Synthesis and characterization of nanostructured ZnO multilayer grown by DC magnetron sputtering

• Produce of multilayer of ZnO by thermal oxidation of Zn layer in 1, 2, and 3-steps.
• Optical and structural properties of ZnO multilayer analyzed by PL, XRD, SEM, AFM.
• Multilayer of ZnO shown high transmittance and low structural defect.
• Multilayer coating method leads to decrease of roughness and scattering on light.

A novel method is presented for fabrication of zinc oxide nanolayers (ZnO) by coating multiple layers of ZnO through thermal oxidation of zinc (Zn) films on a glass substrate in multiple steps. This technique reduces temperature and time of thermal oxidation, and can be used for coating oxidant materials on low melting point substrates. In several experiments aiming at depositing a ZnO thin film with 300 nm thickness, deposition took place in a single step, two steps and three steps. Each step involved thermal oxidation of the Zn layer with 300 nm, 200 nm, or 100 nm thickness. The structural, morphological, optical and mechanical properties of the ZnO samples deposited in each experiment are investigated. The results of photoluminescence (PL) analysis and Urbach energy measurements indicate that higher transmittance and lower structural defects can be achieved with the samples produced in three steps, each involving deposition and oxidation of a Zn layer with 100 nm thickness. X-ray diffraction (XRD) analysis demonstrates that the degree of crystallinity of the deposited ZnO thin films strongly depends on the deposition steps. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) image analyses show that the size of grains and surface roughness of ZnO multilayers are lower than ZnO monolayer. Moreover, the mechanical properties of samples improved with increasing the deposition steps.