Preparation of ZnO:CeO_2x thin films by AP-MOCVD: Structural and optical properties

The growth of columnar CeO₂, ZnO and ZnO:CeO_2-x films on quartz and AA6066 aluminum alloy substrates by economic atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD) is reported. A novel and efficient combination of metal acetylacetonate precursors as well as mild operating conditions were used in the deposition process. The correlation among crystallinity, surface morphology and optical properties of the as-prepared films was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM) and UVvis spectroscopy. The synthesized films showed different crystallographic orientations depending on the ZnO and CeO₂ lattice mismatch, cerium content and growth rate. The CeO₂ films synthesized in this work showed plate-like compact structures as a result of the growth process typical of CVD. Both pure and ZnO:CeO_2-x films were obtained with a hexagonal structure and highly preferred orientation with the c-axis perpendicular to both substrates under the optimal deposition conditions. The microstructure was modified from dense, short round columns to round structures with cavities ("rose-flower-like" structures) and the typical ZnO morphology by controlling the cerium doping the film and substrate nature. High optical transmittance (>87%) was observed in the pure ZnO films. As for the ZnO:CeO_2-x films, the optical transmission was decreased and the UV absorption increased, which subsequently was affected by an increase in cerium content. This paper assesses the feasibility of using ZnO:CeO_2-x thin films as UV-absorbers in industrial applications.