【作者】 李强；

【导师】 辜敏；

【作者基本信息】 重庆大学 ， 安全技术及工程， 2011， 博士

【摘要】 TeOx基非线性光学薄膜材料具有优良的非线性光学性能,在光通讯、光计算机、光信息处理等方面具有良好的应用前景。电化学-溶胶凝胶法制备薄膜结合了溶胶凝胶法和电沉积法的优势,能够制备出结构和性能优异的复合薄膜材料。本论文以TeO₂-SiO₂复合溶胶作为电解液,利用电化学-溶胶凝胶法在ITO导电玻璃基底上制备了Te/TeO₂-SiO₂复合薄膜;该薄膜经过热处理制备出了α-TeO₂-Te/TeO₂-SiO₂复合薄膜;采用Z-scan方法研究了这两种薄膜的三阶非线性光学性能。以正硅酸乙酯和异丙醇碲为先驱体在真空手套箱中成功制备出了澄清透明的TeO₂-SiO₂复合溶胶,而且溶胶在空气中能长期保持稳定,为电化学制备薄膜提供了基础。采用循环伏安、Tafel曲线、交流阻抗电化学方法研究了在TeO₂-SiO₂复合溶胶中制备薄膜的机理。循环伏安结果表明,TeO₂-SiO₂体系的电化学诱导溶胶凝胶过程中包含了Te的电沉积:在析氢电位下,阴极表面区域pH值升高的诱导作用使得在电极表面生成了TeO₂-SiO₂复合凝胶薄层;与此同时发生了Te的电沉积,使Te共沉积于TeO₂-SiO₂薄膜中,从而形成Te/TeO₂-SiO₂薄膜。采用Tafel曲线测试了复合溶胶体系中的Te电沉积过程的动力学参数,其交换电流密度为9.66×10-7 A-cm-2,传递系数α=0.149。电化学阻抗谱显示在阴极电位下电极表面能够生成薄膜,电化学阻抗谱中存在的较大弥散效应表明制备的薄膜是镶嵌结构。SEM/EDX表征结果表明:采用恒电位法制备的Te/TeO₂-SiO₂复合薄膜中镶嵌了大量Te单质颗粒,其粒径为100 300 nm。薄膜中的Te/Si比值随沉积电位和沉积时间不同而变化,在中间电位（-0.8 V附近）处Te/Si比值最高并且Te/Si比值随沉积时间相对较稳定;而在较正（-0.1 V, -0.4 V）和较负电位（-1.5 V）下Te/Si比值较低;在较正和较负电位下,随着沉积时间延长,薄膜中的Te/Si比逐渐升高。随着沉积时间延长,薄膜中的Te颗粒逐渐长大,颗粒形状由圆球形逐渐长大成六棱柱状。XRD、TG结果表明,制备的Te/TeO₂-SiO₂复合薄膜经过热处理后,由于Te颗粒在空气中部分被氧化成α-TeO₂,从而可得到α-TeO₂-Te/TeO₂-SiO₂复合薄膜。采用Z-scan法测试了薄膜的非线性折射系数、非线性吸收系数和三阶非线性极化系数。制备的薄膜都属于自散焦、饱和吸收材料,Te/TeO₂-SiO₂复合薄膜的三阶非线性极化系数χ（3）达到10-14 （m/V）2（或10-6 esu）,α-TeO₂-Te/TeO₂-SiO₂薄膜也具有同等量级的非线性极化系数,两者都远高于碲酸盐玻璃类材料。凝胶薄膜中的TeO₂和镶嵌其中的α-TeO₂都具有[TeO4]单元的三角双锥结构,这是产生高非线性极化的原因之一,此外,薄膜中镶嵌的具有良好导电性的Te晶体颗粒也起到了重要作用:一方面,颗粒表面等离子体的共振吸收对非线性光学效应有巨大的放大效果;另一方面,Te颗粒中的自由电子在电磁场作用下发生定向移动,生成强的电偶极子,从而产生很强的极化。更多还原

