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

TL;DR

This study systematically explores how transition-metal phthalocyanines interact electronically and magnetically with Ag(100), revealing charge transfer, magnetic moment variations, and complex phenomena like Kondo effects and vibrational excitations.

Contribution

It provides new insights into the charge transfer, magnetic properties, and hybridization effects of TMPc molecules on Ag(100), combining experimental and theoretical approaches.

Findings

All TMPc molecules receive approximately one electron from the substrate.

Different TMPc molecules exhibit varying magnetic and electronic behaviors, including Kondo regimes and exchange coupling.

Observation of Kondo resonances and vibrational excitations in NiPc and CuPc.

Abstract

We present a systematic investigation of molecule-metal interactions for transition-metal phthalocyanines (TMPc, with TM = Fe, Co, Ni, Cu) adsorbed on Ag(100). Scanning tunneling spectroscopy and density functional theory provide insight into the charge transfer and hybridization mechanisms of TMPc as a function of increasing occupancy of the 3d metal states. We show that all four TMPc receive approximately one electron from the substrate. Charge transfer occurs from the substrate to the molecules, inducing a charge reorganization in FePc and CoPc, while adding one electron to ligand \pi-orbitals in NiPc and CuPc. This has opposite consequences on the molecular magnetic moment: in FePc and 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 Pc ligand, leaving the TM spin unperturbed. In CuPc, the presence of both TM and ligand spins leads to a triplet ground state arising from intramolecular exchange coupling between d and \pi electrons. In FePc and CoPc the magnetic moment of C and N atoms is antiparallel to that of the TM. The different character and symmetry of the frontier orbitals in the TMPc series leads to varying degrees of hybridization and correlation effects, ranging from the mixed-valence (FePc, CoPc) to the Kondo regime (NiPc, CuPc). Coherent coupling between Kondo and inelastic excitations induces finite-bias Kondo resonances involving vibrational transitions in both NiPc and CuPc and triplet-singlet transitions in CuPc.