Surface and interface analysis of ITO/Rubrene using AFM and XPS

The surface morphology and the interface electronic states of Indium-tin-oxide (ITO)/Rubrene were investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The AFM results manifest that the Rubrene film deposited on ITO is very uniformity. The XPS results show that there are three main peaks in the C1s spectrum of the origin surface, which located at 282.50, 284.70, 289.30 eV, respectively. They are associated with C-Si, CO, C-C bonds. With the increasing of sputtering time, the peak corresponding to the aromatic C becomes intensely while the other peaks disappear rapidly. As the removing of the oxygen contamination on the surface, the O1s peak weakens firstly and then strengthens gradually. The O atoms mainly bond to C, and form OC, C-O-C and aldehyde group in the interface. The peaks of In3d and Sn3d strengthen slowly, and become stable near the interface of ITO/Rubrene. The peak of C1s, In3d and Sn3d moves toward lower binding energy, indicating an inter-diffusion system formed by the interaction of Rubrene film and ITO in the interface.