Surface plasmonics of nanomaterials has been one of the main research themes in nanoscience. Spherical and elongated nanoparticles show their corresponding unique optical features mainly depending on the physical dimensions. Here we successfully synthesized Au nanorings having Pt framework (Pt@Au nanorings) with high uniformity through wet-chemistry. The synthetic strategy consisted of serial reactions involving site-selective growth of Pt on the rim of Au nanoplates, subsequent etching of Au nanoplates, followed by regrowth of Au on the Pt rim. In this synthetic method, Au(3+) ions exhibited dual functionality as an etchant and a metal precursor. The resultant product, Pt@Au nanorings, exhibited unique localized surface plasmon resonance (LSPR) bands originating from the Au shell. The inner Pt skeleton turns out to be important to hold structural stability.
We present a simple synthetic method for hexagonal Au nanoplates. Selective etching of specific facets of triangular nanoplates has led to the shape transformation. Also, the high quality of hexagonal Au nanoplates allows one to identify the higher-order plasmon resonance bands in addition to the dipole mode.
We synthesized hollow Au-Ag nanospheres (NSs) by employing a galvanic replacement reaction between HAuCl4 and Ag NSs. Uniform Ag NSs with controllable sizes were synthesized as sacrificial templates by a seed-mediated strategy. The atomic ratio of Au to Ag in Au-Ag NSs was tunable by controlling the reagent concentration. UV-vis extinction spectra acquired from well-dispersed colloidal NS solutions were used to investigate the optical properties of the solutions. In addition to a common dipole mode exhibited on most transition metal nanoparticles, we observed a quadrupole plasmon resonance mode when the diameters of the Ag and Au-Ag NSs were larger than 100 nm. The quadrupole and dipole peaks both shifted to longer wavelengths with increased Au content in Au-Ag NSs. The experimental observation of optical properties of hollow Au-Ag NSs was compared with the theoretical simulation using DDA calculation, showing a good agreement.
Core−shell (Au@Ag) bimetallic nanoparticles containing a Au nanodisk in the core were synthesized using Au nanodisks as seeds. The growth direction of the Ag shell on the gold nanodisks could be tuned by the presence of iodide ions. Without the I − ions, the Ag shell was formed homogeneously over the entire surface of the flat Au nanodisks, while the presence of I − induced the selective coating of the Ag shell in the direction perpendicular to the basal plane of the nanodisks. The resulting core−shell (Au@Ag) bimetallic nanoparticles could be further converted to hollow nanostructures containing a central Au nanodisk via galvanic replacement reactions.
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