Adsorption, metalation and magnetic properties of tetra phenyl porphyrins on metal surfaces

Traditional semiconductor technology will reach a size limit within the next few years. A possible solution could be the use of organic molecules in technological applications as single functional units in metal-organic based devices; the success of this approach strongly depends on the understanding of the behaviour of these molecules on metallic surfaces. The interaction with metallic substrates and the interaction between the molecules themselves determine the electronic and magnetic properties of the system, and it is thus of fundamental interest to study these metal-organic interfaces both in the case of single molecules and layer structures. In this thesis, an extensive study of the electronic and magnetic properties of tetra-phenyl-porphyrin (2H-TPP) molecules adsorbed on metal surfaces is reported. By means of scanning tunnelling microscopy (STM) we studied the adsorption geometry of these molecules on the Au(111), Ag(111) and Cu(100) surfaces. By using X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, a temperature-induced conformational adaptation reaction of the 2H-TPP molecules adsorbed on the Au(111) and Ag(111) surfaces, upon annealing at 550 K, is described. A possible dehydrogenation reaction, with the formation of new C-C bonds, could explain the rotation of the molecule phenyl rings parallel to the surface plane and the associated increasing in the molecule-substrate interaction. In-situ metalation of porphyrins in ultra-high vacuum is obtained by two methods: in the first one, the metalation of 2H-TPP on Ag(111) is achieved by direct metal evaporation (Mn, Rh and Fe) on the molecular layer; in the second case we report the self-metalation of 2H-TPP through the coordination with a metal atom from the Fe(110) and Al(111) substrates. In addition, we investigated the effects of metalation and temperature-induced conformational adaptation on the molecule-substrate interaction, by means of XPS and NEXAFS, in the case of CoTPP on Ag(111). The magnetic properties resulting from the metal coordination are studied by X-ray magnetic circular dichroism (XMCD). Here, a description of the magnetic coupling of a MnTPPCl single layer with a Fe(110) ferromagnetic substrate is disclosed. Moreover, we focused on the study of the magnetic properties and exchange coupling of two layer of molecule and a ferromagnetic thin film. In the case of a MnTPP layer on FeTPP/Fe(110) the magnetic coupling extends to the second layer of molecules, for which the magnetization is opposite with respect to the substrate.