Optical response and spill-out effects of metal nanostructures with arbitrary shape

In this paper, we propose a simple model to incorporate the spill-out effect of metal nanostructures, which can impact the nanostructure plasmonic properties prominently. Based on Maxwell's equations, this model divides the smeared-out area into a certain number of thinner layers, and thereby the spatial variable of dielectric function can be adjusted into an integer number. In principle, through the finite element method, the model can be applied to arbitrarily shaped metal nanostructures with spill-out effects. As demonstrative examples, the optical resonance spectra of sodium and potassium metal spheres were computed using the proposed model, and the redshifted plasmon peaks were attained and compared to previous research to support the model. Last, we successfully applied the proposed method to particles with lower symmetry relative to sphere particles, such as prolate spheroids and coned particles, and achieved redshift resonance with the consideration of spill-out layers. (C) 2021 Optical Society of America