In a classical electrodynamics, the strength of plasmon resonances of two closely spaced metallic particles increases as the particle gap size decreases. In contrast, quantum mechanics predicts that electron tunneling will strongly diminish the dimer plasmon strength for subnanometer separations. Scholl et al. directly observe the plasmon resonances of coupled metallic nanoparticles as their separation is reduced to atomic sizes.
Jonathan Scholl, Aitzol Garcia-Etxarri, Ai Leen Koh, and Jennifer A Dionne
Nano Lett. 2012