Determining the Molecular Dipole Orientation on Nanoplasmonic Structures

We developed a theoretical method to investigate the effects of the orientation of a molecular monolayer on plasmonic systems. Molecular layers strongly alter the plasmonic resonance of nanoparticles, affecting their ability to couple to other nanoparticles and quantum emitters. The ability to understand how the coating impacts the optical properties of the nanostructures is critical for the application of plasmonics in areas such as light detection, sensing, and plasmon-enhanced solar energy conversion. We extend the three-dimensional finite-difference time-domain method to include molecular layers with induced dipoles at an arbitrary orientation relative to the nanostructure's surface. Numerical calculations show how the orientation of molecular dipoles affects the plasmon resonance of both tetrahedral and ellipsoidal nanoparticles. Finally, we demonstrate how the layer impacts the coupling between ellipsoidal nanoparticle and a colloidal quantum dot.