Comparison of optical constants of sputtered MoS2 and MoS2/Al2O3 composite thin films

Owing to excellent mechanical and wear properties, MoS2/Al2O3 composite thin films have been studied extensively in the recent past. In this work, thin films of MoS2 and MoS2/Al2O3 composites were deposited on silicon substrates using reactive DC magnetron co-sputtering. The chemical composition in terms of at% and wt% of the composite thin films was confirmed using energy dispersive X-ray spectroscopy. It was evident that the elements were exactly in the same stoichiometric contents as required by their respective empirical formulae. The structural morphology of the grains was visualized using a field emission scanning electron microscopy. The images showed that MoS2 thin film consisted of large sized grains with a number of spaces, but MoS2/Al2O3 composite showed a very smooth surface without any cracks or free spaces. Furthermore, spectroscopic ellipsometry study was conducted by making a fitting model and comparing the calculated values with it. Refractive index n, extinction coefficient k, thickness t and absorption coefficient alpha were calculated. From absorption and depolarization of light, it was deduced that MoS2/Al2O3 composite was a very good absorber of high energy rays and a very good reflector of low energy rays in IR region. Optical energy band gap of MoS2 came out to be 2.68 eV and while that of MoS2/Al2O3 composite remained 2.19 eV.