Enhanced optical forces between coupled resonant metal nanoparticles.

We investigate numerically the optical forces between noble metal nanoparticles sustaining localized surface plasmon resonances. Our results first point out enhanced binding optical forces compared with dielectric nanoparticles and nonresonant metallic nanoparticles. We also show that under suitable illumination conditions, short-range forces tend to make the nanoparticles cluster, leading to intense and localized hot spots in the interstices. This effect corroborates recent experimental observations of an enhanced Raman signal in trapped metal sphere ensembles.