Microstructural characterization, optical and photocatalytic properties of bilayered CuO and ZnO based thin films

Highlights: • High quality bilayered Zn–Cu oxide thin films were deposited by aerosol assisted CVD. • Detailed microstructural characterization was performed by XRD and electron microscopy. • Absorbance of bilayered films shows a shift of absorption edge toward visible region. • Optical band gap or nearly 3.2 and 2 eV was determined for ZnO and Cu oxide. • High photocatalytic activity around 90% was obtained for bilayered samples. - Abstract: In this work, it is presented the synthesis, microstructural characterization and photocatalytic properties of bilayered CuO–ZnO/ZnO thin films onto borosilicate glass and fused silica substrates. The films were deposited by aerosol assisted chemical vapor deposition, using an experimental setup reported elsewhere. Deposition conditions were optimized to get high quality films; i.e. they were structurally uniform, highly transparent, non-light scattering, homogeneous, and well adhered to the substrate. Different Cu/Zn atomic ratios were tried for the upper layer. The microstructure of the films was characterized by grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy. GIXRD results indicate the presence of ZnO Wurzite and Cu oxide phases. Results of SEM and HRTEM analysis of the cross sectional microstructure showed that the films were composed of compact and dense layers with no visible evidence of an interfacial boundary or porosity. Optical absorbance of the bilayered films showed a clear shift of the absorption toward the visible range. Optical band gap was determined roughly at 3.2 and 2 eV for ZnO and Cu oxide, respectively. Photocatalytic activity of the samples, for the degradation of a 10⁻⁵ mol dm⁻³ solution of methylene blue (MB), was determined after 120 and 240 min of irradiation with an UV-A source. Around 90% of MB degradation was reached by bilayered films with roughly 50 at.% of Cu in the upper Zn–Cu oxide layer deposited onto a ZnO buffer film