X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), atomic force microscopy (AFM) and X-ray diffraction (XRD) were applied to investigate the electronic structure and molecular packing of C8-BTBT on HOPG with an ultrathin C-60 interlayer. It was found that C8-BTBT displays a Vollmer-Weber (V-W) growth mode on HOPG, with an ultrathin C-60 interlayer (0.7 nm). Compared to the uniform lying-down growth mode as directly grown on HOPG, the C8-BTBT molecules here adopt a lying-down orientation at low coverage with some small tilt angles because the pi-pi interaction...
