Evolutionary Plasmonic Properties of Single Truncated Ag Nanowire-on-Au Film Nanocavity

Noble metal nanocavities have been widely demonstrated to possess great potential applications in nano-optics and nanophotonics due to their extraordinary localized surface plasmon resonance. However, most metal nanocrystals synthesized by chemical methods often suffer from truncation with different degrees due to oxidation and dissolution of metal atoms at corner and edges. We investigate the influence of shape truncation on the plasmonic properties of single Ag nanowire on Au film nanocavity using the finite difference time domain method. When the Ag nanowire (the circumradius R₂ = 50 nm) is gradually truncated from pentagonal to circular geometry, the scattering peak position of the nanocavity shows prominent blue shift from 962 nm to 608 nm, suggesting a nonnegligible role of truncation on plasmonic properties. The electric field strength and charge distribution of the structure reveal the evolution from dipole mode to quadrupole mode. It is also found that the plasmon resonance wavelength is linearly dependent on the truncation ratio R₁/R₂ (R₁ is the inradius) and the modulation slope is also reliable to the size of Ag nanowire. Our observations could shed light on developing high-performance tunable optical nano-devices in future.