It is also due to the vertical growth of ZnO rods and their high surface areas as suggested by Xu et al. [29]. The calculated ratio of the intensity of UV emission to the intensity of green emission, I UV/I Visible, obtained in this work is shown in Figure 3b (inset). As a comparison, the results obtained for the electrodeposition on SL graphene [30] were

also plotted in the same figure. It can be seen that both spectra show a similar tendency. It can be seen that see more the sample grown on ML graphene at a current density of −1.0 mA/cm2 shows the highest value of 1.6 which seems to indicate the optimum current density for this work. The sample grown at a current density of −2.0 mA/cm2 shows the highest green emission compared to the other samples or the lowest I UV/I Visible value, which indicates that there may be more defects induced during the growth such as O vacancies [43]. Ahn et al. reported that the sensitivity of gas sensing

increases linearly with the sample having high green emission intensity or, in other words, with the structure having large defect density [14]. Therefore, it seems to suggest that the sample with large structural defect also has several interesting applications. Growth mechanism To understand the growth mechanism, we have investigated the surface and cross-sectional structures selleck chemical ADP ribosylation factor both

at the initial stage of the growth, i.e., before reaching the ST point, and after 1 h of actual growth. As the procedure of a study at the initial growth, the samples were grown at several growth times, i.e., 10 s (T = 23°C), 1 min (T = 30°C), 5 min (T = 52°C), 10 min (T = 68°C), and 15 min (T = 80°C). The current was fixed at −1.0 mA/cm2. The current was immediately turned off after reaching these growth times, and at the same time, a sample was immediately taken out from the electrolyte and immersed into DI water to remove any residue. Figure 4a shows a FESEM image of bare ML graphene used in this work. It can be seen that the differences in contrast and brightness of the image represent the differences in thicknesses of graphene. The dark color shows the thicker graphene, while the bright color shows the thinner graphene. Figure 4b shows an image after the growth time of 10 s. It can be seen that the surface was covered with a high density of white ZnO cluster-like spots. This indicates that the nucleation of ZnO starts aggressively in a short time after the introduction of current even at a low temperature of 23°C. With the increase of growth time to 1 min (T = 30°C), it can be seen that almost the entire surface was covered with the ZnO thin layer with a rough morphology in different brightness levels, as shown in Figure 4c.