Angular-dependent photoemission studies of indium tin oxide surfaces
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Indium tin oxide (ITO) surfaces were treated by solvent cleaning, by plasma of oxygen, argon, nitrogen and by argon ion (Ar+) sputtering. Angular-dependent X-ray photoelectron spectroscopy (ADXPS) and ultraviolet photoelectron spectroscopy (UPS) were used to determine the chemical composition, the chemical states and the work function after each treatment. It was found that oxygen plasma and nitrogen plasma chemically reacted with the ITO surfaces. Yet little etching of the surface can be observed after plasma treatments. Among all treatments, oxygen-plasma-treated ITO achieved the highest work function of 4.40 eV, whereas Ar+-sputtered ITO surface had the lowest work function of 3.90 eV. The stoichiometry of the ITO surface is shown to be the major controlling factor of the ITO work function.
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