表面電漿分裂盤耦合結構的增強法諾共振現象

Abstract

我們提出了結合法諾共振與耦合效應的金屬表面電漿結構-奈米分裂圓盤。透過結構中大扇形在邊界上所形成的四極的電荷分布與小扇形靠近時所引發出的Dark模態以形成法諾共振。透過法諾共振在光學頻譜上的小線寬與耦合效應形成的高強度電場，使該結構能夠適用於生物或化學等感測。 在本論文中，我們主要著重在透過改變奈米分裂圓盤的幾何結構參數優化並增強法共振的現象，包括:角度、結構間距以及分裂原點，使其能夠產生理想的法諾共振譜線。模擬以及實驗結果顯示此結構的法諾共振半高寬、共振波長、電場強度等基本特性與結構的幾何參數有極大相關性。為了評估此結構對環境感測能力以及生物分子感測能力，我們進行了相關的實驗。在環境感測實驗中，透過減小結構間距，因電場強度的提升以及法諾共振半高寬減小，使環境感測的優質能夠有所提升。在生物分子感測實驗中，利用此結構感測牛血清白蛋白與結構之間鍵結，能夠觀察到共39奈米的共振波長變化。透過此研究，我們了解了法諾共振的產生以及對感測能力的影響，這對未來設計各種表面電漿感測器有極大的幫助。

We propose a metal plasmonic structure, split-nanodisk, which combine the Fano resonance and coupling effect. By the quadrupolar like charge distribution of antibonding mode at the edge of major sector induce the quadrupolar dark mode of minor sector and result in the generation of Fano resonance. Due to the narrow line width of Fano resonance and strong electric field enhancement by coupling effect, this structure can be applied to biomolecular or chemical sensing. In this thesis, we focus on enhancing and optimizing the Fano resonance by geometry tuning of split-nanodisk including slice angle, gap size and slice origin shift to generate ideal narrow Fano line shape. The results of simulation and experiment show that the plasmonic properties including line width of Fano resonance, resonance wavelength and electric field intensity are dependent on the structural geometry. In bulk refractive index sensing, by decreasing gap size, the electric field intensity increase and line width of Fano resonance decrease that make figure-of-merit improve. In biomolecular sensing, split-nanodisk structure were applied to detect the binding of protein BSA. We observe total wavelength shift of 39 nm of BSA binding to a MUA-coated gold split-nanodisk structure. By this study, we realize the generation and the influence to sensing ability of Fano resonance. This greatly helps us design of various plasmonic sensor in the future.