溶胶-凝胶ZnO薄膜及其纳米棒阵列生长机制和性能研究

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	溶胶-凝胶ZnO薄膜及其纳米棒阵列生长机制和性能研究
	黄楠
学位类型	博士
导师	姜辛 ; 孙超
	2011
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	溶胶-凝胶法微观结构氧化锌物理性能 Sol-gel Technique Micostructure Zinc Oxide Physical Property
摘要	"氧化锌（ZnO）是一种宽禁带（3.37 eV）半导体，室温下具有较高的激子束缚能（60 meV），是一种理想的短波长光电子材料，可应用于太阳能电池的窗口材料、表面声波器和气体传感器等众多领域。然而，本征态的ZnO薄膜电导率较低，需要通过掺杂III或IIV主族元素来提高其电导率，以满足实际应用的要求。其中Al掺杂的ZnO薄膜是目前研究最为广泛和深入的掺杂体系，这种薄膜具有在氢气等离子体中性质稳定、无毒和造价低廉等优点。与气相沉积技术对比，溶胶-凝胶技术拥有设备简单、成本低、成膜温度较低、易于实现成分的精确控制和可实现在大面积基片和特殊形状器件上镀膜等优点。因此，基于溶胶-凝胶技术开发的ZnO薄膜具有重要的应用价值。目前对溶胶-凝胶ZnO的研究主要集中于实验参数对薄膜光学、电学性能的影响上，而就其溶胶-凝胶过程对薄膜微观结构的影响则研究较少。本文试图建立过程参数与薄膜结构及最终性能的关系，为最终控制薄膜生长及调控性能提供理论基础和实验依据。实验表明，通过改变Al的掺杂浓度，薄膜从开始的柱状结构转变为粒状薄膜并最终发展成为一维纳米结构。经过一系列的检测分析，最终建立了一个生长模型，就ZnO薄膜随Al含量变化所引起的微观结构转变进行了解释。TEM结果表明，溶胶-凝胶ZnO纳米棒是大量小晶粒依据取向连接机制聚合形核和后续外延生长的结果。本论文发展了一种无模板溶胶-凝胶技术来制备有序ZnO一维纳米结构阵列，通过精心设计实验实现了一维纳米棒的可控性制备。TEM结果表明，ZnO纳米棒为单晶结构，其生长方向为[0001]方向。进一步分析表明，位于基片和纳米棒之间的薄膜的取向是决定纳米棒排布方式的关键因素，发现在具有高度择优取向的薄膜上可以获得良好垂直排布的纳米棒阵列。由于无需借助种子层和模板，因此这是一种可直接用来制备有序纳米棒阵列的技术，具有很好的商业应用前景。另外，通过增加提拉-热处理循环次数，成功制备了大长径比的ZnO纳米结构阵列，其光致发光谱呈现紫外光发射，绿光发射和蓝光发射等多个发射峰。本文通过设计梯度涂层对纳米棒形成的具体过程进行了探讨研究。我们还利用了纳米压痕系统，对单根ZnO纳米棒的力学性能进行了研究。最后经过简化实验过程达到了一步合成致密、大长径比ZnO有序纳米棒阵列的目的。实验结果表明溶胶浓度、提拉速度和热处理制度等因素对纳米棒生长过程产生影响，论文最后还对其光学性能进行了研究。关键词：溶胶-凝胶法，微观结构，氧化锌，物理性能"
其他摘要	"ZnO is an outstanding semiconductor with a wide band-gap (3.37 eV) and a large binding energy (60 meV) at the room temperature, which makes it an ideal room-temperature optoelectronic material. It has been applied as the substrate materials for solar cells, for making surface acoustic wave device and gas sensors. However, intrinsic ZnO has high electrical resistance, it was therefore always doped by group-III or VII elements to meet the application requirements. Among most of doping systems, Al doped ZnO thin films or nanostructures have been extensively studied, owing to its high stability under hydrogen plasma, non-toxicity and low-cost. Normally, doping of Al in ZnO is mainly achieved by magnetron sputtering. Compared with the vapor deposition method, the sol-gel technique has the advantages of simple, accurate in doping control, suitable for large-scale production, and low energy consumption. The studies about Al-doped ZnO films and their nanostructures derived from the sol-gel technique have been mainly focused on establishing a correlation between experimental parameters and physical properties. Attention has rarely been placed on understanding the effects of process parameters on the microstructure and morphology evolution of the films, although it is well-known that the properties of the film strongly depend on their internal microstructures. Such a study is imperative to the better understanding of the growth mechanism which in turn will aid to controll the growth of the ZnO films eventually imparting the tailoring and designation of the physical and chemical properties of the films. In the present work, the microstructure evolution of Al doped ZnO with different Al doping level was investigated. The film microstructure changes from columnar to granular and to nanorods with increasing Al content. Based on the overall results, a two-step growth model was proposed which reveals the mechanism of the microstructure evolution of Al doped ZnO film. The growth of ZnO nanorod arrays derived from template-free sol-gel technique was studied by tailoring experimental parameters. The ZnO nanorod obtained from this method is single-crystalline structure and the growth direction is along [0001]. The dependent of alignment of nanorods on the experimental parameters was discussed in detail. The orientation of the nanoparticles-packed film controlled by pre-heating and withdrawal speed is responsible for the alignment of the nanorods. Thus, well-aligned ZnO nanorod arrays are obtained from the film with a good orientation in the c-axis direction, while the randomly oriented arrays are formed on the film with an improper c-axis orientation. Noted this film has been formed during the growth process of nanorods, and the specific preparation doesn’t need. Therefore, our study is expected to pave a way for direct growth of oriented nanorods by low-cost solution approaches. Adding the dip-coating layers, a thicker oriented ZnO arrays can be obtained through pre-heating at 240 oC and annealing at 550 oC for 1 h. Apart from a strong UV emission at 381 nm and a broad green emission centered at 494 nm, a blue double-peak was observed at 451 and 486 nm, respectively. The detailed growth process of ZnO nanorods by sol-gel technique was discussed by designing the gradient layer. At last, the mechanical of the ZnO nanorods was investigated by nanoindentation system and compression tests were performed with three different indenters. A one-step sol-gel approach was demonstrated on the growth of large-scale, oriented and dense higher aspect-ratio nanorods. It is highlighted that the experimental parameters such as sol concentration, dip-coating speed, and reactive temperature play an important role in the growth of the nanorods. Finally, the structure and photoluminescence properties of the nanorods were discussed. Key words: Sol-gel technique, Micostructure, Zinc oxide, Physical property"
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64283
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	黄楠. 溶胶-凝胶ZnO薄膜及其纳米棒阵列生长机制和性能研究[D]. 北京. 中国科学院金属研究所,2011.