發展週期性結構表面增強拉曼散射基板及其高靈敏分子檢測應用

Abstract

表面增強拉曼散射是改善拉曼散射強度不足的方法之一，而表面增強拉曼散射之所以能改善的原因有二：利用電磁場增強的方法、與利用電荷轉移增強效應。其中電磁場增強的效果比電荷轉移的效果強上許多，因此許多科學家致力於這方面的研究。若要使電磁場增強，則拉曼的基板製備就會是一個很重要的課題。隨著奈米材料製備技術的成熟，各種基板不斷發展，但都以增強表面電漿子共振為主，形貌上屬於球狀、針尖狀、直接蒸鍍金屬等。本論文欲以光捕捉之光學基板為主，製作一週期性一維光柵基板。因一維光柵的具有調變光的振幅與相位的特性，讓光能在光柵中來回傳遞，達到共振效果，使訊號放大。我們以電子束微影系統搭配乾蝕刻技術，製作相同深度但不同週期與工作週期的光柵結構，並以苯甲酸作為待測藥品，得到最佳的訊號增強光柵結構。我們也討論入射雷射的偏振對訊號強度的影響，佐證我們的光柵結構應用於表面增強拉曼散射時，其訊號增強原因屬於光學表現。

Surface Enhanced Raman Scattering (SERS) is one of the methods to improve the weakness of Raman Spectrum. The mechanisms that makes SERS improve the signal intensity are: the electric field enhancement and the carrier transmission enhancement. According to the fact that electric field effect can provide a stronger enhancement than the chemical effect, numerous scientists commence to do a lot of research on the electric field effect of SERS. If the electric field effect is going to be implemented to enhance the Raman Intensity, solving the problem of the SERS-active substrate is a necessity. As the nano technique matures, various types of SERS-active substrates are fabricated. Nevertheless, most of substrates, which is designed for the enhancement of surface plasmon effect, are sphere liked, tip liked and metal evaporated. Therefore, this thesis would like to use one-dimensional grating as the pattern of our periodically structured SERS substrate. Grating can modulate the amplitude and the phase of incident light, leading to the light be trapped and resonate between two gratings, and consequently contributing to the signal enhancement. We utilized E-beam lithography system with dry etching method for the fabrication of precise grating pattern. After that, a SERS substrate with different period and grating duty cycle is obtained. As a result, we chose benzoic acid as the analyte because it is the typical model of aromatic carboxylic and common preservative in food safety problem. We also demonstrated that by changing the polarization of incident laser, the SERS intensity became weak when the mode is shifted from TE to TM. Conclusively, we proposed a special designed grating account for the enhancement effect in SERS.