Angle- and energy-resolved plasmon coupling in gold nanorod dimers.

The plasmon coupling in the dimers of Au nanorods linked together at their ends with dithiol molecules has been studied. The plasmon coupling in the dimers composed of similarly sized nanorods gives antibonding and bonding plasmon modes. The plasmon wavelengths of the two modes have been found to remain approximately unchanged, with the scattering intensity ratio between the antibonding and bonding modes decaying rapidly as the angle between the nanorods is increased. This plasmon coupling behavior agrees with that obtained from both electrodynamic calculations and modeling on the basis of the dipole-dipole interaction. The electric field in the gap region is largely enhanced for the bonding mode, while that for the antibonding mode is even smaller than the far field, highlighting the importance of selecting appropriate plasmon modes for plasmon-enhanced spectroscopies. An anti-crossing-like behavior in the plasmon coupling energy diagram has further been revealed for linearly end-to-end assembled dimers composed of differently sized nanorods. This result will be useful for plasmonic applications where the plasmon wavelength is required to be controllable but without sacrificing the electric field enhancement.