Reductive ion insertion into thin-film indium tin oxide (ITO) in aqueous acidic solutions: the effect of leaching of indium from the ITO

The etching of indium-tin oxide (ITO) in acidic solution has been investigated electrochemically via conductivity change, cyclic voltammetry and in situ UV-visible spectroscopy. It is seen that the ITO has a new color and lower conductivity when reduced. Proton insertion is faster than proton extraction, with (D) over bar = 7.0 x 10(-11) cm(2) s(-1) and 2.4 x 10(-11) cm(2) s(-1) respectively. Spectroscopic ana Kinetic results in terms of a possible mixed-valent solid-state material comprising In(I)-In(III) oxides, although it is concluded that such a system does not, in fact, exist. It is shown that the chemical reactivity of reduced ITO is more-or-less the same as the oxidized material, but the observed changes result from a decreased mechanical strength causing HxITO to disintegrate faster than ITO. Implications are discussed for ITO-based devices that contain traces of aqueous acid.