通過與具有表面等離子體激元特性的金屬納米晶複合，半導體納米材料的捕光能力可以得到很大地提高。銀、金納米晶因其獨特的表面等離子體特性，已被廣泛應用于半導體複合物的製備。其中通過沉積或者粘合方式得到的複合物存在一定弊端，比如：金屬納米晶暴露在實驗環境中，導致其團聚、變形、脫落、或者長大，使原有的獨特表面等離子特性改變或消失。核/殼結構納米材料可以有效地避免以上問題，因而表現出優越的光活性。爲了進一步拓寬金屬/半導體核/殼結構在光能捕獲方面的應用，我们需要深入理解製備過程中表面等離子體激元特性及材料結構的變化、設計合成新的納米材料。在這篇畢業論文中，我研究了在製備Ag/Ag2S核/殼結構過程中的表面等離子體特性及材料結構的變化，制備了Au/TiO₂核/殼結構，并對他們的應用及表面等離子體共振激元特性進行了研究。 / 理解硫化過程有助於更好的控制其表面等離子體特性和結構組成。因此，我分別從實驗和數值模擬兩方面研究了銀納米立方塊在硫化過程中表面等離子體特性及其相應Ag/Ag₂S 核/殼的組成及結構的變化。硫化反應分別在溶液及單顆粒環境下進行。同時，我們應用數值模擬計算揭示硫化過程中表面等離子體特性及模式變化。實驗和數值計算均表明硫化反應首先發生在銀納米立方塊的棱角和頂點。隨著反應的進行，銀立方塊被逐步鈍化為球狀銀納米顆粒。與此同時，納米立方結構的尺寸也隨之小幅增加。 / 二氧化鈦是一種重要的被應用於光能捕獲的半導體納米材料。因其低毒性、生物兼容性、化學及熱穩定性、耐光腐蝕性以及資源豐富等特點，TiO₂ 已經被廣泛研究。但是TiO₂僅在紫外光區具有光化學活性，這大大限制了其在光能捕獲方面的應用。儘管Au/TiO₂核/殼結構複合物可以提高TiO₂在可見區的光催化活性，但是對於該核/殼結構的合成鮮為報導，而且已報導的工作也是限制在以金納米球作為核層。與金納米球相比，金納米棒具有更引人關注的表面等離子體特性，例如金納米棒具有更高的電場增強，而且金棒的縱向共振波長可以從可見區調控到近紅外區。因此金納米棒/二氧化鈦核/殼結構可以更有效的提高二氧化鈦的光捕獲能力。在此論文中，我發展了一種合成Au/TiO₂核/殼結構的方法，并研究其在光能捕獲方面的應用。在該方法中，我選擇三價鈦作為鈦源，可控合成了Au/TiO₂ 核/殼結構。通過對核的尺寸及殼層厚度的調節，實現了對核/殼結構的共振波長的調控。另外這種方法也適用于其他單組份或者雙組份的鉑、鈀、金納米晶。爲了驗證在光能捕獲方面的應用潛能，Au/TiO₂核/殼結構納米材料被作為散射層而應用於染料敏化太陽能電池中，結果發現這種電池具有較高光電轉化效率。另外，我們還研究了表面等離子體共振激元增強下的活性氧化物的生成。再者，具有較高介電常數的二氧化鈦殼層可以與金納米晶核耦合產生法諾共振效應。結果表明金納米棒的橫向、縱向共振峰均能和殼層材料發生共振耦合而產生對應的法諾效應。納米棒的縱向共振峰的可調性實現了對應的法諾共振峰的可調性。同時，包覆二氧化鈦殼層后，金納米棒的橫向共振模式被大幅放大。 / 本論文的研究有利於人們了解金屬/半導體納米結構的設計及應用。硫化過程中表面等離子體共振激元特性及結構變化的研究，對具有特定組分及共振特性的複合物的設計合成具有指導意義。對貴金屬/半導體核殼結構製備、共振特性及應用的研究也擴展了其在光能捕獲方面的應用。 / Over the past several years, integration of metal nanocrystals that can support localized surface plasmon has been demonstrated as one of the most promising methods to the improvement of the light-harvesting efficiency of semiconductors. Ag and Au nanocrystals have been extensively hybridized with semiconductors by either deposition or anchoring. However, metal nanocrystals tend to aggregate, reshape, detach, or grow into large nanocrystals, leading to a loss of the unique properties seen in the original nanocrystals. Fortunately, core/shell nanostructures, circumventing the aforementioned problems, have been demonstrated to exhibit superior photoactivities.To further improve the light-harvesting applications of (plasmonic metalcore)/(semiconductor shell) nanostructures, it is vital to understand the plasmonic and structural evolutions during the preparation processes, design novel hybridnanostructures, and improve their light-harvesting performances. In this thesis, I therefore studied the plasmonic and structural evolutions during the formation of (Ag core)/(Ag₂S shell) nanostructures. Moreover, I also prepared (noble metal core)/(TiO₂shell) nanostructures and investigated their plasmonic properties and photon-harvesting applications. / Clear understanding of the sulfidation process can enable fine control of the plasmonic properties as well as the structural composition of Ag/Ag₂S nanomaterials.Therefore, I investigated the plasmonic and structural variations during the sulfidation process of Ag nanocubes both experimentally and numerically. The sulfidation reactions were carried out at both the ensemble and single-particle levels.Electrodynamic simulations were also employed to study the variations of theplasmonic properties and plasmon modes. Both experiment and simulation results revealed that sulfidation initiates at the vertices of Ag nanocubes. Ag nanocubes arethen gradually truncated and each nanocube becomes a nanosphere eventually. The cubic shape is maintained throughout the sulfidation process, with the edge lengthii being increased gradually. / TiO₂ is one of the most important semiconductors that are employed inlight-harvesting