金奈米粒子在平面波照射下的遠距離穩定與近距離結合

Long-range and short-range interactions of gold nanoparticles irradiated by plane wave

趙學昱(Hsueh-Yu Chao)

指導教授 ： 郭茂坤

國立臺灣大學/工學院/應用力學研究所/碩士(2016年)

https://doi.org/10.6342/NTU201601958

摘要

本文研究多顆球型與桿型的金奈米粒子，在線性偏極光與圓形偏極光照射下，表面電漿子共振所產生的力學行為，以Maxwell電磁理論為基礎，配合多重中心展開法，及Maxwell應力張量，計算奈米粒子上電磁場產生的應力、光力或光力矩。
本研究發現雙顆或三顆同尺寸的金球在線性偏極光與圓形偏極光照射下，皆有近距離相吸與遠距離穩定平衡兩種平衡方式，並找出遠、近距離穩定平衡的分界線，此分界線大約為水中波長的一半。在線性極化光下，當金球在近距離作用範圍內，金球會以平行極化方向上直線排列並相吸；而在遠距離作用範圍，金球將彼此間隔某些固定距離，此些距離大約為水中波長的整數倍，並沿垂直極化方向成一直線排列。在圓形偏極光下，當金球在近距離作用，金球除了互相吸引且呈直線排列外，更將繞著系統中心公轉且同時自轉；隨著金球之間距離靠近，自轉的角動量逐漸轉換為公轉的角動量。在遠距離作用範圍，金球彼此之間除了仍會依一定距離穩定直線排列，也有自轉與公轉的現象。不同尺寸的奈米金球，皆有上述的現象，但所受力隨著尺寸減小而變少。
奈米金桿方面，本研究探討兩根不同尺寸的金桿在不同波長與位置下的受力情形。研究發現在不同的入射波長下，金桿皆會以各自的長軸共振波長(LSPR)為分界點，分別轉向垂直或平行極化方向，稱之為桿的垂直模態或平行模態。若入射光波長同時小於兩根金桿的長軸共振波長，則兩根金桿皆會轉向垂直極化方向並以並排結合(side-by-side)的方式相吸結合。若波長大於兩者的長軸共振波長，則兩根金桿皆會轉向平行極化方向並以頭尾相接(end-to-end)的方式相吸結合。若波長介於兩金桿的長軸共振波長之間，兩尺寸不同的金桿會依據波長轉向各自的平行模態或垂直模態，呈現T字形結合相吸(T-combination)。三根同尺寸的金桿，也依據入射波長的不同有類似的頭尾相接或並排結合的情形。

關鍵字

近距離相吸 ； 遠距離穩定平衡 ； 長軸共振波長 ； 並排結合 ； 頭尾相接 ； T字形結合

並列摘要

This thesis studies, the light-driven interactions of the gold nanorods and nanoballs irradiated by linear or circular polarized light. Optical forces and torques on those nanoparticles based on Maxwell electromagnetic theory, with the Maxwell stress tensor and multiple multipole method (MMP).
For gold nanoballs, there are two different interaction behaviors, which are categorized by the separation distance between nanoballs. If the separation distance of gold nanoballs is shorter than λ/2n, nanoballs behave as short-range interaction. Under linear polarized light, nanoballs attract each other and their line of centroid parallel to the polarization direction of the light. Under circular polarized light, nanoballs still attract each other, and get angular momentums for spin and revolution. If the separation distance of gold nanoballs is longer than λ/2n, nanoballs behave as long-range interaction. Under linear polarized light, nanoballs repulse each other until the distance of nanoballs reach the integer multiples of the wavelength in water, and their line of centroid perpendicular to the polarization direction of the light. Under circular polarized light, nanoballs still repulse each other until the distance between nanoballs reach mλ/n, and get angular momentums for spin and revolution.
For gold nanorods, the key factors of the interaction are the wavelength and polarization of our incident light. If the wavelength is shorter than the longitudinal surface plasmon resonance (LSPR) of both nanorods, nanorods turn their longitudinal axes to be perpendicular to the polarization direction and combine side-by-side. If the wavelength is longer than the LSPR of both nanorods, nanorods turn their longitudinal axes to parallelize to the polarization direction and combine in end-to-end way. If the wavelength is between the LSPR of two different rods, the longer and shorter nanorods turn their longitudinal axes to be perpendicular and parallel to the polarization direction respectively, and combine in T-shape.

並列關鍵字

short-range interaction ； long-range interaction ； longitudinal surface plasmon resonance ； side-by-side ； end-to-end ； T-shape

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