Jinhwa Heo

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.

Optical nonlinearities of Au nanoparticles and Au/Ag coreshells

Au nanoparticles exhibited both negative and positive nonlinear absorptions with ground-state plasmon bleaching and free-carrier absorption that could be origins of the saturable and reverse-saturable optical properties. Au/Ag coreshells displayed only positive nonlinear absorption and reverse-saturable optical properties as a function of excitation intensity at the edge of surface-plasmon resonance, which implies no ground-state plasmon bleaching and the existence of two-photon absorption.

Controlled synthesis and characterization of the enhanced local field of octahedral Au nanocrystals

Octahedral Au nanocrystals with localized surface plasmon-assisted enhancing optical properties can be prepared in aqueous solution via the forced reduction of Au ions by ascorbic acid through the addition of NaOH.

Nanoparticle assembly on nanoplates

By using dithiol linkage or biological interaction, Au nanoparticles are readily assembled on the single-crystalline Au nanoplates with well-defined geometries.

Electromagnetic Contribution to Surface Enhanced Raman Scattering of Rhodamine 6G Molecules on Rice-Shaped Au Nanocrystals

The factor of electromagnetic contribution to SERS of Rh6G on rice-shaped Au nanocrystals was estimated to be around six-order higher than Raman scattering of Rh6G.