Top-down and bottom-up methods are two types of approaches used in nanotechnology and nanofabrication . The bottom-up approach is more advantageous than the top-down approach because the former has a better chance of producing nanostructures with less defects, more homogenous chemical composition, and better short- and long-range ordering . Semiconductor nanorods (NRs) and nanowires possess convenient and useful physical, electrical, and optoelectronic properties, and thus, they are highly suitable for diverse applications [3, 4].
ZnO, one of the II-VI semiconductor materials, has attracted considerable interest because of its wide bandgap (approximately 3.37 eV), high exciton binding energy (approximately 60 meV), and long-term stability [5, 6]. ZnO has been applied in various applications, such as in light-emitting diode , gas and chemical sensors [8–10], ultraviolet (UV) detector [11, 12], solar cell [13, 14], and biomolecular sensors [15, 16]. To create high-quality ZnO NRs, various techniques have been proposed, such as the aqueous hydrothermal growth , metal-organic chemical vapor deposition , vapor phase epitaxy , vapor phase transport , and vapor–liquid-solid method .
Among these methods, the aqueous hydrothermal technique is an easy and convenient method for the cultivation of ZnO NRs. In addition, this technique had some promising advantages, like its capability for large-scale production at low temperature and the production of epitaxial, anisotropic ZnO NRs [21, 22]. By using this method and varying the chemical use, reaction temperature, molarity, and pH of the solution, a variety of ZnO nanostructures can be formed, such as nanowires (NWs) [16, 23], nanoflakes , nanorods , nanobelts , and nanotubes .
In this study, we demonstrated a low-cost hydrothermal growth method to synthesize ZnO NRs on a Si substrate, with the use of different types of solvents. Moreover, the effects of the solvents on the structural and optical properties were investigated. Studying the solvents is important because this factor remarkably affects the structural and optical properties of the ZnO NRs. To the best of our knowledge, no published literature is available that analyzed the effects of different seeded layers on the structural and optical properties of ZnO NRs. Moreover, a comparison of such NRs with the specific models of the refractive index has not been published.