Structural, Optical, and Mechanical Properties of Steam–Oxidized MgO–Al₂O₃ Co–Deposited Mixed Thin Films: Influence of Oxidation Temperature

Thin film coatings play a crucial role in various technological applications, including optoelectronics, protective layers, and display technologies. This study investigates the structural, optical, and mechanical properties of MgO-Al₂O₃ co-deposited mixed thin films prepared via steam oxidation of vacuum-evaporated Mg-Al mixed metal thin films. The films, with a controlled thickness of 300 nm, were oxidized at varying temperatures (573 K, 623 K, and 673 K) to analyze their phase composition, surface morphology, optical transmittance, band gap, refractive index, adhesion, and intrinsic stress. X-ray diffraction (XRD) confirmed the formation of a cubic MgO-dominated structure, while Al₂O₃ remained amorphous, indicating a stable mixed oxide formation. Scanning electron microscopy (SEM) revealed a transition from granular and cauliflower-like morphologies in pure Mg and Al films to a well-decorated granular structure in co-deposited films, further evolving into agglomerated grains upon oxidation. Higher oxidation temperatures enhanced optical transmittance (above 450 nm), band gap (2.9–3.4 eV), and refractive index (1.69–1.72), attributed to improved stoichiometry and reduced grain boundary scattering. Mechanical properties, including adhesion (33–39.9 × 10⁴ N/m²) and intrinsic tensile stress (55–80 × 10⁷ N/m²), increased with oxidation temperature due to enhanced crystallinity and interfacial bonding. However, higher temperatures also induced void formation, contributing to intrinsic stress. These findings highlight the tunability of MgO-Al₂O₃ thin films for advanced applications, particularly in plasma display panels (PDPs), where improved durability and optical performance are critical. The study demonstrates that oxidation temperature is a key parameter in optimizing the functional properties of co-deposited oxide thin films.