【作者】 王丹丹；

【导师】 杨景海；

【作者基本信息】 中国科学院研究生院（长春光学精密机械与物理研究所） ， 凝聚态物理， 2010， 博士

【摘要】 氧化锌纳米材料由于其本身材料特性和形状特性,在光电子器件及自旋存储器件方面有着广泛的应用前景,对其材料本身的研究以及对其掺入其他离子以达到优化或赋予新的光学、磁学性能的研究对这种材料的发展和应用具有极其重大的理论研究价值和实际应用价值。本论文旨在采用传统的气相传输法和化学方法成功制备出垂直衬底生长的纳米线及其他纳米结构的未掺杂/掺杂的氧化锌,并利用X射线衍射仪、透射电镜、X射线光电子能谱、X射线精细结构分析技术、原子力显微镜、超导量子干涉仪、光致发光谱、拉曼光谱仪、荧光光谱仪等测试手段对样品的可控生长、结构、光学及磁学性能进行了详细的研究。首先,我们采用传统的气相传输法,优化实验条件成功制备出垂直衬底生长的氧化锌纳米线,并对纳米线的生长机制、催化剂对纳米线的影响进行了研究,研究结果表明催化剂的厚度对纳米线的尺寸有很大的影响,尺寸越大,纳米线的直径越大。同时,我们对纳米线的光学性能也进行了研究。发光中心位于520 nm的发光峰来源于氧空位,对于紫外发光,当激发功率增加时,紫外发光峰出现了蓝移,这主要是由于纳米线表面在氧空穴的作用下产生表面自建电场,激发功率增加越来越多的电子和空穴分离,在表面自建电场的作用下,电子和空穴会向相反的方向运动,更多的空穴集中在表面,与表面氧空位所捕获的电子中和,使得表面内建电场减小,从而导致向上的能带弯曲程度变小,增加了激子的跃迁能量产生的。其次,我们选择稀土元素对氧化锌进行掺杂,对其性能进行研究。主要集中在两种稀土元素的掺杂研究:1. Eu离子掺杂氧化锌纳米材料。我们采用两步法,即溶胶-凝胶法制备反应源,气相传输法制备纳米线,采用水热法制备了由纳米片组成的微米花,并对纳米线和微米花的结构、成份和光学性能进行了研究。结果表明,Eu离子已经成功掺杂进入氧化锌晶格,并且采用紫外激发,在光致发光谱图中我们也观察到了Eu离子细锐的发光峰,并证明了这个发射峰是ZnO到Eu离子的能量传递产生的。通过对后处理样品的光致发光谱图和时间分辨光谱的研究表明,这种能量传递与材料中的氧空穴有很大的关系,氧空穴越多能量传递越强,表明这种缺陷可以作为能量传递的能量陷阱,有利于能量传递。在微米花中同时存在氧空穴及氧间隙两种缺陷,我们观察到二者的发光峰。2. Nd离子掺杂氧化锌纳米线。同样采用两步法,与制备Eu掺杂氧化锌不同,我们采用简单的固相反应法制备了反应源,然后采用气相传输法制备纳米线。经结构、成分分析表明Nd离子已经掺入纳米线中,磁性测试表明掺入Nd离子后,样品表现出室温铁磁性。并且有较大的矫顽力和形状各向异性,磁化强度也有明显的各向异性。磁性的来源主要是氧空穴诱导的Nd离子长程相互作用。较大的矫顽力主要是由Nd本身相对于过渡族元素较大的磁各向异性,和缺陷的钉扎作用产生的。而磁化强度的各向异性是由Nd的轨道磁矩产生的。本文的研究结果不但为制备未掺杂/掺杂的氧化锌纳米材料提供了可参考的制备条件。对于其光学和磁学性能研究也得到了一些有益的结果,为未掺杂/掺杂的氧化锌纳米材料更好和更广泛的应用提供了理论依据并奠定了实验基础。更多还原

【Abstract】 ZnO nanomaterials have great potential applications in the photoelectronic devices and spintronic device owing to the native properties and shape characters. Therefore, it is very important to do the research on the fabrication and properties of undoped and doped ZnO nanomaterials. The main points for this thesis are not only successfully realize the synthesis of undoped/doped ZnO nanomaterials, and also investigate the structure and optical properties in detail by the methods of field emission scan electron microscope (SEM), transmission electron microscope (TEM), resonant Raman, photoluminescence (PL), time resolved PL spectrum, spectrofluorimeter and superconducting quantum interference device (SQUID).In the thesis, firstly, vertical aligned ZnO nanowires were successfully prepared on the substrate with Au layer by the classical vapor transport method. Results show that the thickness of the catalyst has big effect on the size of the nanowires, the thicker catalyst, and the bigger diameter of the nanowires. At the same time, we investigate the optical properties of vertical undoped ZnO nanowires. UV emission displayed an evident blueshift with increasing excitation power and the corresponding energy shift might be as large as 10 meV. This anomalous phenomenon correlates to the band bending level caused by the surface built-in electric field due to the existence of substantial oxygen vacancies. By increasing the excitation power, the enhanced neutralization effect near the surface will reduce the built-in electric field and lead to a reduction of band bending which triggers the blueshift of the UV emission. Secondly, we choose the rare earth element as the dopant, and investigate the structure and properties of rare earth doped ZnO. We mainly focus on two rare earth elements doping as follow:1. Eu doped ZnO. We synthesize the Eu doped ZnO by two methods; one includes the synthesis of the source powders by a sol-gel method and the growth of nanowires by vapor transport method; another one is the growth of nanosheets based microflower. Then we investigate the properties of Eu doped ZnO. Results show that the Eu ion has doped into the matrix of ZnO. Under the UV excitated, there is a sharp red emission related to the intra-4f transitions of Eu3+ ions. Our systematic studies on photoluminescence (PL) excitation, temperature-dependent photoluminescence and time-resolved photoluminescence suggest that intrinsic defects, in particular singly ionized oxygen vacancies, can serve as the media for the energy transfer from the ZnO host to the Eu3+ ions. For the nanosheets based microflower, there are both the oxygen vacancy and oxygen interstice defects, and we also observe the red peak due to energy transfer from the ZnO host to the Eu3+ ions.2. Nd doped ZnO. We synthesize the Nd doped ZnO nanowires by two steps method including synthesis of source powders the solid state reaction method and the growth of nanowires by vapor transport method. XRD, TEM, XPS and EDS results confirm that the Nd has doped into the matrix of ZnO. The Nd doped ZnO nanowires show room temperature ferromagnetic properties. They have large coercivity and shape anisotropy. The magnetic moment also show anisotropic properties. The ferromagnetic properties are due to the bound magnetic polaron mechanism. The oxygen vacancies polarize the magnetic dopants and form the polarons, and the interaction of the adjacent polarons made the Nd doped ZnO nanowires give the ferromagnetic properties. The higher coercivity is due to the magnetic anisotropy and the pining effect of the defect in Nd doped ZnO nanowires. The anisotropic property of magnetization is due to the orbital contribution of the Nd magnetic moment.This thesis not only provides the optimized growth conditions for undoped/doped ZnO nanomaterials, but also obtains some beneficial results in aspects of their optical and magnetic properties, which builds theoretical and experimental foundation for much better and broader applications of undoped/doped ZnO nanostructures.更多还原