Plasmonic Metallic Nanostructures: Synthesis And Applications

Surface plasmon resonance is a phenomenon that arises from the collective oscillation driven by the electromagnetic field of light. It has potential applications in sensing, fluorescence, waveguide, solar cells and so on, which have attracted a lot of attention. One of the most important properties of surface plasmon is enhancing the local filed near the surface of metallic particles greatly, which can enhance the Raman scattering intensity (SERS) and excitation intensity of fluorophore nearby. As the size, shape and structures will influence the intensity and position of surface plasmon, it is meaningful for applications to prepare metallic nanostructures of different size and shape and study the kinetic and thermodynamic factors.In this dissertation, several kinds of Au and Ag nanostructures were prepared with wet chemical methods. The factors that would influence the morphology and size were systematically investigated. The growth mechanism was also studied. And then, films composed of metallic particles were prepared through a self-assembly process, and the SERS properties were tested. Moreover, the coupling between metallic nanoparticles and quantum dots was analyzed. The primary significant results of this thesis are summarized as follows:(1) Silver particles of different size were prepared through a one-step reaction. The experimental parameters including the concentrations of PVP and AgNO3, the amount of ammonia added and reaction temperature influenced the size of the samples. Two growth modes were put forward: diffusion growth and aggregation-based growth. Small particles grew up by diffusion, while large particles grew up by aggregation.(2) Films composed of closely-packed silver particles were prepared through oil-water self-assembly. The films enhanced the Raman signals of R6G and pMA, and the enhancement effect correlated with the particle size. Films of closely-packed particles showed better enhancement than that composed of sparse particles. Ag island films were obtained by annealing the closely-packed particles and the size of the Ag islands the distance between particles were controlled by the layers of the film and the annealing temperature.(3) SiO2@Ag particles with smooth and thickness-controllable Ag shells were prepared with an improved seed-mediated electroless method. PVP of proper concentration and the rapid growth of the silver nuclei were essential to obtain perfect silver shells. The thickness of the silver shells was controlled by the amount of SiO2 spheres. By raising the concentrations of the reactants, SiCO2@Ag particles with high yield were produced. The SiO2@Ag particles displayed tunable extinction peaks spreading from the visible to near infrared region, which was dependent on the thickness of the Ag shells. The SERS effect correlated with the morphology of the Ag layers.(4) A kind of flower-like silver structures consisted of a silver core and several rod-like tips protruding in three dimensions were fabricated using a rapid reaction without the limitation of surfactants. By raising the concentrations of the reactants, more rod-like tips with smaller size on one core were obtained. TEM and XRD analysis suggested that some rods had the FCC structure, and others had the HCP structure. It was observed that the formation of the HCP phase was the result of rapid and free growth of silver nuclei under the special reducing agent-CH2O. The formation of the flower-like silver particles was induced by the anisotropic growth of HCP silver and the adsorption of HCOOH-the oxidation product of CH2O.(5) Expanding the strategies of preparing the flower-like silver particles onto the silica spheres decorated with silver nuclei, echinus-like SiO2@Ag structures, which was the hybrid structures of SiO2@Ag core-shell and silver rods were obtained. In the echinus-like SiO2@Ag structures, HCP phase of Ag was also observed. The rods on the silver shells became smaller and denser after raising the reactant concentrations. It was found that the rapid and free growth of silver nuclei on the silica spheres under the special reducing agent was also very important.(6) Gold nanorods of different aspect ratios were prepared using an seed-mediated method, in which AA was used in the growth step. Dogbone-like gold nanorods were obtained by adding superabundant AA into the growth solution. A new peak arose in the absorption spectrum of the dog-bone gold nanorods. By coating the rods with a thin silica layers, the quenching effect of gold on CdTe quantum dots was reduced. The lifetime of the excitation state of CdTe quantum dots was reduced due to the surface plasmon of gold nanorods.(7) Films of closely-packed Ag@SiO2 or Au@SiO2 particles were obtained by oil-water interfacial self-assembly. Due to the isolation of silica layers on the surface of the metallic particles, the plasmon coupling between the metallic particles was avoided. So the films displayer similar narrow extinction peaks as that of the dispersed particles in solution. Films of Ag@SiO2 particles with thin silica layers enhanced the Raman signals of R6G.