To gain detailed understanding of both the seed layer
clustering and subsequent ZnO nanostructure formation, it was important to understand the clusterization processes exhibited by different Au layer thicknesses: in our experiment, 6 and 12 nm. To follow MK0683 purchase the change in Au layer morphology and to evaluate the size distribution of Au nanoparticles, SEM images were assessed. Figure 1 shows typical SEM images of the nanoparticles HSP inhibitor obtained for the different Au layer thicknesses followed by thermal annealing at 800°C in Ar ambient without ZnO growth precursors. For both thicknesses, the Au films were effectively converted into uniformly distributed spherical and/or hexagonal-like nanoparticles. This behavior can be explained by the non-wetting GSK1904529A characteristics between Au and SiC substrate interface. Notably, with increasing Au film thickness from 6 to 12 nm, the coverage density of Au nanoparticles were found to decrease from around 130 μm-2 (Figure 1a) to 5 μm-2 (Figure 1b),
respectively. As expected, the thickness of the initial Au layer strongly affects the density of the Au nanoparticles and, hence, as shown later in this work, the density of the resulting ZnO nanostructures produced. The insets in Figure 1a, b show the Au cluster size distribution for the Au layer thickness of 6 and 12 nm, respectively annealed at 800°C for 30 min in Ar ambient. Based on these observations, we first carried out the growth on the 6-nm Au seed layer samples. In Figure 2a, b, typical SEM and STEM images of ZnO NWs grown at 850°C for 90 min are presented. From Figure 2a, b, it can be seen that a high-density Urease NW with an exceptional degree of material orientation perpendicular to the SiC substrate is achieved. From the SEM and STEM images, typical NW length and diameter were determined to be around 1 to 2 μm and 30 to 140 nm, respectively (longer nanowires can be obtained simply by increasing the growth time). Based on the nanowire length and growth time, the growth rate for the present NWs was determined to be approximately 15 to 20 nm/min. Figure 2c,d shows typical SEM and STEM
images of vertically oriented ZnO NWLs grown at 900°C for 180 min. From Figure 2c, d, it is noticeable that the measured height and widths of the NWLs were also found to be consistent with those measured for the NWs, thus suggesting a similar growth process for both types of nanostructures. Figure 1 SEM images of (a) 6-nm and (b) 12-nm ‘seed layer’ Au thin film annealed at 800°C on SiC substrate. Figure 2 Typical SEM and STEM ZnO nanoarchitectures images. (a) 22° side-view SEM image of ZnO NWs. Inset shows the high magnification of the sample. Scale bar is 1 μm. (b) Corresponding STEM image of the sample. Inset shows the high magnification of the sample showing the presence of Au nanoparticles at the ZnO/SiC interface. Scale bar is 500 nm. (c) Top-view SEM image of ZnO NWLs.