“…Sol–gel technique [12], electrodeposition [13], chemical bath deposition [14], hydrothermal synthesis [15], thermal plasma [16], atomic layer deposition [17] or thermal evaporation [18], sputtering or radio frequency reactive magnetron sputtering [19], air plasma spraying [20,21], ablation techniques [22], and co-precipitation [23] have all been used to prepare ZnO thin films. Some researchers have reported the use of two-step processes, such as spin coating followed by growth treatment [24].…”