Evidence for capping-layer effects on the morphology and plasmon excitation of Ag nanoparticles

Abstract

The structure and optical response of Ag nanoparticles capped with dielectric BN, Al2O3, and Y2O3 layers have been studied. The morphological evolution of the nanoparticles has been investigated in detail by high-angle annular dark-field (HAADF) imaging in a scanning transmission electron microscope and by optical transmittance measurements and simulations of surface-plasmon resonances. We show that the quantitative analysis of plane-view HAADF images enables the average morphology of individual embedded nanoparticles to be revealed. It thus provides a simple method to investigate capping-layer effects, which are demonstrated to be characterized by a substantial reduction of the aspect ratio of the nanoparticles and have been evidenced to strongly depend on the nature of the cap as well as on the size of the nanoparticles. These results suggest that both the morphological and optical properties of noble metal nanoparticles can be tuned by using capping-layer effects and by choosing capping materials with appropriate physicochemical and electronic properties.