【作者】 田玉；

【导师】 李金钗；

【作者基本信息】 武汉大学 ， 粒子物理与原子核物理， 2010， 博士

【摘要】 纳米材料因为具有奇特的光学、电学、磁学、力学以及催化等物理化学性质,引起了科研人员的广泛关注。纳米材料的性能显著地依赖于其形状与尺寸,因此获得尺寸与形貌可控的纳米材料是当前广大科学工作者们努力的方向。与一般材料相比,氧化锌是一种具有优异压电和光电特性的直接带隙宽禁带半导体材料,它的多变的形态结构直接决定其物理性质及应用潜力。对于氧化锌,虽然许多种类的纳米结构已经被合成出来,但空心球结构的制备依然是对材料学家的一大挑战。我们知道,空心纳米结构具有更高的比表面积,更大的长径比,因而在催化、传感器、生物科学、药物输送、储存、释放系统和纳米反应器等领域有极大的应用潜力。因此,发展工艺简单、普适的可控合成空心氧化锌纳米结构的技术仍是十分必要的,对进一步拓展氧化锌材料的应用领域有重要意义。本论文采用模板法,利用模板的空间限域作用和模板的调控作用,有目的地对氧化锌的结构、尺寸、形貌等进行控制。利用锌粉作为先驱模板,结合热蒸发法来制备氧化锌,获得空心微球结构,研究了实验条件对它们纳米结构的影响。并利用热蒸发法制备三维氧化锌枝状纳米结构,深入研究纳米结构的发光性质和生长机制。主要工作和结果如下：本文的主要工作和取得的主要结果如下：本论文主要采用热蒸发法,利用锌粉作为先驱模板,成功制备Zn0空心微球结构,并且微球的表面生长了呈放射状的均一纳米杆。氧化锌空心微球的生长过程应分为两个阶段：一、氧化锌空心壳的形成过程；二、壳上纳米杆的生长过程。通过对试验参数的调整,对这些纳米材料的生长行为以及微结构进行剖析后,了解到空心微球结构对锌粉先驱模板的选取及模板与源材料的共同作用有着非常大的依赖性,而且锌粉的尺寸形状直接决定了空心球的形状和大小。同时还研究了它的光学性能,并结合其生长环境的变化,对其生长机制进行了初步探讨。采用先驱模板的机制,提供了一个简单易行的制备空心微球结构的方法。该工艺技术简单、制备成本较低。锌粉模板在反应后直接转化成Zn0空心微球,并没有任何污染,无需高温或化学去除模板,保持了样品的形状及纯度。由于生长过程中实验参数的影响,总会导致所得材料的晶体结构或形态结构的不同,并最终影响微／纳米材料的性质。因此,研究微／纳米材料的生长机制,是实现其控制合成的关键影响因素。如合成温度、压力、气流速度、气体分压及衬底,这些影响因素将引起氧化锌晶体生长的千变万化,同时这也为氧化锌的控制生长提供了机会。我们着重研究了合成温度对其纳米结构的影响,也研究了气体流量、气压及附加蒸发源种类的影响。研究发现,微球表面上纳米结构对生长温度最为敏感；其它因素也会影响ZnO空心微球表面纳米结构。此外,还比较了有代表性的几种不同表面形态的ZnO空心微球的光致发光谱特性。经过试验工艺的探究,为实现其它类似氧化物空心结构的可控生长提供了一个简单易行的途径。在478℃温度下采用热蒸发纯Zn粉的方法合成了形貌诱人的ZnO三维枝状纳米结构。该结构由氧化锌主干和垂直于主干、指向各方向的纳米线所组成。其中,ZnO三维枝状纳米结构为具有六方纤锌矿的结构,枝状纳米线沿[0001]方向生长。不同温度的合成实验揭示,枝状纳米结构对合成温度比较敏感。它的光致发光谱表明它有较强的紫外发光,可能在光催化、气敏传感器及染料敏化太阳能电池领域及纳米光电器件方面有潜在的应用。更多还原

