Correlation between Gas Mixing Ratio and Functional Properties of Sputtered Zinc Oxide Nanostructures for UV-Induced Antibacterial Applications

Zinc oxide (ZnO) nanostructures were synthesized using reactive DC magnetron sputtering, and their structural, optical, morphological, and antibacterial properties were systematically investigated. X-ray diffraction analysis confirmed the formation of single-phase hexagonal wurtzite ZnO crystals with high crystallinity. The average crystallite size was estimated using the Scherrer equation. Field emission scanning electron microscopy analysis showed that the gas mixing ratio plays a key role in morphology control, with dominant particle sizes ranging from 40 to 50 nm across all tested ZnO samples. Energy-dispersive X-ray spectroscopy confirmed the high degree of purity of the synthesized ZnO nanostructures and showed Zn and O elements, without detectable impurities. Fourier transform infrared spectroscopy spectra exhibited a characteristic Zn–O stretching vibration band near 444 cm–1, along with additional bands of bending and stretching vibrations of hydroxyl groups due to adsorption of water molecules on the film surface. Optical measurements revealed strong absorption at 370 nm, high visible transparency, and a direct band gap in the range of (3.56–3.78 eV) depending on the deposition condition. ZnO nanostructures synthesized at a gas mixing ratio of (80:20)% were selected for the antibacterial evaluation against Pseudomonas aeruginosa, based on the combined structural, morphological, and optical characteristics, demonstrating notable intrinsic antimicrobial performance. This activity significantly improved to nearly 96% inhibition of bacterial growth when acting as a photocatalyst under UV-A irradiation. These findings highlight the potential of sputtered ZnO nanostructures as transparent, UV-active materials with strong antibacterial properties, and emphasize the critical role of gas mixing ratios in tailoring their characteristics for biomedical applications.