A General Way to Control the Reversal of Near Field Optical Binding Force between Plasmonic or Dielectric Dimers

TL;DR

This paper presents a universal method to reverse near field optical binding forces between plasmonic or dielectric nano-dimers by breaking symmetry at an air-water interface, applicable to various shapes and verified through simple experiments.

Contribution

It introduces a general approach to control and reverse optical binding forces in nano-dimers of different shapes by symmetry breaking at interfaces, a novel concept in the field.

Findings

Force reversal achieved by symmetry breaking at interfaces.

Reversal explained via Fano resonance and interference effects.

Reversal not observed in homogeneous media.

Abstract

Controlling the near field optical binding force can be a key factor for particle clustering, aggregation and localized surface plasmon sensors. 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). 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. The force reversal is achieved by simple breaking of symmetry, considering the nano particles are half or less than half immersed in an inhomogeneous dielectric background, i.e. at air-water interface. Such reversals have been explained based on Fano resonance, interference fields, unusual behavior of optical Lorentz force and image charge theory. 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. Our proposed configuration provides a generic mechanism of archiving binding force reversal for both plasmonic and dielectric objects, which can be verified by very simple experimental set-up.