利用點擊化學反應使異質奈米粒子組裝為法諾電漿共振體

Using click reaction to assemble chains of heterogeneous nanorods as plasmonic Fano resonator

陳琛(Chen, Chen)

指導教授 ： 黃哲勳

國立清華大學/理學院/化學系/碩士(2015年)

https://doi.org/10.6843/NTHU.2015.00102

摘要

當兩個金屬奈米棒距離非常近時，會發生共振產生耦合會在此間隙中產生非常大且集中的光場，此光場可以增進光與物質之間的作用，也提供奈米尺度下控制光與物質作用的可能。重要的應用之一，是將兩種具不同共振的奈米金屬棒連接，使其耦合時在奈米間隙中產生的極強光場，以有效的增益非線性光學信號，例如混頻或倍頻的產生。另一個重要的應用就是利用金屬棒的亮模態與另一金屬棒的暗模態重疊，而這不對稱金屬棒之間的間隙可以在光譜上產生法諾共振(Fano resonance)，其共振位置上呈現極為陡峭的不對稱光譜線，這在生物環境感測上是一個非常重要的現象。到目前為止，前述非均相粒子耦合結構大部分都是經過由上而下(top-down)的製作方式，如電子束顯影製程、聚焦離子束蝕刻，缺點是製作時間長且花費昂貴。我們的目標是使用下而上(bottom-up)的化學反應來製作結構，我們在這裡採用點擊反應(click reaction)來連接兩個不同長寬比的金屬棒，以共價鍵連接兩個經設計過具有不同長寬比的金屬棒，使其在相連後產生預期之共振行為，未來希望可以做為非線性光學增益物質或高靈敏感測器，與下而上的物理蝕刻方式比較，點擊反應的產率幾乎可達90%，間隙長度可調，且可低成本大量製作；與利用DNA共軛螺旋方式相比，點擊反應之鏈結連接是共價鍵，強度高不易分解且不受環境條件影響。
我們利用植晶法合成的奈米金柱表面充滿界面活性劑溴化十六烷基三甲銨的雙層結構。為了合成頭端對頭端的奈米金棒鏈，我們將進行click reaction的分子接在奈米金棒的頭端。在此之前我們必須對奈米金棒進行預處理。我們發現溴化十六烷基三甲銨分子對金的晶面有不同的吸附力，因此我們可以很精準得控制乙腈與水之間的比例以此剝除溴化十六烷基三甲銨的雙層結構。 我們可以獲得頭端是裸露表面、側端是佈滿溴化十六烷基三甲銨分子的奈米金柱，如此一來進行反應的分子可以輕易地接在奈米金柱的頭端。而在奈米金柱鏈的間隙只有2至3奈米。在這麼小的間隙中能夠產生強大的場甚至在非線性光學的範圍中得到有趣的現象。我們利用點擊反應製作的非均相奈米結構的方法可低成本大量製作且結構不易分解，對於奈米偵測以及奈米尺度下的非線性光學信號產生是非常簡單而快速的，希望未來能夠利用自製的結構進行非線性光學信號的調控。

關鍵字

表面電漿共振 ； 點擊化學 ； 奈米粒子

並列摘要

At resonance, two coupled metallic nanorods generate highly enhanced and localized optical field in the gap that promotes light-matter interaction. For coupled heterogeneous nanorods, the highly enhanced field in the gap results in very efficient non-linear optical signal generation at the nanoscale like four-wave mixing. One of the important applications is that if bright mode of short nanorod and the dark mode of long nanorod are turned to spectrally overlap, the resulting asymmetric gap antennas can exhibits asymmetric Fano-like sharp dips in the resonance spectrum, which is of great interest in nano-sensing. So far, well-defined Fano resonators are mostly fabricated using cost inefficient top-down methods, such as electron beam lithography. Our goal is to use click reaction which gives almost 100% product yield to link nanorods with different aspect ratios. Since the nanorods are covered with CTAB bilayer before pre-treatment we have to partially remove the surfactant bilayer in order to bind our linker molecules to the surface of gold nanorods. Here we removed the CTAB surfactant by using acetonitrile. We found that the adsorption of CTAB on Au is facets-dependent and the ratio of ACN to water plays a major role is controlling the partial removal of CTAB bilayer. In order to synthesize head-to-head linkage of nanorods, we have to precisely control the ACN/H2O so that only the ends of nanorods expose and the linker molecules attach only to the exposed ends. In such a way, we generate chains of hetero-nanorods with extremely small gap that ensures a strong coupling and facilitates the asymmetric line shape as well as non-linear signal generation. We have carried out time-dependent spectral analysis on the solution and performed finite-difference time-domain simulations to verify the resonances. Our method is simple, low cost and the product can be used for nano-sensing and nanoscale nonlinear signal generation.

並列關鍵字

Surface Plasmon Resonancce ； Click Chemistry ； Nano Particle

參考文獻

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