High spatial and energy resolution electron energy loss spectroscopy of the magnetic and electric excitations in plasmonic nanorod oligomers

We leverage the high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron microscopy to study the hybridization of cyclic assemblies of plasmonic gold nanorods. Detailed experiments and simulations elucidate the hybridization of the coupled long-axis dipole modes into collective magnetic and electric dipole plasmon resonances. We resolve the magnetic dipole mode in these closed loop oligomers with electron energy loss spectroscopy and confirm the mode assignment with its characteristic spectrum image. The energy splitting of the magnetic mode and antibonding modes increases with the number of polygon edges (n). For the n=3-6 oligomers studied, optical simulations using normal incidence and s-polarized oblique incidence show the respective electric and magnetic modes' extinction efficiencies are maximized in the n=4 arrangement. (C) 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Automated summary

This study leverages the high spatial and energy resolution of monochromated aberration-corrected scanning transmission electron microscopy to investigate the hybridization of cyclic assemblies of plasmonic gold nanorods. The experiments and simulations reveal the coupling of long-axis dipole modes into collective magnetic and electric dipole plasmon resonances, with findings on the energy splitting of the magnetic mode and antibonding modes for oligomers with different polygon edges. Optically, it was found that the extinction efficiencies of electric and magnetic modes are maximized in the n=4 arrangement among the oligomers studied.