Effect of Thickness on Photocatalytic Properties of ZnO thin films Deposited by RF Magnetron Sputtering

Abstract

Zinc oxide (ZnO) thin films were deposited on soda lime glass substrates by using the RF magnetron sputtering technique. The deposition process was carried out in a system initially evacuated at $\pmb{7x10}^{-\pmb{5}}$ torr and a working pressure of 10−3 torr in a pure argon atmosphere, at room temperature. A 2“ diameter and $\pmb{1}/\pmb{4}$ ” thick ZnO target (99.999%) was used. A target-substrate distance of 10 cm, and a working power of 125 W were kept constant. The films were deposited at different thicknesses, 50 to 400 nm. The thickness, the optical, structural and morphological properties were analyzed by profilometry, UV-Vis spectrophotometry, x-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. Additionally, three ZnO thin films were used to analyze the photocatalytic performance by using an $\pmb{1x10}^{-\pmb{5}}$ molar aqueous methylene blue (MB) solution, under the irradiation of ultraviolet light with a wavelength of 232 nm, during 5 h. The degradation of MB was carried out by absorbance measurements in the range of 400 to 800 nm every 30 min. The ZnO films showed a wurtzite hexagonal structure with a preferential growth in the (002) planes and good homogeneity. The results obtained from the study of the degradation of methylene blue showed that the ZnO film with a thickness of 400 nm presented the best photocatalytic response.