光子晶體的等效介電係數表面與奈米粒子散射之間的影響

Abstract

不同材料的奈米粒子被外加電磁場激發時，其光學特性已經被許多研究團隊廣泛討論，近期有些研究團隊將奈米粒子放置在具有高反射特性的金薄膜上，當P極化光入射時，在長波長下能夠量測到明顯的散射訊號，奈米粒子與金薄膜間的空隙會產生電場侷域性增強的現象。在此篇論文中，我們使用常見的一維光子晶體，即布拉格反射器(Distributed Bragg reflector, DBR)取代金薄膜作為奈米粒子的高反射基板，探討DBR基板對於奈米粒子其散射訊號的影響。 我們利用光學薄膜矩陣法計算出DBR的等效介電係數，從計算結果中可以得知，在接近頻帶邊緣的波長位置下，DBR具有等效介電係數趨近於零值(epsilon-near-zero, ENZ)的特性，並且從模擬及量測上觀察到奈米粒子的共振頻率會出現在DBR的等效ENZ波長附近。另外，DBR基板對於奈米粒子的散射訊號影響則會與奈米粒子的結構高度有關。

When the nanoparticle of different materials are polarized in a regular direction, the nanoparticle will have localized optical resonance at a particular wavelength. The wavelength of optical resonance would be influenced by the refractive index of the surrounding medium of the nanoparticle. In this work, silver and silicon nanoparticles would be fabricated on the top surface of the one-dimension photonic crystals-Distributed Bragg reflector (DBR), and the scattering signal would be measured by the dark-filed microscopy. The real part of effective permittivity of the DBR exhibit the near-zero condition at the wavelength near the band edge, so that the nanoparticles of the different materials have special scattering response for the DBR substrate. In the photonic band gap, the real part of effective permittivity also exhibit conditions that are extreme negative. Therefore, the nanoparticles of the different materials also have the different scattering response in the photonic band gap.