【Abstract】 Due to the excellent optical nonlinearity, TeOx based nonlinear optical material thin films have promising applications in optical communication, optical computer and optical information processing etc. For the preparation of their thin film, electrochemistry-sol-gel method takes the advantages of both sol-gel and electrodeposition methods, which help to fabricate high quality thin films of the composite materials. In this dissertation, using TeO₂-SiO₂ composite sol as electrolyte, Te/TeO₂-SiO₂ composite thin films was successfully prepared on the ITO glass by the electrochemical sol-gel method.α-TeO₂-Te/TeO₂-SiO₂ composite films were further obtained by thermo treatment of Te/TeO₂-SiO₂ composite thin films. In addition, third-order optical nonlinearities of as-prepared two kinds of composite films were studied by Z-scan technique.Firstly, TeO₂-SiO₂ composite sol was successfully prepared by using TEOS and Te（OPri）₄ as precursors. The as-prepared TeO₂-SiO₂ composite sols are very stable in ambient condition for long time, which make it easy for preparation of thin films by electrodeposition. The deposition mechanism of the composite film was then studied by using the cyclic-voltammetry （CV）, Tafel plot and AC impedance techniques. The CV measurements showed that electrochemically induced sol-gel process included the electrodeposition of Te. The increase of local pH value in the anode area due to the evolution of hydrogen resulted in the formation of TeO₂-SiO₂ composite films. Because of the simultaneous electrodepositon Te occurred, Te/TeO₂-SiO₂ composite film finally formed. The Tafel plot was used to study the kinetic parameters of the deposition of Te, which showed the exchange current density i0 = 9.66×10^-7 A-cm^-2,and transfer coefficientα=0.149. Electrochemical AC impedance studies showed that the composite film could be formed in the cathodic potential range. The obvious dispersion effect in the AC impedance spectroscopy indicated the as-prepared thin films were of mosaic structure.The morphology and the composition of Te/TeO₂-SiO₂ composited films were then studied by scanning electronic microscope （SEM） and energy dispersive X-ray spectroscopy （EDS） techniques. It was shown that Te particles with size of 100 to 300 nanometers were uniformly embedded in the as-prepared composited films. The EDX measurement showed that the Te/Si ratio in the composite films depended on deposition potential and time. High Te/Si ratio appeared at potentials about -0.8 V was high and relatively stable. However, when the potentials were more positive （-0.1 V and -0.4 V） or more negative （-1.5 V）, the values of Te/Si ratio decreased. However, its value increased with the increase of deposition time. With the deposition time prolonging, the Te particles grew larger, and their shapes changed from spherical shape to hexagonal prism. XRD and TG measurements showed that Te particles were partially oxidized toα-TeO₂ during the thermo treatment in air, resulting in the formation ofα-TeO₂-Te/TeO₂-SiO₂ composite films.The nonlinear refractive index （γ）, nonlinear adsorption coefficient （β） and third order nonlinear susceptibility （χ（3）） of composite films were tested by Z-scan technique. It was found both composite films belonged to self-defocused and saturated absorption materials.χ（3） of Te/TeO₂-SiO₂ composite films reached 10-14 （m/V）2 or 10-6 esu, and that ofα-TeO₂-Te/TeO₂-SiO₂ composite films are in the same order, which was much higher than that of tellurite glass.Both TeO₂ andα-TeO₂ embedded in the thin film consists of [TeO₄] units with trigonal bipyramid structure, which are the source of large nonlinear effect. In addition, the good conductivity of Te particles may also play important role in the excellent nonlinear property. On the one hand, the surface plasmon resonance absorption of Te particles may greatly enhance third-order nonlinearities due to the giant amplification of local electric field. On the other hand, there are a great amount of free electrons on/in metal particles surfaces, which move directionally under electromagnetic field and form strong electric dipole, resulting in strong polarization.更多还原