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SiO2光子晶体的自组装制备及其光子带隙性质研究-方俊-2007

2013年06月17日 11:52 方俊 点击:[]

 

 作者姓名  方俊
 中文论文题名  SiO2光子晶体的自组装制备及其光子带隙性质研究
 外文论文题名  INVESTIGATION OF SELF-ASSEMBLED SILICA PHOTONIC CRYSTALS AND  THEIR BANDGAP PROPERTIES
 论文提交日期  2007-06-24
 学位年度  2007
 中文论文关键词  光子晶体,胶体晶体,垂直沉积法,SiO2胶体球,表面改性,丁二酸,双尺寸分布
 外文论文关键词  photonic crystals, colloidal crystals, vertical deposition method, SiO2 colloidal spheres, surface modification, succinic acid, bimodal size distribution

 

中文论文文摘


    光子晶体是一种具有光子带隙的周期性电介质结构,落在光子带隙中的光将不能传播。光子晶体由于具有独特的调节光子传播状态的功能,成为实现光通讯和光子计算机的基础,是信息功能材料研究的前沿领域。
目前,光子晶体的制备是发展光子晶体的关键,而可见光和近红外波段光子晶体的制备更是难点。将亚微米级单分散颗粒实现三维有序聚集组装成胶体晶体是制备可见光和近红外波段光子晶体的有效方法。
    本论文采用单分散SiO2胶体球作为胶体光子晶体的组成基元,通过丁二酸酯化改性提高SiO2胶体球的表面电荷密度和球间静电排斥作用,运用垂直沉积法在水溶液中自组装得到可见光和近红外波段的SiO2光子晶体,并探讨了具有双尺寸分布SiO2胶体球的成核和生长机理及其组装。通过X射线衍射分析仪(XRD)、傅立叶红外光谱仪(FT-IR)、扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)、Zeta电位、紫外-可见-近红外(UV/Vis/NIR)透射光谱等分析测试手段对制备的材料、胶体晶体的结构与性能及它们之间的关联规律进行了表征和研究。
    利用经典St?ber法,在乙醇介质中,以氨作催化剂,正硅酸乙酯(TEOS)为硅源,通过TEOS的水解和缩聚反应制备单分散SiO2球形颗粒。主要研究了TEOS及催化剂氨水的量对于SiO2胶体球粒径大小和粒径偏差的影响。XRD分析表明所合成的SiO2胶体球为无定形态。FT-IR结果表明SiO2胶体球表面富含羟基,为接枝丁二酸进行化学改性奠定基础。SEM结果显示所合成的SiO2胶体球粒径在292~473nm范围内、粒径相对标准偏差小于5.0%,随氨水量增加,SiO2胶体球的粒径逐渐变大,且粒径偏差减小,同样增加TEOS的量也可以得到粒径大且粒径偏差小的SiO2胶体球。
    为了提高SiO2胶体球的表面电荷密度和球间静电排斥作用,将丁二酸通过酯化反应化学键合到SiO2球表面上。FT-IR和XPS结果证明丁二酸一端的羧基与SiO2胶体球表面的羟基发生了酯化反应。Zeta电位和标准氢氧化钠滴定测试结果显示,经丁二酸表面改性后,SiO2胶体球在水溶液中的Zeta电位从?53.72mV提高到?67.46mV,表面电荷密度从0.19μC/cm2提高到0.94μC/cm2,提高了将近5倍。
    以粒径为292nm和473nm的SiO2胶体球为结构基元,采用垂直沉积法在水溶液中组装可见光和近红外波段的SiO2胶体光子晶体。利用SEM观察胶体晶体的形貌、结构特点和缺陷情况,利用UV/Vis/NIR透射光谱研究胶体晶体的不完全光子带隙效应。讨论了丁二酸改性、悬浊液浓度、胶体球粒径、组装温度、pH值、热处理温度、入射光角度对所得到的SiO2胶体晶体形貌和光子带隙的影响。结果表明:对比未改性的SiO2胶体球,丁二酸改性的SiO2胶体球形成的胶体晶体有序性更好,相应的带隙深且窄;所得到的SiO2胶体晶体为fcc周期结构,表面为(111)晶面,呈正六边形排列,在胶体晶体中存在裂纹、空位、位错等缺陷;胶体晶体的厚度直接依赖于悬浊液的浓度,随浓度增加,胶体晶体的层数相应增加,悬浊液质量分数为0.3%时可得到质量较好的SiO2胶体晶体;胶体球粒径的大小在透射光谱中表现为带隙中心位置的不同,且符合布拉格定律,对于粒径为292nm和473nm的SiO2胶体球,相应的光子带隙位置分别在604nm和1047nm处,而且随着入射光和胶体晶体表面法线方向的夹角变大,光子带隙发生蓝移,说明SiO2胶体晶体的光子带隙为赝带隙;沉积温度和pH值对胶体晶体的影响较大,温度为40℃和pH值为7.0时,可得到最为紧密的六方排列形式;经过热处理后的SiO2胶体晶体结构更为致密,缺陷减少,光子带隙发生蓝移,且变窄和加深。
    在制备单分散SiO2胶体球的反应体系中引入NaCl电解质,发现了SiO2胶体颗粒的双尺寸分布现象。合理的解释了双尺寸分布SiO2胶体颗粒产生的原因,提出了双尺寸分布的SiO2胶体颗粒的成核和生长机理。并利用所得到的双尺寸分布SiO2胶体颗粒在乙醇溶液中自组装得到具有类似立方ZnS结构的SiO2胶体晶体。
    本论文研究工作在以下几方面做出了创新性成果:1)提出了采用丁二酸改性SiO2胶体球以增加其表面电荷密度的新方法;2)在水溶液中自组装制备出密排结构的SiO2胶体晶体并对制备影响因素进行了详细分析;3)制备出具有双尺寸分布的SiO2胶体球并加以组装。

