Facile preparation of ZnO nanostructured thin films via oblique angle ultrasonic mist vapor deposition (OA-UMVD): a systematic investigation

Ultrasonic mist vapor deposition (UMVD) is a widely used facile technique to prepare ZnO thin films. The surface properties of prepared thin films can be tuned via easily controllable UMVD deposition parameters. Herein, we utilized an oblique angle (OA) geometry in UMVD system named as OA-UMVD. The angle between incident flow and substrate (theta(s)) was changed from 0 degrees to 45 degrees. Alteration of theta(s) as well as substrate temperature (T-s) resulted in the deposition of ZnO thin films with different morphologies. For mild nozzle-substrate distance (D = 3 cm), fine vertical ZnO nanosheets with length of 123 nm and thickness of 23 nm were obtained for low T-s (330 degrees C) and small theta(s) (approximate to 0 degrees). By increasing both T-s and theta(s), ZnO nanorods gradually appeared on the surface. Both nozzle-substrate distance (D) and T-s showed similar effect on deposition rate (R-d), and R-d decreased by increase of D and T-s, while deposition rate increased for larger theta(s). Confocal microscopy results revealed that using low T-s (330 degrees C), short distance (D = 1.5 cm) and large theta(s) (45 degrees) resulted in high macroscopic surface roughness (MRs) of 98 nm, while high T-s (500 degrees C), long D (5 cm) and small theta(s) (approximate to 0(circle)) created compact and smooth surface with low MRs of 5 nm, in accordance with transmittance results. The ZnO wurtzite crystal structure was approved via X-ray diffraction patterns. The crystallite size in the layers was affected only by T-s, and theta(s) had no significant effect on the layers' crystallinity. Obtaining different ZnO nanostructures with different MRs via easily and accurately controllable growth parameters is a great advantage for our employed OA-UMVD system, which could be used to prepare ZnO thin films with desired morphologies for widespread application fields.