金屬奈米領結形孔洞-襯墊結構之光學感測特性研究

Abstract

我們在本研究中提出一種新穎的侷域性表面電漿共振金屬奈米領結型孔洞-襯墊結構，本結構的領結型孔洞結合了耦合與lightning Rod效應，造就了極為集中於結構間隙的侷域性表面共振電場分布。此外，所提出的結構亦具有極簡化的製程方法，讓本結構適用於製作在光纖上，並可作為生物、化學等感測應用，在實驗與模擬上，我們發現此結構主要具有兩種模態，基本與高階模態；其中基本模態由於較強的電偶極矩可產生較強的侷域性表面電漿共振場強，而針對該模態我們也利用改變結構參數來探討電漿模態，包括間隙距離與結構周長對於共振波長與電荷分布之間的關聯性。此外，我們亦針對本文所提結構結構在環境感測、主動可調式共振波長、以及粒子光學捕捉上的潛力進行研究。在光學折射率感測上，我們取得了非常高的折射率感測靈敏度達1620nm/RIU；而我們也透過將結構埋於PDMS中，以拉伸方式達成了主動可調式共振波長的功能；在粒子捕獲的模擬中，透過具有間隙為30奈米的BAPPU結構，可對20奈米的聚苯乙烯粒子可產生高達7989 pN/W的光學箝制力，未來期望我們的結構能製作於光纖上，達到其多功能光學奈米元件的應用。綜上所述，我們相信本文所提出的BAPPU結構可以實現多功能的光纖探針與光學處理器。

We propose a novel metallic nano-bowtie aperture with projected pad underneath (BAPPU) with localized surface plasmon resonance (LSPR). In this structure, the bowtie aperture induces strong near-field in the gap region owing to coupling effect and lightning effect. In addition, our proposed BAPPU structure can be realized via simplified fabrication process, which make fabricating it on fiber-tip possible and useful in biologic and chemical sensing. In experiments and simulations, we found that there are two significant LSPR modes, fundamental and high order modes, in BAPPU structure. The fundamental mode processes stronger field intensity because of its powerful dipole moment. In addition, for the fundamental mode, via geometry tuning, we also investigate the dependence of gap distance, length, and width on resonance wavelength and charge distributions. Furthermore, we also investigate the capabilities of BAPPU in optical sensing, wavelength tuning, and nanoparticle trapping. In optical index sensing, high sensitivity of 1620 nm/RIU is observed. 1620nm/RIU；In addition, by embedding bowtie pad within PDMS, wavelength tuning via stretching is achieved. In the simulation of optical trapping via BAPPU with 30 nm gap distance, the optical force is as high as 7989 pN/W for trapping 20 nm polystyrene particle. Therefore, we believe our proposed BAPPU can achieve versatile on-fiber probe and optical manipulator.