奈米金團簇與石墨烯奈米結構的光學特性與應用

Optical Properties and Applications in Gold Nanoclusters and Graphene Nanostructures

林子能(Tzu-Neng Lin)

指導教授 ： 沈志霖

中原大學/理學院/物理研究所/博士(2015年)

https://doi.org/10.6840/CYCU.2015.00187

摘要

奈米材料是指其粒徑小於約100奈米以下之材料，在其獨特引人注意之尺度下，恰可作為宏觀與微觀世界之橋樑。隨著科技的進步，對於製做奈米材料的技術有著越來越多的進展，在此過程中發現到奈米材料其性質已與其原有之屬性大不相同。因為奈米材料不僅具有小尺寸特性外，其獨特的物理和化學性質包括光學、電學、磁學和機械之特性，相對於塊材來說，已有著明顯的改變。
量子點為一種半導體的奈米粒子，經過多年來許多學者的研究，量子點有著更多不可忽略的潛力如:螢光亮度強、光穩定性佳(即螢光時效久，沒有光漂白作用)、用單一波長雷射就可激發不同粒徑的量子點、藉由調控粒徑大小來改變螢光波長、螢光波形狹窄且對稱、載子生命期長、可重複激發與好的生物接枝特性等。不過，大部分的量子點都是以毒性重金屬鎘為主，由於考量到生物安全性與環境保護，侷限了量子點在生醫與其他方面的應用。為了讓量子點能廣泛應用於生醫及其他領域，找尋較無毒性的量子點材料，希望能發展出低環境污染、低生物毒性、高生物相容性的環保量子點為另一大重要課題。
在本論文研究當中，我們提出一種低毒性且簡易合成的螢光金奈米團簇，與環保且快速製備的石墨烯量子點。這項研究的結果在生醫檢測與細胞標定上，希望具有前瞻且重要的貢獻。論文的內容可簡要的分成四個部份：
1. 硫醇基包覆之螢光金奈米團簇的位置選擇性光激螢光光譜研究
至今，螢光金奈米團簇的發光機制仍存在著許多爭議。因此，為了瞭解載子在復合放光的過程，我們改變不同激發波長來量測硫醇基包覆之螢光金奈米團簇光激螢光與時間解析螢光光譜。當激發光源界於1.6 eV至2.1 eV時，螢光光譜有紅位移與半高寬的改變，更近一步從時間解析螢光光譜發現螢光金奈米團簇的載子復合時間是跟激發能量有相當關係，藉此提出螢光金奈米團簇位置選擇性螢光光譜模型，主要為載子受到侷域態的影響。
2. 開發波導式螢光共振能量轉移平台用於螢光金奈米團簇偵測雙氧水
以波導式螢光共振轉移技術發展螢光金奈米團簇為主之生醫感測器為此章節的目標。螢光金奈米團簇是一種無毒的材料，因此結合螢光金奈米團簇與螢光共振能量轉移所設計的生物探針技術，將對分子生物結構與分子生物交互作用有更多的研究應用。利用光學波導方式量測由InGaN量子井傳遞給螢光金奈米團簇之螢光共振能量轉移現象來偵測雙氧水的濃度。藉用光激螢光光譜量化出雙氧水濃度與螢光強度改變之關係；再者由時間解析光激螢光瞭解雙氧水造成光焠滅之機制。此技術的開發有利於大範圍偵測與直接觀察。
3. 探討InGaN量子井與氧化石墨烯間距離相關之螢光共振能量轉移
研究InGaN量子井與奈米材料之間非輻射的能量轉移現象。藉用時間解析光激螢光光譜探討改變施子與受子之距離其載子生命期的變化。當受子為氧化石墨烯時，結果可知其能量轉移過程是利用二維偶極磁矩-二維偶極磁矩相互作用，則關係成倒數二次方反比(d-2)，而最大能量轉移效率為施子覆蓋層為2nm時達82%。
4. 運用雷射削融法製備氧化石墨烯奈米結構：從奈米緞帶到量子點之形狀可調
氧化石墨烯為石墨烯之衍生物，可視為在一石墨烯基面上接上許多含氧官能基，造成由 sp2和 sp3鍵結之碳原子所組成的混和式原子和電子結構。石墨烯量子點由於尺寸在 20nm以下表現出更強之量子侷限與邊界效應，因此，在太陽能光電元件、發光二極體與生物感測器等許多領域上，具備相當潛力的應用前景。在本論文中，提出一種新穎且快速的雷射削融法處理氧化石墨烯水溶液來製備其奈米結構。隨著處理時間上的不同，可發現到氧化石墨烯奈米結構會形成幾種特定形狀之奈米薄片 (正方形、長方形、三角形、六角形、圓盤狀)，更進一步利用光激螢光與時間解析螢光光譜來研究石墨烯量子點的光學特性，其載子復合過程與本身邊界結構之侷域態能階有關。

