ZnO thin films with controllable morphologies and crystal orientation fabricated by the mist spin spray method

Abstract

ZnO thin films with controllable morphologies were fabricated using the simple and cost-effective mist spin spray (MSS) method at 70 °C. The MSS technique involves the reaction between an inorganic zinc salt precursor and a strong base in mist particles. The thin films obtained by the MSS method exhibited advantageous characteristics, including strong adhesion to the glass substrate, high uniformity, high crystallinity, negligible impurities, and no requirement for post-annealing treatment. The morphology of the thin films could be readily modified from nanoparticles to nanorods simply by changing the molar ratio of zinc(II) ions (Zn²⁺) to hydroxide ions (OH⁻) in the reaction solution. The preferred orientation of the thin films was along the [001] direction at a Zn²⁺/OH⁻ molar ratio of 1:4 and transitioned to the [100] direction at a Zn²⁺/OH⁻ molar ratio of 1:10. The Zn²⁺/OH⁻ molar ratio also influenced the optical absorption peak and band gap of the ZnO thin films because of changes in the grain size. The ZnO nanoparticles observed in the films fabricated with lower Zn²⁺/OH⁻ molar ratio are thought to primarily result from the nucleation process. Conversely, the nanorods consisting of both primary and secondary nanostructures observed in the films fabricated with higher Zn²⁺/OH⁻ molar ratio formed through nucleation and a subsequent crystal growth process.