利用光柵結構以增強拉曼散射之研究

Study of Enhanced Raman Scattering with Grating

林暉凡(Hui-Fan Lin)

指導教授 ： 管傑雄

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.03360

摘要

本實驗利用電子束微影技術製作出高深度之一維奈米光柵結構，用以增強拉曼散射訊號。這是個前驅性之研究，應用結構的創新與良好的成果，相信可以為後續之研究帶來微薄之力。
元件之製作係利用電子束微影技術設計並曝光出奈米線寬與週期之光柵，再利用ICP-RIE之乾蝕刻技術，蝕刻出高深度之光柵結構。本論文分成兩個實驗進行，首先將製作出之樣品光柵量測矽TO模態的增強拉曼散射訊號，第二部分為將樣品光柵鍍上銀薄膜，滴上極稀薄濃度之腺嘌呤(Adenine)溶液，量測分子之增強拉曼散射訊號。
實驗中，我們針對元件的結構改變的參數為光柵之線寬與週期，實驗得知此兩參數對於拉曼增強的效應都有其影響。實驗結果共分成兩部分討論；第一部份的研究中，我們利用矽之奈米光柵結構增強矽基板之矽TO模態的拉曼散射訊號，而量測方式分成為TE模態與TM模態。我們未歸納出線寬的大小對於拉曼訊號有無特定之線性關係，但在TM模態量測時，拉曼散射強度對線寬的改變較TE模態時影響更大，我們認為，這是由於當入射光進入光柵後會有橫向散射波，激發光柵壁側向拉曼散射訊號，且TM模態的影響比TE模態大。關於週期的影響，對於TE模態與TM模態有稍許的不同，雖然在改變週期的情況下，無論是TE或是TM模態都有一特定週期(P )有最高峰值之拉曼散射訊號，但於程度來說，TM模態無論大小或是起伏都比TE模態來的大。在週期較大時，TM與TE模態的影響較為接近，但是越接近峰值的週期P 時，TM模態所產生的效應比TE模態高出許多。當週期持續變小時，TM模態甚至變得比TE模態所產生的訊號更小。許多的物理意義仍有待解答，在此研究中只能用簡單的圖像說明。
第二部分是利用鍍銀之奈米光柵以增強極稀薄濃度之分子溶液之拉曼散射訊號。本次實驗獲得的最大成果即是我們能夠量測到比傳統之拉曼光譜量測方法所能檢測之濃度低10個數量級的濃度溶液。在能夠量測到最低濃度的樣品中，以線寬120 nm與150 nm的樣品所能量到的濃度為最低，約10 至10 g/c.c.，而線寬增加或減少都無法再將可量測濃度往下推進，反而在量測上變得更弱。當週期變化時，強度與週期的關係非呈現一線性變化，預測若將週期參數範圍加大，才能更瞭解其趨勢。
利用光柵結構增強拉曼散射是一個前驅性的研究，許多原因我們仍然持續研究中，但是如此不錯的成果給了我們繼續研究的力量，未來我們希望能夠更明白其物理機制外，也希望能夠結合半導體製程製作出方便且精確性高之整合性光學量測元件，並能做更多的應用。

關鍵字

光柵 ； 拉曼 ； 奈米 ； 電子束 ； 光學檢測 ； 腺嘌呤 ； 稀薄濃度溶液檢測

並列摘要

In the experiment, we use E-beam lithography to fabricate one-dimensional grating with deep nanostructure in order to enhance Raman scattering. This is a precursor research, and it is believed that the innovation of application and great result will benefit the following research.
The process to make the grating is first pattern-designing and exposure by E-beam lithography, and second etching by ICP-RIE. There are two experiments in the thesis. The first experiment is to measure the enhanced Raman scattering of silicon TO mode from silicon grating, and the second one is to measure the enhanced Raman scattering of rare concentration solution with grating deposited by silver thin film.
In this thesis, we modulate the line width and the period of grating. It can be verified by our experiment that both of the parameters has effects on the intensity of enhanced Raman scattering. I separate the results into two sections. In the first section, we fabricate silicon grating to enhance Raman scattering of silicon TO mode, and we supply TE and TM mode incident light sources for measurement. We don’t generalize the linear relationship between the line width and the stimulated Raman scattering, but at TM mode the influences from the line width is greater than that at TE mode. It can be thought that the incident light into grating will scatter the transverse wave so that the wave will stimulate the Raman scattering of silicon TO mode from the wall of grating and moreover the effect of wave at TM mode is stronger than that at TE mode. By modulating the period of grating, we can observe some different results from TM mode and TE mode. Whether at TM or TE mode the Raman intensity has a peak value (P ), nevertheless the change of intensity at TM mode has strong degree than that at TE mode. For wider period, the influences from TM and TE mode are approximate. But decreasing the period of grating to P , we can observe that the intensity from TM mode grows up faster. However, when the period is narrower than the P , the signal from TM mode is smaller than that at TE mode.
The second section is the results and discussion of enhanced Raman scattering of rare concentration solution with grating deposited by silver thin film. The great result is that we get the Raman scattering of molecule solution of which the concentration is rarer by 10 than that can be measured by the traditional Raman detection. Of all the samples with line width 120 nm and 150 nm can measure the lowest concentration which is about 10 to 10 g / c.c., however the samples with the wider or narrower line width will not measure the signal of such low concentration. With modulating the period, we observe that the in intensity is not linear relevant to the periods.
To enhance the Raman scattering with grating is a forerunner research, and consequently there are lots of research are going to be done. The great result inspires us to continue. In the future, we hope to understand the mechanics, and to integrate the semiconductor process to fabricate the integrated optical detection devices.

並列關鍵字

grating ； Raman ； e-beam ； optical detection ； adenine ； nanotechnology ； TM ； TE

參考文獻

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