Influence of cavity geometry towards plasmonic gap tolerance and respective near-field in nanoparticle-on-mirror

In this work, we emphasize the importance of cavity geometry along with nanoparticle shape and plasmonic nanogap (based on a nanoparticle on a metallic film (NPOM) design) which plays significant role in understanding the complex plasmonic mode characteristics involving nanoparticle and gap mode resonances. The cross-section imprint of planar cavity on metallic film plays decisive role in near field enhancement properties at similar NP size and plasmonic nanogap conditions for spherical and cubical NPOM systems. By mimicking the NPOM structure to metal-insulator-metal design, we understand the resonant emission differences for the respective plasmonic modes. Influence of dominant and weaker gap mode resonances resulted in an interesting optical behavior (fluctuations in near field enhancement strength) in NP mode in case of cubical nanostructures. By such extensive investigation and interpretation of sub-wavelength complex plasmonic mode characteristics, various practical applications in plasmonics field can be accomplished. [Display omitted] •The cross-section imprint of plasmonic nanocavity's volume or area influences near-field enhancement.•Understanding the complex plasmonic modes properties based on nanoparticle morphology in NPOM based.•Interesting fluctuations in NP mode's nearfield strength in the presence of gap mode.