O)TiPc has also been studied at the electrochemical interface on HOPG [210] and Au (1 1 1) [211]. (O)VPc adsorbed on HOPG (in vacuum) in an oxygen-up orientation [212,213], while mixed orientations were observed on Cu(1 1 1) and Au(1 1 1) [213]. Pure (O)TiPc↑ island were found on Cu(1 1 1) above 0.8 ML [213].…”