Sung-Hyun Ahn

Real-Space Mapping of the Strongly Coupled Plasmons of Nanoparticle Dimers

We carried out the near-field optical imaging of isolated and dimerized gold nanocubes to directly investigate the strong coupling between two adjacent nanoparticles. The high-resolution (approximately 10 nm) local field maps (intensities and phases) of self-assembled nanocube dimers reveal antisymmetric plasmon modes that are starkly different from a simple superposition of two monomeric dipole plasmons, which is fully reproduced by the electrodynamics simulations. The result decisively proves that, for the closely spaced pair of nanoparticles (interparticle distance/particle size approximately 0.04), the strong Coulombic attraction between the charges at the interparticle gap dominates over the intraparticle charge oscillations, resulting in a hybridized dimer plasmon mode that is qualitatively different from those expected from a simple dipole-dipole coupling model.

Electroless deposition of SERS active Au-nanostructures on variety of metallic substrates

In this study, flower-like Au structures (three dimensional branched nanoparticles) were constructed by using a simple, template-free and cost effective electroless plating method. The key synthesis strategy was to perform controlled plating of Au on a variety of metals (Ag, Cu and Pt) deposited on the Si substrate. Herein, gold is deposited purely as a result of reaction of chemicals in bath to form Au nanoflowers/lawns. The size and shape of the Au nanoflowers could be tailored by controlling the immersion Au plating time on multitude of metallic substrates. Time course measurements by SEM and HRTEM were used to follow reaction progress and evolution of flower-like shape. The generation of unique and reproducible morphological Au nanostructures onto each substrate implies that the Au nanostructures are substrate dependent. Fast Fourier Transform measurements were conducted using HR-TEM on isolated samples that proved the presence of anisotropic growth of Au polycrystalline structures. The gold nanostructures have shown the surface-enhanced Raman scattering (SERS) by detecting the enhanced Raman spectra of 4-Aminobenzenethiol (4-ABT) molecules. The enhancement of Raman signal was stronger for Au structures built on Pt or Ag thin films. The Au nanoflowers produced by this simple method exhibited effective surface-enhancement for biosensing applications.