Bimetallic gold-silver nanorods produce multiple surface plasmon bands.

The optical properties of two-component nanorods (NRs) consisting of Au and Ag blocks were investigated. The overall optical properties of the nanorods were tailored by controlling block length. We observed two independent transverse modes in the Au and Ag blocks. Depending on the relative fraction of Au and Ag blocks, the intensity of the transverse modes varied without noticeable peak shifts. However, the strong intraparticle surface plasmon coupling between Au and Ag blocks resulted in the collective appearance of longitudinal LSP modes, including higher-order modes. This experimental observation suggests that the free electrons in Au and Ag blocks oscillate in a coherent fashion along the long axis of NRs, while there is no significant interaction in the free electron oscillation along the short axis of NRs.