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분야
docx1. Introduction
2. Experimental
3. Result and discussion
4. Conclusion
5. References
3.1 Morphologies and structure(SEM)
Fig. 1 (a)shows SEM image of as-obtained ZnO nanowires of in the first step ranging from 80 to 400 nm in diameters and about 4 mm in length. Gold particles at the tips of the nanowires can be seen in Fig. 1(a). This indicates that the ZnO nanowire growth was governed by a VLS process. Fig. 1(a) shows ZnO nanowires obtained under the same condition as the ones in Fig. 1(a). But as they were grown in the margin, the size were much larger and the catalyst particles cannot be seen clearly at the tips of the nanowires under the resolving capability of the SEM. The VLS growth mechanism is identical to the published papers (Huang et al., 2001; Wang, 2004). We also found that the ZnO nanowires were distributed in the area deposited with Au film, and there was no nanowire in the area without Au film. This confirms catalytic action of Au during the growth of ZnO nanowires.
Fig1. (a) ZnO nanowires grown in the margin.
(b) ZnO nanowires with gold particle at the tips.
The morphology and structure of the prepared products at step two were analyzed by SEM. Fig. 1(b) shows the SEM image of samples fabricated at step two, displaying an interesting hierarchical pure ZnO nanostructure with lengths of several decade microns. The high-magnification images of single ZnO nanostructure in Fig. 1(d) and (e) reveal that they are composed of central axial nanowires surrounded by radially oriented nanorods with 6-fold structural symmetry. Fig. 1(f) shows the side-wall image of hierarchical ZnO nanostructure with widths of 70–-120 nm and average length of around 600 nm. The high-magnification image of the single nanorod on the side-wall displays columniform structure with a conic tip which is quite different from the hexagonal structure in Fig. 1(d), indicating that the ZnO nanorods are not synthesized through the layer-by-layer growth model. It is noticed that under the bottom of nanorods, ZnO layer with the 608 angle between the nearest neighbors is formed on the side-wall of central axial nanowires, as shown with white arrow in Fig. 1(e) and (f); Meanwhile, the large nanoclusters are found existing on the bottom of nanorods, as shown with black arrows in Fig. 1(f). These observations imply the following formation process of nanorods: At the initial stage of heating, the ZnO layer is first formed on the surface of nanowires. And then with the continuous supplementation of Zn and ZnOx, they nucleate on the surface of ZnO layer and form the large nanoclusters. With the further absorption, ZnO nanorods grow from the top of nanoclusters.
Fig. 2 (c) low magnification SEM image of the two-step-prepared product, (d) and (e) high-magnification SEM image of single hierarchical pure ZnO nanostructure, (f) SEM image of nanorods on the side-wall of central axial nanowire.
3.2 XRD pattern
Fig.3 is the XRD pattern of as-synthesized ZnO nanowires of in the first step.
All diffraction peaks match well with the characteristic peaks of ZnO
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