關鍵字

金奈米團簇 ； 光激螢光 ； 螢光共振能量轉移 ； 脈衝雷射削融法 ； 氧化石墨烯 ； 波導 ； 時間解析

並列摘要

Nanomaterials typically possess sizes less than approximately 100 nm and have been attractive for their unique roles in bridging the missing link between the macroscopic and the microscopic view of the world. With the advances of science and technology, the processes of the fabrication techniques increase more and more progress and bring up the properties of nanomaterials with different nature instincts. Nanomaterials have advantages of small size and unique physical and chemical properties such as quantum confinement and surface effects. Therefore, nanomaterials have been produced and applicated in the high-tech industry and have a significant impact on the world.
Quantum dots (QDs) are semiconductor nanoparticles that can serve as powerful fluorescent labels for tracking biological processes in live cells due to their unique properties such as broad excitation spectra, narrow emission spectra, tunable emission peaks, long fluorescence lifetimes, and negligible photobleaching. In additional, QDs have ability to be conjugated with proteins, making them excellent probes for bioimaging applications. However, semiconductor QDs containing heavy metal are toxic, making them unsuitable for in vivo clinical application, and may pose risks to human health as well as the environment. In this dissertation, we have investigated the luminescence properties of Au nanoclusters (AuNCs) and developed a green and facile synthesis for carbon-based quantum dots. The results of this study should be very valuable for both academic and industrial applications. The highlights of our achievements are briefly described below.
1. Site-selective photoluminescence in thiol-capped gold nanoclusters
Photoluminescence (PL) from the thiol-capped AuNCs has been investigated under site-selective excitation. By means of a spectrally tunable excitation source, site-selective PL is a technique to reveal the relaxation of excited carriers in the luminescence processes. Upon scanning the excitation light with energy below 2.1 eV down to 1.6 eV, the PL narrows and begins shifting linearly with excitation energy. The time-resolved PL was studied and the PL decay traces of Au NCs were found to depend on the excitation and emission energies. The slow carrier relaxation in the localized states is suggested to be responsible for the line narrowing and peak-shift in the site-selective PL.
2. Waveguide Based Energy Transfer with Gold Nanoclusters for detection of Hydrogen Peroxide
H2O2 detection that uses fluorescence resonance energy transfer from InGaN quantum wells to Au nanoclusters via optical waveguiding has been developed. This new type of energy transfer with optical waveguides has an important benefit, i.e., the acceptor is excited solely by energy transfer from the donor, avoiding unwanted excitation from the incident light and leading to an accurate energy transfer efficiency. Steady and time-resolved PL studies have been used to demonstrate the waveguide-based energy transfer. H2O2 detection is achieved by the quenching of the red emission from AuNCs. Advantages of the sensing technique include capability of visual detection and large area analysis.
3. Distance dependence of energy transfer from InGaN quantum wells to graphene oxide
Distance-dependent energy transfer from an InGaN quantum well to graphene oxide (GO) by the time-resolved PL have been studied. A pronounced shortening of the PL decay time in the InGaN quantum well was observed when interacting with GO. The nature of energy transfer process has been analyzed and we find the energy-transfer efficiency depends on the 1/d2 separation distance, which is dominated by the layer-to-layer dipole coupling. The maximum energy transfer efficiency of this system can be as high as ~82%, which is promising for realization in sensing applications.
4. Laser-Ablation Production of Graphene Oxide Nanostructures: from Ribbons to Quantum Dots
A new one-step method for the preparation of GO nanostructures has been developed by pulsed laser ablation in GO solution. The formation of different shapes of GO nanostructures such as ribbons, nanoflakes (including nano-squares, nano-rectangles, nano-triangles, nano-hexagons, and nano-disks) and QDs have been demonstrated by scanning electron microscopy and transmission electron microscopy. Photoreduction for the GO occurred during irradiation by the pulsed laser. The GO QDs exhibit a blue PL, originating from recombination of the localized carriers in the zigzag-edge states.

並列關鍵字

fluorescence resonance energy transfer ； waveguide ； graphene oxide ； photoluminescence ； gold nanocluster ； time-resolved ； pulsed laser ablation

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