磁控溅射法制备氮掺杂的TiO₂薄膜及其光学性能研究

【作者】 江洪湖；

【导师】 姚合宝；

【作者基本信息】 西北大学 ， 凝聚态物理， 2010， 硕士

【摘要】 近年来,人们发现TiO2光催化材料还具有净化空气、杀菌、除臭、超亲水性等功能,并已经广泛应用于抗菌陶瓷、空气净化器、不用擦拭的汽车后视镜等领域。半导体纳米TiO2因其化学性质稳定、无毒和能有效去除大气和水中的污染物而成为解决能源和环境问题的理想材料,并引起了各国研究者广泛的兴趣。但是TiO2是宽禁带(Eg=3.2ev)半导体化合物,只有波长较短的太阳光能(<387nm)才能被吸收,而这部分紫外线(300～400nm)只占到达地面上的太阳光能的4%～6%,太阳能利用率很低。而可见光却占了太阳光能总量的45%,因此缩短催化剂的光学禁带宽度使吸收光谱向可见光扩展是提高太阳能利用率的技术关键。其对应的非金属掺杂有望实现能带工程和其他有利功能,引起了人们的广泛关注和研究。本文制备氮掺杂的TiO2纳米薄膜就是其中较为典型的一种,它在不降低紫外光光催化活性的基础上,还可以加强TiO2纳米薄膜在可见光范围的扩展程度和吸收强度。用不同方法制备的TiO2-xNx薄膜性能参数差异较大,目前文献报道的多数是采用溶胶-凝胶、加热、离子注入和激光脉冲沉积等方法制备的。本工作用射频磁控溅射法在普通玻璃衬底上生长了TiO2-xNx薄膜,并研究氮氩流量比、工作气压、衬底温度、溅射功率和退火温度对其结构和光学性能的影响。第一章首先介绍了TiO2材料的基本性质及其应用,然后对TiO2-xNx薄膜材料的国内外研究进展做了详细介绍,并阐述了课题选取的意义。第二章介绍了薄膜的制备以及其测试表征。本章先介绍薄膜的制备方法,主要是磁控溅射方法的介绍。本论文用JGP-560型超高真空多功能磁控溅射系统,采用纯度为99.9%的TiO2陶瓷靶材,在玻璃衬底上淀积了不同条件的TiO2-xNx薄膜。射频电源的频率为13.56MHz,系统的背景真空度为3×10-4Pa,溅射功率范围为50～250W,溅射气体使用氩气,反应气体为氮气。我们采用XRD分析薄膜的晶体结构；用AFM观察薄膜表面形貌；由透射光谱、PL谱等研究薄膜的光学性质。第三章采用与TiO2薄膜对比的方法研究了TiO2-xNx薄膜的结构和光学性能。X-射线衍射谱(XRD)显示了薄膜只有A(101)一个衍射峰,表明TiO2-xNx薄膜具有择优取向生长的趋势。通过AFM观察薄膜的表面形貌可知,氮掺杂后薄膜的表面比较光滑,氮元素抑制了薄膜中多晶结构的形成。两个样品的XPS图谱显示：N元素确实进入到薄膜的晶格内,主要是以取代氮的形式存在,少部分以间隙氮的形式存在。TiO2-xNx薄膜在可见光区的平均透过率高达80%以上,在紫外区都有一个陡峭的吸收边,由此计算出薄膜的光学禁带宽度约2.44ev。室温光致发射光谱中观测到了五个发光峰,分别以340nm(A)为中心的近紫外发光带；380nm(B)、430nm(C)和470nm(D)为中心的三个紫外发光带；535nm为中心的蓝色发光带(E)。A峰是来源于激子的直接复合；B峰是能带之间的辐射复合发光；C峰是由于浅层缺陷捕获的激子发光；D峰是表面态和缺陷捕获的激子发光；E峰是由于氮的掺入形成过多的氧空位引起的自发捕获的电子空缺复合发光。第四章讨论了制备条件对TiO2-xNx薄膜性质的影响。分析了氮氩流量比、工作气压、衬底温度、溅射功率和退火温度对TiO2-xNx薄膜的结构和光学性能的影响。采用控制变量法,逐个改变薄膜的生长条件,找出晶体结晶度高、缺陷少、晶粒大小均匀和光学性能优良的制备工艺参数；分析薄膜的发光特性,对各个参数对薄膜的发光特性的影响做了初步的探讨,提出薄膜吸收边红移的理论假设。第五章给出了论文的主要结论,并且对掺氮TiO2薄膜材料的发展前景进行了展望。更多还原

