Plasmonic or dielectric dimers: A generic way to control the reversal of near field optical binding force

Controlling the near field optical binding force is an emerging new area of optical manipulation. So far, there is no generic way to reverse the near field optical binding force for plasmonic or dielectric nano-dimers of distinct shapes (cube, cylinder, ring, sphere); and specially for homodimers. In this article, for both plasmonic and dielectric objects, we have demonstrated a general way to control the reversal of near field binding force for different shaped dimer sets applicable for both homodimers and heterodimers. The force reversal is achieved by simple breaking of symmetry, considering the nanoparticles are half or less than half immersed in an inhomogeneous dielectric background, i.e. at air-water interface. However, if the dimer set is placed over a dielectric interface or fully inside a homogeneous medium, the sign of binding force does not reverse. Such force reversals for plasmonic dimers have been explained based on Fano resonance, interference fields, Lorentz force and image charge theory. The mechanism of binding force reversal is quite different in dielectric dimers, which has been explained mainly based on electric dipole moment, magnetic dipole moment and the interaction between electric and magnetic dipole moment. Our proposed idea can be verified by simple experiment.