以時域有限差分法模擬二維奈米金屬粒子之表面電漿共振現象

Abstract

表面電漿共振(surface plasmon resonance)現象發生於金屬與介電質的交界面，為金屬內之自由電子受入射光激發，產生集體式的偶極振盪。近年來，此現象正廣受各界領域學者所關注與研究。本論文即採用時域有限差分法(finite-difference time-domain method)，模擬探討二維奈米銀粒子在可見光波段照射下的表面電漿共振與侷域場增強現象。 時域有限差分法是將馬克斯威爾方程式(Maxwell’s equations)作差分離散化，並藉由蛙跳(leapfrog)方式，交互計算時間與空間中的電場與磁場場量。本論文分別探討單顆與多顆二維奈米銀粒子系統在不同的結構參數變化下，諸如：粒子半徑、間距、數目以及入射光角度等對表面電漿共振行為之影響，並藉由計算散射系統的散射截面積(total scattering cross section)，模擬求得奈米粒子之表面電漿共振波長。

The optical properties of metal nanoparticles have long been of interest for scientists, beginning with Faraday’s investigations of colloidal gold in the middle 1800s. Recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range size, shapes and dielectric environments. In this thesis, we investigate the theory and simulation of plasmon resonances of interacting silver nanoparticles by employing the finite-difference time-domain method and Drude model. Discussion of the analytical and numerical methods for calculating total scattering cross section is included in this thesis; in addition, optical properties for various parameters are analyzed, such as different radius, separation distance and incident direction. While individual particle exhibit a single plasmon resonance, we observe a complex spectrum of resonances for interacting structures. It is found that the number and magnitude of the different resonances depend on the illumination angle and on the distance between the particles.