The photo-catalytic activity of the catalysts is highly dependent on the adsorption behavior and the separation efficiency of the pairs e^- and h⁺ [1]. The coupling between ZnO, which is an excellent photo-catalyst for the degradation of organic and inorganic pollutants as well as hazardous waste in water and air (due to its photo-sensitivity, no -toxicity and its direct 3.2 eV and indirect 2.45 eV optical gap values), with a second non-sensitive wide band gap semiconductor proved that was an effective method to improve their photo-catalytic activities. In particular the mixing between the ZnO and ZnAl₂O₄ (Eg = 3.8 eV) band gap structures ensures the separation efficiency of the e^- and h⁺ generated pairs. The ZnO-ZnAl₂O₄ mist has high photo-catalytic activity due the presence of the spinel phase with high surface area and thermal stability [2]. ZnAl₂O₄ is a spinel-type complex oxide. This compound is nontoxic, inexpensive and very stable material. ZnAl₂O₄ is of interest due to its combination of desirable properties such as high mechanical resistance, high thermal stability and low surface acidity [3]. It is used in many catalytic reactions [4].

The aim of this work is the control of the ZnO/ZnAl₂O₄ films synthesis on glass, silicon and ITO substrates (for a better application) as well as the study of their growth and the correlation of the stresses with the structural and optical properties. A simultaneous formation, according to XRD, of ZnO and ZnAl₂O₄ phases on glass substrate from the annealing at 500°C-2h is observed and confirmed by EDX. The (D_ZnO and D_ZnAl2O4) crystallites size grown on Si are much higher than those on glass. Tensile stresses between 0,031 and 0,469 GPa for the ZnO layers and compressive one for ZnAl₂O₄ ~ -0,227 and -0,404 GPa in ZnO/ZnAl₂O₄ annealed between 650 and 500 °C. ZnO nanorods are detected by SEM. The ZnO/ZnAl₂O₄ films, as characterized by UV-visible spectroscopy, are highly transparent in the visible and near infrared regions.

References

[1] Y. Jianhui, Z. Li, L. Xiaoyan, Z. Xiuxiu and D. Chaohua, Chemical Science Review and Letters, 3 : 12 (2014), 1080-1090.

[2] Kumar K, Ramamoorthy K, Koinkar PM, Chandramohan R, Sankaranarayanana K, Journal of  Crystal Growth, 289 (2006), 405-407.

[3] M. Zawadzki, Solid State Sciences, 8 (2006), 14–18.

[4] R. Thinesh Kumar, Clament Sagaya Selvam N, Ragupathi C, L. J. Kennedy, J. Vijaya, Powder Technology, 224 (2012), 147-154.