可調式寬頻電漿子熱點之製作及應用

Fabrication of Ag Nanostructures Using the Femtosecond Laser for Broadband and Tunable Plasmonic Enhancement

黃信維(Hsin-Wei Huang)

指導教授 ： 蔡定平

國立臺灣大學/理學院/物理研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.10732

摘要

本論文研究領域為奈米光學，主要探討光與奈米尺度金屬結構的交互作用。當光照射在金屬奈米結構，入射光部分能量將被金屬奈米結構吸收而產生共振，若金屬奈米結構與金屬奈米結構間隙小至數奈米，此奈米間隙會產生很強的侷域電場，此強大的侷域電場稱之為電漿子熱點(plasmonic hotspot)。一般製作能夠產生電漿子熱點的金屬奈米結構其製程是比較複雜的，也很難控制電漿子熱點的位置及強度。本論文提出一個簡單又快速的方法製作這種具有電漿子熱點的金屬奈米結構，除了可以控制電漿子熱點的位置及強度之外，也具有光學上寬頻的響應。實驗上利用濺鍍機鍍上氧化銀薄膜，以波長為800 nm的超快雷射當光源聚焦在氧化銀薄膜上，此時會有數奈米到數十奈米且高密度的銀奈米結構出現，因為其結構顆粒大小不一，可以對應到不同波長的吸收，如此將具有寬頻表面電漿共振，意味工作波長也是寬頻，因為銀奈米結構密度非常高，具有許多銀奈米結構所構成的奈米間隙，當光入射時將會產生電漿子熱點。此外調控超快雷射的入射功率，會產生不同表面形貌的銀奈米結構，其電場強度隨著結構而改變，如此即可製作可調式寬頻電漿子熱點結構。利用超快雷射製作銀奈米結構具有強大的侷域電場以及寬頻吸收的特性，將其應用在使半導體量子點發光增強、拉曼訊號增強。

關鍵字

表面電漿子 ； 電漿子熱點 ； 寬頻吸收 ； 奈米結構 ； 雷射加工 ； 電漿子增強

並列摘要

Using a femto-second laser, we have transformed the laser-direct-writing technique into a highly efficient method that can rapidly process glass substrate into aggregates of Ag nanoparticles that provide plasmonic enhancement. The processed AgOx thin films showed enhanced optical absorption over a broad spectral range. The treated AgOx thin film can effectively function as an active substrate for surface enhanced Raman scattering measurement. Degree of Raman enhancement can be tuned by controlling the processing laser power. The large pulse power delivered by the femto-second laser allows for a continuous scan across the sample surface at the fast processing rate of more than 300μm2/min, which is at least two orders of magnitude faster than other reported laser-direct-writing techniques with either continuous or nano-second lasers. In addition, the hotspots are found to be uniformly distributed over the treated area. The laser-generated Ag nanostructure can also be used to enhance the fluorescence of semiconductor nanocrystals as high as four fold. This technique offers an efficient and cost effective approach to develop large area active substrates from AgOx thin films for plasmonic enhancement applications.

並列關鍵字

Surface plasmons ； Plasmonic hotspots ； Broadband absorption ； Nanostructures ； Laser fabrication ； Plasmonic enhancement

參考文獻

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