Characterization of indium-tin-oxide films treated by different procedures: effect of treatment time in aqua regia solution

The properties of a commercial indium-tin-oxide (ITO) layer deposited on glass substrates were evaluated as a function of the treatment time in diluted aqua regia solution. The samples were characterized by atomic force microscopy (AFM), bulk conductivity, ellipsometry, energy-dispersive X-ray analysis (EDX), contact angle/surface energy, and work function measurements. The results show that shorter times of treatment do not affect significantly the ITO properties but decrease the ITO thickness. For longer times (more than 30 min), although the work function and In/Sn ratio are not affected by the treatment, conductivity, roughness, UV–VIS absorption spectra, and refraction index values are greatly affected. Contact angle and surface energy data indicated that the dispersive component of the surface energy was not affected by the treatments. However, a strong decrease in the polar contribution occurred, indicating that ITO surface becomes more hydrophobic as the chemical treatment proceeds. These treated surfaces can interact more strongly with nonpolar materials, such as poly-(p-phenylene-vinylene) derivatives, resulting in a strong polymer ITO adhesion that can improve the efficiency of polymer light-emitting diodes (PLEDs).