【作者】 田建军；

【导师】 褚君浩； 杨平雄；

【作者基本信息】 华东师范大学 ， 微电子学与固体电子学， 2012， 博士

【摘要】 近年来,二氧化钛(Ti02)由于在很多方面实际的和潜在的应用而备受关注。许多研究表明混晶Ti02(含有锐钛矿相和金红石相)具有比锐钛矿相更高的活性,而且对混合介质光学性质的研究能为制备渐变折射率材料提供借鉴,所以对混晶Ti02的制备和物性研究显得很有意义。混晶Ti02可以通过控制锐钛矿相向金红石相的转变获得。许多因素影响着Ti02从锐钛矿相到金红石相的转变(以下简称相变),如反应气氛、退火温度、颗粒尺寸、退火时间和掺杂等。掺杂对Ti02相变的研究虽然很多,但是还存在一些问题,例如杂质对相变的影响和机制还存在争议；许多研究是以粉体为研究对象,而对Ti02薄膜中的相变研究较少；混晶Ti02薄膜的光学性质的研究也较少等。在本文中,我们用溶胶凝胶法制备了Ti02薄膜、掺杂Ti02薄膜、BaTiO3薄膜和BaTiO3/doped-TiO2/LaNiO3多层薄膜,开展了一些工作,取得了一些成果,主要内容如下：1.石英衬底上Ti1-xCoxO2(0≤x≤0.1)薄膜(金红石相)的光学性质研究。实验发现,随着Co掺杂的增加,光学禁带宽度先增加后减小,这是由于光学禁带宽度增加和光学禁带宽度减小两种机制的竞争引起的。X射线衍射(XRD)结果表明所有薄膜是金红石相；原子力显微镜(AFM)结果表明,随着Co的增加,晶粒变小,薄膜表面变得致密和平滑；随着Co的增加,金红石相的主要Raman模式峰位向低频移动；在透射光谱中发现,随着Co掺杂的增加,薄膜的吸收边先“蓝移”后“红移”；根据Tauc law得到光学禁带宽度(以下简称禁带宽度),其值在3.10和3.26eV之间变化,在Co掺杂为0.03左右时禁带宽度达到最大值为3.26eV左右；用Swanepeol方法对透射光谱处理得到膜的厚度、折射率,折射率随着Co掺杂的增加而增加；由于Co掺杂引起薄膜中的压应力增加,晶粒尺寸效应以及金红石相Ti02的减少而促使禁带变宽；另一方面,Co掺杂引起带隙中的杂质带和缺陷能级而使带隙变窄,这两种机制的竞争导致了带隙先增加后减小2.Si衬底上Co、Ni和Fe掺杂TiO2薄膜的制备和相变研究。Co、Ni和Fe都加速了Ti02薄膜的相变,金红石相含量随掺杂的增加呈”s”形变化。相同掺杂量时,Co掺杂Ti02薄膜的相变激活能最小,Fe掺杂Ti02薄膜的相变激活能最大。利用XRD和Raman光谱研究Ti02薄膜中的相变。首先研究了退火温度、退火时间和旋涂层数对Ti02薄膜相变的影响,三个因素都可以加速相变。接着研究了Co、Ni和Fe掺杂Ti02薄膜中的相变,三种掺杂都能够加快相变,随着掺杂量的增加,金红石相含量先是缓慢增加,接着快速增加,然后又变缓,即变化呈现“S”形；掺杂引入的氧空位以及晶格畸变使相变激活能降低,因此掺杂加速了相变。然后比较了相同含量的Co、Ni和Fe掺杂对Ti02薄膜相变的差异,Co掺杂对相变的加速大于Fe和Ni掺杂,而Ni掺杂对相变的加速大于Fe掺杂,这是由于掺杂离子的半径和化合价的差异引起的。最后研究了薄膜表面形貌随掺杂量的变化。AFM结果显示随着掺杂增加,薄膜的表面首先逐渐变得粗糙,接着变得平整,然后又变得粗糙,这可能与相变过程中锐钛矿相和金红石相的晶格膨胀和收缩有关。3.BaTiO3/Ti0.9Co0.1O2/LaNiO3(BTO/TCO/LNO)多层薄膜的制备和研究。实验发现,TCO的存在可以明显降低介电损耗。首先研究了600、650、700和750℃退火温度对Si衬底上BaTiO3(BTO)薄膜的结构和形貌的影响,AFM结果显示退火温度升高,钙钛矿BTO结晶更好,但750℃退火的薄膜表面因大颗粒出现而变粗糙；采用椭圆偏振光谱研究了不同退火温度对BTO薄膜光学性质的影响；介电函数实部随光子能量的增加先增加后减小；在光子能量小于禁带宽度的区域,介电函数的虚部几乎是零,当光子能量大于光学禁带宽度,随着光子能量的增加介电函数的虚部快速增加,然后又变为缓慢增加；随着退火温度升高,BTO的禁带宽度从4.21eV减小到3.69eV,这可能与温度升高引起的晶粒变大和氧缺陷增加有关。接着研究了BTO/LNO薄膜和BTO/TCO/LNO薄膜的电学性质。与BTO/LNO薄膜相比,复合薄膜的剩余极化没有很大的变化,但复合薄膜的矫顽电压增加和介电损耗降低。TCO的位置对多层薄膜的性能有很大影响,BTO/TCO/LNO薄膜的介电损耗最小4. Co、Ni和Fe掺杂Ti02混晶薄膜的光学性质。掺杂Ti02薄膜的介电函数实部和虚部随光子能量的变化规律是一般介电材料的色散行为。随着掺杂的增加,禁带宽度先是缓慢减小,接着快速减小,然后又变为缓慢减小,这是一个与Ti02相变有关的现象。首先利用透射光谱研究了石英衬底上Ni掺杂Ti02混晶薄膜的光学性质,获得了紫外-近红外区域的介电函数、禁带宽度和薄膜厚度；介电函数实部随着光子能量的增加先增加后因为Van Hove奇点的存在而减小；介电函数的虚部在光子能量小于禁带宽度的区域几乎是零,随着光子能量增加到大于禁带宽度,介电函数的虚部快速增加,然后又变为随光子能量缓慢增加；随着Ni掺杂的增加,禁带宽度从3.65eV缓慢变为3.64eV,接着快速减小为3.45eV,然后又缓慢减小,这与薄膜中相的成分有关。然后对Si衬底上Co、Ni和Fe掺杂Ti02混晶薄膜进行了椭圆偏振光谱研究,得到了薄膜的厚度、介电函数和禁带宽度；介电函数随光子能量的变化关系和禁带宽度随掺杂量的变化关系同石英衬底上Ni掺杂Ti02混晶薄膜的结果是相似的。更多还原

【Abstract】 In recent years, Titanium dioxide (TiO2) has been intensively studied because of its actual and potential application in many fields. Many studies show that the mixed crystalline TiO2with anatase and rutile phase (M-TiO2) has higher activity than anatase phase, and study on optical properties of mixed media is beneficial to the preparation of the graded-index films, so a study on the M-TiO2is very meanful. The M-TiO2may be fabricated by controlling anatase