| Zinc oxide is an importantⅡ-Ⅵcompound semiconductor material, with a band gap of 3.37eV at room temperature and exciton binding energy of 60 meV. ZnO is a high-quality piezoelectric, sensing and optical material, which has been widely used in optoelectronics facilities, light-emitting diode, catalytic reaction, and gas sensors. Recently, some morphology of ZnO, such as column, line, rod, belt, tube, ring, tetrapod and flower-shaped nanostructures have been fabricated by chemical vapor deposition, liquid phase method, template method, RF magnetron sputtering, metal organic vapor phase epitaxy, molecular beam epitaxy and so on. In this paper, we have fabricated the column-shaped, hexagonal prism-shaped, tetrapod-shaped and Mg doped pencil-shaped ZnO micro and nanostructures on pretreated Mg(NO3)2/Si substrates by CVD method. The microstructure, component, morphology, and photoluminescence properties were investigated carefully. In addition, we also studied the influence of magnesium oxide layer to the growth of ZnO structures, and Mg doped influence to the pencil-shaped ZnO structures. The main results we have obtained in this study are as follows:1. Column-shaped ZnO micro/nano-structuresMgO layer was prepared on the the Si(111) substrates, and then column-shaped ZnO structures were synthesized by CVD method in a horizontal tube furnace. Compared with the uncoated MgO Si (111) substrates, MgO layer can solve the troublesome lattice mismatch problem in the heteroepitaxy and promote the growth of ZnO columns effectively. The diameter of ZnO was in the range of 85 nm - 900 nm, and a length of 200 nm - 3μm. In this letter, base on the SEM images of columns with different reaction times, we have discussed the growth mechanism and photoluminescence properties of the ZnO columns.2. Hexagonal prism-shaped ZnO micro/nano-structuresWe have fabricated two types of ZnO hexagonal micro/nano prisms on MgO-coated Si (111) substrates by the CVD method. One type of the structrues is regular hexagonal microprisms, while the other type is agg twin boundary extending down its entire length. The structural analysis confirm that the structures are perfect single crystals with hexagonal wurzite structure along the [0001] growth direction. The optical properties and growth mechanisms of the micro/nano prisms were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and photoluminescence (PL).3. Tetrapod -shaped ZnO micro/nano-structuresNovel ZnO micro/nano-tetrapods were fabricated firstly via using of ZnO and active C as raw materials on MgO-coated Si (111) substrates by CVD method. These novel tetrapods have extra prisms on their legs, which will make it to be a new member of the ZnO family. Base on the characterization of the tetrapods, we can observe that the structures are single crystal with the wurtzite hexagonal structure, and the growth direction of the tetrapods changes from [0001] to [0111]. In addition, the octahedral multiple twin model and polar surfaces are proposed for interpreting the growth of the tetrapods.4. Mg doped pencil-shaped ZnO micro/nano-prismsDue to the strong ultraviolet (UV) emission at room temperature, ZnO micro/ nano prisms have potential application in the short-wave light-emitting photonic devices. With the development of ZnO-based devices, it is necessary for us to dope appropriate elements into ZnO, which can improve their optoelectronic properties effectively. In this paper, Mg doped pencil-shaped ZnO micro/nano-prisms were successfully fabricated by simple CVD method. Doping with the Mg element may modulate the value of the band gap and increase the UV luminescence intensity. The CVD method produces a large quantity of single crystal of ZnO at low cost. Therefore, it may be interesting for commercial-scale production. |
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