Conformational degree and molecular orientation in rubrene film by in situ x-ray absorption spectroscopy

Abstract

The conformation degree and molecular orientation during the growth of rubrene films on Si(111) and Au(111) have been studied by in situ x-ray absorption spectroscopy. The backbones of rubrene molecules on Au(111) are twisted at the first few layers; in contrast, no appreciable twisting is observed on Si(111) even at a thickness of approximately 1.5 nm. The planarization of the backbone in the first few layers is due to strong molecule-substrate interactions between rubrene and Si(111). The rubrene molecules on Au(111) have a backbone tilt angle of 41°and a phenyl side group tilt of 64°with respect to the substrate surface, suggesting the crystalline nature of the films. Ex situ atomic force microscopy measurements confirm that the rubrene film grown on Au(111) is crystalline and the growth direction is along its crystallographic c axis. © 2007 American Institute of Physics.