Effects of Oxygen Plasma Treatments on the Work Function of Indium Tin Oxide Studied by in-situ Photoelectron Spectroscopy

Using UV and X-ray photoelectron spectroscopy (UPS and XPS), we have studied the work function (WF) evolution and chemical changes of an indium-tin-oxide (ITO) surface after a series of in-situ oxygen plasma treatments (OPTs). We took special care not to damage the sample's surface with OPT by employing the weakest possible plasma conditions. Even after such gentle OPT the WF of ITO dramatically increased up to 6.6 eV after about 300 s of OPT. The carbon contamination at the surface was completely removed after only 40 s of the gentle OPT. However, in contrast to similar studies, the compositions and the chemical states of In, Sn, and O at the ITO surface showed only minimal changes as confirmed by XPS core-level peak analyses.