Size-controlled gold nano-tetradecapods with tunable optical and electromagnetic properties

The synthesis of novel branched Au nanocrystals with a well-defined and size-controllable dualistic structure, Au nano-tetradecapods, is presented. Using seed mediated growth and kinetically controlled reaction conditions, Au nano-tetradecapods with fourteen branches grown preferentially on the vertices of an Au rhombic dodecahedral core are obtained. The size of the branches is easily and readily controlled by simply varying the volume of HAuCl₄ solution added or the reaction temperature, or both. The localized surface plasmon resonance peak of the Au nano-tetradecapods can be finely manipulated over a broad range of visible light through the selective tuning of their branch sizes. The enhanced and tunable electromagnetic properties of the Au nano-tetradecapods are numerically analyzed using the finite-difference time-domain method and they are experimentally applied as effective surface enhanced Raman scattering substrates as well. In addition, it is found that the branch/core size ratio derived from the dualistic structure is a critical parameter for determining and controlling the properties of Au nano-tetradecapods.