半導體量子點和奈米金屬結構之交互作用研究

Investigation of the coupling between semiconductor quantum dots and metal nanostructures

陳志瑋(Chih-Wei Chen)

指導教授 ： 陳永芳

國立臺灣大學/理學院/物理研究所/博士(2010年)

https://doi.org/10.6342/NTU.2010.01591

摘要

在本論文中，我們研究了半導體量子點結合了金屬奈米粒子、金屬奈米團簇的物理特性。在第一部分，我們引用了結合聚二甲基矽氧烷(PDMS)的簡單方法來研究混合不同大小的鉻化硒量子點之間的能量轉移現象。並且利用相同的方法，在第二部分我們研究了金奈米粒子的表面電漿影響鉻化硒量子點的光學特性。在第三部分，我們研究無毒的銀奈米粒子的表面電漿造成與可發光金奈米團簇高靈敏度發光改變的現象。最後在第四部份同樣利用聚二甲基矽氧烷製作二氧化矽包著金奈米柱的柵狀結構。並結合了鉻化硒量子點，我們發現了量子點的螢光被增強且產生了光學的偏振特性。
1. 結合鉻化硒量子點與彈性模的可調控能量轉移
我們引進了一個簡單的方法來研究同種量子點間的距離與能量轉移現象的關係。特別的是不需要製作很多樣品來改變濃度，利用具有可伸縮特性的聚二甲基矽氧烷彈性膜即可改變混和大小的鉻化硒量子點間的能量轉移現象。我們的結果符合Föster型態的能量轉移，其中量子點間的距離R0與能量轉移效率E符合E=1/[1+(R/R0)6]的關係。
2. 利用彈性模來調控金奈米顆粒與鉻化硒量子點組合的螢光強度
我們利用簡單的方式來研究半導體量子點與金屬奈米粒子的間的距離與發光的關係。同樣的不需改變金屬與半導體的混合農度，將鉻化硒量子點與金奈米顆粒埋入伸縮性強的聚二甲基矽氧烷膜之中，我們可以輕易的改變半導體的發光強度。我們發現隨著兩種粒子的距離改變，發光強度會有增強與減弱的效應。這個現象是因為表面電漿引發局部電場增強，使半導體的發光變強；而另一方面半導體的載子可經由能量轉移到金屬表面而使發光衰減。
3. 應用銀奈米顆粒與金奈米團簇的表面電漿與能量轉移的高靈敏度檢測器
在研究發光的金奈米團簇與銀奈米顆粒子的作用中，我們發現了金的發光對於銀粒子的存在非常敏感。值得注意的是，金奈米團簇的發光強度可以因此衰減了幾百倍。我們利用表面能量轉移的機制來解釋這個現象。而能量轉移效率χ與粒子間距離的關係符合χ=1/[(1+d/d0)4]。這樣高靈敏的發光改變，並結合了無毒的金團簇與銀顆粒，非常適合發展生物檢測與藥物傳遞的應用。
4. 鉻化硒量子點在金屬奈米柱柵狀結構下由表面電漿產生的光學偏振特性
藉由結合柵狀結構的表面電漿共振，我們可以簡單的控制鉻化硒量子點的光學偏振特性。簡單的利用聚二甲基矽氧烷當作轉印的方式，我們可以製作結構良好的金奈米柱的的柵狀結構。我們發現在柵狀結構上的鉻化硒量子點，顯現了明顯的光學偏振特性。值得注意的是，偏振的方向與柵狀結構的方向垂直。而這樣的結構適合發展光學轉換器與偏振特性的發光二極體。
本論文之研究結果不但增進對奈米材料的理解，亦可以對其應用有很大的助益。

