Microstructural and optical studies of CuO thin films prepared by chemical ageing of copper substrate in alkaline ammonia solution

In this paper, we report on the time-dependent development of cupric oxide films by chemical modification of copper substrates submerged horizontally in a room temperature 75 mmol/L ammonia solution at pH 11, over a period of nine days. Morphological and structural characterization of the oxide-substrate tandems were carried out by SEM-EDX and XRD, while the relative directional spectral absorptivity and reflectivity were determined by Vis-NIR spectrometry. The ageing process, controlling both the color and morphological structure of the predominately amorphous-CuO/Cu, has positively contributed to the enhancement of spectral absorptivity, while band gap values evolve from 1.29 to 1.39 eV for exposure times from 36 to 168 h.