Superlattice Plasmons in Hierarchical Au Nanoparticle Arrays

Periodic metal nanoparticle (NP) arrays support narrow lattice plasmon resonances that can be tuned by changing the localized surface plasmons of the individual NPs in the array, NP periodicity, and dielectric environment. In this paper, we report superlattice plasmons that can be supported by hierarchical Au NP arrays, where finite arrays of NPs (patches) are organized into arrays with larger periodicities. We show that superlattice plasmons can be described by the coupling of single-patch lattice plasmons and Bragg modes defined by the patch periodicity. Superlattice plasmon resonances are often significantly narrower than that of single-patch lattice plasmon resonances and exhibit stronger local peak fields. By varying the periodicity of the patches, we demonstrated that the number and spectral location of superlattice plasmon resonances can be tailored in hierarchical Au NP arrays. These narrow superlattice plasmon resonances open prospects in ultrasensitive sensing and energy transfer and plasmon amplification in plasmonic cavities.