Nanocross: A Highly Tunable Plasmonic System

With the help of electron energy loss spectroscopy (EELS) in a scanning transmission electron microscope (STEM) and boundary element method (BEM) simulations, we have shown that silver nanocross can be used to tune the plasmon modes and especially the higher order modes in a very controlled manner. Morphing a nanorod to a nanocross by growing another arm along the perpendicular bisector of a nanorod can lead to a spectacular evolution of various order modes in the EEL spectra. One can keep a mode fixed in energy while bringing the next higher order mode close to it, or even make it cross. This allows one to control the relative separation of energy of the plasmon modes. Hybridization of individual nanocross plasmon modes have also been studied by bringing two nanocrosses close together along one of their arms. An analytical approach based on first order perturbation theory and symmetry arguments based on group theory aptly fits the experimental observations.