The Influence of Cavity-Induced Plasmonic Coupling on Near-Field Enhancement in Cube-in-Cube Nanoparticles

Internal nanostructures in plasmonic nanoparticles (NPs) have received comparatively limited attention, relative to external morphology and material composition. In particular, the influence of an internal cavity between the core and shell on plasmonic coupling and field enhancement remains poorly understood. In this study, we investigate the effect of cavity size within cube-in-cube (CiC) NPs on interparticle plasmonic interactions. Using dimers as a model system, we find that increasing the internal cavity size significantly enhances near-field coupling despite maintaining a constant interparticle spacing. This enhancement correlates with stronger scattering signals, indicating that the cavity facilitates a more effective field propagation beyond the shell. These results demonstrate that the cavity not only is a passive structural feature but also actively modulates spatial field distribution and plasmon mode overlap. By tuning the internal cavity without altering the particle's outer geometry, both intra- and interparticle interactions can be precisely controlled, introducing internal architecture-based nanoscale optical control.