Influence of Rapid Thermal Annealing (RTA) on the Properties of Indium Oxide Nanostructures

In the present paper, In₂O₃ NPs were synthesized by a wet-chemical method, in the absence and presence of the surfactant, and deposited as thin films on silicon substrates. After deposition, the films were subjected to rapid thermal annealing (RTA) at 550 °C, 750 °C, and 900 °C, for 300 s, under an inert atmosphere. The correlation between the morphological, structural, and optical characteristics, the wetting capacity of In₂O₃ films synthesized under different synthesis conditions, and the influence of the RTA treatment are presented. The vibrations of In-O bonds for In₂O₃ samples were confirmed using FTIR spectroscopy. Structural analysis shows that In₂O₃ NPs have a cubic crystalline structure, but with the increase in temperature at 900 °C, diffraction peaks characteristic of the tetragonal phase of indium appear, correlated with a decrease in lattice parameters, as a result of the crystallinity. The morphology of the In₂O₃ samples was studied by SEM, revealing predominantly spherical and uniformly distributed particles with nanometric sizes. The absorption spectra of the In₂O₃ NPs showed peaks in the ultraviolet region, and the high energy bandgap value of the In₂O₃ films varied between 3.28 and 4.33 eV, depending on the samples and RTA treatment. The contact angle measurements of In₂O₃ films determined the wetting capacity of the surface, reflecting changes in surface morphology and structure induced by the RTA process. The results suggest that In₂O₃ thin films with spherical nanoparticles, good wettability, and percolation can be used for the development of sensors with increased selectivity and sensitivity.