Preparation and Surface Plasmon Resonance of Cap-shaped Zinc Nanostructures

Cap-shaped zinc nanostructures were prepared with vacuum thermal evaporation method by depositing Zn films onto the monolayer arrays of SiO2 nanoparticles. The morphologies, structures, and optical properties of the samples were characterized and investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-Vis absorption spectroscopy. SEM images indicated that the composite nanoparticles were incompletely encapsulated and their surfaces were relatively rough. XRD results showed that the Zn films prepared on the top of SiO2 nanoparticles exhibited a polycrystalline hexagonal structure. Absorption spectra indicated that the cap-shaped zinc nanostructures had obvious absorption bands ranging from 570 to 760 nm, which were attributed to the longitudinal dipole surface plasmon resonance (SPR). The SPR band was found to red-shift with increasing the thickness of Zn cap or the diameter of SiO2 core. While the core diameter increased to 500 nm, the cap-shaped zinc nanostructures exhibited an additional quadrupole SPR band at around 412 nm.