Core-Shell Nanocuboid Dimers with Nanometric Gaps

Nanometric gaps in plasmonic structures can lead to huge optical near fields and, related, to strongly enhanced interaction of molecules and light. Nanocavities formed by sphere-on-film or cube-on-film systems were recently established as promising systems, eventually reaching the strong coupling regime. However, such structures are limited with respect to being bound to a surface and by having no means of adjusting the resonance wavelength to the requirements of arbitrary analytes, independent of the gap width. We suggest and investigate in this paper silver-gold compound nanocuboid dimers in colloidal solution as potential structures to mitigate both limitations. We analyze the dimers' plasmonic properties by a combination of optical spectroscopy, electron energy loss spectroscopy, and numerical simulations, focusing on the longitudinal dimer geometry and the dominant light-coupled plasmon mode. We then calculate optical field enhancements under light and electron excitation to assess the cuboid dimer's potential in sensing and spectroscopy applications.