Optimized spray pyrolytic fabrication of engineered hexagonal ZnO nanorods: structural, optical, and electrical properties

Abstract

The spray pyrolysis method was effectively utilized for fabricating ZnO on ultrasonically cleaned glass substrates at various deposition temperatures of 275, 325, 375, and 425 °C. The influence of deposition temperature on ZnO has been widely studied due to its impact on various material properties, such as structure, morphology, composition, optical, and electrical characteristics. XRD analysis confirms that the ZnO are made of small crystallites with a hexagonal wurtzite structure. The FE-SEM investigation demonstrated the formation of highly ordered porous surface structure made up of hexagonal-shaped nanorods. The EDX examination shows the reduction in oxygen content relative to the zinc content in the ZnO. AFM analysis shows that the RMS surface roughness reaches its highest value of 310.59 nm for ZnO fabricated at 375 °C. Using XPS analysis, existence of Zn²⁺ oxidation state in ZnO is verified by examining binding energy of Zn 2p levels. The BET results reveal that ZnO has specific surface area of 3.7 m²/g, pore width of 10.51 nm, and pore volume of 0.031 cm³/g. The wettability evaluation of ZnO surface showed left and right contact angles of 135.90° and 132.64°, respectively, indicating its hydrophobic nature. For direct allowed transition, optical investigation showed that with an increase in deposition temperature, band gap falls from 3.24 to 3.14 eV. When ZnO nanorods is subjected to increasing frequencies of electric field, the dielectric constant as well as loss tangent falls whereas AC conductivity rises. DC resistivity measurement demonstrated the semiconducting nature of ZnO nanorods.

Graphical Abstract