applications. It has been extensively studied for a variety of applications by virtue of its low toxicity, biological compatibility, chemical and thermal stability, resistance to photocorrosion, and relative abundance. However, the photocatalytic activity of TiO₂ is limited to the UV region because of its wide bandgap, which limits its applications in light harvesting. Although (Au core)/(TiO₂ shell)nanostructures can improve the photocatalytic activities of TiO₂ in visible light, it hasonly been demonstrated in a few experiments and has been limited with Au nanospheres. Compared with Au nanospheres, Au nanorods offer more attractive plasmonic features, including stronger electric field enhancements and synthetically tunable longitudinal plasmon wavelengths over the visible to near-infrared region. The coating of Au nanorod therefore can largely improve light harvesting capabilityof TiO₂. In this thesis, I developed a facile and versatile method for the preparation of(Au nanocrystal core)/(TiO₂ shell) nanostructures by using a Ti(III) compound as thetitania precursor. By employing Au nanorods with different sizes and varying the shellthickness, the plasmonic bands of the core/shell nanostructures can be tailored. TiO₂can also be grown on other monometallic and bimetallic Pd, Pt, Au nanocrystals. As aproof-of-concept application, (Au nanorod core)/(TiO₂ shell) nanostructures wereutilized in dye-sensitized solar cells to function as a scattering layer. The resultantsolar cells exhibited higher power conversion efficiencies with a thinner thickness compared to the traditional TiO₂ solar cells. In addition, I also examined the property of plasmon-enhanced reactive oxygen species generation. Moreover, the TiO₂ shell with a high refractive index can efficiently couple with the plasmon resonance modesof the Au nanorod core, leading to Fano resonances. Fano resonances for both the transverse and longitudinal plasmon modes were simultaneously observed. The longitudinal Fano resonance is tunable by changing the plasmon energy of thenanorod core. In addition, coating with TiO₂ intensifies the transverse plasmon modeof the Au nanorod core. / I believe that my research study will be very helpful for the design and applications of metal/semiconductor nanostructures. The full understanding of the plasmonic and structural evolutions during the preparation processes will be useful for designing metal/semiconductor hybrid nanomaterials with desired compositions and plasmonic properties. The efforts towards the investigations of the preparation, plasmonic properties, and applications of (noble metal core)/(semiconductor shell) nanostructures are important for widening their light-harvesting applications. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Fang, Caihong = 具有表面等離子體激元特性的金屬/半導體核/殼納米結構 / 房彩虹. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references. / Abstracts also in Chinese. / Fang, Caihong = Ju you biao mian deng li zi ti ji yuan te xing de jin shu/ban dao ti he/qiao na mi jie gou / Fang Caihong.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1077628 |
| Date | January 2014 |
| Contributors | Fang, Caihong (author.), Wang, Jianfang (thesis advisor.), Chinese University of Hong Kong Graduate School. Division of Materials Science and Engineering, (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource, electronic resource, remote, 1 online resource (xiv, 156 leaves) : illustrations (some color), computer, online resource |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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