 

外文论文文摘


    Photonic crystals are materials with regular periodicity of dielectric structures, which can create a range of forbidden frequencies called photonic bandgap. Photons with energies lying in the bandgap cannot propagate through the medium. Photonic crystals have the ability to manipulate, confine, and control light, thus provide the opportunities to shape and mould the flow of light for photonic communication technology and photonic computer and become the frontier of functional materials.
    Presently, the fabrication of photonic crystals, especially those in visible or near-infrared region, is the key to the development of photonic crystals. And the most effective way to fabricate photonic crystals with visible or near-infrared bandgap is the self-assembly approach, namely, assembly of the colloidal crystals by monodisperse and sub-micrometer colloidal spheres.
    In this thesis, SiO2 colloidal spheres were prepared for using as building blocks of photonic crystals, and modified with succinic acid in order to enhance their surface charges and electrostatic repulsive forces, then they were self-assembled into photonic crystals in visible or near-infrared region from aqueous colloidal solution by the vertical deposition method, moreover, the preparation and assembly of SiO2 colloidal spheres with bimodal size distribution were studied. The synthesized materials, structures and properties of the SiO2 colloidal crystals and their relationship were analyzed by XRD, FT-IR, SEM, XPS, Zeta potential and UV/Vis/NIR transmission spectra.
    Firstly, SiO2 colloidal spheres were synthesized by hydrolysis of tetraethyl orthosilicate (TEOS) in alcohol-water mixed medium using ammonia as catalyst. Effects of concentrations of ammonia and TEOS on the SiO2 particle size and size deviation were mainly investigated. XRD and FT-IR results respectively show that the prepared SiO2 colloidal spheres are non-crystalline and there are hydroxyl groups on the surface of SiO2 colloidal spheres, which are favorable to surface modification with succinic acid. SEM images indicate that the obtained SiO2 spheres are highly uniform with diameters ranging from 292nm to 473nm and with relative standard deviation less than 5.0%, and when the concentrations of either ammonia or TEOS is increased, the particle size increases and the relative standard deviation decreases.
    After the SiO2 colloidal spheres were prepared by St?ber method, they were modified with succinic acid. FT-IR and XPS results indicate that one end of succinic acid is chemically bonded to the SiO2 spheres through esterification and the other could ionize in water. Zeta potential of the modified SiO2 spheres in water solution is improved from ?53.72mV to ?67.46mV, and surface charge density of the modified SiO2 spheres is enhanced from 0.19μC/cm2 to 0.94μC/cm2.
    Finally, opal photonic crystals with visible and near-infrared photonic bandgap were assembled by vertical deposition method from aqueous colloidal solution using SiO2 colloidal spheres with diameters of 292nm and 473nm as building blocks. The morphology, structure and defects were investigated by SEM images, and the incomplete bandgap properties were confirmed by UV/Vis/NIR transmission spectra. Effects of modification, colloid concentration, particle size, temperature, pH value, sintering treatment and incident angle on the morphology and photonic bandgap properties of the obtained SiO2 colloidal crystals were discussed. The results show that: the succinic acid modified SiO2 spheres can assemble into more ordered structure and the corresponding photonic bandgap is deeper and narrower compared to the unmodified SiO2 spheres; the obtained SiO2 colloidal crystals are fcc structure with each sphere neighbouring six others in a layer and (111) planes parallel to the substrate, and have cracks, dot defects and line defects; the number of colloidal crystals layers is related to the colloid concentration, with colloid concentration increasing, the number of the layers correspondingly increases, and under the concentration of 0.3wt%, SiO2 colloidal crystals with relatively high quality can be obtained; SiO2 colloidal crystals consist of spheres with diameters of 292nm and 473nm have the bandgap at 604nm and 1047nm respectively, which are near to the calculated values by Braag law, and with the incident angle increasing, a blue shift of the photonic bandgap happens, which indicates that the bandgap is incomplete; temperature and pH value have great influence on the assembly of SiO2 colloidal crystals, and under 40℃ and the pH value of 7.0, the most close-packed structure can be obtained; after sintering treatment, there are less defects in the colloidal crystals and the structures are more closed, correspondingly, photonic bandgap has a blue shift and becomes more deeper and narrower.
    Additionly, in this thesis, SiO2 colloidal spheres with bimodal size distribution were prepared by the hydrolysis of TEOS in alcohol-water mixed medium with the ammonia as catalyst when NaCl electrolyte was introduced into the system. A model of nucleation and growth mechanism of SiO2 colloidal spheres with bimodal size distribution was proposed. And then SiO2 colloidal crystal which has the zinc blende structure was self-assembled by vertical deposition method in alcoholic solution using SiO2 colloidal spheres with bimodal size distribution.
    The innovative points of this thesis are as follows: 1) a new method to enhance surface charge on SiO2 spheres via modification with succinic acid was presented; 2) the detailed influences on assembly of SiO2 colloidal crystals from aqueous solution were investigated; 3) the preparation and assembly of SiO2 colloidal spheres with bimodal size distribution were studied.

    

 

 

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