Synthesis And Surface Plasmonic Properties Of Dielectric/Metal Core-shell Composite Nanoparticles

In this article, the reduced symmetry composite nanoparticles (NPS) andcompletelyencapsuled NPS were fabricated by physical and wet chemical method, respectively. By usingTEM, SEM, AFM, XRD and UV-Visible-NIR absorption spectra, the composite NPS werecharacterized and investigated. The influences of the dimensions of the NPS and theenvironmental refractive index were studied and discussed in detail.Well dispersed SiO₂ NPS were synthesized by the improved Stober method firstly. Usingthe gold NPS as surface seeds, the completely encapsuled SiO₂/Au and rice shaped Fe₂O₃/Au,Fe₂O₃/Ag core-shell composite NPS were synthesized by the wet chemical assembly method. Byinvestigating the morphologies and structures, it was found that the gold seeds played animportant role in the metal shell forming process.The self assembly structures of SiO₂ NPS were formed on quartz and glass slide. Based onthe self-assembly NPS, the reduced symmetry NPS were fabricated by vacuum evaporation andsputtering method, and finally the well dispersed composite NPS were received followed bysonication. The composite NPS are incompletely encapsuled and cap-shaped with diameters of100 nm to 500 nm. While the shell thickness is smaller than 50 nm, the well dispersed NPScould be obtained easily.The plasmonic properties of the composite NPS were investigated in detail. As to the coreshell NPS fabricated by the chemical method, the results showed that the optical plasmonresonance red shifted until a complete.shell was formed at the beginning. While the shell growedthicker, the plasmon resonace bule shifted. The plasmon resonace peak of Fe₂O₃/Au, andFe₂O₃/Ag composite NPS red shifted and became much more broad in the forming process,which was due to the complex effect of the transverse and longitudinal plasmon modes.The as prepared metal nanocaps exhibited tunable optical properties that the plasmonic peakcould blue shift and red shift while the shell thickness and the core diameter become larger,respectively. The plasmonic properties could also be influenced by the surrounding environment.With the refractive index increasing, the plasmonic wavelength red shifted, which was muchmore obvious than the corresponding planar metal films.