Angular-dependent photoemission studies of indium tin oxide surfaces

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