奈米金屬顆粒之表面電漿共振效應研究

Abstract

本論文研究主要為使用三維有限元素法模擬計算不同幾何形狀、粒徑大小、粒子數目及排列之奈米金屬顆粒，由不同偏振方向及入射波長之平面電磁波入射時，產生之相異表面電漿共振現象。我們的研究對象，包括：雙顆及多顆排列之銀(Ag)奈米圓球、單根金(Au)奈米圓柱，以及兩三角形金奈米薄膜所構成之領結型天線結構。 第一部分我們研究奈米銀球之表面電漿現象，計算其近場電場振幅及遠場散射截面積、吸收截面積等物理量以了解其所對應之表面電漿共振模態及共振波長。模擬結果顯示，兩顆奈米銀球和多顆奈米銀球所構成之鏈狀波導結構的表面電漿共振現象，可藉由變化奈米銀顆粒的直徑大小、間距、入射電磁波長、入射電磁波之行進方向及電場偏振方向等因素來加以改變。 第二部份為了研究奈米金棒的表面電漿共振效應，我們選擇四種不同比例的奈米金棒，改變了奈米金棒的長短軸，計算並觀察在縱向及橫向表面電漿模態下，奈米金棒的近場電場振幅分佈，以及散射截面積和吸收截面積隨著波長變化的關係。 第三部份對於構成領結型天線之兩奈米金薄膜，我們變化中心間隙、觀測平面高度、以及天線之薄膜厚度，來觀測特定偏振行為下之天線結構的侷域光場現象，並對其做定性的分析討論。 模擬結果顯示，不同奈米金屬顆粒之排列與結構設計，可使其成為有效的可見光吸收體與散射體等應用，期待未來可將此研究結果作為進一步應用在奈米光電元件、奈米感測元件、奈米生醫光電等前瞻性科技領域之基石。

In this thesis, we use three-dimensional finite element method (FEM) to study the surface plasmon resonance (SPR) effects of metallic nanoparticles, which are of different shapes, sizes, numbers, and orientations when the particles are illuminated by a plane wave with different polarization and wavelength. In the first part of this thesis, we investigate the phenomenon of SPR of silver nanospheres, the near-field distribution as well as the far-field scattering and absorption spectra are calculated to investigate the corresponding SPR modes and wavelengths. Simulation results show that the SPR effects of two and multiple silver nanospheres can be changed by controlling the particle size, gap of the silver nanospheres, as well as the propagation directions and polarizations of incident waves. In the second part of this thesis, we study the SPR effects of a single gold nanorod, which is of different aspect ratio. The properties of the near-field light intensity distributions as well as the far-field scattering and absorption spectra for longitudinal and transverse SPR modes are discussed. Finally we study the system of bow-tie antenna consist of two triangular gold nanoparticles, we change different geometric parameters of the bow-tie antenna, such as their gap distance or thickness, and discuss their optical responses to specific polarization light. The simulation results show that through suitable designing the structure and arrangement of metal nanoparticles, they can become efficient nano scatters or absorbers of visible light. These results can further be applied to the design of nanophotonic or nanobiomedicine devices, such as nanowaveguides, nanosensors, nanodetectors etc.