Solution Preparation And Self-Assembly Of Gold Nanoparticles

Gold nanoparticles show some unique properties of small-dimension-effect, surface effect, quantum size effect, etc. due to their high area ratio , surface-energy and surface-activation , which make their catalytical , optical , electronical and biological applications promising and make them an ideal candidate for nano-material preparation and nano-device fabrication. The resulting physical and chemical properties strongly depend on the particle size, interparticle distance, nature of the protecting organic shell, and shape of the nanoparticles, and so it is especially important that monodisperse gold nanoparticles with unique size and shape as well as specific ligands can be prepared by controlled process. This thesis reports the synthesis of gold nanoparticles with different dimensions , shapes , and ligands via a series of solution synthesis methods from the initial raw material HAuCl4, , such as direct-reduction by citrate, seed-mediated growth method and direct-reduction by sodium methylmethacrylate (SMA) as well as two-phase method. Gold nanoparticles synthesized here are characterized by Transmission Electron Microscopy (TEM) , Scanning electron microscopy (SEM) , UV-Vis Spectroscopy and Particle Diameter Analysis (PDA). We find that the plasmon resonance absorbance is red-shifted by increasing particle diameter or aspect ratio, while is blue-shifted significantly with a broadened plasmon bandwidth when particle diameter decreases to the range of 1~2nm and partial nanoparticles share ligands in common (small interparticle distance), due to the onset of quantum size effects that become important for particles with core sizes smaller than 3 nm in diameter.Thin metal films, especially metal island films, attract considerable interest in view of their unique optical properties and potential applications, such as Surface-Enhanced Raman Scattering (SERS) , Plasmon Resonance Absorbance (PRA) etc., which can be controlled by varying the particle dimension, shape and the metal film thickness. Thin and transparent metal surfaces are required since these allow the spectroscopic characterization of self-assembly metal films with glass substrates usually. ITO glass is chosen as the substrate in this study, which is functionalized by silane to improve the contact between the surface of substrate and gold nanoparticles. The monolayers and bilayers of gold nanoparticles are then prepared by self-assembly method, whose morphology and optical properties are characterized by TEM , SEM and UV-Vis Spectroscopy. The optimum time of self-assembly process is 2h, and theresulting monolayers of gold nanoparicles are red-shifted from 521 nm to 651 nm in UV-Vis spectrum when compared with the nanoparticles in aqueous solution, which is the overall conclusion of both the change of dielectric surroundings and interparticle distance. The bilayer is red-shifted by 16nm compared with the monolayer due to the particle coupling effect. The process and mechanism for self-assembly of gold nanoparticles at the interface of H2O/HCCl3 in DGI/SDI system is also investigated here.