Fabrication of nanostructured CuO thin films with controllable optical band gaps using a mist spin spray technique at 90 °C

Abstract

A solution-based process, termed the mist spin spray method, was developed to fabricate nanostructured CuO thin films on seed-free glass substrates. In this method, a copper amine complex solution and a NaOH solution are separately atomized by ultrasonication to generate mists. These mists are subsequently sprayed onto a substrate heated to 90 °C and fixed on a rotating platform to grow crystalline CuO thin films at atmospheric pressure. This one-step method enables the generation of phase-pure, dense and crack-free CuO thin films below 100 °C. CuO thin films approximately 30 nm in thickness exhibited good adhesion to glass substrates, and the concentrations of NH3 and NaOH in the initial solutions were found to affect both the film morphology and optical band gap. Specimens prepared using higher NH3 and NaOH concentrations had larger grain sizes, while those fabricated using a low NaOH concentration showed a porous structure. A higher optical band gap was found to correlate with smaller grain sizes in the films.