Formation of metallic nanoclusters in oxygen deficient indium tin oxide films

Abstract

The composition, structure, microstructure, and properties of indium tin oxide films grown by pulsed laser deposition at room temperature and under vacuum were studied. The films are highly nonstoichiometric, with about 20% oxygen deficiency, and present a semiconductor behavior between 300 and 15 K, followed by a superconducting transition at about 7 K related to the presence of In or In-Sn nanoclusters embedded in a stoichiometric indium tin oxide matrix, i.e., nanocomposite films are formed by the phase separation of oxygen deficient metastable indium tin oxide. The solid-liquid and liquid-solid phase transitions of the metallic nanoclusters were evidenced by resistivity measurements in the 300 to 450 K range. The films grown at room temperature are partially crystallized. Actually, stoichiometric indium tin oxide crystallites are observed in the as grown films. After thermal treatment (<450 K), both stoichiometric indium tin oxide crystallites and the tetragonal phase of the metallic In are observed in the nanocomposite films. The size of nanoclusters (from 5 to 30 nm), which depends on the thermal treatments and crystallization, and the microstructure of the nanocomposite films were confirmed by HRTEM measurements.