Si@Au Core–Shell Nanostructures: Toward a New Platform for Controlling Optical Properties at the Nanoscale

Hybrid dielectric–metal colloid nanoparticle heterostructures have recently attracted attention in both fundamentals and applications. In this paper, we developed a new approach based on mechanical grinding and chemical synthesis in order to obtain hybrid dielectric–metal nanoparticles. By increasing the amounts of the stabilizing agent (polyvinylpyrrolidone (PVP)), three different types of hybrid colloidal structures were obtained, Si/Au core–island, core–shell, and core–shell oligomers heterostructures, respectively. The obtained colloidal heterostructures were analyzed by dynamic light scattering (DLS) and scanning electron microscope (SEM) measurements. Moreover, the optical properties of hybrid nanostructure have been carefully studied. A splitting was observed in the extinction spectra of colloidal solutions for different Si/Au colloidal heterostructures compared to Si colloidal nanoparticles, attributed to the hybridization of plasmon. Thanks to photolitholographic and drop-cast deposition techniques on a substrate, we were able to locate the colloidal nanoparticles heterostructures and to measure the backward scattering spectra using single-particle dark-field scattering spectroscopy. To better understand scattering results, FDTD simulations of scattering cross-section and electric near-field distributions were performed. As is well-known, the scattering spectrum of the pristine Si core is dominated by electric and magnetic dipolar modes in the visible region. More importantly, the scattering spectra of Si/Au core–island and core–shell support several phenomena such as collective magnetic dipolar modes and multiple Fano lineshapes. Our finding highlights the potential of our dielectric–metal heterostructures as a platform for studying light–matter interactions at the nanoscale.