title: Plasmonic percolation: plasmon-manifested dielectric-to-metal transition.
abstract: Percolation generally refers to the phenomenon of abrupt variations in electrical, magnetic, or optical properties caused by gradual volume fraction changes of one component across a threshold in bicomponent systems. Percolation behaviors have usually been observed in macroscopic systems, with most studies devoted to electrical percolation. We report on our observation of plasmonic percolation in Au nanorod core-Pd shell nanostructures. When the Pd volume fraction in the shell consisting of palladium and water approaches the plasmonic percolation threshold, ~70%, the plasmon of the nanostructure transits from red to blue shifts with respect to that of the unshelled Au nanorod. This plasmonic percolation behavior is also confirmed by the scattering measurements on the individual core-shell nanostructures. Quasistatic theory and numerical simulations show that the plasmonic percolation originates from a positive-to-negative transition in the real part of the dielectric function of the shell as the Pd volume fraction is increased. The observed plasmonic percolation is found to be independent of the metal type in the shell. Moreover, compared to the unshelled Au nanorods with similar plasmon wavelengths, the Au nanorod core-Pd shell nanostructures exhibit larger refractive index sensitivities, which is ascribed to the expulsion of the electric field intensity from the Au nanorod core by the adsorbed Pd nanoparticles.
authors: Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
authors: Huanjun
authors: H
authors: Chen
authors: Feng
authors: F
authors: Wang
authors: Kun
authors: K
authors: Li
authors: Kat Choi
authors: KC
authors: Woo
authors: Jianfang
authors: J
authors: Wang
authors: Quan
authors: Q
authors: Li
authors: Ling-Dong
authors: LD
authors: Sun
authors: Xixiang
authors: X
authors: Zhang
authors: Hai-Qing
authors: HQ
authors: Lin
authors: Chun-Hua
authors: CH
authors: Yan
mesh_terms: D003198:Computer Simulation; D017097:Electric Impedance; D006046:Gold / Q000737:chemistry*; D008027:Light; D008422:Materials Testing; D008956:Models, Chemical; D010165:Palladium / Q000737:chemistry*; D012542:Scattering, Radiation; D020349:Surface Plasmon Resonance / Q000379:methods*
chemical_list: D010165:Palladium; D006046:Gold