Low-Temperature Synthesis and Optical Properties of Gel and Ceramic Photonic Crystals Made up of High Dielectric Constant Materials

本研究的目的是建立溶胶-凝胶法制备二维TiO_2和BaTiO_3凝胶和陶瓷光子晶体的低温合成方法，并对所得晶体的光学性能进行评价。1)前驱体溶胶溶液的合成：以异丙醇钛、Ti(O-i-Pr)_4、聚乙二醇（PEG：摩尔质量=400）、乙二醇单甲醚（EGMME）为溶剂和水解醇盐的水混合制备TiO_2前驱体溶液，组成为Ti(O-i-Pr)_4: EGMME。H_2O = 1:3:1（摩尔比），并以乙醛钡Ba(OC_2H_5)_2为原料，用同样的方法制备了BaTiO_3前驱体溶液。这些前驱体溶液在Si和MgO衬底上自旋涂覆时，得到了各自材料的无裂纹凝胶膜。2)抗蚀剂模具的制备：首先在Si . More和MgO衬底上采用自旋镀膜的方法制备了1μm左右的抗蚀剂薄膜，然后利用电子束光刻技术在抗蚀剂衬底上形成具有不同气孔半径r和气孔间距（晶格常数）a值的六边形气孔阵列。根据光子带结构的计算，理论上确定了抗蚀剂模的r和a值，以使所制备的光子晶体在可见光区表现出完整的光子带隙。3) TO_2和BaTiO_3凝胶光子晶体的制备；我们成功地在Si和MgO衬底上分别制备了由TiO_2和BaTiO_3前驱体柱的六方阵列组成的二维光子晶体，将前驱体溶胶溶液浇铸到抗蚀模中，干燥，然后用去除剂化学去除抗蚀模。在去除抗蚀模之前，必须完全去除目前方法无法在抗蚀模上形成的gal膜。我们成功地用CF_4/C_3F_8气体干刻蚀法刻蚀了它。4) TiO_2和BaTiO_3陶瓷光子晶体的制备：将前驱体光子晶体在500 ~ 800℃的空气中烧结得到TiO_2和BaTiO_3陶瓷光子晶体。得到的光子晶体没有明显的晶格紊乱，前驱柱几乎没有坍塌，但由于烧制过程中前驱柱的收缩，导致前驱柱的尺寸发生了显著变化。在波长400 ~ 1000nm范围内，分别对具有不同rand a值（r=110nm, a=400nm）、（125nm, 450nm）和（125nm, 500nm）的TiO_2陶瓷光子晶体和具有不同rand a值（a=450nm, rl=0.19）的BaTiO_3陶瓷光子晶体在TE和TM模式下的Γ-Mand f- k0方向进行了TE和TM模式下的光学反射测量，在计算的波长附近，所有光子晶体都观察到不同的反射峰。结果表明，本研究首次成功地制备了光学区具有沿壁发育光子带隙的二维陶瓷光子晶体。少

The objective of this study is to establish a low temperature synthesis method for fabricating two-dimensional TiO_2 and BaTiO_3 gel and ceramic photonic crystals by sol-gel processing using resist molds and also to evaluate the optical properties of the obtained crystals.The obtained results are summarized as follows:1) Synthesis of precursor sol solutions : We prepared a TiO_2 precursor solution by mixing titanium isopropoxide, Ti(O-i-Pr)_4, poly(ethylene glycol) (PEG: molar weight=400), ethylene glycol monomethyl ether (EGMME) as a solvent and water for hydrolysis of the alkoxide to have the composition Ti(O-i-Pr)_4: EGMME : H_2O = 1:3:1 (in molar ratio), and also prepared a BaTiO_3 precursor solution by using the same procedure with barium ethoxide, Ba(OC_2H_5)_2. These precursor solutions gave crack-free gel films of the respective materials when spin-coated on Si and MgO substrates.2)Preparation of resist molds : We first prepared resist films of around 1μm by spin coating on Si … More and MgO substrates, and then formed hexagonal arrays of air holes with various values of air holes radius r and spacing between holes (lattice constant) a in the resist alms using electron beam lithography. The values of r and a of the resist molds produced were theoretically determined from photonic band structure calculations to allow the photonic crystals to be fabricated exhibit complete photonic band gaps in the visible region.3)Fabrication of TO_2 and BaTiO_3 gel photonic crystals : We succeeded in fabricating two-dimensional photonic crystals consisting of hexagonal arrays of TiO_2 and BaTiO_3 precursor pillars on Si and MgO substrates, respectively, by casting the precursor sol solutions into the resist molds, drying, then followed by removing the resist molds chemically with a removal agent Prior to the removal of resist molds it is necessary to remove completely a gal film that the present method unavadably form on the resist mold, and we succeeded in ding it with a dry etching technique using CF_4/C_3F_8 gas.4) Fabrication of TiO_2 and BaTiO_3 ceramic photonic crystals : TiO_2 and BaTiO_3 ceramic photonic crystals were obtained by sintering the precursor get photonic crystals at temperatures of 500 to 800℃ in air. The obtained photonic crystals showed no appreciable lattice disorder of the crystals, with little collapse of the precursorpillars, though significant changes in the size of the pillars due to their shrinkage during firing were observed5) Evaluation of optical properties of the obtained photonic crystals : Optical reflection measurements in the wavelength range of 400 to 1000nm were carried out for TiO_2 ceramic photonic crystals with different rand a values of (r=110nm, a=400nm), (125nm, 450nm) and (125nm, 500nm) and for a BaTiO_3 ceramic photonic crystal with a=450nm and rl=0.19 in the Γ-Mand f-Kdrections of the crystals for both TE and TM modes, in which distinct reflection peaks were observed for all the photonic crystals at around wavelengths calculated. The results dearly demonstrate that 2D ceramic photonic crystals with wall-developed photonic band gaps in the optical regime have been successfully fabricated for the first time in this study. Less