Geometry-Dependent Surface Plasmonic Properties and Dielectric Sensitivity of Bimetallic Au@Pd Nanorods

Bimetallic nanoparticles have attracted increasing interest because of their unique optical, electronic, magnetic, and catalytic properties which are different from that of their individual constituent metals. In this paper, we report a facile route to the synthesis of Pd-covered and Pd-tipped gold nanorods (AuNRs). And finite-different time-domain (FDTD) is also applied to simulate the longitudinal surface plasmon resonance (SPRL) characteristics for two different layered growth modes. The simulated absorption spectra agree with the experimental results. For the Pd-covered AuNRs, it is found that the SPRL shows a red-shift with shell thickness less than 2 nm. And then, the SPRL blue-shifts and gradually approaches to the absorption peak of Pd nanocuboids with increasing Pd shell thickness. While the SPRL of Pd-tipped AuNRs red-shifts with increasing Pd tip-particle size, it is revealed that the bimetallic Au@Pd NRs have higher refractive index sensitivities than that of AuNR cores. The tunable SPRL and higher refractive index sensitivities of bimetallic Au@Pd NRs may lead to great potential applications in many Pd-catalyzed reactions and provide an important reference of Pd nanostructures for SPR-based sensing.