陽極氧化鋁表面增益拉曼基板之訊雜比優化

Abstract

結合陽極氧化鋁模板與金屬顆粒球設計之表面增強拉曼散射(SERS)基板，過去經常利用金屬奈米顆粒球的電偶極共振偶合來增強近場，來產生所謂的熱點來增益拉曼訊號。然後，在增強表面電場的同時，穿透進金屬顆粒球的電場也隨之增高，造成在測量時，往往會得到較高的連續背景值，而使得整體訊號的訊雜比降低。因此，在本論文中，我們研究了一系列不同直徑及間隙大小的銀奈米顆粒球陣列之近場特徵，以及探討其對SERS訊號之近場增益、背景值與訊雜比之局部效應與整體平均值影響。接著，為進一步達到訊號增益與訊雜比的提升，我們探討了金屬顆粒球陣列結合週期性光柵的雙共振SERS基版，系統性的分析週期性光柵的高度、週期以及氧化鋁的厚度以優化金屬顆粒球之侷域性表面電漿共振與週期性光柵產生之表面電漿共振的耦合，相較於平面型SERS基版，此雙共振基版成功提升SERS訊雜比達2.7倍。

In the past, the anodic aluminum oxide template combined with metallic nano-particles have been one of popular designs for the enhancement of Raman scattering signal. Generally, the coupling of the electric dipole resonances among nanoparticles was applied to create strong near-field intensity, the so-called “hot spot” for surface-enhanced Raman scattering (SERS) substrate. Despite of SERS signal enhancement, a broadband background continuum, arisen from the penetration field inside the nanoparticles, was commonly observed and deteriorates the signal-to-background (S/B) ratio. In this thesis, we thoroughly investigate the near-field features of the plasmonic resonances by changing the diameters of silver nanoparticles and gap size. Their effects on the SERS enhancement, background value and S/B ratio were studied by considering both the local field amplification and ensemble-average effect. In addition, a double resonance substrate comprising of silver nanoparticles on periodic gratings was developed to further enhance both the near-field enhancement and the S/B ratio. A systemic study of the effect of the grating modulation depth, period, and the thickness of anodic aluminum oxide were performed to optimize the coupling of localized surface plasmon and surface plasmon polaritons for achieving higher S/B ratio. The double resonance substrate reaches 2.7 times enhancement of S/B ratio than the planar SERS substrate.