Effects of gas flow ratio and annealing on the structure and optical band gap of Mo2C thin films

Abstract

Molybdenum carbide (Mo2C) has attracted increasing attention in the fields of photocatalysis, electrocatalysis, and superconductivity due to its unique structure and electronic properties. In this work, Mo2C thin films were prepared by RF magnetron sputtering to investigate the effects of CH4 flow rate and post-annealing on the structure and properties of the thin films. Results show that the grains of the prepared films are uniform and gradually decrease with the increase in CH4 flow rate. Face-centered cubic Mo2C exists in the films and preferentially grows from (002) crystal planes parallel to the substrate. After annealing and recrystallization at 850 °C, β-Mo2C mainly exists in these films. The prepared Mo2C thin films all have semiconductor properties. The optical band gap of Mo2C films increases first and then decreases with the increase in CH4 flow rate. Meanwhile, the luminescence intensity of Mo2C films increases first and then decreases with the rise in CH4 flow. The analysis of the first principles calculation shows that this performance is due to the different etching degrees of Mo2C films with different CH4 flow rates, the thermal vibration of the gap C atom, and the change in the ratio of C sp2/sp3.