探討銀之合成技術與其於電漿子光學上之應用: 表面電漿極化子傳輸、光降解、表面電漿極化子振幅調制技術

Synthesis and applications of visible plasmonic Silver: Far surface plasmon polariton (SPP) propagation, excellent photodegradation, and SPP amplitude modulations

張正偉(Chang, Cheng Wei)

指導教授 ： 嚴大任

國立清華大學/工學院/材料科學工程學系/博士(2016年)

摘要

表面電漿極化波是於近場介電質金屬介面間傳輸，其傳輸損耗在電漿子光學元件中如共振態或電漿耦合情形是一門重要課題。在可見光波段下，銀雖有相對其他金屬而言較低之吸收損耗，但其損耗不僅是原自其能帶傳輸所造成，有相當一部分原因是來自銀本身材料缺陷或有其他不純物參雜造成。在本研究我們首先發展硝酸輔助合成單晶大微米銀板，其具有量產優勢且最大側邊長可長至50微米。在本研究會討論其生長機制與展現其表面電漿極化波傳輸增益，我們發現在巧妙控制硝酸與乙二醇濃度可以有效控制銀板生長大小，且相比於電子束蒸鍍製程所鍍銀薄膜，單晶銀板有其兩倍等效傳輸距離，證實銀板可當作電漿子光學材料且具有低材料缺陷、不需鍍緩沖層、且可轉移至任意基板之優勢。
利用上述製程我們也可巧妙控制銀板邊長在3-5微米，藉由鋪平銀板於其上長氧化鋅奈米線，可以有效增強光觸媒活性，使用穿透式電顯與X光能譜儀可證明氧化鋅與銀為直接接觸和有光電子傳遞現象。氧化鋅與銀直接接觸可有效使光電子自氧化鋅電子電洞對分離後傳至銀上，減少再復合現象產生，我們利用降解亞甲基藍溶液得到證實，其異質結構有1.35倍之動力常數，我們也利用工程品質因數來對其他文獻所發展之異質結構做比較，發現此異質結構有較佳之工程品質因數。
最後，我們使用金屬銀與電漿子魚骨結構製作兩種表面電漿極化振幅調制器。一是使用角頻率差1.66 MHz在魚骨結構表面進行調制，另一則為使用偏振態旋轉頻率與偏振態本身做調制，其訊號為1-10k Hz。此優勢為可以有效縮小光學調制器之大小與降低損耗，我們相信此二種訊號調制方式可以有效所小現階段使用之振幅調製器與提升振幅調制訊號之訊號碼(目前多為八至十六碼，利用本偏振調制方式可以容納更高位數)。

關鍵字

微米銀板 ； 表面電漿極化子傳輸距離 ； 光觸媒 ； 光降解 ； 表面電漿極化子 ； 表面電漿極化子振幅調制

並列摘要

Since surface plasmon polarition (SPP) waves propagate in the definite dielectric/metal region, the propagation loss is an important issue and related to the optical responses like on-resonance states or coupling frequencies. In visible region, plasmonic material Ag has attracted great attentions because of low absorption loss. However, the losses in Ag are not only attributed to the interband or intraband transitions but also to the surface defects and the impurities. We herein develop a fabrication method called HNO3-assisted polyol reduction method that possesses mass production single-crystalline Ag microplates with the largest lateral size up to 50 μm. The growth mechanism and the improved SPP propagation length are investigated, showing that the concentrations of ethylene glycol (EG), HNO3 dominate the growth of Ag microplates and the SPP propagation length is 2 folded longer than the typical E-gun deposited Ag thin film. Such the ultralarge Ag microplates can serve as the low defected, versatile used, buffer layer free plasmonic platform
Furthermore, using HNO3-assisted polyol reduction method can control the lateral size of Ag microplates. The use of relatively small size Ag microplates with 3-5 μm is carried out for sinking the photogenerated electrons in the ZnO/Ag heterostrcuture. The growth of ZnO nanowires on Ag microplates shows that the directly contact and the charge transfer effect are confirmed by TEM and XPS observation. The ZnO/Ag contacts can effectively enhance the photocatalytic activity in photoinduced degradation processes, showing that the kinetic constant for our ZnO/Ag heterostructure possesses 1.35 folds than the pure ZnO nanowires. The figure of merit (FOM) value is used for fairly comparing the ability of photodegradation among other ZnO/Ag heterostructure, revealing that our ZnO/Ag heterostructure has a better performance than others (1.02 × 10-2).
In the final part, we use metallic Ag and plasmonic Fishbone (FB) structures to develop two kinds of SPP amplitude modulation (SPPAM). One is the use of angular frequency difference to serve as a modulation signal and beats on 1.66 MHz, showing that beat frequency SPPAM works beyond SPP subwavelength region and can be readout by the oscilloscope construction. The other is the use of changing polarization states frequencies and polarization states that can act as the modulation signals in the ranges of 1-10k Hz, showing that the intensity difference between the left/right-sided FB structures with the modulation signals. Taking the advantages of reducing the power consumption and the channel length, we believe that the compact SPPAMs can be used for miniaturizing the modulators and upgrade the 8/16 coding bits to multi-bits.

並列關鍵字

Ag Microplates ； SPP Propagation length ； Phtocatalysis ； photodegradation ； Surface Plasmon Polaritons ； SPP Amplitude Modulations

參考文獻

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