利用近場光學顯微術研究表面電漿偏極子於金奈米線陣列之傳遞現象

Study of Surface Plasmon Polariton Propagation on Gold Nanowire Arrays by Near-Field Scanning Optical Microscopy

黃志翰(Jyh-Hann Huang)

指導教授 ： 林鶴南

國立清華大學/工學院/材料科學工程學系/碩士(2008年)

https://doi.org/10.6843/NTHU.2008.00244

摘要

目前引起眾人興趣的表面電漿偏極子(surface plasmon polaritons, SPPs)是因電子集體振動而產生並具空間侷限性的電磁波，由於表面電漿偏極子的特殊性質，許多二維的元件可被廣泛應用於奈米光子學及生物感測器，如表面電漿反射鏡、分光器、光波導等。
本研究使用利用近場光學顯微術，來觀察金圖案上的表面電漿偏極子激發與傳遞現象，在金圖案的製作上分成兩部分，金奈米線陣列是由原子力顯微術之機械力微影製作，其他圖案則是利用電子束微影來製作。利用TM偏極化綠光雷射，入射於稜鏡造成全反射來激發金圖案上的表面電漿偏極子，並使用近場光學顯微術來觀察其表面的光分布情形。
當光源平均照射在5 μm寬20 μm長的金微米線上時，在金表面上觀察到明顯的表面電漿波干涉條紋，其波長量出來為480 nm，與理論計算之數值相當吻合(λsp = 471 nm)，當雷射照射於金微米線的一端，在另一端發現表面電漿的傳遞現象及散射現象。對於金奈米線(寬130 nm, 長15 μm)陣列，雷射光分為兩種入射方式，當入射方向與陣列方向平行，雷射光照射於金奈米線陣列的一邊，在金奈米線陣列另一邊觀察到表面電漿波干涉條紋，波長量測出來為479 nm，再次與理論結果相吻合；當入射方向與陣列方向垂直，則觀察到在金奈米線兩旁的電磁場比在石英玻璃上的電磁場強度約增強了3.5倍。最後，當金線的表面電漿偏極子被激發時，施加電壓於金線兩旁，觀察到表面電漿波干涉條紋因電流通過而出現擾動現象。

關鍵字

表面電漿偏極子

並列摘要

Surface plasmon polaritons (SPPs), which are spatially confined electromagnetic modes related to collective electron oscillations, are now attracting substantial interests. Due to the unique characteristics of SPP, two dimensional devices such as SP mirrors, SP beam splitters, SP waveguides, etc. can be found in a broad range of applications including nanophotonics and biological sensing.
In this work, SPP excitation and propagation on gold patterns are studied by near-field optical scanning microscopy (NSOM). For constructing the gold patterns, AFM nanomachining is used to create nanowire arrays. On the other hand, e-beam lithography is used to define other patterns. The SPPs are excited by an attenuated total reflection (ATR) configuration with the use of a transverse magnetic polarized laser source (532 nm). The optical distributions on the gold patterns are studied by a commercial NSOM.
By illuminating gold microstripes (5 μm in width and 20 μm in length) uniformly, the optical image shows the excitation of SPPs with an obvious interference pattern. The measured wavelength of 480 nm is in good agreement with the calculated wavelength of the surface plasmons (λsp = 471 nm). By illuminating one side of a gold microstripe, SPP propagation and scattering at the other side is observed. A gold nanowire (130 nm in width and 15 μm in length) array is illuminated by focusing a laser beam with two types of incident direction. With the incident direction parallel to the nanowire array, SPPs are excited on one side of the array and propagating to the other side. The measured wavelength of 479 nm is again in good agreement with the calculated wavelength. With the incident direction perpendicular to the nanowire array, the electromagnetic field enhancement on both sides of nanowires is 3.5 times larger than that on the quartz. Finally by applying a voltage between the two sides of a gold microstripe when SPPs are excited, the disturbance of the SPP interference pattern is observed when a current passes through the microstripe.

並列關鍵字

Suface plasmon polaritons

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