Organic-Metal Hybrid Interfaces at the Mesoscopic Scale

The molecule-substrate interaction plays a key role in controlling charge injection in organicbased devices. Charge transfer at the molecule-metal interface strongly affects the overall physical and magnetic properties of the system, and ultimately the device performance. This thesis reports theoretical and experimental evidence of an unexpectedly high charge transfer rate to nickel tetraphenyl porphyrin (NiTPP) molecules adsorbed on Cu(100). The exceptional charge transfer leads to the filling of the unoccupied orbitals up to LUMO+3. As a consequence of this strong interaction with the substrate, the resulting adsorption geometry is highly distorted. For this reason, scanning tunneling spectroscopy cannot reliably probe the states related to the macrocycle. Molecular orbital tomography, instead, provides access to the NiTPP macrocycle electronic states and determine the reordering and filling of the LUMOs upon adsorption. The overall energy level alignment of the molecular states, upon adsorption on the metal surface, is shown to be only weakly dependent on the metal ion within the porphyrin, as well as on the symmetry of the crystalline substrate. On the other hand, the molecule-substrate interaction is weaker when CoTPP and NiTPP are deposited on the Ag(110) surface in comparison to Cu substrate, resulting in the filling of only the degenerate LUMO and LUMO+1. The control over the molecule-substrate interaction can also be achieved by functionalization of the organic layer with a proper axial ligand. We show in this work that exposure of the NiTPP/Cu(100) to nitric oxide weakens this interaction: while the charge transfer rate between the Ni porphyrin and the copper surface is reduced, a new electronic state, related to the NO-NiTPP complex, appear in the valence band. Notably, for the first time, we propose here a cis-dinitrosyl ligation mechanism between the NO molecules and the porphyrin layer, leading to the formation of (NO)2-NiTPP complex already at room temperature.