金球陣列鑲嵌矽基電漿子奈米天線之製備與波長選擇性光開關特性研究

Fabrication of Au-Nanocrystal-Array/Si Plasmonic Nanoantennas and Their Wavelength-Selective Photoswitching Property

林裕凱(Yu-Kai Lin)

指導教授 ： 陳力俊 ； 周立人

國立清華大學/工學院/材料科學工程學系/博士(2013年)

摘要

在本論文中，我們以一種結合膠體粒子微影法與金屬催化化學蝕刻法的方式第一次成功的製備出具有金球陣列鑲嵌之矽基電漿子奈米天線，而這種製備方法具有容易且所需成本不昂貴的優點。金球陣列鑲嵌之矽基電漿子奈米天線主要是將金奈米晶體陣列以可調控的包埋深度鑲嵌進矽基板所構成，而且此奈米天線的光電流增益特性具有光波長選擇性。
在金球陣列鑲嵌之矽基電漿子奈米天線的製作過程中，金屬催化化學蝕刻法被用來調控金奈米晶體鑲嵌進矽基板的深度，藉此讓奈米天線展現出局部表面電漿子共振光響應特性與波長選擇性光電流增益特性。相較於一般電漿子奈米天線是將金奈米顆粒置於矽基板表面，金球陣列鑲嵌之矽基電漿子奈米天線的強近場增強效應會隨金奈米晶體陣列鑲嵌的深度增加而變強。除此之外，由於局部表面電漿子共振光響應特性容易因周圍環境的介電常數的不同而改變，所以藉著調整金奈米晶體陣列的鑲嵌深度，我們可以控制此奈米天線的光響應特性。
在此論文中，我們利用有限差分時域法來模擬奈米天線的近場分佈，藉此驗證此種奈米天線所具有的波長選擇性光電流增益特性是來自於金奈米晶體的局部表面電漿子共振所引發在其周圍的矽產生局部電場增益。同時論文實驗的結果中，奈米天線局部表面電漿子共振波長的最大值也相當符合模擬結果。
我們利用不同波段的雷射在暗場條件上進行各組奈米天線的波長選擇性光電流增益的測量。在多次雷射光開關循環下的再現性測試可以證明此類型奈米天線可做為光學開關元件。實驗結果顯示，當具有不同金奈米晶體陣列鑲嵌深度的多組奈米天線照射到符合其局部表面電漿子共振波長最大值的雷射光時，在小於200毫伏的偏壓下，具有波長選擇性的光電流增益可高達70 %。此外，實驗的趨勢也符合有限差分時域法的模擬，證明出金奈米晶體產生的局部電場增益增加周圍矽的光吸收能力，因此具有波長選擇性光電流增益特性。
最後，金球陣列鑲嵌之矽基電漿子奈米天線在局部表面電漿子共振光響應特性與具有波長選擇性光電流增益特性有很好的調控能力，這樣的特性可應用於低功耗奈米光學開關、奈米光電與光學通訊裝置上，此外，此奈米天線的製程也可以很容易的與現今矽半導體製程技術結合。

關鍵字

局部表面電漿共振 ； 光響應 ； 金屬奈米晶體陣列 ； 金屬協助化學蝕刻 ； 具波長選擇性光學開關

並列摘要

Au-nanocrystal-array/silicon nanoantennas exhibiting wavelength-selective photocurrent enhancement were successfully fabricated by a facile and inexpensive method combining colloidal lithography (CL) and a metal-assisted chemical etching (MaCE) process for the first time. These nanoantennas comprise Au nanocrystal arrays inlaid in silicon substrates with controllable degree of immersion.

The localized surface plasmon resonance (LSPR) response and wavelength- selective photocurrent enhancement characteristics were achieved by tuning the depth of immersion of Au nanocrystal arrays in silicon through a MaCE process. Compared to conventional Au particles on Si, the high near-field enhancement increases with the fraction of their volume in intimate contact with the substrate in the Au nanocrystal array inlaid Si structure. On the other hand, LSPR responses, which are extremely sensitive to dielectric properties of metal and the surrounding environment, can be tuned by the depth of immersion of Au nanocrystal array on/in silicon.

The wavelength selectivity of photocurrent enhancement contributed by LSPR induced local field amplification was confirmed by simulated near-field distribution. The wavelength maximum of LSPR scattering (max) exhibits sensitivity to the surrounding environment and shows consistence with the simulated results obtained by the finite-difference time-domain (FDTD) method.

The wavelength-selective photocurrent enhancement characteristics were measured under illumination of lasers of different wavelengths and under dark conditions. In addition, the repeatability of wavelength-selective photocurrent enhancement was also tested by multiple ON/OFF cycles and can be exploited as photoswitches. The wavelength-selective photocurrent enhancement (>70 %) operated under low voltage (<200 mV) was achieved under laser illumination coincident to its LSPR max. In addition, the wavelength-selective photocurrent enhancement can be elucidated by the FDTD simulations of the near-field enhancements (|E|^2), which can intensify local electromagnetic field and optical absorption. The good tunability over LSPR responses and wavelength-selective photocurrent enhancement characteristics can be exploited as low power-consumption photoswitches and nano-optoelectronic and photonic communication devices. Furthermore, it can be integrated into the well-developed Si-based manufacturing process.

並列關鍵字

localized surface plasmon resonance ； photoresponce ； metal nanocrystal array ； metal-assisted chemical etching ； wavelength-selective photoswitches

參考文獻

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