Nanocomposite indium tin oxide thin films: formation induced by a large oxygen deficiency and properties

We report on the formation and properties of nanocomposite indium tin oxide thin films which are grown by pulsed-electron beam deposition under a low oxygen pressure leading to the formation of highly non-stoichiometric indium tin oxide films. For growth at room temperature these films are amorphous and insulating, while at higher temperatures, the oxygen deficiency leads to a disproportionation reaction with the formation of metallic clusters (indium or indium tin clusters) embedded in a stoichiometric crystalline indium tin oxide. This matrix is well crystallized and even epitaxial for growth on c-cut sapphire single crystal substrates. The presence of the metallic clusters induces specific transport properties, i.e. a metallic conductivity at room temperature followed by a superconducting transition at low temperature (about 6 K). Moreover, the solid-liquid and liquid-solid phase transitions in the metallic clusters can be clearly seen from the resistivity curves as a function of temperature (in the room temperature to 450 K range), through specific changes in resistivity and the appearance of a hysteresis cycle.