高靈敏之X型超材料吸收體折射係數感測器

Highly sensitive X-shaped metamaterials absorber for refractometric sensing

胡於庭(Yu-Ting Hu)

指導教授 ： 嚴大任

國立清華大學/工學院/材料科學工程學系/碩士(2019年)

摘要

表面電漿共振為存在於金屬及介電層介面之自由電子集體震盪，此現象之共振條件隨週遭折射率改變，透過共振條件改變我們可以判斷介電層之折射係數變化，當介電質之折射係數增加，共振光譜便會產生紅移，因此可將表面電漿共振應用於折射係數感測器上，表面電漿共振具有即時性以及無須標定等特性在感測方面有十分廣泛的應用。應用奈米級等離子體超材料之折射係數感測器可透過局域表面電漿共振的方式產生更強之局域電磁場增益，使其靈敏度大幅提升。
我們設計一個 X 型超材料吸收體折射係數感測器，並透過 CST 軟體模擬和實際樣品偵測定義其靈敏度。X 型金屬共振器可產生高階之四級共振，此共振模式具高靈敏度和高吸收率。金屬-介電層-金屬之高吸收率吸收體也能大幅提升共振之靈敏度和品質因子，同時將其介電層設計為不連續結構使其間隙共振能與目標物更有效接觸。本篇論文中，為了探討我們所設計的折射係數感測器之偵測能力，我們將其與其他三種結構：係環共振器不連續吸收體、X 型共振器連續吸收體及單層X 型共振器進行靈敏度之比較。在模擬中我們得到 X 型超材料不連續吸收體其靈敏度可達1527.3nm/RIU，此一靈敏度數值遠高於其他結構。在實驗中，我們使用聚甲基丙基酸甲酯(PMMA)作為固態量測樣品來定義其實驗上之靈敏度，其實驗結果之靈敏度可達 1886.9nm/RIU 並呈現良好線性關係。我們進而使用氣態丁烷做為目標物以觀察其對氣態樣品之靈敏度，結果發現儘管在光譜上有明顯紅移，但再現性以及線性關係不佳，無法達到定量分析的目的。總結來說，我們所設計之X型非連續超材料共振器具有相當高之折射係數靈敏度及固態樣品偵測能力，然而若要使其具氣態樣品之偵測能力仍需改良其樣品吸附力。

關鍵字

超材料 ； 折射係數感測 ； 吸收體

並列摘要

Surface plasmon resonance (SPR) is the collective oscillation of free electrons at the interface between metal and dielectric layers. The resonant condition of SPR is dominated by refractive index of surrounding environment. Once the refractive index of surrounding dielectric increase, resonance in optical spectrum will red shift, thus SPR can be applied on refractometric sensor. SPR refractometric sensor can provide a real-time and label-free platform that has wide applications of sensing. Nano-scale plasmonic metamaterial based refractometric sensor utilize localized surface plasmon resonance (LSPR) to generate stronger localized electromagnetic field enhancement that significantly increase the sensitivity of the sensor.
We design a X-shaped metamaterials absorber for refractometric sensing purpose and demonstrate its sensitivity through CST software simulation and sample detection. X-shaped metallic resonator (XPS) induce high order quadrupole resonance mode with high absorption and high sensitivity. Absorber with metal-insulator-metal (MIM) structure provide ultrahigh absorption to increase both sensitivity and quality factor of the resonance. Meanwhile we design a discrete MIM structure that enable the gap resonance can directly contact with target sample effectively. In this thesis, to investigate the sensing ability of our purposed refractometric sensor, we compare the sensitivity with other four kinds of structure: single-ring resonator (SRR) discrete MIM absorber, XPS continuous MIM absorber, single layer XPS and single layer SRR. From simulation result the sensitivity of discrete MIM-XPS can reach 1527.3nm/RIU which
is the highest among all the structures. For experiment, we take PMMA as our solid state detection target to demonstrate the experimental sensitivity, the experiment results show high sensitivity of 1886.9nm/RIU and exhibit well linear relationship. We further take gaseous butane as our sensing target. The experiment results show evident resonance red shift, however the results show poor reproducibility and linear relationship, the device lack of ability of quantitative measurement for gaseous sample. In conclusion, we demonstrate a X-shaped metamaterial absorber with high sensitivity based on refractometric sensing and ability of solid state sample detection. However, the improvement of adhesion is still required for gaseous state sample detection
demand.

並列關鍵字

Metamaterial ； refractometric ； sensor ； absorber

參考文獻

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