Screening the 4f-electron spin of TbPc2 on metal substrates by ligand channeling
Bis(phthalocyaninato)lanthanide (LnPc2) double-decker-based devices have recently raised a great deal of interest for data encoding purposes. Although the 4f-electrons of lanthanide ions play a key role in the experimental methodology, their localized character, deeper in energy than 3d ones of transition metals, hampers a detailed investigation. Here, our approach consists in a follow-up of the entanglement process with other molecules and with the substrate electrons by means of a space-resolved detection of the Kondo resonance by scanning tunneling spectroscopy (STS), using different substrates (from weak to strong interaction). It is found that the TbPc2 molecules firstly interact with their environment by means of the π-radicals of the ligand. The radical spin of TbPc2 can be identified by STS on a weakly-interacting substrate like Au(111). In the case of a Ag(111) substrate, we are able to analyze the effect of an electron transfer on the molecule (pairing-up of the radical spin) and subsequent quenching of the Kondo resonance. Finally, on a strongly interacting substrate like Cu(111), a significant rearrangement of electrons takes place and a Kondo screening of the 4f electrons of the Tb ion of TbPc2 is observed. By comparative STS measurements on YPc2, that has empty 4d and 4f shell, we prove that the Kondo resonance measured in the center of the TbPc2 molecule is indeed stemming from the 4f-electrons. At the same time, we provide evidence for the hybridization of the 4f states with the π electron.