金奈米結構在近紅外光照射下對奈米粒子之光力作用

Abstract

本文研究在三維空間中以多種入射波源照射單顆及雙顆金球結構，探討在近場時抓取奈米粒子之光力作用。使用多重中心展開法(multiple-multipole expansions method)計算電磁場，並配合Maxwell應力張量計算奈米粒子所受之光力，藉此探討單顆及雙顆奈米金球結構在抓取奈米金球及奈米聚苯乙烯時所產生之現象。 本研究發現使用奈米金球結構抓取奈米金球時，在高斯光束照射下，僅會吸附至結構，抑或是被結構排斥，遠離結構。在平面波照射下，僅有靠近結構之一小部份會受影響，其餘沿平面波傳遞方向移動。 使用奈米金球結構抓取奈米聚苯乙烯球時，高斯光束照射下，則會產生靜滯點，靜滯點受到極化方向影響，改變結構中心與xz平面之距離可控制靜滯點。結構中心遠離焦平面或遠離入射光軸皆會使靜滯點周圍之力變小使得其穩定性降低。在平面波照射下，則會產生一層保護層使得上下分離，僅有當奈米粒子從低於某高度掉落時才有機會進入近場平衡點，當高度過高時金球會被排斥，使其遠離結構。

The objective of this research is to discuss a single and a dimer gold nano-sphere structure are irradiated by a variety of incident waves in a three-dimensional space, with emphasis on the optical forces exerted on nanoparticles in the near-field. MMP (multiple-multipole method) was used to calculate the induced electromagnetic field, and the Maxwell stress tensor theory was adopted to calculate the optical force exerted on the nanoparticles. This study found that when the gold nano-sphere structure is irradiated by Gaussian beam to grab a gold nano-sphere, the gold nano-sphere will either be adsorbed by the structure or be repelled far away from the structure. When irradiated by plane wave, only when the gold nano-sphere is near the structure will be affected. Otherwise, it will move in the same direction of plane wave. When the gold nano-sphere structure is irradiated by Gaussian beam to grab a polystyrene nano-sphere, the system will generate stagnation points. Stagnation points are affected by the direction of polarization. We can change the distance between the center of the structure and xz plane to control the position of stagnation points. The center of the structure moving away from focal plane or the optical axis will decrease the stability. When irradiated by plane wave, the system will generate a layer which will separate the space into up and down parts. Only when the polystyrene nano-sphere move into the down part would there be chance for it to move into the near-field stagnation point. Otherwise, it will be repelled far away from the structure.