奈米結構之吸收器與發射器

Abstract

自從表面電漿於1958年由實驗證實其存在，相關的研究動能仍未停息直到今日，本論文將描述數種具有表面電漿特性的奈米結構，從吸收器到發射器。由於所提及結構皆選用金為金屬材料，我們將藉由一組介電常數的解析模型了解金在可見光下的光學特性，以推算奈米球與多層膜的色散關係。我們發現一種特殊的吸收機制在奈米核殼粒子裡，因為此奈米球殼的大小大於入射光波長的十分之一，故此吸收機制是經由多個高階模態干涉所形成，光漩渦亦伴隨此吸收機制出現。藉由調整奈米結構的形狀，我們研究兩種週期性結構對表面增強拉曼散射的影響，一種是週期性類三維表面電漿晶體，另一種則是週期性帶角錐倒三角形結構，前者我們藉由形變可以了解破壞共振的結構，後者我們利用改變角錐高度可以得到最好的電場增強效應。當越來越多人研究表面增強拉曼散射的同時，散射光的指向性越來越受到重視，我們將多層金屬環附加在一個偶極子發射器上，不僅於近場增強電場效應，於遠場亦改善了指向性，此外，經由實驗結果也印證了我們的理論設計。

Since the surface plasmon was discovered in 1958, the upward trend in this field does not stop until today. This dissertation demonstrates several plasmonic components from absorbers to radiators. The noble metal gold is selected to be the metallic material in the following designs, therefore, an analytic model of dielectric function for gold is introduced to derive the dispersion relations of some fundamental geometries, such as multilayer structures or core shell nanoparticles. A special mechanism of absorption induced by the core shell nanospheres was found. Because the particle size is larger than the sub wavelength of incident light, the mechanism of absorption can be treated as the result of multi-modes combination and the associated circulation of energy flow is found inside the core shell nanospheres. Two periodic structures were studied for surface enhanced Raman scattering by controlling the geometries to enhance the electric field.. One is the quasi-3D plasmonic crystal and the other is the inverted pyramidal structures with tips. As the development of surface enhanced Raman scattering becomes flourish, the directivity of scattering light is getting attention. Thus, in the final part, the structure of concentric rings for a dipole radiator is proposed. The function of the multi-ring not only enhances the electric intensity of near field but also improves the directivity of scattering light, which is taken from the radiation pattern of far field. Furthermore, the experimental result proves the proposed concept.