Plasmonic interactions and optical forces between au bipyramidal nanoparticle dimers.

Area of Science:

• Plasmonics
• Nanophotonics
• Computational Electromagnetics

Background:

• Optical forces can assemble nanoparticles into ordered arrays.
• Anisotropic nanoparticles with plasmon excitations offer enhanced nonlinear responses and sensing capabilities.
• Simulations of plasmonic interactions are crucial for developing these applications.

Purpose of the Study:

• To investigate the near- and far-field optical properties of gold bipyramidal nanoparticle pairs.
• To calculate optical forces between these nanoparticles in various configurations.
• To compare the optical forces between bipyramids and nanospheres.

Main Methods:

• Rigorous three-dimensional, finite-difference, time-domain (FDTD) calculations.
• Analysis of absorption and scattering spectra.
• Maxwell stress tensor formalism for optical force calculation.

Main Results:

• Spectra and forces are highly dependent on nanoparticle geometry and separation.
• Head-to-tail and face-on bipyramidal dimers show red-shifted plasmon resonance with decreasing separation; side-by-side dimers show a blue shift.
• Head-to-tail configurations exhibit large resonant field enhancements and optical forces significantly exceeding those of nanospheres.

Conclusions:

• The geometry of gold bipyramidal nanoparticles dictates their plasmonic behavior and optical forces.
• Strong plasmon coupling and large optical forces are achievable in specific configurations, particularly head-to-tail.
• Simulation results align with experimental observations of nanoparticle trapping.