利用金屬表面電漿光學性質製成的光調控裝置

Tunable optical devices based on metallic surface plasmons arising from nanostructured materials

陳中澤(Chung-Tse Chen)

指導教授 ： 陳永芳

國立臺灣大學/理學院/物理研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.00297

摘要

本論文中，我們將探討如何利用金屬粒子的表面電漿來調控硒化鎘及鋅銅銦硫兩種量子點的發光，以及電漿光子晶體及其與金屬的複合結構的光學特性。金屬表面電漿的激發波長可因外界環境、金屬奈米結構週期及大小等等來改變，利用這個特性，我們將之與其他材料結合，包括量子點、光子晶體及液晶，來製成各種光電元件及感測元件，而這些有趣並創新的研究成果，必會對於光電元件的未來發展有正面的影響。本論文主要分成四個部分，茲摘要如下：
1. 存在於摻雜金奈米粒子及鎘化硒量子點的液晶裝置中的激子及表面電漿子的可調控交互作用在第一部分中，我們將介紹一種可調控光的摻雜金奈米粒子及硒化鎘量子點的液晶裝置。我們利用外加電壓，即可微調此裝置的發光波段。這是因為同樣存在於裝置中的金奈米粒子，其含有的表面電漿子的激發波長可藉由液晶折射率的改變而調控，進而利用表面電漿子與硒化鎘量子點的激子的交互作用，使得鎘化硒量子點的發光波長也隨之改變。這個利用金奈米粒子調控光的策略可以運用到其他類似的光電元件，同時也推動它的發展。
2. 利用金奈米粒子加強無鎘的鋅銅銦硫-硫化鋅複合量子點的光學特性在第二部分，我們則探討金屬奈米粒子對於鋅銅銦硫-硫化鋅複合量子點的影響。我們發現若將此量子點裹上一層二氧化矽隔絕層來控制其與金奈米粒子的距離，可以讓鋅銅銦硫-硫化鋅複合量子點的亮度加強三倍，增加其量子產率，並意外地發現可以縮小其頻寬，使其對於單一色發光裝置有更好的應用。我們的發現讓此量子點在發光二極體的應用中能有更好的發揮。
3. 電漿光子晶體中的異常穿透現象的調控在第三部分，我們用膠體顆粒球組成光子晶體，再鍍上金形成電漿光子晶體結構。結構中異常穿透現象的穿透波段一般來說是根據布拉格繞射理論推算，但我們發現它與金屬層的厚度及外界環境也有很深的關連。此一結果是因為位於金屬層上下表面的表面電漿會產生交互作用，因而影響穿透光波長的位置。根據這個新發現的結果，我們將此裝置與液晶結合，形成一個可用電場調透穿透光波長的裝置。此裝置充分運用了金屬、光子晶體及液晶的特性，並啟發了此種複合結構的未來。
4. 金屬-絕緣層-金屬的電漿光子晶體結構中的巨大吸收頻譜位移現象在第四部分中，我們進一步將電漿光子晶體製成金屬-絕緣層-金屬結構，並研究此改變對於原有電漿光子晶體吸收頻譜的影響。很意外地，我們發現這種新型的金屬粒子-絕緣層-金屬球殼週期結構可以將原有的吸收波峰紅位移高達450奈米，此位移遠高於所有先前的結果。這個位移現象可以以絕緣層厚度控制，而吸收波段也可由內層金屬球殼大小來調控。根據本實驗的結果，此金屬複合結構應有著極強的電磁場，並可應用到生物感測系統及其他光電元件上。

關鍵字

金屬表面電漿 ； 金奈米粒子 ； 硒化鎘量子點 ； 銅銦硫量子點 ； 發光增益 ； 光調控 ； 液晶 ； 電漿光子晶體 ； 金屬-絕緣層-金屬複合結構 ； 光偵測器

並列摘要

In this thesis, we have reported the interesting optical properties and applications of several novel hybrid devices consisting of metal nanostructures and other optoelectronic materials, such as quantum dots (QDs), liquid crystal (LC), and photonic crystal composed of colloidal nanospheres. There are four parts in this thesis. In part 1, we introduced an tunable optical device consisting of Au nanoparticles, CdSe QDs and LC. With an external bias, the emission wavelength of CdSe QDs can be tuned easily and reproducibly. In part 2, by the aid of surface plasmon of Au nanoparticles, we introduced a route to enhance the emission intensity and shorten the bandwidth of nontoxic ZnS(CuInS2) (ZCIS) quantum dots. In part 3, we introduced the tunability of the extraordinary optical transmission of plasmonic photonic crystal (PPC) composed of colloidal periodic array coated by Au. The transmission peak position of PPC can be controlled by Au thickness, the refractive index of surroundings, and an external bias through integrating LC. In part 4, a new metal-insulator-metal (MIM) PPC structure would be presented. There exists a strong SP coupling in the MIM PPC structures containing metallic nanoparticles, which can be controlled by the thickness of the dielectric layer.

