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標題: | 發展平行化三維有限差分時域數值模型以研究電漿子奈米結構及其應用 Developing Parallel 3D FDTD Numerical Models for Studying Plasmonic Nanostructures and Their Applications |
作者: | Hui-Hsin Hsiao 蕭惠心 |
指導教授: | 張宏鈞(Hung-Chun Chang) |
關鍵字: | 表面電漿,異常穿透,雷達截面積, Surface Plasmon,Extraordinary Transmission,RCS, |
出版年 : | 2013 |
學位: | 博士 |
摘要: | 本論文旨在發展一平行化之三維有限差分時域模擬器並將其應用在研究下列三大主題。首先,我們探討一由金屬光柵/介質/金屬膜構成的新穎材料吸收結構,此結構中之侷域表面電漿共振模態類似於x方向之費布力-佩若共振,並由金屬光柵及金屬膜上之激發電流與介質中之位移電流形成了電流迴圈以致等效上同時形成一磁矩。此外,我們進一步探討由兩個金屬光柵/介質/金屬膜反向堆疊而成之複合結構,而其中上下共振器之電流迴圈形成反向之磁矩且較強之磁矩位於較薄之介質層中。實驗上可量測到2階之表面電漿共振模態(入射角等於12度),但由於偶數階模態在正向入射時無法被激發使得在模擬頻譜上沒有看到2階模態。
第二主題則是關於異常穿透現象。我們首先觀察週期性U型漸變到H型孔洞結構之穿透頻譜與近場分佈,發現對於表面電磁模態與伍德異常現象,其部分近場特徵與理論分析相符。接著我們著重在利用孔形共振之近場特徵結合對稱性以預測複雜孔洞結構中之有效共振路徑,預測的結果與模擬結果十分吻合,並利用矩形波導近似公式我們可以進而估計共振波長,與模擬結果相比誤差在11%以下。此外,對於具有多重孔洞之結構,我們也探究了孔洞距離對於共振頻譜的影響,以了解孔洞間之耦合現象的重要性。 最後,我們研究造成細菌在由奈米銀顆粒與陽極的二氧化鋁所組成之透明基板上具有高對比顯微影像之物理機制,藉由比對基版本身以及在基板上加入細菌的反向散射雷達截面積,我們發現兩者雷達截面積的差異在表面電漿共振的範圍內較為明顯。此外,從近場的分析上,電場(磁場)場強在細菌覆蓋的面積下減弱(增強)的現象也在共振的範圍較為顯著。接著我們探討由奈米球與介質殼奈米球組合之基板的光學現象,我們發現電場場強主要聚集在介質殼奈米球與奈米金球的接觸點,反之介質殼奈米球間的接觸點則沒有明顯的場強分佈;而磁場則是均勻的分佈在表面上,因此對於遠場的散射量可能有較大的貢獻。 In this dissertation, a parallelized three dimensional (3D) finite-difference time-domain (FDTD) numerical simulator is developed and applied to the study of the following three main topics. First, we start with the discussion for a basic metallic-grating/dielectric/metal (MDM) metamaterial absorber structure. The localized surface plasmon (LSP) resonances within this structure in fact are associated with the x-directional Fabry-P´erot like resonances, and the induced surface currents within the metallic strip and metallic film accompanied with the displacement currents within the dielectric layer form a current loop for the LSP mode, thus resulting a non-zero magnetic moment. Besides, we further investigate a more complex structure with two inversely-stacked MDMs, and the current loops between the top and bottom resonators construct two opposite-signed magnetic moments with the intense one residing in the thinner dielectric layer. The 2nd LSP mode is measured by the experiment under the incident angle θ = 12◦, while it is absent in the simulated spectra as a result of no net dipole for even order LSP modes under normal incidence. The second topic is related to extraordinary transmission (EOT) phenomenon. We first examine the transmission spectra and near-field distributions of periodic U- to H-shaped apertures and find some unique near-field profiles for surface electromagnetic modes and Wood’s anomalies are consistent with the theoretical studies. Then, we focus on the near-field characteristics for shape resonances combined with the symmetric requirement to predict the shape resonant paths for more complex-shaped apertures. The predictions agree well with the real resonant modes calculated by the FDTD method. By applying the modified approximation equation for the cutoff wavelengths of the rectangular waveguide, we can further estimate the resonant wavelengths with the error below 11 % compared with FDTD results. Besides, the spectral effect of the separation distances between apertures within one unit cell is analyzed, which demonstrates the coupling between adjacent slits would play a role in the variation of the spectra. Finally, we study the physical origin for the high-contrast microscopic image of a transparent silver nanoparticles/anodic aluminum oxide (Ag-NPs/AAO) SERS substrate. By analyzing the backward-scattering radar cross section (RCS) for the substrate and for the system with a bacteria residing above the substrate, we find the difference of the RCS will be more obvious within the range of the plasmonic resonance. In addition, from the near-field features, the hot spots become a little bit dimmer (bighter) for |E| (|H|) distributions within the area covered by the bacterium for the LSP resonance, while those differences become indistinct for the off-resonant situation. Moreover, we also investigate the optical properties of a hybrid nanoshell-nanosphere SERS substrate. From the near-field analyses, we find the electric fields are strongly localized near the contact points between the nanoshells and gold nanospheres compared with those sites between nanoshells, while the |H| distributions are quite uniform among the surfaces, and thus would be more probable to contribute to the far-field scattered power. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/62936 |
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顯示於系所單位: | 光電工程學研究所 |
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