Variation in zinc phthalocyanine molecular orientation on SrTiO3(100) surface

Abstract

The molecular orientation of zinc phthalocyanine (ZnPc) thin films grown on SrTiO3(100) substrate was studied using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results revealed that the molecular orientation changed with the deposition of ZnPc. At the deposition of 0.4 monolayer equivalent (MLE), the π* resonance at grazing incidence was more prominent than that at normal incidence, indicating a lying configuration. By comparing the experimental results with theoretical calculations, the molecular orientation angle for the ZnPc ultrathin film was estimated to be 30°. During the deposition upto 4.3 MLE, the orientation angle increased with increasing ZnPc molecular density in the layer and reached 61°, which is close to that of the α-crystalline films. The dependence of the molecular orientation on the deposition amount indicates that the molecular orientation in the ZnPc ultrathin films is governed by the ZnPc molecular density on the SrTiO3(100) substrate surface.