The surface morphology of the grown ZnO strongly depends on the Vistusertib substrate temperature.
From the surface and cross-sectional images, it can be seen that the grown ZnO structures show three different morphologies, i.e., nanocluster, nanorod, and thin film structures at 600°C, 800°C, and 1,000°C, respectively. As shown by the EDX spectra, only Zn, O, Si, and carbon (C) elements were detected in all samples. The total compositional atomic percentages of Zn and O for the as-grown structures were found to be 87% for 600°C and 80% for both 800°C and 1,000°C. However, the composition ratio of Zn atoms to O atoms in samples decreases with the increase of temperature where the ratio is found to be 0.55, 0.33, and 0.23 for temperatures of 600°C, 800°C, and 1,000°C, respectively. This result shows that the nucleation of Zn particles is less promoted at high temperature. It is speculated that such tendency may be due to the formation selleck screening library of large etch pit and less horizontal Depsipeptide nucleation which is explained in the growth mechanism. Detection of C element confirmed the presence of graphene
on SiO2/Si substrate and was not etched away during the growth process. The calculated density of nanorods for samples grown at 800°C was estimated to be around 6.86 × 109 cm-2 which is relatively high and comparable to other synthesis techniques either on graphene [1, 2] or Si substrate [29]. Table 1 summarizes the density, diameter, length, and average aspect ratio of the grown ZnO including comparison with other works. Figure 2 FESEM images and EDX spectra of grown ZnO. (a) 600°C. (b) 800°C. (c) 1,000°C. Table 1 Density, diameter, length, thickness, and average aspect ratio of the grown ZnO structures Temperature (°C) Density (cm-2) Diameter of nanorods/nanoneedles (nm) Length of nanorods (nm) Thickness (nmn Average aspect ratio This work 600 – - – ~200 – 800 6.86 × 109 50-150 200-380 – 2.85 1,000 – - – ~60 – [1] 400 4 × 109 100 ± 10 1,000 ± 100 – 10.0
600 8 × 107 90 ± 20 4,000 ± 600 – 44.4 750 5 × 107 – 3,500 ± 500 – - [29] 800 1.2 × 108 200-500 – - – Figure 3a shows the measured XRD spectra for the sample grown at different substrate temperatures. The as-grown ZnO at 600°C and 800°C exhibit hexagonal wurtzite structure indicated Quinapyramine by the presence of prominent peak at approximately 34.46° corresponding to ZnO (002) diffraction peak. A relatively high intensity of this peak indicates that the preferred growth orientation of the as-grown ZnO is towards the c-axis and it is consistent with the FESEM image shown in Figure 2. A very weak peak, approximately at 36.4° corresponding to ZnO (011) diffraction peak, was also observed in samples grown at 600°C and 800°C. However, no prominent peak of ZnO was observed for the sample grown at 1,000°C due to the very thin thickness of the grown layer. Figure 3 XRD (a) and PL spectra (b) of grown ZnO structures.