Defining the plasmonic cavity performance based on mode transitions to realize highly efficient device design

Abstract

Designing and realizing high-potential applications in the fields of energy conversion, fuel generation, sensors, and photonic devices require a precise understanding of fundamental plasmonic properties. In the above-mentioned applications, a plasmonic nanoparticle on mirror (NPOM) nanostructure is employed as one of the key fundamental components. However, NPOM's plasmonic properties are not understood in detail, especially in terms of mode transitions along with the edge effect, which is a crucial requisite in devising device efficiency. In this work, we classified the plasmonic nanocavity strength and its respective near-field enhancement deterioration rate% based on mode transitions and the edge effect, which plays a significant role in defining the device efficiency. Superior light properties with a slower near field enhancement deterioration rate% (55%) from the NPOM nanostructure can be observed when it exhibited an unchanged dipolar mode (in the high plasmonic nanocavity strength region) in combination with the edge effect (medium to NP-only strength region). In the case of the quadrupolar to dipolar mode transition, two interesting cases of surface charge evolution are reported: case one – smaller near-field enhancement numbers are obtained when the NP surface charge close to the metallic mirror disappears during the mode transition; and case two – higher near-field enhancement numbers are obtained when the NP surface charge close to the metallic mirror dominates during the mode transition. Irrespective of both scenarios, the quadrupolar to dipolar mode transition resulted in a rapid near field enhancement deterioration rate% (case one – 86%, case two – 81%). We find that the NPOM nanostructure with a combination of an unchanged dipolar mode and edge effect property can uplift the efficiency of devices in multiple applications.