Influence of the oxygen pressure on the preferred orientation and optical properties of the pulsed-laser deposited Mn_1.56Co_0.96Ni_0.48O_4±δ thin films

Mn_1.56Co_0.96Ni_0.48O_4±δ (MCN) thin films with different oxygen pressures (in the range of 2 × 10⁻⁴ to 2 Pa) are prepared on Si(100)/SiO_x substrates by pulsed laser deposition technique. Effects of oxygen pressures on the microstructure and optical properties of the prepared thin films are investigated in detail. The grain sizes of films gradually decrease and the preferential orientation of the MCN films change from (400) to (113) as the oxygen pressure increases. The x-ray photoelectron spectroscopy results show that the composition of these films is proximity to that of the bulk material. In addition, the Mn³⁺/Mn⁴⁺ pairs increase with an increase in the oxygen pressures increase. From spectroscopic ellipsometer spectroscopy, it is found that both the refractive index n and extinction coefficient k of the (400)-oriented films have no obvious peaks, whereas in the (113)-oriented films, peaks are exist. This feature typically originates from a change in the crystal structure as oxygen pressures increase. Furthermore, the Raman active mode (around ca. 650 cm⁻¹) of (400) films almost disappears, whilst the active mode in (113) films remain. - Highlights: • The Mn_1.56Co_0.96Ni_0.48O_4-δ (MCN) spinel films are deposited by pulsed laser deposition process at different oxygen pressures. • The preferential orientation of the films changes from (400) plane to (113) as the oxygen pressure increases. • The E_g of the (113) film is twice as large as that of the (400) film. • The Raman active mode (around ca. 650 cm⁻¹) can be observed in the (113) films while not in the (400) film.