Results and discussion As comparison, firstly, the hydrothermal growth of #VS-4718 supplier randurls[1|1|,|CHEM1|]# ZnO using the same composition of electrolyte and temperature was performed in the same setup. As shown in Figure 2a, the

grown ZnO nanostructures are nanorod clusters with very low density, and the structures are not vertically aligned. This is not consistent with the results obtained in [23], probably because the growth was not done in a high-pressure container or autoclave. Next, the growth at the preheated stage, i.e., initial growth, was investigated. The growth was performed in a heated mixture of equimolar of Zn (NO3)2 · 6H2O and HMTA with applied current densities of -0.1, -0.5, -1.0, -1.5, and -2.0 mA/cm2. As shown in Figure 2b, c, d, e, f, different morphologies of ZnO nucleation structure were observed. The structures seem to be strongly dependent on the applied current density. At low current density of -0.1 mA/cm2, a very thin ZnO layer containing nanodot structures was obtained (Figure 2b). When the current densities were increased to −0.5 and −1.0 mA/cm2, a ZnO layer with nanoporous-like morphological structures was observed as shown in Figure 2c, d, respectively. The porosity seems to decrease with the

increase of current density, where a ZnO layer without porous-like structure was observed at the current density of -1.5 mA/cm2 as shown in Figure 2e. At high current density of -2.0 mA/cm2, a ZnO layer containing nanocluster structures was observed CA4P as shown in Figure 2f. The growth of the vertical nanorods based on those formed seed structures is expected to have been enhanced after the ST point or during the actual growth. Since the reaction of electrolyte is considerably premature at temperatures below 80°C, the crystallinity of the seed structure is not good. This is simply proved by the EDX analysis (data is not shown), where the compositional percentage of zinc (Zn) and oxygen (O) is low which is in the range

of 50% to 60% in spite CYTH4 of the additional compositional percentage of O from the SiO2 layer. Figure 2 SEM images of ZnO structures. (a) Top-view SEM images of ZnO structures grown at a current density of 0.0 mA/cm2 (hydrothermal). (b)-(f) Top-view and cross-sectional SEM images of the initial ZnO structures grown at current densities of -0.1, -0.5, -1.0, -1.5, and -2.0 mA/cm2, respectively. Finally, the complete growth (i.e., initial plus actual growth) of the ZnO nanostructures according to the time chart shown in Figure 1c in a heated mixture of equimolar of Zn (NO3)2 · 6H2O and HMTA at applied current densities of -0.1, -0.5, -1.0, -1.5, and -2.0 mA/cm2 was carried out. Figure 3a, b, c, d, e shows the top-view and cross-sectional SEM images of the grown structures. It is noted that the grown structures show identical morphologies throughout the whole surface area of the graphene.