Growth evolution and customized attributes of catalyst-free ZnO nanowires: role of varied Ar/O2 flow rate

Abstract

This paper reports a tailored structure, morphology, optical behavior, and growth evolution of catalyst-free ZnO nanostructures (ZONSs) synthesized on quartz substrates using the wet thermal evaporation method. The as-prepared samples were thoroughly characterized to determine the influence of varying rates of Ar and wet O2 gas flow (150, 250, and 350 sccm) on their overall properties. Scanning electron microscopy (SEM) images revealed the formation of high-quality ZONSs of various shapes, including nanowires, aligned nanorods, and nanorods-like tetrapods with different dimensions. X-ray diffraction (XRD) patterns displayed the most intense diffraction peak at (002), which was attributed to the preferred growth orientation and crystallinity of such nanomaterials. Photoluminescence (PL) spectra showed an enhancement in the peak intensity. The position of the ultraviolet emission peak of ZONSs was red-shifted as the gas flow rate increased. Raman spectra exhibited the high-intensity E2 and very weak (suppressed) E1L Raman mode for all samples, indicating the accomplishment of good crystal quality in wurtzite hexagonal crystalline ZONSs of the samples. Furthermore, the optimum flow rate for synthesizing high-density, superior quality, and higher nanocrystalline ZONSs was found to be 350 sccm. This work can contribute toward the development of the production of various nano-optical devices.