Mapping the Reversible Charge State Control of an Iron Tetraphenyl Porphyrin Molecule Adsorbed on a CaF 2 /Si(100) Semi-Insulating Surface at Low Temperature (9 K)
Résumé
This article presents a study concerning the charge state control of single iron-tetraphenyl porphyrins (FeTPP) molecules when adsorbed on a semi-insulating monolayer of CaF2/Si(100) surface. The charge state of the FeTPP molecule is regulated by employing tunneling electrons from a low-temperature scanning tunneling microscope (STM) operating at 9 K. We show that once the charge is loaded into the FeTPP molecule, the molecule can be laterally manipulated across the surface without losing its charge state. The charge state change is reversible and the FeTPP molecule can be restored, at will, to its initial neutral state. A precise analysis of the STM topographies and dI/dV curves acquired on the FeTPP molecule before and after the electronic charge loading allows mapping the spatial charge state variations in the molecule as well as a conductance hysteresis effect, indicating the formation of an anion. Numerical simulation based on the density functional theory exploiting the virtual crystal approximation (VCA) method allows reproducing the trends of our experimental results and shows that the change in charge state affects specific areas of the molecule. Our theoretical investigations suggest that the molecular charge state variations can be monitored via STM topographies treatment and its local density of state distribution. This information can be related to the spatial distribution of the magnetic moment within the FeTPP molecule while the delocalization of the charge appears to depend on the total spin state of the central iron atom.
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