Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
ACS Nano. 2012 Aug 28;6(8):7162-71. doi: 10.1021/nn302220y. Epub 2012 Jul 11.
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.
渗滤通常是指在双组分系统中，当一个组分的体积分数逐渐跨越一个阈值时，电、磁或光学性质突然发生变化的现象。渗滤行为通常在宏观系统中观察到，大多数研究都集中在电渗滤上。我们报告了在金纳米棒核-钯壳纳米结构中观察到的等离子体渗滤。当壳层中钯和水的体积分数接近等离子体渗滤阈值，约 70%时，纳米结构的等离子体从红移到蓝移相对于无壳的金纳米棒发生转变。这种等离子体渗滤行为也通过对单个核壳纳米结构的散射测量得到了证实。准静态理论和数值模拟表明，随着钯体积分数的增加，壳层介电函数的实部从正到负的转变导致了等离子体渗滤。观察到的等离子体渗滤与壳层中的金属类型无关。此外，与具有相似等离子体波长的无壳金纳米棒相比，金纳米棒核-钯壳纳米结构表现出更大的折射率灵敏度，这归因于被吸附的钯纳米颗粒将电场强度从金纳米棒核心中排出。
