Facet-engineered In ₂ O ₃ thin films: Oriented growth control for enhanced photocatalytic water treatment

Abstract

This study explores air pressure (0–0.3 bar) effects on ultrasonic spray-deposited In 2 O 3 films at 400°C. XRD confirms pressure-induced (400) orientation (with larger crystallites of ∼65 nm and ∼50.5 nm at 0.3 bar and 0.2 bar, respectively, compared to ∼38 nm at 0.1 bar) versus (222) dominance (25.3 nm at 0 bar). Film thickness was found to increase substantially with air pressure, measuring 110 nm (0 bar), 240 nm (0.1 bar), 410 nm (0.2 bar) and 488 nm (0.3 bar). AFM reveals the 0.3 bar films exhibit maximal roughness (29 nm), compared to 13 nm at 0 bar, 17 nm at 0.1 bar and 18 nm at 0.2 bar) and defined grain structures. These films demonstrate optimal electrical resistivity (1.2 × 10 −3 Ω cm, significantly lower than the values of 20 Ω cm at 0 bar, 1 Ω cm at 0.1 bar and 9.8 × 10 −1 Ω cm at 0.2 bar) and complete photocatalytic acid neutralization (pH 7.3 vs 5.8 for 0 bar). The enhanced performance originates from (100) facet-dominated charge transport and abundant Inᵢ³⁺/Vₒ•• defects. A pronounced decrease in atomic oxygen concentration from 90.01% at 0 bar to 51.7% at 0.3 bar, as verified by PL spectroscopy, supports this mechanism. Our results establish air pressure as a simple yet effective tool for simultaneous control of crystallographic orientation and multifunctional performance in transparent oxide films, with direct implications for photocatalytic and optoelectronic applications.