to rutile phase transformation (ART). Many factors influence the ART, such as atmosphere, temperature, grain size, time, and dopant. The influence of dopant on the ART has been widely investigated; however, the mechanism of dopant catalyzing the ART is disputed. In addition, many studies have focused on the ART of powders TiO2, whereas very limited research has been reported regarding the ART in Tio2films and optical properties of M-TiO2films. This is detrimental to the research and application of TiO2. In this study, metal ion doped TiO2(MI-TiO2) films were fabricated by sol-gel method, and influence of dopant on the ART and optical properties of M-TiO2films were investigated and discussed. Additionally, BaTiO3film and BaTiO3/(rutile MI-TiO2) multilayer films were fabricated and studied. The main work and results are as follows:1. Optical properties of rutile Ti1-xCoxO2films (0≤x≤0.1) on quartz substrates. The OBG first increase and then decreases with higher Co content, reaching its maximum value when x is about0.03. The competition between increasing and decreasing mechanisms of OBG leads to the phenomena.X-ray diffraction (XRD) pattern indicate all films are rutile phase. Atom force microscope (AFM) results show that with increasing Co content, surface of the films becomes smooth and compact. Raman spectra indicate Raman bands slightly shift low frequency with increasing Co content. It can be seen from transmittance spectra that the fundamental absorption edge first shows the blue shift and then the red shift. According to Tauc’s law, the optical band gap (OBG) was got from transmittance spectra. The OBG varies between3.10and3.26eV. The OBG increase and then decreases with higher Co content, reaching its maximum value when x is about0.03, which was not reported by other groups. Refractive index and thickness of Ti1-xCoxO2films were obtained by fitting transmittance spectra with Swanepoel method. Refractive index value increases with increasing Co content. Decrease of grain size, compressive stress, and reduction of rutile TiO2increase OBG; and defect and impurity decrease the OBG. The competition between increasing and decreasing mechanisms of OBG leads to the strange change of OBG.2. Fabrication and the ART of MI-TiO2films on Si substrates. Co, Ni and Fe doping catalyze the ART. The evolution of rutile content with dopant content is an "S" shape. At the same dopant content, the active energy of the ART of Co-doped TiO2film is the least.XRD results show that annealing temperature, annealing time and spin-coating layers catalyze the ART of TiO2films. XRD and Raman results indicate that Co, Ni and Fe doping catalyze the ART. With increasing dopant content, rutile content first increases slowly, then quickly, and finally slowly again, i.e. the evolution of rutile content with dopant content