Strong and tunable absorption in coupled nanoparticle–cavity systems for plasmonically enhanced hot electron devices

Designing plasmonic systems with tailored resonances based on ultra-small metal nanoparticles (NPs) is fundamental for functional hot electron devices. Here, a coupled NP array–optical cavity system is demonstrated to enhance and control the absorption in small NPs. We show that the interaction between cavity modes and resonances of fully embedded NPs leads to a variety of optical behavior. Analytical and numerical models provide a conceptual understanding of the coupling mechanism, highlighting the role of NP density. In the strong-coupling regime, strong and tunable absorption resonances are achieved by a facile variation of the cavity length, while modification of NP positions allows us to excite or avoid peak splitting in the absorption spectra. Furthermore, hybridizing NP–cavity modes achieves narrow-linewidth resonances, translating to a four-fold increase in the quality factor compared to isolated NP arrays. This work provides prescriptive guidelines for the design of efficient plasmonically enhanced hot electron devices.