Interfacial electronic structure of copper phthalocyanine on a gold surface studied by synchrotron radiation photoemission

We have studied copper phthalocyanine (CuPc) molecules deposited on a clean gold surface via synchrotron radiation photoemission. The persistent appearance of Au4f surface core-level emission in a series of depositions suggests columnar growth of the adsorbed molecules covering only one-fifth of the surface. Molecular adsorption reduced the line intensity of emission from the Au surface slightly and also produced a shortened core-level shift, which demonstrates weakened s-d hybridization of the surface band. Moreover, manifestation of excess charge in the C1s core, along with an induced component in the Au4f core, indicates that charge polarization occurred at the organic/metal contact. The interface introduces an electronic state 1.09 eV below the Fermi level. Further analysis reveals that only the carbon atoms in the benzene rings are affected upon adsorption, suggesting that the molecular plane lies flat on the surface without changing the nominal bent configuration.