奈米金顆粒之侷域表面電漿子共振特性數值研究

Abstract

本論文中，我們利用數值模擬計算金奈米柱、金奈米環、金奈米 球殼在其侷域表面電漿子共振模態時的散射、吸收截面積以及單位體 積散射、吸收截面積。其中，金奈米柱、金奈米環、金奈米球殼的模 擬結構及尺寸皆著重在現今製程容許度以及合理之波段範圍。數值結 果顯示金奈米柱的吸收截面積及散射截面積小於金奈米環及金奈米球 殼。而在單位體積散射、吸收截面積的計算中，金奈米柱則為三者中 最高，金奈米環次之，金奈米球殼則為最低者。 我們另外計算了金奈米顆粒在溶液或組織中的隨機指向分布狀態 所產生的效應，可以發現在隨機指向分布時的金奈米顆粒的侷域表面 電漿子共振強度會依其模態所對應的軸向幾何對稱性而有所衰減，另 外，藉由改變金奈米環的高度，我們有效設計一個金奈米環，使其在 隨機指向分布的狀態下，其散射、吸收截面積衰減的效應能有效的減 小。

In this thesis, the numerical results of overall absorption and scattering cross sections and cross sections per metal volume of Au nanorod (NRO), nanoring (NRI), and nanoshell (NS), based on the commonly used localized surface plasmon (LSP) resonance modes, with various sizes and aspect ratios (ARs) in the reasonable ranges, which are determined by the practical fabrication capability and application wavelength ranges, are compared. The results show that the overall absorption and scattering cross sections of NRO are generally smaller than those of NRI and NS. However, in terms of cross section per Au volume, those of NRO are the highest among the three types of Au nanoparticle (NP), followed by NRI and then NS. We also evaluate the effects of NP random orientation distribution in a solution or tissue in practical applications. It is found that with random orientation, the reduction range of extinction cross section depended on the geometry symmetry property of the electron oscillation axis in the concerned LSP resonance mode. Then, we designed an Au NRI to make the resonance wavelengths of its symmetric dipole mode and axial dipole mode the same by increasing the ring height. In such an Au NRI of a large ring height, the reduction ranges of scattering and absorption cross sections were significantly decreased.