具手徵性金奈米結構陣列之圓二色性分析

Abstract

本論文探討二維金膜孔洞陣列結構和三維金奈米螺旋陣列結構的圓二色性 (Circular Dichroism, CD)。第一部分探討橢圓金奈米孔洞陣列的圓二色性，透過改變了橢圓與晶格對稱軸的角度、晶格尺寸、金膜厚度與橢圓展弦比，在穿透、吸收能量和圓二色性上產生的差異；孔洞陣列缺陷分析，該部分延續六方最密堆積的橢圓金奈米孔洞陣列結構，在週期性結構增加不同形狀和尺寸的結構來引入輻射性質，將原本由於Bloch條件而駐留於金膜表面的表面電漿子，透過次級結構的導入與輻射至遠場的能量進行轉換，進而在特定的波長處的穿透能量頻譜產生額外的能帶，將入射的平面波聚焦形成類似點光源的形式，電場分布亦會產生駐留於特定一孔洞的現象；多層銀膜孔洞的部分則探討各個不具手徵性的陣列疊合產生圓二色性和對於品質因子(Figure of Merit, FoM)所造成的影響，多層銀結構造就了更長的孔洞深度使入射波能完整的共振以形成單頻的響應，進而降低FWHM提升FoM。 第二部分探討三維的核殼金奈米螺旋結構的圓二色性和手徵密度(Chiral Density)，三維結構相較於二維孔洞陣列，提供了更多波段良好的圓二色性，透過調整螺線半徑和螺距，分析了其穿透、吸收頻譜和圓二色性的變化，並進一步探討吸收圓二色性與結構手徵密度強度分布的關係。設計上適當的螺線半徑和螺距可以使螺旋結構內外分別產生高強度且相反手徵密度，進而利用此近場增強的效果提升應用端檢測特定旋性生物分子和手徵性藥物分子的訊號。

This thesis explores the circular dichroism (CD) of two-dimensional gold film nanohole arrays and three-dimensional gold nanohelices arrays. The first part investigates the circular dichroism of elliptical gold nanohole arrays. By altering the angle between the elliptical holes and the lattice symmetry axis, lattice size, gold film thickness, and elliptical aspect ratio, differences in transmission, absorption energy, and circular dichroism are observed. The analysis of defects in the nanohole arrays extends the study of hexagonally close-packed elliptical gold nanohole arrays by introducing periodic structures with varying shapes and sizes to induce radiative properties. This modification allows surface plasmon polaritons, which are originally confined to the gold film surface due to Bloch conditions, to convert into radiative energy in the far field through the incorporation of secondary structures. This results in additional energy bands in the transmission energy spectrum at specific wavelengths, with the incident plane wave focusing to form a point source-like effect, and the electric field distribution showing localization within specific nanoholes. The section on multi-layered silver nanohole arrays explores how the stacking of non-chiral arrays induces circular dichroism and its impact on the Figure of Merit (FoM). The multilayer silver structure creates deeper holes, allowing for complete resonance of the incident waves to form single-frequency responses, thereby reducing the full width at half maximum (FWHM) and enhancing the figure of merit (FoM). The second part investigates the circular dichroism and chiral density of three-dimensional core-shell gold nanohelices structures. Compared to two-dimensional nanohole arrays, the three-dimensional structures provide more bands with strong circular dichroism. By adjusting the spiral radius and pitch, the changes in transmission, absorption spectra, and circular dichroism are analyzed. Furthermore, the relationship between absorptive circular dichroism and the distribution of chiral density in the structure is explored. Appropriately designed spiral radius and pitch can create high-intensity and oppositely oriented chiral densities inside and outside the spiral structure. This near-field enhancement can be utilized to improve the detection signals of specific chiral biomolecules and chiral drugs in practical applications.