An amount of 0.317 g (0.02 M) of zinc acetate dihydrate in 30 mL of methanol was taken and heated to 60 °C while being evenly stirred for 20 min. The temperature of the solution was kept constant at 60 °C, and it was stirred consistently for a period of two hours after the addition of a stabilizer that consisted of 1 mL of ethanolamine. After this period was finished, the solution was left out at room temperature for twenty-four hours so that the zinc oxide seed layer solution could be obtained. Then, using a spin coater, 40 L of zinc oxide seed layer solution was applied to the cleaned silicon substrates. A two-step spin coating was used for a uniform film coating. To achieve a homogenous ZnO seed layer, successive applications of 1000 rpm for 10 s and 1500 rpm for 40 s were used. After deposition, the substrates were heated at 120 °C for 20 min, and the procedure was repeated twice. Later, the substrates coated with the zinc oxide seed layer were placed in a tungsten boat and kept inside a furnace tube at a high temperature (500 °C) for annealing for 2 h. Furthermore, by fabricating multiple samples of ZnO NRs using the same process and comparing the diameters of the as-grown ZnO NRs on the Si substrates, the repeatability of the ZnO seed layer was confirmed. The uniformity of the diameter distribution across multiple samples was maintained. Through this method, seed layer thicknesses of around 23.41 ± 0.23 nm and diameters of the NRs of around 128.50 ± 0.66 were maintained constantly in all our samples. In the supporting information file, Section S1 , the SEM top view and cross-section view of the deposited ZnO seed layer, distribution of the seed layer thickness, and distribution of NR diameters are provided.
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