Abstract
In this paper, the plasmon coupling effect between two gold nanospheres on a gold slab is investigated. At plasmon resonance frequencies, electrons on the surface of the slab are absorbed into spheres and contribute to plasmon oscillation. This effect can enhance the local electric field and optical coupling force between the two spheres.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. For complex nanosystems composed of metallic nanostructures, various plasmonic coupling effects between the structures are very interesting and useful. The near field coupling effects can produce 'hot spots' and further enhance the local field. Plasmonic coupling is also able to produce a strong optical force between the nanostructures. Such forces can affect the signal of surface-enhanced Raman spectroscopy or result in aggregation of nanosystems.
Main results. The plasmonic coupling effect between gold nanospheres on a gold slab is investigated. Aided by the slab, the two spheres can exchange current. When positive charges accumulate in one sphere, negative charges accumulate in the other. Impressive local field enhancement can be obtained between two spheres, much stronger than that between two spheres without a slab. The exchange current also introduces a strong plasmon coupling force between the two spheres. Due to opposite charge accumulation at two spheres, they attract one another at the resonance frequency.
Wider implications. The impressive local field enhancement introduced by exchange of current between two spheres may possibly be used to enhance Raman scattering, single molecule detection, near-field optical manipulation and many other applications in the future.
Figure. The incident plane wave propagates along −y-direction, with its polarization in the x-direction. Open boundaries are used in all directions.