Crystallization-dependent structural and optical properties of Mn_1.56Co_0.96Ni_0.48O₄ thin films grown by chemical solution deposition on Si (100)

Mn₁.₅₆Co_0.96Ni_0.48O₄ (MCN) thin films are deposited onto Si (100) substrate under different post-annealing temperatures of 450 °C and 600 °C. As identified by the X-ray diffraction (XRD) and SEM, pronounced difference in crystallinity is observed between the film annealed under 600 °C and 450 °C. Spectroscopic ellipsometry spectra, infrared transmission and reflection spectra are measured to compare and analyze the optical properties of the crystalline and non-crystalline MCN thin films. Ellipsometry measurement demonstrates the n, k spectra in the visible-to-near infrared range (300–1000 nm), indicating three absorption peaks locating at 1.6 eV, 2.6 eV, and above 3.5 eV for the crystallized sample, which corresponds to the charge-transfer (CT) transition involving O²⁻ (2p) and Mn⁴⁺ (3d) ions, O²⁻ (2p) to Co²⁺ (3d) ions, and O²⁻ (2p) and Mn³⁺ (3d) ions, respectively. Transmittance and reflectance spectra in the near infrared (1.3 µm)-to-far infrared (25 µm) range are also investigated. A two-oscillator model is performed to directly analyze the combined transmission and reflection spectra in the far infrared (400 cm⁻¹–800 cm⁻¹) to acquire the optical constants, where the difference of n, k values of the crystallized and non-crystalline MCN films in reststrahlen band is investigated for the first time.