Numerical optimization of gold-dielectric nanoparticle heterostructures for surface plasmon resonance engineering

Metallic nanoparticles are a very attractive and fascinating material due to their multifunctional properties, such as surface plasmon resonance absorption and excitation band tuning. In particular, these properties are proved to be valuable in photothermal therapeutic applications, where the tunable, efficient near-field enhanced ablation or photothermal energy conversions can be used to destroy cancerous cells. A similar mechanism can be applied for threedimensional multilayer nanopatterning of polymer matrix doped with NPs, where the field enhancement and photothermal energy conversion are utilised to produce micro-explosions and voids. Previously, it was reported that engineering the morphology of nanoparticles (rod and shell shape) can greatly enhance the field enhancement and photothermal conditions. Here, we numerically study the field enhancement efficiencies of nanparticles with heterogeneous morphologies (such as metal - dielectric - metal core-shell structures), and compare their efficiencies to conventional nanosphere and nanoshell structures. Unlike the previous approximate analytical models, the SPR excitation and field enhancement efficiencies are numerically simulated, using the frequency-dependent finite-difference time domain method under tightly focused ultrashort pulse laser irradiation to accurately emulate the experimental conditions.