Corundum nanostructure ITO film fabrication: An approach for physical properties assessment

Corundum (hexagonal) structure indium tin oxide (h-ITO) nanocrystals have been synthesized by subjecting an aqueous solution of In and Sn chlorides (Sn/In 8 wt.%) to a hydrothermal process followed by annealing at 450 °C in forming gas for 1 h. The annealing temperature was selected based on thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA) of the dried precipitated powder, which showed a stable weight and phase at temperatures above 420 °C. X-ray diffraction (XRD) patterns showed the formation of orthorhombic InOOH precipitates that is transformed, after annealing, into h-ITO nanocrystals with 32 nm average crystal size. For nanostructure film deposition, dispersed sols of the prepared nanocrystals were spun coated on glass substrates. The films were densified by UV irradiation, whilst four-probe method was used to measure its sheet resistance. A sheet resistance as low as 10.6 kΩ □ have been reached. Scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) showed that the films have high surface roughness and nanopores. The transmittance spectra of the nanostructure films were measured in the UV–vis–NIR wavelength range. In addition to its low resistivity, nanostructure h-ITO films showed a wide range of transparency.