週期性奈米天線之角落半徑效應及表面抗反射結構應用於表面增強拉曼散射

Effects of Corner Radius on Periodic Nanoantenna and Anti-reflection Textured Structures for Surface-enhanced Raman Spectroscopy

趙柏凱(Bo-Kai Chao)

指導教授 ： 薛承輝

國立臺灣大學/工學院/材料科學與工程學研究所/博士(2016年)

https://doi.org/10.6342/NTU201610206

摘要

本研究共分為兩個主題。第一部分主要討論週期性奈米天線中角落半徑效應對表面增強拉曼光譜的影響。角落半徑的概念可使用於在電子束微影製程中，由於有效波束加寬在結構角落所造成的製程限制。本研究的主要目的為探討角落半徑對三種不同結構(領結型、正四邊形對、正五邊形對)，其電磁場增益效果與共振波長的影響。在利用實際製備的金領結型奈米結構中，由於侷域表面電漿共振產生的表面增強拉曼光譜，其增益因子可利用拉曼光譜以及時域有限差分法進行探討。經由模擬而得到的增益因子對角落半徑的影響與實驗相符，並可利用冪次法則關係進行擬合。此外當角落半徑增加時，最大共振波長產生藍移的現象，其原因為電荷集中的分布範圍擴大。對於其他的正多邊形對結構而言，角落半徑取代內角角度而成為電磁場增益效果的主要影響因素，其原因為表面電荷傾向侷域在角落。各別週期性正多邊形對奈米結構，其共振波長變化的微分與間隙尺寸和角落半徑的乘積也可利用冪次法則關係進行擬合。
本研究第二部分，主要利用濕式蝕刻法及島狀微影技術製備鍍有奈米金顆粒之高表面積及低反射率的表面增強拉曼基板，其光學性質可利用時域有限差分法進行探討並與積分球反射率及暗場散射光譜的量測結果相符。經過原子力顯微鏡的量測，金字塔奈米柱結構擁有相當大的表面積，並造成光源的多次反射，兩者皆對表面增強拉曼光譜的增益效果提供幫助。擁有金字塔奈米柱結構的表面增強拉曼光譜基板與平面金薄膜的基板相比，可提供2個指數以上的增益幅度。雖然表面增強拉曼光譜的訊號在不同量測位置的增益強度不一致，但整體而言，擁有金字塔奈米柱結構的表面增強拉曼光譜基板較擁有其他結構的基板其增益較果為佳。

關鍵字

角落半徑 ； 電漿子學 ； 時域有限差分法 ； 表面增強拉曼散射 ； CsCl 奈米島狀結構 ； 抗反射

並列摘要

Two main research topics were shown in the present study. In the first topic, the corner radius effects in periodic nanoantenna for surface-enhanced Raman spectroscopy (SERS) were discussed. Corner radius is a concept to approximate the fabrication limitation due to the effective beam broadening at the corner. The purpose of the present study is to investigate the effects of corner radius on the electromagnetic field enhancement and resonance wavelength for three periodic polygon dimers of bowtie, twin square, and twin pentagon. The enhancement factor of surface-enhanced Raman spectroscopy due to the localized surface plasmon resonances in fabricated gold bowtie nanostructures was investigated using both Raman spectroscopy and finite-difference time-domain (FDTD) simulations. The simulated enhancement factor versus corner radius relation was in agreement with measurements and it could be fitted by a power-law relation. In addition, the resonance wavelength showed blue shift with the increasing corner radius because of the increasing dispersion of concentrated charges in a larger area. For different polygons, the corner radius instead of the tip angle is the dominant factor of the electromagnetic field enhancement because the surface charges tend to localize at the corner. Also, the fractional resonance wavelength shift versus the product of gap size and corner radius relation could be fitted by a power-law relation for each periodic polygon dimer nanostructure.
In the second part, a high surface area and low reflection textured surface-enhanced Raman scattering substrate with plasmonic gold nanodroplets fabricated by wet etching and island lithography was reported. The optical properties obtained from the finite-difference time-domain simulation results showed the agreement with reflection and dark-field scattering measurements. According to the AFM and reflection measurements, the nanopillar-on-pyramid structure provided large surface area and multiple reflections for SERS enhancements. The SERS enhancement of nanopillar-on-pyramid SERS substrate was about 2 orders of magnitude larger than the gold film substrate. Although the SERS signals varied in the different measured regions, the SERS substrates with nanopillar-on-pyramid structure always have the stronger enhancement factor than the other SERS substrates.

並列關鍵字

Corner radius ； Plasmonics ； Finite-difference time-domain method ； Surface-enhanced Raman scattering ； CsCl nanoisland ； Anti-reflection

參考文獻

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