Inverse Design of Metal Nanoparticles' Morphology

The current praxis of designing plasmonic devices by hand, mainly guided by qualitative arguments, often derived from simplified semianalytical theories, significantly limits the accessible design space and, consequently, the achievable performances. In the present work, we propose a rigorous inverse design method to engineer three-dimensional metal nanoparticles according to a preassigned objective function, coupling an efficient global optimization algorithm to a full-retarded, electromagnetic solver based on the surface integral equation method. Thus, we use the proposed strategy to design the morphology of metal nanoparticles, maximizing the electric field average on their surface. We performed the optimization by varying the exciting wavelength in the ultraviolet and visible spectral ranges and the particle's material among the most used plasmonic materials, namely, gold, silver, and aluminum, obtaining different corresponding optimal shapes. General design criteria of nanoparticle's shape and size for best enhancement of electric fields are obtained. The automation of nanoparticles design enables the engineering of numerous nanoscale optical devices such as plasmon-enhanced Raman sensors, photodetectors, light sources, and more efficient nonlinear optical elements for on chip integration.