金屬奈米結構在高斯光束下之光力學分析

Optomechanics of Metal Nanostructures Irradiated by Gaussian Beam

黄茂昌(Mao-Chang Huang)

指導教授 ： 郭茂坤

共同指導教授 ： 廖駿偉

國立臺灣大學/工學院/應用力學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201802731

摘要

本文數值模擬分為三類：(1) 一自由奈米粒子與一固定奈米金屬粒子(三維運動)，(2) 雙顆與三顆自由奈米金屬粒子，(3) 多顆奈米金桿在高斯光束(Gaussian beam)線性與圓形極化下之光學行為，使其金屬粒子產生表面電漿共振(surface plasmon resonance；SPR)，採數值理論多重中心展開法(multiple-multipole expansions method)計算電磁場，藉由Maxwell應力張量計算奈米粒子光力與光力矩，同時引進流線(streamline)，將部分數值結果分析2D/3D視覺化，探討自由與固定一金屬奈米粒子之三維光學行為、雙顆與三顆奈米金屬粒子之軸向公轉與側向自旋運動與多顆金桿之結合或穩定平衡運動。
本研究發現一自由與一固定奈米金屬粒子在高斯光束照射下，所產生光學行為為三維運動，其多數實驗者只觀察到部分行為，而本文將光學運動行為分為接觸模式(contact mode)與非接觸模式(non-contact mode)，觀察其奈米粒子之流線(streamline)，發現其自由奈米粒子之運動行為非常複雜。
雙顆與三顆自由奈米金屬粒子在高斯光束照射下，因電磁場之扭曲，造成奈米金屬粒子逆向公轉與傾自轉軸之自旋。相較於平面波之光源，其改變高斯光束之帶寬可決定公轉之方向與自旋光力矩之大小。
多顆奈米金桿之結合或穩定平衡運動，在入射波長接近長軸表面電漿子共振特性(longitudinal surface plasmon resonance ; LSPR)時，多顆奈米金桿在線性極化下會以頭尾相接(end-to-end)或並排結合(side-by-side)；若在圓形極化時，則各自排開產生公轉與自旋。

關鍵字

二維/三維流線 ； 接觸與非接觸模式 ； 逆軸向公轉 ； 側向自旋 ； 多聚體結合

並列摘要

The numerical results of this article are divided into three parts. The first section is a free nanoparticle and a fixed metallic nanoparticle, the second is orbit-spin interation of two or three free nanoparticles, and the last is analyzing optomechanics of multiple nanorods irradiated by linear-polarized or circular-polarized focused Gaussian beam. The Surface of the metallic nanoparticle will produce surface plasmon resonance (SPR). We use both Multiple-Multipole expansions method (MMP) and Maxwell stress tensor to express optical force and optical torque analysis. At the same time, the streamline is introduced to plot some partially numerical results via 2D/3D visualization in order to discuss optical motions, inclusive of a free and a fixed metal nanoparticles, longitudinal orbit and transverse spin torque among two and three metal nanoparticles, and the interactions or stable interactions among a lot of Au nanorods.
This article has found that a free and fixed metal nanoparticles irradiated by Gaussian beam can be regarded as three-dimensional motions. Most experimenters only happen to observe partial motions, and the results of optical motions will be divided into two modes, defined as contact mode and noncontact mode. According to observing streamlines of the free nanoparticle, it is obvious that optical motions of the free nanoparticle are extremely complicated.
Due to the twisted electromagnetic field, two and three free nanoparticles irradiated by linearly or circularly polarized focused Gaussian beam result in negative orbital torque and transverse spin torque. Compared to plane wave, the direction of orbital torque and the magnitude of spin toque can be determined by changing the waist width of Gaussian beam.
In the case of interaction or stable motions, when the incident wavelength is close to the longitudinal surface plasmon resonance (LSPR), many Au nanorods in linear polarization would interact in ways of end-to-end or side-by-side modes; if in circle polarization, they will repel and form orbital-spin motions.

並列關鍵字

2D/3D streamline ； contact and noncontact mode ； negative orbital torque ； transverse spin torque ； interaction among nanoparticles

參考文獻

[1] S. J. Park, T. A. Taton, and C. A. Mirkin, “Array-based electrical detection of DNA with nanoparticle probes,” Science 295, 1503-1505, 2002.

[2] J. J. Storhoff, A. A. Lazarides, R. C. Mucic, C. A. Mirkin, R. L. Letsinger, and G. C. Schatz, “What controls the optical properties of DNA-linked gold nanoparticle as¬semblies,” J. Am. Chem. Soc. 120, 4640-4650, 2001.

[3] K. L. Kelly, A. A. Lazarides, and G. C. Schatz, “Computational electromagnetics of metal nanoparticles and their aggregates,” IEEE Comp. Sci. Engi. 3, 67-73, 2001.

[4] X. Huang, H. Ivan, W. Qian, and A. Mostafa, “Cancer cell imaging and photothermal therapy in the near-infrared region by using gold nanorods,” J. Am. Chem. Soc. 128, 2115-2120, 2006.

[5] J. J. Mock, M. Barbic, D. R. Smith, D. A. Schultz, and S. Schultz, “Shape effects in plasmon resonance of individual colloidal silver nanoparticles,” J. Chem. Phy. 116, 6755-6759, 2002.