以銀光柵和金光柵模擬與驗證拉曼增強效應

Abstract

拉曼增強效應是目前理論上與研究上熱門的議題，並廣泛的被應用在各個領域，如生物上的蛋白質研究、醫藥領域的免疫檢測等，這都是因為拉曼增強效應具有快速且準確分析單分子的能力，也因此各種拉曼增強的技術不斷推陳出新，如表面增強拉曼效應、針尖拉曼增強效應等，但至目前為止，能夠將拉曼增強效應「量化」的研究尚無人能夠突破，即拉曼增強的倍數仍然無法定量。本篇論文的目的是透過實驗室新開發的光學模擬計算方法，並搭配合適的實驗環境及量測技巧，期望在拉曼量測下，可以得到訊號增強倍數量化的結果。 本實驗室光學計算方法主要針對週期性光柵結構做模擬，我們發現光柵會因其材質不同、線寬週期不同、深度不同或代測物之介電常數不同，而導致光柵周圍局部電磁場的分佈不一樣，透過模擬，我們找到一個能夠將能量放大的光柵環境，這個環境是設法將水這個物質引入光柵溝槽中，藉由水-介電常數大的特質，將垂直入射光柵的光侷限在水中，也就是說入射能量在水中會產生共振增強的現象，若待測物的分子存在水中，此分子即可得到訊號的放大，這個現象在論文本文中會詳細說明，而依據此模擬，我設計了拉曼即時(real-time)的量測方法來達成此模擬條件。在實驗過程中我們另外發現，在光柵表面有自組裝單層薄膜的產生對於拉曼訊號增強有一定的影響，因此，為驗證此現象，我分別在金光柵及銀光柵表面生成化合物，並加水覆蓋在其上，在此環境下做拉曼即時量測，我們確實得到了訊號增強的結果。在模擬和實驗的數據比較中，我們雖然無法精準預測實驗結果，但模擬和實驗兩者仍有一定的相依性存在。

Raman scattering enhancement has been a popular research topic and applied to various fields such as biological protein research and medical immune examination. Raman scattering have the character of rapidly and precisely analyzing molecular structure. Moreover, new techniques of Raman scattering have constantly been invented including surface-enhanced Raman scattering (SERS) and tip-enhanced Raman scattering (TERS) etc. However, there is no research dealing with quantifying the effect of Raman enhancement, that is to say that the enhancement of Raman signal cannot be quantitatively determined. Therefore, under proper experimental environment and gauging skills, the research aims to quantify the enhancement of Raman signal using our lab’s newly developed Optical Computing Method. The newly developed Optical Computing Method is to simulate periodic grating structure first. We found that grating due to their different materials, different line width period, depth, or different dielectric constant of measuring target, which lead to different local electromagnetic field distribution around grating. By simulating grating structure, we discover a grating environment which can enhance signal. Because of the large dielectric constant of water, making water into the trench of grating will restrict the vertical incident light within the water. The indecent energy will generate resonance in the water and thereby enhance signal. The more detailed phenomena are articulated in the thesis. Based on the simulation, I designed a real-time gauging method to create the simulated condition. During the experiment, I noticed that the self-assemble monolayer (SAM )on the surface of grating influences the effect of Raman enhancement. Therefore, I produced compound on the surface of golden grating and silver grating respectively and cover them by water. Doing the Raman real-time gauging in the aforementioned environment successfully generated the result of signal enhancement.