Electronic and structural properties of the CuPc/Al(100) organic-inorganic interface were investigated by means of a multitechnique experimental approach based on synchrotron radiation. The chemical selectivity of X-ray photoelectron spectroscopy (XPS) was used to investigate the electronic structure of copper-phthalocyanine (CuPc) as a function of the molecular thickness ranging from the submonolayer to 40 angstrom. Photoemission from core levels shows a dramatic alteration of the electronic structure of molecules localized at the interface. At the lowest CuPc coverages, the complete reduction of the oxidation state of copper was observed, while C 1s and N 1s shake-up satellites were no longer visible. Both findings are explained with a sizable charge transfer from the substrate to the molecule involving the b(1g) (Cu 3d-derived) and the LUMO hybridized with the substrate conduction band. The linear polarization of the synchrotron light was employed in X-ray absorption near-edge spectroscopy (XANES) to determine the orientation of CuPc molecules. Molecular planes oriented almost perpendicular with respect to the metal surface were observed from the second layer on.
Ruocco, A., Evangelista, F., Gotter, R., Attili, A., Stefani, G. (2008). Evidence of charge transfer at the Cu-phthalocyanine/Al(100) lnterface. JOURNAL OF PHYSICAL CHEMISTRY. C, 112(6), 2016-2025 [10.1021/jp076299q].