Crystalline structure, morphology, and topography analysis of spin-coated ZnO and ZnO:S microstructures

The physical properties of materials can be precisely altered by doping them with a low concentration of foreign elements, a process that has a direct and significant impact on surface morphology and topography. This study investigated the effects of low sulphur (S) doping on zinc oxide (ZnO) microstructures. Pure ZnO and S-doped ZnO (ZnO:S2 and ZnO:S4, with 2 % and 4 % sulphur, respectively) were deposited on rotating glass substrates via the sol-gel spin-coating method. Subsequent analysis using complementary techniques revealed that as the S concentration increased from 0 % to 4 %, the ZnO microstructures changed from a globular to a rod-shaped morphology. This was accompanied by a concurrent increase in both particle size (confirmed by SEM) and crystallite size, from 39 to 55 nm (confirmed by XRD). All samples maintained a hexagonal zincite ZnO crystalline structure. Optical analysis showed a decrease in visible range transmittance and a slight reduction in the bandgap value (Eg) with increasing doping. AFM imaging revealed that at a low concentration (2 % S), the surface became smoother and was characterized by a valley-dominated topography. A further increase in S concentration to 4 % resulted in a rougher surface with a pit-rich topography, featuring higher peaks and deeper pits. These results were critically evaluated to determine suitable applications for the spin-coated samples.