本實驗利用表面修飾法(surface decorated method)與種子成長法(seed-mediated growth technique) 在適當的氫氧化鈉NaOH參數下,成功合成出兩種不同形貌的核殼形結構:(1) 粒徑大且獨立性佳的銀顆粒(isolated particles)披覆在二氧化矽微球上;(2) 粒徑小且均勻的銀殼 (incompleted shell)披覆在二氧化矽微球上。 利用場發射掃描式電子顯微鏡(FESEM)與穿透式電子顯微鏡(TEM)觀察其表面形貌,數據分析其銀之粒徑大小與披覆密度。高解析穿透電子顯微鏡(HRTEM) & X光繞射分析儀(XRD)鑑定銀成長晶面,確認銀成功披覆在二氧化矽微球上;並透過X光電子能譜儀(XPS)鑑定銀與二氧化矽載體間具有特殊的binding energy化學位移,證實銀披覆在二氧化矽微球上後,電子由銀轉移至矽與氧,進一步確定銀在二氧化矽的界面為化學鍵結 不同形貌的二氧化矽/銀核殼形結構,呈現多樣的光學特性,研究其表面電漿子的共振(SPR)理論,利用紫外-可見光光吸收實驗(UV-Vis spectrum),觀察其表面電漿共振吸收峰,獨立性佳的銀顆粒隨著粒徑變大,SPR吸收峰紅移;均勻性佳的銀殼隨著銀殼的變厚而藍移,兩者呈現完全不同的光學特性。運用Mie theory與電偶極耦合(dipolar coupling) 效應等理論,成功的將核殼形結構之表面形貌與其特殊的光學特性做結合。 在適當的核殼參數下,模擬出兩種模型(1) 銀顆粒,改變其粒徑與披覆密度參數;(2) 銀殼,改變厚度參數,兩種型態的核殼形結構,與其個別的光學模擬,與實驗有相當大程度的一致性。
Abstract The SiO2/Ag core-shell structure is synthesized via surface decorated method and seed-mediated technique. The morphology of silver layers on silica spheres can be accurately controlled by adjusting the quantity of NaOH. The two different structures are (1) larger and isolated silver particles on the silica spheres; (2) ultrafine and uniform silver nanoparticles on the silica spheres. The morphology of the core-shell structure was observed by scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM). Use HR-TEM and X-ray diffraction pattern (XRD) to identify the crystal plane of silver particles. Furthermore, the X-ray photoelectron spectroscopy (XPS) experiment exhibits the chemical shift of binding energy. The results indicated the electrons were transferred from Ag particles to SiO2 confirming the chemical absorption between the silver particles and silica spheres. The surface plasmon resonance (SPR) peak depended on the morphology of SiO2/Ag core-shell structure and was observed by ultraviolet / visible spectroscopy (UV-Vis) and TEM. The Mie scattering theory and the dipolar coupling effect of neighboring silver particles as a whole may serve as the mechanism of optical properties. Furthermore, the observed SPR band could be tailored as expected by the modeling of optical properties. By adjusting appropriate parameters: (1) various size and coating density of silver particles; (2) various thickness of silver shell, a core-shell structure models and optical modes corresponding to the experimental results can be designed.
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