金奈米粒子群在高斯光束照射之遠距離穩定平衡聚合

Long-range stable-equilibrium grouping of gold nanoparticles irradiated by Gaussian beam

黃成偉(Cheng-Wei Huang)

指導教授 ： 郭茂坤

共同指導教授 ： 廖駿偉(Jiunn-Woei Liaw)

國立臺灣大學/工學院/應用力學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201702018

摘要

本文以線性極化之高斯光束(Gaussian beam)照射多顆金奈米粒子，使粒子產生表面電漿共振(surface plasmon resonance；SPR)，以多重中心展開法(multiple-multipole expansions method)計算電磁場，並透過Maxwell應力張量計算粒子所受光力，去探討金奈米粒子群以一維及二維形式排列產生遠距離穩定平衡之情形。
本研究發現金奈米粒子在高斯光束照射下，所產生之梯度力其作用最顯著之處並非在光束焦平面(focal plane)，而是在遠離焦平面近光束上游處，其作用大於在同一焦平面上縮小帶寬之結果，並發現一維直線排列之結構其最短穩定距離所在光束平面，穩定距離為水中波長整數倍再略短，且其值相較於先前平面波結果更短，但因光束帶寬範圍限制，產生線性排列之金球顆數有限。
相對於在焦平面處三聚體只能以動態行為存在，在光束上游處之梯度力足以將三聚體固定在環境介質中，產生二維平面排列之穩定平衡，其形狀在越往上游處會越趨近於正三角形，並分別改變介質與入射波長觀察其形狀變化，在粒子改為銀球情況下，其穩定形狀並無太大差異，而在較長波常情況下，三角形變得更為扁平。增加金球顆數至五顆後發現穩定平衡依然存在，且在金球群右側也以三角形排列存在，但其底角非常小，以至於在實驗中無法觀察到。

關鍵字

遠距離穩定平衡 ； 高斯光束 ； 梯度力 ； 二維平面排列 ； 三聚體

並列摘要

Using a linearly polarized (LP) Gaussian beam induced gold nanoparticles (GNPs) with stable equilibrium, fabricate 1D line array, The numerical results of MMP illustrate that the ordered 2D patterns of trimer, tetramer and pentamer of multiple GNPs of r= 100 nm can be produced in water at the off-focal plane of Gaussian beam of 800 nm, besides 1D linear array. We find that the gradient force of Gaussian beam at off-focal plane is stronger than shrinking down beam waist directly.
In 1D line array part, the stable-equilibrium distances between gold nanoparticles are closer than plane wave case but still about a wavelength. However, the quantity of GNPs are limited by the range of beam waist. The 2D stable-equilibrium patterns consisting of multiple GNPs with gaps of a wavelength could be induced by linearly polarized Gaussian beam at off-focal plane, besides the 1D array patterns. These stable-equilibrium patterns with gaps, close to a wavelength, are due to the long-range interaction of light with GNPs. Because of the gradient force of Gaussian beam as well as the optical binding force between each GNP and depend on the wavelength and waist. The orientations of these patterns are dependent on the light’s polarization. In contrast, a plane wave can only produce 1D linear array patterns, rather than the ordered 2D cluster patterns.

並列關鍵字

Gaussian beam ； gradient force ； off-focal plane ； 1D linear array patterns ； 2D patterns ； trimer ； pentamer ； long-range interaction

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