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Synthesizing of ZnO Micro/Nanostructures by Thermal Vapor Method with Metallic Reducing Agents

Author: SangDanDan
Tutor: LiHongDong
School: Jilin University
Course: Condensed Matter Physics
Keywords: Metal reducing agents ZnO micro/nanostructures thermal vapor method growth mechanism ZnO/Diamond
CLC: TB383.1
Type: Master's thesis
Year: 2009
Downloads: 74
Quote: 1
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Abstract


In recent years, ZnO-base materials have attracted a great deal of attention with regard to micro and nano-electronic, magnetic, field emission effect applications, since zinc oxide （ZnO） has a wide direct bandgap with a high binding energy of excitions and is room-temperature ferromagnetic. Thermal evapour transport method has been considered as an important approach to fabricate ZnO micro-and /or nano-structures with various features and special properties. In general, the experiments were carried out with the sources of mixed ZnO and reducing agent of carbon. Therefore, finding new source systems is important to extend the researches and applications of ZnO-related materials.Instead of the conventional graphite, new additional reducing agents metal elements have been mixed with ZnO powder to fabricate ZnO micro/nanostructures by a thermal vapour transport method. Due to the strong reducibility for metal elements, the corresponding heating temperature is decreased by 100-500℃compared to the case of graphite, which subsequently decreases the corresponding deposited temperature for the products. The selected products fabricated at the corresponding Theat by the sources of ZnO mixed with Ti,Mn,Fe,Al and Mg powders, respectively. A variety of micro/nano-sized features, such as mirofilms, microrods, nanorods, tetrapods and various hierarchical structures, etc., normally appear in those products. The result of EDX、Raman and XRD indicated that ZnO micro/nanostructures fabricated by Ti, Mn, Fe, and Al as agents are pure. The main diffraction peaks can be indexed as hexagonal wurtzite structure of ZnO. But ZnO products by Mg at 550℃as agents contain a few MgO. Researching on the change of ZnO micro/nano-structures with the deposition temperature, we can find that with the deposition temperature decrease, ZnO saturated vapor pressure is decreased, which resulting in ZnO micro/nanostructures gradually change from the microfilms to nanorods. A high level of oxygen exist at the region close to the open end of the tube has, resulting in the increase of the length of ZnO micro/nano-structures. The change of the working pressure has an important effect on the morphology of ZnO micro/nanostructure. When the experiment is carried under low pressure （<1atm）, aspect ratio of ZnO micro/nanostructures increased. Since Zn vapor which vaporised from the source meterials is restricted at low pressure. Being placed separately for the powder sources of ZnO and addition, a vapor-vapor reduction-oxidation reaction mechanism between the sources is proposed as an important channel to fabricate ZnO. The variation in Theat for the majority of additions is dependent （roughly） on the corresponding data of IE.ZnO nanostructures have been successfully grown on polycrystalline diamond-film substrate exposed in air environment. Field emission measurement show turn on electric field is estimated to be 17Vμm-1 for intrinsic nanodiamond and 4Vμm-1 for ZnO naorods covered nanodiamond. It is evident that the field emission properties of ZnO nanorods fabricated on diamond are considerably improved compared to intrinsic nanodiamond. From the averaged slope of the F-N plot, the field enhancement factorβof intrinsic nanodiamond and ZnO nanorods is estimated to be about 114 and 2381. High field enhancement of the ZnO nanorods covered on nanodiamond is suggested to be the result of a combined effect of the intrinsic geometry of nanorods and nanodiamond.

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