【Abstract】 In recent years, it was discovered that TiO2 photocatalytic materials also have air purification, sterilization, deodorization, super-hydrophilic and other functions. It has been widely used in anti-bacterial ceramic, air purifier, the car rear view mirror and other fields. Nano-TiO2 semiconductor for their chemical stability, non-toxic and effectively removing pollutants from the atmosphere and water, is an ideal material for solving energy and environmental issues and caused widespread interest of national researchers. However, TiO2 is a wide band gap (Eg=3.2ev) semiconductor compounds, only the shorter wavelengths of solar light (<387nm) can be absorbed, which the UV (300～400nm) only reach 4%～6% of the sun light on the ground, solar energy utilization is very low. The visible solar energy accounts for 45% of the total combined amount. To improve the utilization of solar energy, it is a key technology to shorten the catalyst band gap so that the absorption spectrum could extend to the visible spectra. Its corresponding non-metallic element doping is expected to achieve energy band engineering and other beneficial features which has aroused wide spread concern and research. This preparation of nitrogen-doped TiO2 nanometer thin films is the more typical one. It does not reduce the basis of UV photocatalytic activity, but also can enhance the TiO2 nanometer thin films in the visible range of the expansion and intensity of absorption.There have been some reports on the property of TiO2-xNx thin films. TiO2-xNx thin films have different properties by different methods. In this dissertation, the TiO2-xNx thin films have been prepared by RF magnetron sputtering method on glass substrates. The structural and optical properties of TiO2-xNx thin films have been systemically investigated.The influence of conditions, such as the nitrogen argon flow ratio, working pressure, substrate temperature, sputtering power and annealing temperature on the characteristic of TiO2-xNx thin films have been studied.In the first chapter, the characteristic and applications of TiO2 materials have been introduced first.Then the progress of studies on the TiO2-xNx thin film materials have been mentioned and explained the reasons for the selected topic.In the second chapter, the preparation of thin films and their characterization test methods have been introduced. This chapter describes the thin-film preparation methods firstly, mainly for magnetron sputtering introduction. The TiO2-xNx thin films were deposited in a JGP-560-type multi-functional ultra-high vacuum magnetron sputtering system with a purity of 99.9%TiO2 ceramic target on glass substrates. A power supply operated at a crystal frequency of 13.56 MHz; the system background vacuum was 3×10-4Pa. The sputtering power was 50～250W. Argon gas was sputtering gas and reaction gas nitrogen.We use XRD to study the structure of the films, observe thin film surface morphology by AFM and study the optical properties of thin films from transmission spectra and PL spectra.In the third chapter, the structure and optical performance of TiO2-xNx thin films were discussed. X-ray diffraction (XRD) shows only A (101) a diffraction peak, indicating that TiO2-xNx thin films with preferred orientation of the growth trend. From the observation of surface morphology by AFM, the surface of nitrogen-doped films became smoother and N inhibited the formation of multi-crystalline structure. XPS patterns of the two samples show N elements into the film lattice indeed. The main form of nitrogen is substitute nitrogen and another is interval nitrogen. TiO2-xNx thin films are high transparent (大于80%) in the visible region, and has a steep absorption edge in the ultraviolet region. By calculating the optical band gap of films is about 2.44ev. Five emission peaks were observed in Room temperature photoluminescence emission spectra. They were respectively 340nm (A) as the center of the near ultraviolet light-emitting zone; 380nm (B),430nm (C) and 470nm (D) as the center of the three ultraviolet light-emitting zones; 535nm as the center of the blue luminescence band (E). A peak is derived from the direct exciton complex. B peak is the radiation compound luminescence between the bands. C peak is due to shallow defects captured exciton luminescence. D peak is a surface state and defect captured exciton luminescence. E peak is due to excessive oxygen vacancies caused by the formation of a spontaneous capture of electronic vacancy complex luminescence.The fourth chapter discussed the influence of preparation conditions on the structure and optical performance of the TiO2-xNx thin films. Using the control variable method, one by one to change the growth conditions of films, excellent preparation process parameters were found. The films are crystals of high crystalline, defects less uniform grain size and show excellent optical properties, deposited in these parameters. The luminescence mechanism of several light emitting peaks was analysed. We studied the films Luminescence Characteristics of various parameters and presented theoretical assumptions for red-shift of the absorption edge.The last chapter presented the main conclusions of papers and the developping prospect of nitrogen-doped TiO2 films.更多还原