Design of Plasmon Resonance Shifts by the Galvanic Replacement Degree of Au-Ag Nanozappers

Porous plasmonic nanostructures have attracted interest for their built-in cavities, which provide strong localized electric field enhancement and additional plasmon tunability. In this work, we synthesize a series of nanostructures based on Au-Ag nanozappers (similar to a bug zapper in shape and in function of catching photon with the frame) by means of progressive galvanic replacement reactions. Transmission electron microscopy images present evidence that the cavity size of the Au-Ag nanozapper is controllable. Moreover, our synthetic method enables us to design the longitudinal plasmon modes of the Au-Ag nanozappers progressively varied from 660 to 970 nm with nearly the same aspect ratio. To explore the origin of the spectral shift, we analyze the size, the composition, and the void effects of the Au-Ag nanozappers using computational electrodynamics simulations. Our analysis indicates that the longitudinal plasmon modes are less sensitive to the frame composition of the nanozappers, in contrast to their susceptibility to the size and the void effects.