Strong plasmon coupling between two gold nanospheres on a gold slab
  In this work, 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 help enhance the local electric field and optical coupling force between the two spheres. 
H. Liu, J. Ng, S. B. Wang, Z. H. Hang, C. T. Chan and S. N. Zhu
physics.optics cond-mat.mes-hall