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.
Even for a 100 nm interparticle distance or a small change in particle shape, optical Fano-like plasmonic resonance mode usually vanishes completely. It would be remarkable if stable Fano-like resonance could somehow be achieved in distinctly shaped nanoparticles for more than 1 μm interparticle distance, which corresponds to the far electromagnetic field region. If such far-field Fano-like plasmonic resonance can be achieved, controlling the reversal of the far-field binding force can be attained, like the currently reported reversals for near-field cases. In this work, we have proposed an optical set-up to achieve such a robust and stable Fano-like plasmonic resonance, and comparatively studied its remarkable impact on controlling the reversal of near- and far-field optical binding forces. In our proposed set-up, the distinctly shaped plasmonic tetramers are half immersed (i.e. air–benzene) in an inhomogeneous dielectric interface and illuminated by circular polarized light. We have demonstrated significant differences between near- and far-field optical binding forces along with the Lorentz force field, which partially depends on the object’s shape. A clear connection is shown between the far-field binding force and the resonant modes, along with a generic mechanism to achieve controllable Fano-like plasmonic resonance and the reversal of the optical binding force in both far- and near-field configurations.
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