Blue Shift\nof Localized Surface Plasmon Resonance\nof Gold Ultrathin Nanorod by Forming a Single Atomic Silver Shell\nvia Antigalvanic Process

Gold ultrathin nanorods (Au UNRs) are anisotropic nanostructures\nconstructed by attaching gold nanoclusters in one dimension. Au UNRs\nexhibit localized surface plasmon resonance (LSPR) only in the longitudinal\ndirection because their diameter is smaller than the Fermi wavelength\nof an electron (<2 nm). In this study, we found that the LSPR wavelength\nof oleylamine-stabilized Au UNRs is blue-shifted simply by mixing\nwith Ag(I). High-resolution elemental mapping and X-ray photoelectron\nspectroscopy of the resulting UNRs indicate that a Ag monatomic layer\nis formed on the Au UNR surface by the antigalvanic reduction of Ag(I).\nThis process allowed us to synthesize a series of Au@Ag core–shell\nUNRs with LSPR wavelengths in the range of 1.2–2.0 μm.