Nucleation and growth of δ-Bi2O3 thin films on c-sapphire by means of chemical vapour deposition under atmospheric pressure

Cubic bismuth oxide (δ-Bi2O3) films were grown on a c-sapphire substrate under atmospheric pressure by means of halide chemical vapour deposition using BiI3 and O2 as starting materials. The nucleation and evolution of the thin film growth was investigated by varying the growth temperature, and [O2]/[BiI3] molar ratio. The growth process of δ-Bi2O3 was found to be strongly dependent on both [O2]/[BiI3] ratio and growth temperature. SEM observation revealed that nucleation and island formation are initiated in the first 2 min. As the growth time increases, the size of the islands increases and then the islands start coalescing. Finally, the islands converge and film growth starts.