銀奈米柱陣列薄膜在不同厚度下之光學特性研究

Thickness dependent optical properties of a silver nanorod array

陳志輝(Chih-Hui Chen)

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/碩士(2010年)

https://doi.org/10.6841/NTUT.2010.00115

摘要

本研究利用電子槍蒸鍍系統搭配斜向沉積技術(GLAD)製鍍不同厚度的銀奈米柱陣列(NRA)薄膜，並利用Walk-off干涉儀與橢圓偏極干涉儀來量測銀奈米柱陣列薄膜之透射係數與反射係數。在本研究中，定義電場平行於沉積平面者為p偏振光而垂直於沉積平面者為s偏振光，其量測波長為532 nm、639 nm和690 nm，三個波長皆落於可見光波段。利用量測得到的透射係數與反射係數可以進一步得到銀奈米柱陣列薄膜的等效光學常數。當外加磁場垂直於成對銀奈米柱時，奈米柱間的傳導電流與位移電流會產生一個封閉電流迴路而造成磁場共振之現象，其等效介電常數與等效磁導係數的實部可以藉由改變銀奈米柱陣列薄膜的厚度來調變。
此外，我們利用有限時域差分法(FDTD)對不同長度且成對的銀奈米柱做近場模擬，並觀察兩根銀奈米柱間磁場共振之行為，可發現當改變銀奈米柱陣列薄膜的厚度時，材料的等效磁導係數就會有劇烈的變化，且在可見光波段磁場反向共振效果與波長成正比。在本實驗中，p偏振光所量測的銀奈米柱陣列薄膜，所計算出來的等效折射率的實部皆為負值。

關鍵字

超穎材料 ； 負折射率 ； 銀奈米柱陣列

並列摘要

Silver nanorod arrays (NRA) with different thicknesses are deposited using glancing angle deposition (GLAD) technique by electron beam evaporation. The transmission and the reflection coefficients of silver films for p-polarized light and s-polarized light are measured at the wavelength of 532nm, 639 nm and 690nm by walk-off and polarization interferometers. The equivalent electromagnetic parameters of the silver nanorod arrays are obtained by the two coefficients. Due to the magnetic effect, the real part of the equivalent permittivity and equivalent permeability of the silver film can be tuned by varying the thicknesses of the silver nanorod arrays.
Compared with the finite-difference time-domain method (FDTD) simulation, we can find that the inverse magnetic resonance intensity directly proportional to the wavelength in the visible regime. In this experiment, the real part of equivalent refractive index for the P-polarized light is negative at the three thicknesses.

並列關鍵字

Metamaterial ； negative refractive index ； silver nanorod array

參考文獻

[1] Tomoyoshi Motohiro and Y. Taga, “Thin film retardation plate by oblique deposition,” Applied Optics, vol. 28, no. 13, 1989.

[2] Y. Takeda, R. Messier, “Obliquely deposited metal films for polarizers,” Appl. Surf. Sci., vol. 244, pp. 209-212, 2005.

[3] Y. P. Zhao, S. Schultz, P. Markos and C.M. Soukoulis, “Absorbance spectra of aligned Ag nanorod arrays prepared by oblique angle deposition,” J. Appl. Phys., vol. 100, pp. 063527.1-063527.8, 2006.

[4] Yi-Jun Jen,* Akhlesh Lakhtakia,* Ching-Wei Yu, and Chin-Te Lin, “Vapor-deposited thin films with negative real refractive index in the visible regime,” Optics Express 7784, Vol. 17, No. 10, 2009.

[5] J. B. Pendry, A. J. Holden, D. J. Robbins & W. J. Stewart, “Magnetism from Conductors and Enhanced Nonlinear Phenomena,” IEEE Trans. Microw. Theory Tech. vol. 47, no. 11, pp. 2075–2084, 1999.