Au∕CuPc interface: a valence band photoemission investigation.

The formation of the metal-organic interface depositing gold, by thermal evaporation in ultrahigh vacuum conditions, onto a copper phthalocyanine film has been studied by means of ultraviolet photoemission spectroscopy. The evolution of the valence band spectra and in particular of the highest occupied molecular orbitals (HOMO) and of the Au upper states has been followed as a function of gold film thickness. The HOMO peak position is strongly influenced by the Au deposition, suggesting an n-doping process of the organic film. The gold 6s state behavior indicates the formation of small metal clusters whose size increases as a function of the gold deposited. The doping of the organic film determines a strong reduction of the film ionization energy.