三維奈米U型環於可見光波段共振之研究

Abstract

利用次波長的人造結構陣列所製成的超穎材料，擁有一般傳統光學所沒有的特殊光學性質，而現在最普遍用來做超穎材料的結構為隙環共振器（Split Ring Resonators），許多特殊的性質例如磁共振響應、光學的對掌性、負折射現象以及對光譜的調制性都已經被研究發現。在本文中，利用電子束微影以及二次曝光的技術在玻璃基板上製作375x375個底部長度為110 nm、手臂長度為60 nm與週期為200 nm的黃金立體U型環陣列，並且使用有限元素分析法模擬和顯微光譜量測在正向入射的情況下，Ｕ型環的穿透光譜，實驗結果與模擬相當吻合，從結果中我們發現當入射水平方向的偏振光時，會出現一個低階的共振模態，且在此模態下Ｕ型環的中心處會產生一個很強的磁場，接著當我們增長手臂長度時，會出現另外一個比較高階的共振模態，在此模態下會在手臂向外的兩端產生強磁場，而造成此現象的原因主要是由於增加手臂長度，會使得Ｕ型環內部允許存在的駐波數增加，造成不同的電流分布使得磁場發生改變。

Metamaterials are created as an array of artificial sub-wavelength structures, often exhibit unique optical properties which are not found in nature. Metamaterials composited with sub-wavelength split ring resonators (SRRs) have attracted many scientists' attention because of a number of extraordinary properties, such as artificial magnetism, optical chirality and negative refraction index, optical spectrum manipulation. We fabricated of 375x375 vertical U-shape nano gold rings (110 nm x 60 nm x 40 nm) on a fused silica substrate has been successfully implemented by a novel e-beam lithography double exposure process. Plasmonic resonance modes of such structures are investigated by finite-element simulations and optical micro-spectra measurements, which are in excellent agreement with each other. Results show magnetic field solely depends on the resonance mode showing either enhanced between two prongs of vertical U-shape nano ring or enhanced around two prongs of vertical U-shape gold ring.