Anomalous temperature dependence of the conductivity of nanoporous ITO films

Conductivity of thin (∼200 nm) Indium Tin Oxide (TTO) films with pore size ∼2-3 nm demonstrates anomalous temperature behavior. After every heating-cooling cycle conductivity of the films reduced nearly irreversible. After exposing to the air conductivity increased to no more than 10 percent. We explain the effect by combination of water and oxygen adsorption and desorption from the surface and diffusion in the pores. Under heating electron-donor H2O molecules desorb and concentration of charge careers decreases respectively. Histeresis of temperature of conductivity can be related with electron-acceptor oxygen occupying adsorption sites of desorbed water molecules. These effects were never observed previously and result from the porous structure of the films.