Electronic and magnetic properties of molecule-metal interfaces: transition metal phthalocyanines adsorbed on Ag(100)

摘要

We present a systematic investigation of molecule-metal interactions fortransition-metal phthalocyanines (TMPc, with TM = Fe, Co, Ni, Cu) adsorbed onAg(100). Scanning tunneling spectroscopy and density functional theory provideinsight into the charge transfer and hybridization mechanisms of TMPc as afunction of increasing occupancy of the 3d metal states. We show that all fourTMPc receive approximately one electron from the substrate. Charge transferoccurs from the substrate to the molecules, inducing a charge reorganization inFePc and CoPc, while adding one electron to ligand \pi-orbitals in NiPc andCuPc. This has opposite consequences on the molecular magnetic moment: in FePcand CoPc the interaction with the substrate tends to reduce the TM spin,whereas in NiPc and CuPc an additional spin is induced on the aromatic Pcligand, leaving the TM spin unperturbed. In CuPc, the presence of both TM andligand spins leads to a triplet ground state arising from intramolecularexchange coupling between d and \pi electrons. In FePc and CoPc the magneticmoment of C and N atoms is antiparallel to that of the TM. The differentcharacter and symmetry of the frontier orbitals in the TMPc series leads tovarying degrees of hybridization and correlation effects, ranging from themixed-valence (FePc, CoPc) to the Kondo regime (NiPc, CuPc). Coherent couplingbetween Kondo and inelastic excitations induces finite-bias Kondo resonancesinvolving vibrational transitions in both NiPc and CuPc and triplet-singlettransitions in CuPc.