關鍵字

能量轉移 ； 表面電漿 ； 金奈米顆粒 ； 金奈米團簇 ； 金奈米柱 ； 鉻化硒量子點

並列摘要

In this thesis, we have reported the physical phenomena based on the composites of semiconductors quantum dots (QDs), metallic nanoparticles (NPs), and metallic nanoclusters (NCs). In the part 1 we introduced a simple approach to investigate the tunable energy transfer effect of mixed-size CdSe quantum dots combined with elastomeric poly-dimethylsiloxane (PDMS) film. Then following the same approach, in part 2 we investigated the influence of surface plasmon of gold nanoparticles on the optical properties of CdSe QDs embed in elastomeric PDMS film. In part 3, we performed the effect of surface plasmon on highly sensitive energy transfer between the non-toxic metallic silver NPs and gold NCs. In part 4, we demonstrated a novel strategy to fabricate well aligned assembly gold nanorods. It is found that the photoluminescence of CdSe QDs on the structure can be strongly enhanced and revealed optical anisotropic properties.

1. Tunable energy transfer efficiency based on the composite of mixed CdSe quantum dots and elastomeric film
We demonstrate a facile and general approach to investigate the dependence of energy transfer on the separation distance between proximal mixed-size quantum dots. Without varying the mixed concentrations, the tunable energy transfer efficiency is achieved based on the composite of mixed quantum dots and elastomeric film by utilizing the inherent nature of the flexibility of elastomeric film. To demonstrate our working principle, the composite of mixed-size CdSe quantum dots and poly-dimethylsiloxane has been studied. The results clearly show that the energy transfer process between proximal quantum dots follows the Förster resonance energy transfer, in which the dependence of the transfer efficiency E as a function of the donor-acceptor distance R obeys E = 1/[1+(R/R0)6].

2. Tunable emission based on the composite of Au nanoparticles and CdSe quantum dots deposited on elastomeric film
A simple approach to investigate the dependence of emission on the separation distance between semiconductor quantum dots and metal nanoparticles is demonstrated. Without varying the mixed concentrations, a tunable emission is achieved based on the deposition of the composite of Au nanoparticles and CdSe quantum dots on elastomeric film. By utilizing the inherent nature of the elasticity of the elastomeric film, it is found that depending on the separation distance, the emission intensity can be quenched or enhanced. The underlying mechanism can be explained quite well by the interplay between the local field excitation due to surface plasmons and electrons transfer to metal nanoparticles.
3. Highly sensitive emission sensor based on surface plasmon enhanced energy transfer between gold nanoclusters and silver nanoparticles
In the study of interaction between emissive gold nanoclusters and silver nanoparticles, we explored that the emission of gold nanoclusters is very sensitive to the presence of silver nanoparticles. Quite remarkably, the quenching ratio can reach more than several hundred times. We demonstrate that the underlying mechanism can be attributed to the surface energy transfer with the quenching efficiency following the expression χ = 1/[1+(d/d0)4], where d is the distance between gold nanoclusters and silver nanoparticles, and do is the characteristic length of energy transfer. This highly sensitive behavior in the composite consisting of relatively nontoxic gold nanoclusters and silver nanoparticles may find a powerful potential in developing biomedical applications, such as biosensors and drugs delivery.

4. Surface plasmon induced optical anisotropy of CdSe quantum dots on well aligned assembly gold nanorods
A simple approach that can be used to control the optical anisotropy of CdSe/ZnS quantum dots by coupling to the surface plasmon resonance of a metal grating has been demonstrated. We present well aligned assembly gold nanorods grating structure by combining polydimethylsiloxane as a stamp. It is found that CdSe quantum dots on the structure revealed optical anisotropic effect due to the resonance with the transverse surface plasmon mode. It is worth noting that the polarized direction of emission was perpendicular to the axis of grating structure. This well aligned metal structure can be developed for the application of optical devices such as optical switch and polarized light emitted diodes.
The novel phenomena discovered in this thesis not only provide a more detailed understanding of nanomaterials, but also able to enhance their applications.

並列關鍵字

Energy transfer ； Surface plasmon ； Gold nanoparticles ； Gold nanoclusters ； Gold nanorods ； CdSe Quantum Dots

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