奈米顆粒之製備與其應用於光子晶體與電磁波屏蔽之研究

Abstract

近年來，因為奈米材料與奈米結構擁有許多特殊與極好的性質能應用於許多不同之領域，而引起大家的注意與熱烈討論，因此有許多的研究就是主要著重於設計與如何控制奈米材料於製備奈米結構之研究。本論文主要著重於奈米材料(高分子或二氧化矽顆粒以及奈米銀顆粒或奈米銀線)之製備，並且利用這些材料應用於製備光子晶體結構與電磁波屏蔽材料。 在製備光子晶體結構上，首先利用乳化聚合法、無乳化聚合法與懸浮聚合法合成粒徑均一之高分子(聚苯乙烯或聚甲基丙烯酸甲酯)顆粒為模板，於基材上可排列成二維或三維光子晶體之結構，改變不同之顆粒粒徑可得相對應之光能量禁帶，再藉由溶膠凝膠法導入無機之二氧化矽前驅物，而後以階段升溫的方式將高分子模板移除可得到二維或三維規則排列之多孔性材料。由實驗結果可以發現，調配適當的無機物前驅物濃度可以得到二維或三維規則排列之多孔性材料。 除了高分子模板外，二氧化矽粒子也同樣能推疊成排列規則之光子晶體結構，而為了能有效的控制二氧化矽粒子之排列，在此利用二氧化矽包覆四氧化三鐵奈米粒子形成粒徑均一之磁性顆粒(粒徑為700nm)為模板，先以共沉澱法製備四氧化三鐵奈米粒子，再利用溶膠凝膠法以二氧化矽包覆四氧化三鐵奈米粒子，以此粒徑均一之磁性複合粒子為模板，於外加磁場的引導下，可使粒徑均一之磁性粒子整齊的排列於基材上而得三維光子晶體之結構，在光譜測量結果可以發現，所得之磁性光子晶體結構其光能量禁帶為1620nm。 在製備電磁波屏蔽材料上，利用奈米銀顆粒包覆二氧化矽粒子形成複合顆粒，先以溶膠凝膠法合成粒徑均一之二氧化矽顆粒，再與帶硫醇官能基之矽烷反應，將二氧化矽顆粒表面改質成硫醇官能基，再經由氧化還原反應將奈米銀顆粒沉積於二氧化矽表面。藉由調整不同的醇類反應系統，可得不同粒徑之二氧化矽顆粒；改變二氧化矽表面硫醇之改質程度與系統中硝酸銀之添加量，可得不同大小之奈米銀顆粒(2.9 ~ 51.5nm)。將銀包覆之二氧化矽複合粒子塗佈於基材上測試其電磁波屏蔽效果，由實驗中可發現隨著銀含量的提升可使電磁波屏的蔽效果隨之提升，在電磁波頻率為761MHz下其電磁波屏蔽效果可達到32.5dB。 為製備出更佳之電磁波屏蔽材料，在此導入高長徑比之奈米銀線與紫外光可硬化樹脂混合後形成紫外光可硬化奈米銀膠，並利用微影製程得到含銀之一維圖案而應用於電磁波屏蔽。奈米銀顆粒為利用多元醇法在乙二醇下將銀還原成銀種子，藉由添加更多的銀離子與高分子立體穩定劑使其長成線狀或是顆粒狀。奈米銀顆粒和紫外光可硬化樹脂混合後可得紫外光可硬化奈米銀膠，經微影製程後可得負型光阻之圖案。改變不同之奈米銀顆粒型態(球狀或是線狀與球狀混合)與微影圖案，探討對於電磁波屏蔽效果之影響，由實驗中可發現隨著銀含量的提升可使電磁波屏蔽效果隨之提升，並且隨著圖案密度的改變可影響最大屏蔽值之電磁波頻率。經過高溫燒結後，可移除有機高分子留下無機銀顆粒而使圖案線寬變窄，電磁波屏蔽效果可因此大幅的提升。本研究中，僅須添加12wt%的奈米銀線狀與球狀的混合物，就能得電磁波屏蔽效果達30dB之材料。在添加銀含量28wt%時，經過燒結後的試片在414MHz下，電磁波屏蔽效果可達到73dB。

In recent decades, the interests in nanomaterials and nanostructures have been growing rapidly as a result of their distinctive and fascinating properties as well as unique applications in diversified fields. Many researches have addressed on the design and controlled fabrication of nanostructured materials prepared from nanomaterials. In this dissertation, we focus on the preparation of nanomaterials (polymeric and silica microspheres as well as silver nanospheres and nanowires) and their corresponding applications to photonic crystals (PCs) nanostructures and electromagnetic interference (EMI) shielding materials. In the field of PCs nanostructures, we proposed a rapid and feasible method to fabricate two-dimensional (2-D) and three-dimensional (3-D) PCs structures using monodisperse polymeric microspheres as the templates. The approaches toward the creation of their corresponding inversed structures are also described. The inversed structures were prepared by subjecting an introduced silica source to a sol–gel process; programmed heating was then performed to remove the template without spoiling the inversed structures. Thus, 2-D and 3-D PCs and their corresponding highly-ordered inversed multilayer or monolayer structures were developed on the substrate. Besides polymer microspheres, monodispersed silica microspheres could also be prepared and utilized to construct the PCs structures. In order to control the array of silica colloids, we also synthesized monodisperse SiO2 coated magnetic Fe3O4 (SiO2/Fe3O4) microspheres to fabricate magnetic PCs. The magnetic SiO2/Fe3O4 microspheres with a diameter of 700 nm were synthesized in the basic condition with ferric sulfate, ferrous sulfate, tartaric acid and tetraethyl orthosilicate (TEOS) in the reaction system. Monodisperse SiO2/Fe3O4 superparamagnetic microspheres have been successfully used to fabricate PCs under the existing magnetic field. The photonic bandgap of the 700nm SiO2/Fe3O4 magnetic PCs was observed at 1620nm. In addition, we also developed the following nanomaterials: silver-silica composites nanoparticles, silver nanoparticles (Ag NPs) and their applications of EMI shielding materials. The Ag NPs have been immobilized onto silica microspheres through the adsorption and subsequent reduction of Ag+ ions on the surfaces of the silica microspheres. The neat silica microspheres that acted as the core materials were prepared through sol–gel processing, then their surfaces were functionalized using 3-mercaptopropyl trimethoxysilane (MPTMS). The average particle size of the obtained Ag NPs on the silica microsphere was found to be controllable (ranging from 2.9 to 51.5nm) by adjusting the ratio of MPTMS/TEOS and the amount of AgNO3. The silver-silica composites microspheres exhibited an EMI shielding effectiveness (SE) of 32.5 dB at 761 MHz. To improve the EMI SE, we prepared a UV-curable silver nanowire paste comprising a UV-curable resin, photoinitiators, and Ag NPs (nanowires and nanospheres), which was obtained from the polyol process using silver nitrate as the Ag source, ethylene glycol as the solvent and reducing agent, and polyvinylpyrrolidone (PVP) as a polymeric stabilizer that guided the growth of the Ag nanowires. Various patterns of Ag NPs on glass substrates which was obtained using the UV-curable Ag pastes and lithography processes were examined for their use as EMI shielding materials. The electromagnetic wave SE of a pattern prepared using 28% Ag NPs reached 41.3 dB at 780.7 MHz. After sintering, its value increased to 73 dB at 413.8 MHz. The effects on the SE of varying the pattern shape and the content of Ag NPs are also discussed.