以銅為基礎的超常介質之光學性質探討

Abstract

超常介質物質是由週期性排列的二維(或三維)的金屬圖形結構(或是為晶格)組成，蘊含有新奇的光學性質，例如：電漿子共振、人工磁性以及左手物質現象等，皆起因於某特定波長的電磁波(或是光)在沿著金屬陣列的表面傳遞時候，材料所呈現的負的導電係數(ε)、導磁係數 (μ) 及由此而造成負折射率現象。 本論文工作期間，採用以銅化學置換取代一般傳統銅電鍍的實驗方式，建立起一套圖形製程技術，成功地製造了線寬達到次微米的等級的三種銅基超常介質物質的圖形陣列：裂隙共振環(split ring resonator, SRR)、不連續導線(WIRE)以及組合式超常介質物質(composite meta-material, CMM, 由SRR和WIRE組成)，圖形陣列面積大約是0.09cm2。傅式光學轉換紅外線光譜儀(FTIR)被用於實驗研究超常介質物質圖案所產生的光學性質。通過改變入射光的偏極化特性，在600-2000 cm-1波數範圍內，在三種圖案上觀察到了由不同物理機制導致的多各共振模態。為了進一步深入探討這些銅基超常介質物質光學特性之物理內涵，我們亦採用CST MWS軟體按所設計製造的超常介質物質圖形作了電磁模擬，模型計算結果與實驗有較好的符合。

Meta-materials are a group of periodically patterned two-dimensional (or even three-dimensional) metal structures (lattices), which reveal some novel optical properties, such as plasmonic resonance, artificial magnetism, and/or left-handed behaviors, due to existing negative values of permittivity (ε), permeability (μ), and consequent refraction index (n), when electromagnetic (EM) waves (light) propagating along the surface of these pattern arrays at a certain range of wavelengths. By using copper (Cu) chemical replacement instead of electrochemical plating, a new fabrication technology has been developed through this thesis work, and been successfully used in producing Cu-based meta-materials with line-widths at the sub-micrometer-scale. Three types of pattern structures, namely, split ring resonator (SRR), discontinuous wires (WIRE) and composite meta-materials (CMM = SRR+WIRE) were designed and processed forming periodic arrays in the area of about 0.09 cm2. Fourier transfer infrared spectroscopy (FTIR) measurements were engaged for the study of optical properties of these meta-material structures. Over the range of 600-2000 cm-1, several resonance modes with different physics origins were observed from the spectra of three type patterns, when varying the polarization of incident light. EM simulations were also performed using a CST MWS solver for modeling the meta-material behavior at the corresponding wavelength range. Comparison with experiment results were made, in order to facilitate discussions of possible mechanism and physical insights of these Cu-based meta-materials.