The effect of nonhomogeneous silver coating on the plasmonic absorption of Au-Ag core-shell nanorod

Abstract

Plasmonic light absorption properties of bimetallic Au-Ag core-shell nanorod with nonhomogeneous Ag coating are investigated both theoretically and experimentally. When the Ag coating on the Au nanorod is not homogeneous, the overall aspect ratio and Ag composition greatly depends on the coating uniform, which strongly affects intensity changing and wavelength shift of the plasmonic absorption. When the transverse Ag coating is faster than longitudinal coating, the Au-Ag core-shell nanorod could present two intense longitudinal plasmonic absorption peaks with equal intensity and small wavelength gap as the Ag shell thickness has a critical value. Furthermore, this critical Ag shell thickness could be decreased when the Au nanorod core has a small aspect ratio. When the longitudinal Ag coating is faster than transverse coating, the increasing intensity of longitudinal peak corresponding to outer Ag surface is always weaker than the longitudinal peak corresponding to Au-Ag interface. Thus, we cannot obtain two equal intense plasmonic absorption peaks when the longitudinal Ag coating is thicker than the transverse coating. However, the transverse peak corresponding to Au-Ag interface could be enhanced by decreasing the aspect ratio of the Au nanorod core. Thus, we can always find three distinct absorption peaks as the aspect ratio of Au nanorod is decreased and the longitudinal Ag coating is greater than transverse coating. © 2013 The Author(s).