Optical properties of ambient temperature grown nanocrystalline Mg2TiO4 thin films

We report the study of optical properties of nanocrystalline Mg2TiO4 thin films deposited on Si(100) and quartz substrates at ambient temperature in the thickness range of 200–300 nm by RF sputtering a composite target under different oxygen SCCM. The composite target was prepared by mechanochemical synthesis method followed by sintering at 1350 °C for 3 h. Interestingly, the as-deposited film on Si substrate was observed to be crystalline, while the films deposited on quartz substrate showed amorphous nature due to the differences in the surface free energies and the thermal diffusivity of the substrates. Surface morphology and optical transmittance spectra studies revealed that the average particle size in the film increases with increasing the O2 SCCM and the films deposited at higher O2 SCCM exhibit lower transmittance, respectively. In addition, both the refractive index and packing density increase with increasing O2 SCCM, leading to a decrease in the optical band gap from 4.62 to 4.48 eV. Also, the photoluminescence spectra measured at room temperature are significantly affected by the O2 SCCM atmosphere during deposition.