1. Tunable Coupling Between Exciton and Surface Plasmon in Liquid Crystal Devices Consisting of Au Nanoparticles and CdSe Quantum Dots
We report controllable coupling between exciton and localized surface plasmon in a liquid crystal device consisting of gold nanoparticles and CdSe QDs. Through an external electric voltage, the emission wavelength of QDs can be manipulated. The underlying mechanism is based on the fact that by changing the dielectric index of liquid crystal with an external bias, the surface plasmon frequency of metal naoparticles can be adjusted. It is therefore possible to control the energy difference between exciton and surface plasmon resonance, and hence to change their coupling strength. Our strategy may open up a possible route for the development of smart optoelectronic devices with tunable emission color.

2. Enhancement of Emission Characteristics of Cadmium-free ZCIS/ZnS/SiO2 Quantum Dots by Au Nanoparticles
The resonant coupling between cadmium-free I-III-VI2 group QDs and metal nanostructures has been investigated. Via a SiO2-packaging synthetic procedure, the emission intensity of green ZCIS/ZnS QDs can be greatly enhanced by three times through the localized surface plasmon of Au nanoparticles. Moreover, the bandwidth of the emission spectrum can be narrowed by 17 nm, and the resultant quantum yield is more than 50% which sets up the highest reported value up today for green I-III-VI2 QDs. Our strategy for the improved characteristics of emission spectrum may open a facile alternative for the development of cadmium-free QD light emitting diodes and other optoelectronic devices.

3. Tunable Extraordinary Optical Transmission Based on Suface Plasmon of Plasmonic Photonic Crystal
An Au coated two-dimensional colloidal periodic structure, a kind of plasmonic photonic crystal, has been fabricated and characterized. Besides the well-known effect due to Bragg diffraction, it is found that the extraordinary transmission spectra also strongly depend on the thickness of Au film, the refractive index of surroundings, and the coupling between both surface plasmons on the two interfaces of Au film. Based on the above intriguing result, LC and PPC structure were integrated to form a new device, which enables to tune the extraordinary transmission spectra by an external bias. It is expected that the novel properties of PPC shown here, could promote a route for the generation of optoelectronic devices derived from plasmonics and photonic crystals.

4. Giant Spectral Shift of Extraordinary Absorption Arising from Metal Nanoparticle-Insulator-Metal Plasmonic Photonic Crystals
The extraordinary absorption of the metal-insulator-metal (MIM) plasmonic photonic crystal (PPC) based on two-dimensional colloidal periodic structures have been fabricated and characterized. Quite surprisingly, it is found that there exists a huge spectral shift up to 450 nm due to the strong coupling in the MIM structure containing metallic nanoparticles. The peak wavelength of the extraordinary absorption could be tuned by controlling the thickness of the dielectric layer as well as the diameter of colloidal spheres. Based on the tunability of surface plasmon frequency, the MIM PPC structure is a good candidate to facilitate for a variety of application, including optoelectronic devices, surface enhanced Raman scattering, and biosensors.

Our results not only provides a more detailed understanding of surface plasmon resonance integrating with QDs, LC, and photonic crystals, but also demonstrates great potential applications of SPs to improve the optical tunability of optoelectronic devices.

並列關鍵字

surface plasmon ； Au nanoparticles ； CdSe quantum dot ； ZCIS/ZnS quantum dot ； liquid crystal ； tunable light ； emission enhancement ； plasmonic photonic crystal ； metal-insulator-metal structure ； coupling ； sensors

參考文獻

Chapter 1

1. C. P. Poole, F. J. Owens, Introduction to nanotechnology (John Wiley, Hoboken, 2003).

2. J. Gribbin, M. Gribbin, Richard Feynman: A Life in Science (Dutton, 1997).

3. H. Raether, Surface plasmons on smooth and rough surfaces and on gratings (Springer, New York, 1988).

5. U. Leonhardt, Nature Photonics, 1 207 (2007).