Substrate temperature effect on the structural, morphological and optical properties of pyrolyzed bi-phase Cu2O–CuO thin films

Multiphase nanomaterials are fascinating due to the synergistic effect between the crystalline phases that lead to improved device performance. Publications are available for the synthesis of monophasic copper oxides, such as Cu₂O and CuO, and the mixed-phase Cu₂O–CuO counterpart using different synthesis methods. However, literature report is scarce that focuses on the fabrication of bi-phase Cu₂O–CuO thin films by the spray pyrolysis technique without phase transformation to form the monophasic counterparts. The present work attempts to prepare solely mixed-phase Cu₂O–CuO films through small incremental change in substrate temperature, in steps of 20 $°C$. Structural analysis of the pyrolyzed films revealed the formation of a bi-phase Cu₂O–CuO crystal system. The crystallite size increased from 18.64 to 23.94 nm, microstrain decreased from 7.134 $\times {10}^{-4}$ to 5.625 $\times {10}^{-4}$, while stacking faults decreased from 3.753 $\times {10}^{-3}$ to 2.942 $\times {10}^{-3}$ with an increase in temperature. Microstructural analysis showed nanoaggregates with increased particle size at increasing temperature. The films exhibited a common optical bandgap of 2.61 eV. The values of the static refractive index and optical electronegativity were found to be 2.47 and 0.70, respectively. The surface roughness increased from 41.3 to 90.9 nm with substrate temperature.