Characterization of RuO2 and TiO2 sols of different aging times, obtained by forced hydrolysis of appropriate chloride salts, was performed by transmission electron microscopy (TEM). The aging time of TiO2 sols was observed to affect the size of particles as well as the crystallinity of the solid phase of the sols. The surface morphology of RuO2-TiO2 coatings on titanium, obtained by the sol-gel procedure using TiO2 sols of different aging times and RuO2 sol of fixed aging time, was investigated by scanning tunneling microscopy (STM) at three different scan sizes. The STM data indicated uniform microdistribution of the coating material (small microroughness) and an increase in nanoroughness with the aging time of the TiO2 sol. The observed increase in real coating surface area with increasing TiO2 particle size confirms the earlier cyclic voltammetry results. (C) 2003 Elsevier Science (USA). All rights reserved.