Figure 3 shows the SEM images of the ZnO NRAs grown on Figure 3a, the bare CT substrate with the ultrasonic agitation; and in Figure 3b, the seed-coated CT substrate without the ultrasonic agitation For comparison, the external cathodic voltage and growth time were −2 V and 1 h, respectively, as the same condition of Figure 2. As shown in Figure 3a, the ZnO NRAs were grown on the seedless CT substrate. In fact, it was previously understood that the ZnO NRAs could be formed with no seed layer by the ED process [28, 29]. However, the size and distribution of ZnO nanorods were not Selleck PF-6463922 regular and the vertical
alignment was poor. Since the ZnO nuclei were randomly created and organized without seed layer, the ZnO nanorods were formed with different sizes and they were aligned obliquely along each growth direction. For the grown sample without the aid of ultrasonic agitation in Figure 3b, on the contrary, the ZnO NRAs were densely and vertically formed, but many microrods were attached to them. As explained in Figure 2, some zinc hydroxides were already formed in growth solution, and the microrods readily adhered to the ZnO NRAs when the ultrasonic agitation was not applied to the aqueous growth solution. Therefore, the seed layer and ultrasonic
agitation are crucial to obtain the well-integrated ZnO NRAs on CT substrates. Figure 3 FE-SEM Selleckchem Wortmannin micrographs. ZnO NRAs grown on (a), the bare CT substrate with the ultrasonic agitation; and (b), the seed-coated CT substrate without the ultrasonic agitation. For comparison, the external cathodic voltage and growth time were −2 V and 1 h, respectively, as the same condition of Figure 2. Figure 4 shows the SEM images for the synthesized ZnO on the seed-coated CT substrate
at different external cathodic voltages of Figure 4a, −1.6 V; Figure 4b, −2.4 V; and Figure 4c, −2.8 V for 1 h under ultrasonic agitation; and Figure 4d, the current density as a function of growth time at different external cathodic voltages. The insets else of Figure 4a,b,c show the magnified SEM images of the selected region of the corresponding samples. Below −1.6 V of external cathodic voltage, the ZnO NRAs could not be formed due to the insufficient electron supply under a low external cathodic voltage. In JSH-23 nmr contrast, the size of ZnO was dramatically increased with increasing the external cathodic voltage to −2.4 and −2.8 V. In general, the ZnO nanorods may be grown anisotropically under ED conditions. While the Zn2+ ions diffuse rapidly into the polar plane, they cannot diffuse into the nonpolar plane relatively because the hexamine molecules were early attached to the ZnO pillars, thus blocking out the reaction between the Zn2+ and OH− ions [30]. Accordingly, the ZnO nanorods are grown along the polar planes corresponding to the c-axis of wurtzite crystal structure.