Chiral and plasmonic hybrid dimer pair: reversal of both near- and far-field optical binding forces

Abstract

In both the near-field (around 10 to 250 nm interparticle distance) and far-field (around 1 µm to higher interparticle distances) regions, controlling the mutual attraction and repulsion between chiral and plasmonic hybrid dimers using light has not been reported so far to the best of our knowledge. Such control is called controlling the reversal of the optical binding force. In most setups, the reversal of the optical binding force between plasmonic heterodimers vanishes with an interparticle distance of around 100 nm and above due to the disappearance of the Fano resonance. In this paper, we have demonstrated a possible optical setup, illuminated by a linearly polarized plane wave: chiral and plasmonic hybrid dimers over a plasmonic substrate, which supports the reversal of the optical binding force in both the near- and far-field regions. First, by varying the light wavelengths, we have shown that the optical binding force does not reverse for either the chiral homodimers set and or the plasmonic homodimer set for different interparticle distances. Later, we created a hybrid dimer system by placing a plasmonic and a chiral nanoparticle together. Interestingly, at the far-field region, a strong plasmonic resonance is observed, but a reversal of the optical binding force does not occur. Finally, we have placed the same chiral–plasmonic hybrid dimer setup over a plasmonic substrate and the desired result—a reversal of the binding force—is observed due to the induced lateral force on the chiral object (in the presence of the substrate) and the Fano-type resonance in the system. Controlling such near- and far-field optical binding forces can be an important aspect for particle clustering, accumulation, crystallization, and the organization of templates for biological and colloidal sciences in the near future.