is an "S" shape. The doping decreases the active energy of the ART due to oxygen vacancies and lattice deformation, and then catalyzes the ART. By comparison of influence of Fe, Co and Ni doping on the ART, Co’s accelerating effect is the best and Fe’s effect is the worst. This may be related to difference between ion radius and valence of doped ions. AFM results show that with increasing dopant content, the surface of the films first become rough and then smooth, finally rough again, which may be related to the expansion and shrinkage of anatase and rutile unit cells.3. Study on BaTiO3/Ti0.9Co0.102/LaNiO3(BTO/TCO/LNO) multilayer film. The existence of TCO layer is good for decreasing dielectric loss.BaTiO3films (BTO) were deposited on Si substrates, and annealing temperature was600,650,700and750℃, respectively. AFM results indicate that with increasing temperature, BTO with perovskite crystallizes well, but the surface of BTO at750℃becomes rough due to big grain. The optical properties of BTO in the wavelength of visible and ultraviolet were investigated by spectroscopic ellipsometry technique (SE). With increasing temperature, OBG decreases from4.21eV to3.69eV due to the increase of grain size and oxygen vacancies. BTO and BTO/TCO films were deposited on LaNiO3(LNO) substrates. Compared with pure BTO thin films, the remnant polarization of multilayer films had no obvious variety, but the coercive voltage of multilayer films had great increase. The dielectric loss of multilayer films was lower than that of pure BTO thin films. A sandwich structure like BTO/TCO/LNO has the smallest dielectric loss.4. Optical properties of MI-TiO2mixed crystalline films. With increasing dopant content, OBG first decreases, then quickly decrease and gradually decrease again in the end. This may be related to phase composition of the MI-TiO2films.Firstly, dielectric function, OBG and thickness of Ni-doped TiO2films on quartz substrates at UV-visible range were investigated by using the transmittance spectrum technique. In general, with increasing photon energy, the real part of dielectric function increases and gradually nears the maximum, and then decreases due to the Van Hove singularities. And the imaginary part of dielectric function nears to zero in the transparent region and sharply increases further increasing photon energy in the absorption region. With increasing Ni content, OBG slowly decrease from3.65eV to3.64eV, then quickly decrease to3.45eV, and gradually decrease again in the end. This may be related to phase composition of the Ni-doped TiO2films. Secondly, dielectric function, OBG and thickness of MI-TiO2mixed crystalline films were investigated by SE. The evolution of dielectric function with photon energy and the change of OBG with dopant content are similar to those of Ni-doped TiO2films.更多还原