[19] and Humayun et

al. [21]. This can be due to the large quantity of absorbed oxygen created by the rapid photoresponse on the ZnO surface when illuminating by visible light, which slow down the photocurrent generation process [22]. Figure 3 Photocurrent of ZnO NRs. Plot of photocurrent density (J) versus time (t) for one-dimensional ZnO NRs prepared by HTG and VTC methods. In order to enhance the photoresponse of the VTC-grown ZnO NRs, the ZnO NRs were Regorafenib concentration synthesized on the one-dimensional Si NWs trunk to induce the hierarchical Si/ZnO trunk-branch nanostructures for improvement in light trapping ability. selleck chemicals llc Figure 4a,b shows the morphology of the Si NWs grown by our home-built plasma-assisted hot-wire chemical vapor deposition system. The length of the Si NWs is about 1 to 1.5 μm. HRTEM micrograph in Figure 4c shows that the NWs exhibit single crystalline structure. Note that the crystalline Si structure shows the greatest electrical conductivity, therefore, it serves as a good junction between ZnO NRs and the conducting electrode. The NWs reveal tapered

morphology with base and top diameters of about 200 nm (Figure 4a,b) and 20 nm (Figure 4c), respectively. Basically, quantum effect of Si NWs will occur when the diameter of Si NW is less than 10 nm [23]. Therefore, it shows that Si NW will have the same bandgap as the bulk Si. FESEM images shown in Figure 5a,b are corresponded to the planar and side views of the hierarchical Si/ZnO trunk-branch NSs. It could be seen from the image that the lateral growth of ZnO NRs are evenly distributed on the sides and caps of the Si trunk nanowires. PF299804 nmr With the assistance of the ZnO seeds which acted as preferred growth sites,

ZnO vapor molecules tend to absorb and elongate from the ZnO seeds on the surface of the Si NW trunk, forming ZnO NR branches. The size and distribution of the Fenbendazole ZnO seeds on the Si NWs’ surfaces thus play a crucial role in the growth of the Si/ZnO trunk-branch NSs. Estimation from the transmission electron microscope (TEM) image (Figure 5c) gives a length and diameter of about 300 and 120 nm, respectively, for the ZnO NR branches. In general, the length of the ZnO NR branches is much smaller than the VTC-grown planar ZnO NRs (nearly 2 μm) under the same deposition condition; however, the NRs’ density per area is considerably higher. HRTEM micrograph in Figure 5d reveals an ordered lattice arrangement, indicating a single crystalline structure for the ZnO NR branches. Figure 4 Morphology of the Si NW trunk. (a) Surface and (b) side morphologies of the Si NWs prepared by a plasma-assisted hot-wire chemical vapor deposition technique. (c) HRTEM micrograph of the Si NWs. Figure 5 3-D Si/ZnO hierarchical NWs. FESEM (a) planar and (b) cross-section views of the Si/ZnO hierarchical NWs. (c) TEM image of a typical Si/ZnO hierarchical NW. (d) HRTEM micrograph taken from the ZnO branches.