金、銀、銅及其核殼奈米粒子之合成、自組裝及其光學特性之研究

Abstract

本論文架構有三個主題：各式金屬奈米粒子的合成、自組裝散佈技術及其光學特性之探討。奈米粒子合成的部分，主要以多元醇法成功製備純金屬Ag、Au、Cu奈米粒子及Au/Ag與Au/Cu核殼奈米粒子。透過TEM觀察證明，以此方法所合成之奈米粒子其粒徑尺寸較小(小於20nm)且分佈範圍狹窄。製程中所添加之保護劑PVP可以防止金屬粒子氧化，並有助於控制奈米粒子之分散性，甚而可以藉由反應溫度及PVP添加比例之變化，控制奈米粒子之結構。 藉由製程參數之調控，奈米粒子經常呈現與塊材截然不同之結構，其性質也與塊材迥異。本研究特別針對此些特殊結構，其中包括Decahedral與FCC結構之Ag奈米粒子，以及Icosahedral與FCC結構之Cu奈米粒子，進行一系列之XRD結構模擬，期以XRD非破壞性檢測，來快速獲得奈米粒子之結構資訊。根據本研究之結論，利用XRD即能有效區別Decahedral、Icosahedral、FCC等不同結構。 本研究主要利用二種散佈技術將奈米粒子散佈於光學玻璃基板之上，以利下一階段之光學測試。其一係利用傳統之旋轉塗佈法，將製備所得完成清洗之奈米粒子乙二醇溶液，以低速旋轉塗佈來獲得Ag、Au、Cu、Au/Ag及Au/Cu奈米粒子薄膜。另一方法係利用塊式高分子來進行奈米粒子自組裝，將PVP-coated Ag奈米粒子加入塊式高分子PS-P2VP形成微胞溶液後，再利用高速旋轉塗佈將Ag奈米粒子成功自組裝至基板上，並藉由退火熱處理使Ag奈米粒子達到均勻性分佈。 塗佈所得之奈米粒子膜，再利用UV-vis光譜儀，探討奈米粒子溶液及固態薄膜厚度對吸光光譜之影響。本研究以Mie理論為基礎，成功計算出Ag、Au、Cu、Au/Ag及Au/Cu奈米粒子溶液之吸收光譜，並進一步發現奈米粒子薄膜與溶液態之吸收光譜結果差異甚大，薄膜吸收波峰會產生相對於溶液態紅位移之現象，且隨薄膜厚度的增加而增加，並達到一個飽和定值。

This thesis contains three main topics: synthesis, self-assembling dispersions and the optical properties of various metallic nanoparticles. Firstly, we have successfully synthesized pure Ag, Au, and Cu nanoparticles as well as core-shelled Au/Ag, and Au/Cu nanoparticles by the polyol process. According to TEM analysis, the mean diameters of nanoparticles prepared were found to be smaller than 20 nm with a narrow size distribution. In the polyol process, PVP acts as a nucleation promoting agent for nanoparticles, a stabilizer for mono-dispersion, and a protective agent for oxidation. By varying the reaction temperature and PVP concentration, nanoparticles with different structures can be obtained for the further study. Nanoparticles usually exhibit distinct structures as well as properties comparing with bulk materials. In order to distinguish these special structures, FCC, Decahedron and Icosahedrons, by nondestructive characterization of X-ray diffraction, a serious of theoretical X-ray diffraction patterns were calculated and compared with experimental data. The results clearly show that X-ray diffraction can effectively distinguish these structures and is in good agreement with the observation of HRTEM. For the optical examinations, the nanoparticles prepared were dispersed onto the optical glass by two ways, i.e. typical spin-coating and block-copolymer self-assembling methods. For the prior method, the washed Ag, Au, Cu, Au/Ag and Au/Cu nanoparticles were dissolved in the ethylene-glycol, and then spun with low speed to obtain nanoparticle thin film with various film thicknesses. For the posterior method, PVP-coated Ag nanoparticles were added into the block copolymer PS-P2VP micellar solution, and then spun with high speed to prepare self-assembly Ag nanoparticle thin films. Following with annealing treatments, various periodic patterns of Ag nanoparticle thin films were obtained. The absorption spectra of nanoparticle solutions and the obtained nanoparticle thin films with various thicknesses were then characterized by UV-vis spectrum spectroscopy. In our research, we have successfully simulated the absorption spectra of Ag, Au, Cu, Au/Ag and Au/Cu nanoparticle solutions based on Mie theory. A dramatic change on the absorption spectra was found between aqueous solutions of nanoparticles and nanoparticle thin films. The peak position of the thin film is greatly red-shifted from the general position observed for the nanoparticles in the aqueous solution. With the thickness increases, red-shifts were initially enhanced and then to reach a saturated value.