Akademik Veri Yönetim Sistemi
Journal of Alloys and Compounds, cilt.1053, 2026 (SCI-Expanded, Scopus)
This work systematically investigates the influence of sputtering power (125–225 W) on the structural, electrical, and optical properties of Co₃O₄ thin films. Room-temperature conductivity exhibits a nonlinear dependence on power, reaching its maximum at 150 W (6.83 × 10⁻⁴ Ω−1·cm⁻¹) and decreasing at both lower and higher powers (e.g., 225 W: 1.93 × 10⁻⁴ Ω−1·cm⁻¹). Optimal performance is achieved at 150–200 W due to a favorable balance between crystallinity and defect density. Measurements that depend on temperature indicate two modes of conduction: non-adiabatic small polaron hopping (SPH) at elevated temperatures (with activation energies ranging from 0.059 to 0.077 eV) and three-dimensional Mott variable-range hopping (VRH) occurring below 260 K, with a transition observed between 180 and 270 K. These findings underscore the significance of intrinsic polaronic transport in applications such as catalysis, energy storage, and sensing. Optical measurements reveal two direct transitions: a weakly power-dependent ligand-field (d–d) transition at Eg1∼1.24–1.35 eV and a ligand-to-metal charge-transfer at Eg2∼1.76–2.20 eV. For 125–200 W, Eg2 linearly increases with oxygen content, indicating a progressively sharper absorption onset. The 225 W film, while exhibiting the lowest oxygen content and reduced conductivity, shows the largest Eg2. It also shows the most pronounced spinel phase, consistent with high-power growth that densifies the film and strengthens preferred orientation. These results suggest that the apparent optical gap is governed primarily by absorption-edge sharpness and microstructure, rather than Co/O ratio alone.