Microstructure of ZrO2 films: Hydrophilic properties and optical band gaps

We investigate the influence of substrate temperature on the physical and optical properties of ZrO2 thin films produced via radio frequency (RF) magnetron sputtering. Our results reveal that substrate temperature significantly impacts crystallinity, surface topography, and phase composition of the films. XRD patterns indicate a transition from a dominant tetragonal phase at room temperature (RT) to a mixed tetragonal-monoclinic phase at 400 ºC. AFM analysis demonstrates an increase in surface roughness and grain size with rising film temperatures, resulting in 3D spatial patterns characterized by a pronounced broadening of multifractal spectra, suggesting enhanced surface complexity. Optical assessments show a temperature-dependent reduction in the energy gap (Eg) and changes in transmittance spectra, correlating with grain growth and phase transitions. Wettability analysis, via water contact angle measurements, reveals improved hydrophilicity at elevated temperatures due to increased surface roughness. Thus, our findings provide key insights into the structural, morphological, and functional attributes of ZrO2 thin films, offering valuable guidance for optimizing their properties for potential applications in nanotechnological approaches, e.g., optical coatings, sensors, and electronic devices. © 2025 The Authors