【Abstract】 Oxide nanomaterials have attracted worldwide attention and laid some foundation for the nanodevices due to their unusual optical, electronic, magantic, mechanical and catalytic properties. It is well known that the properties of nanomaterials are sensitively dependent on both the shape and size. Therefore, the most important problem faced by the scientists is how to fabricate nanostructures with the controllable shape and size. In comparison with other nanostructures, ZnO hollow nanostructures exhibit stronger or novel functionalities due to their higher surface area and their capability of forming composite structures by embedding specific particles in their interiors, and they thus may find potential applications in a wide range of areas, including catalysis, drug delivery, storage and release systems, bioencapsulation, nanoreactors, and templates for functional architectural composite materials. Although, many hollow Oxide nanomaterials have been fabricated, the synthesis of ZnO hollow structures still remain a big challenging subject to chemists and material scientists. Therefore, it is highly necessary to explore simple and general accesses to preparing oxide nanomaterials with desired dimensions and sizes.In this dissertation, valuable explorations have been carried out to prepare hollow ZnO microspheres using thermal evaporation by Zn powder precursor-template, and the effect of the experimental conditions including growth temperature, air pressure, flow rate of Ar and air on surface morphology of ZnO hollow spheres have been scrutinized in detail. ZnO dendritic nanostructure has been synthesized on silicon (100) substrates by thermal evaporation of metal Zn powder at relative low temperature, as well as their formation mechanism and the novel properties of the as-obtained nanostructures. The main points can be summarized as follows:We have realized the synthesis of uniform zinc oxide (ZnO) hollow spherical structure consisting of highly radial and oriented ZnO nanorods, which results from a facile precursor-templated through thermal evaporation at a relative low temperature without any catalyst. Two main growth steps may occur in the process:the first step is formation of hollow ZnO shell when air was introduced into the tube at 400℃, Zn atoms on the surface of Zn microsphere reacted with O atoms to form thin ZnO shell layer on the surface of Zn microsphere. The second step is the growth of the ZnO nanorods on the surface of the microsphere. The nanocrystalline protrusions on the surface of ZnO sphere shell are very beneficial to the preferred aligned growth of ZnO nanorods. In this approach, pre-deposited Zn powder particles on Si substrates act as temporary templates to form hollow ZnO sphere shells, while additional Zn powder acts as a Zn source to grow single crystal nanorods/nanowires on the surfaces of spherical shells. Lacking the need for the additional template removal is an important advantage of this approach over others and it therefore can be used to prepare hollow ZnO nano/microsphere shells and hollow ZnO microspheres with nanorods/nanowires at low cost and at large scale. These kinds of special high surface area hollow spherical structures may find potential applications in photocatalysis, light-weight composite fillers, acoustic insulation, UV nano/micro-optoemission devices and photoanodes of dye-sensitized solar cells.By optimizing the experimental parameters, the obtained results demonstrate that the morphology of ZnO is very sensitive to growth temperature, air pressure, flow rate of Ar and air and Zn powder precursor. Detailed structural analyses confirm that this microstructure exhibits a wurtzite hexagonal phase, and there arenanorods, nanowires, tower-like nanorode, particle et.al growing on the shells of ZnO hollow spheres. The formation mechanism of the microstructure is proposed to be a vapor-solid process. This method may provide a simple and versatile approach to large-scale production of hollow spherical ZnO structure and other hollow nanomaterials.Intriguing ZnO three-dimensional (3D) dendritic nanorods on silicon substrates have been successfully synthesised by thermal evaporation of pure zinc powder at a relative low temperature of 478℃without any metal catalyst. ZnO dendritic nanostructure exhibits unique shape and it is composed of stems and nanorod branches. It is found that the nanorods are single crystalline wurtzite structures, and each nanorod grows along the [0001] direction. At different growth temperatures, the shapes of ZnO nanostructures can be altered. System analysis reveals that the formation and morphology of ZnO dendritic nanostructures are sensitive to the growthtemperature. Finally, room temperature photoluminescence spectrum is also investigated,revealing that the ZnO dendritic nanostructure could find application in UV optoelectronic devices; the nanostructure implies some potential applications for nanoscale functional devices.更多还原