Au, Ag, Cu and their core-shell nanoparticles: synthesis, self-assembly and tunable optical properties.
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.
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