銀奈米結構之負折射率與負折射現象以及在長程表面電漿激發之應用

Negative Refractive Index, Negative Refraction and Long-Range Surface-Plasmon-Polariton Wave in Nano-Scale Silver Films

游竟維(Ching-Wei Yu 游竟維)

指導教授 ： 任貽均

國立臺北科技大學/電資學院/光電工程系研究所/博士(2010年)

https://doi.org/10.6841/NTUT.2010.00182

摘要

本論文主要研究在銀奈米尺度結構下的長程表面電漿波與負折射率、負折射現象。在二維的銀奈米結構方面，我們利用歸一導鈉法，分析稜鏡耦合系統{稜鏡/等效耦合層/銀薄膜(20 nm)/等效基板層};當在界面{銀薄膜(20 nm)/等效基板層}上的等效導納高於金屬本質導納ηm 之對應點-ηm時，金屬軌跡在導納圖上具有非常大之圓軌跡，此為長程表面電漿在銀薄膜激發時之重要特徵;在這裡，具高、低折射率的對稱膜堆被做為等效耦合層，用來連接金屬薄膜的等效導納至稜鏡的折射率，以造成全反射衰減;在這裡我們提出三種等效耦合層之連接方式，並比較其對於長程表面電漿波傳播長度之影響。此外，藉由導鈉分析法，我們設計可同時以p與s偏極光，在入射波長632.8nm及相同入射角度下激發長程表面電漿波之週期性多層膜結構。
此外，我們使用光追跡法分析負折射現象在三維的銀奈米線結構發生之條件。此單軸具吸收材料具有複數的三主軸折射率，當以p偏極光斜向由介電質層入射界面{介電質層/單軸具吸收材料}時，其等效折射率與複數的波向量依然滿足Fresnel方程式;在這裡我們將傳播在此單軸材料內的電磁場以複數偏極向量形式表示，並計算其波印亭向量;此外，我們在入射波長365nm及633nm下，分別分析波印亭向量、波向量在銀奈米線結構具有的負折射現象。
在三維的銀奈米結構方面，我們在實驗上使用斜向角度沉積法，在沉積角度86度(與基板法角的夾角)下製鍍各種具銀奈米結構之負折射率薄膜，如銀柱狀陣列、鋸齒狀與S型結構。我們利用分離式及偏極干涉儀在可見光波長下(532nm,639nm與690nm)，量測此奈米薄膜的等效透射及反射係數，求得p偏極光與s偏極光之等效效介電係數、導磁係數、阻抗與等效折射率。此外，我們在沉積角度 86度下搭配交錯沉積技術，製鍍對稱與不對稱的鋸齒狀結構，並利用有限時域差分法模擬近場在單個奈米結構內的反磁現象，分析結構的外型對於此共振效應之影響。當奈米結構柱子間具有反磁偶磁共振行為時，薄膜的等效導磁係數之實部小於零。

關鍵字

銀奈米結構 ； 負折射率 ； 負折射 ； 長程表面電漿波

並列摘要

In this work, negative refractive index, negative refraction and long-range surface-plasmon-polariton (LRSP) propagation in nano-scale silver films were analyzed and investigated. Silver films with negative refractive index were fabricated and demonstrated in the visible regime.
First, we use the normalized admittance diagram (NAD) analysis to design the prism-coupling system {prism/ equivalent coupling layer(ECL) /silver film(20nm) /equivalent substrate(ES)} for LRSP propagation in two-dimensional nanostructure of silver. The excitation of LSPP waves is characterized as a huge open loop of the NAD of the metal film at a designated angle of incidence. We propose three kinds of ECLs to complete the multilayer LSPP design: the intrinsic admittances of the ECLs are (i) real , (ii) infinite, and (iii) imaginary. Periodic symmetrical film stacks are used as the ECL to achieve the coupling effects. In addition, the multilayer structure for exciting s- and p-polarized LRSP propagation simultaneously is designed at the wavelength of 632.8 nm.
Negative refraction in three-dimensional nanostructures of silver is interpreted and analyzed using the complex ray tracing method. When the p-polarized incident light is incident on the {dielectric medium/uniaxial absorbent material(with complex-valued three principal indices)} interface, the effective refractive index experienced by the p-polarized light and the complex-valued wave vector of the refracted light still satisfy the Fresnel equation. Therefore, we can calculate the refracted angles of the wave vector and Poynting vector and analyze the conditions of the negative refraction in silver nanowires. Negative refraction of the Poynting vector and backward wave phenomenon in the silver nanowires are interpreted and presented at the wavelengths of 365 nm and 633 nm.
Several three-dimensional nanostructures of silver, such as nanorod arrays (NRA), zigzag and S-shaped structures, are deposited using glancing angle deposition (GLAD) technology. The equivalent transmission and reflection coefficients of the films are measured by walk-off and polarization interferometers in the visible regime. The retrieval method is used to recover the equivalent relative permeabilities , permittivities , admittance z, and refractive indices n of the films for p and s polarizations. We demonstrate that and satisfies the inequality and the real parts of n for p-polarized incident light are negative at the wavelengths of 532 nm, 639, and 690 nm. In addition, the zigzag structures with different shapes are fabricated using bideposition technique. We use the finite-difference time-domain (FDTD) method to simulate the magnetic reversed field in a single zigzag structure. The shape effect on the real parts of the equivalent permeabilities for zigzag structures is investigated.

並列關鍵字

Negative refractive index ； Negative refraction ； Long-range surface-plasmon-polariton waves ； Nano-scale silver films

參考文獻

[1] H. Raether, Surface plasmons on smooth and rough surfaces and on gratings (Springer-Verlag, Berlin Heidelberg, 1988).

[2] E. N. Economu, “Surface plasmons in thin films,” Phys. Rev. 182, 539-554 (1969).

[3] C.-W. Yu and Y.-J. Jen, “Effects of the equivalent coupling layer on ultra-long-range surface-plasmon-polariton waves “Opt. Express 18, 7982-7993 (2010).

[4] Y.-J. Jen,, A. Lakhtakia, C.-W. Yu and T.-Y. Chan, “Multilayered structures for p- and s-Polarized long-range surface-plasmon-polariton propagation,” J. Opt. Soc. Am. A 26, 2600 -2606(2009).

[5] F. Yang, J. R. Sambles and G. W. Bradberry, “Long-range modes supported by thin films,” Phys. Rev. B 44, 5855-5872 (1991).