Growth of zinc phthalocyanine onto ZnS film investigated by synchrotron radiation-excited X-ray photoelectron and near-edge absorption spectroscopy

The molecular ordering and orientation of zinc phthalocyanine (ZnPc) on a ZnS film as well as the chemical properties of the interface were investigated by X-ray photoelectron and absorption spectroscopy with synchrotron radiation excitation. Core level photoelectron spectra of the substrate and the ZnPc film indicate a weak interaction at the interface. We observe a high molecular ordering, which is enhanced with increasing film thickness. A standing (or highly-tilted) molecular orientation in about 8 nm-thick ZnPc films is deduced from the polarization dependence of the N K X-ray absorption spectra. The same result was obtained from excitation energy dependence of the intensity ratio of the two carbon species in C 1s core level spectra. The annealing of the sample up to about 400 °C causes a desorption of ZnPc and a stronger interaction between remaining molecules and ZnS.