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In realizing excellent plasmonic devices, a methodology based on flexibility and simplicity in fabrication, minimal sensitiveness to smaller nanoscale errors, larger dielectric layer thickness with superior device characteristics, and low-cost process is critically crucial for next-generation devices with multiple applications. One such attractive device is a plasmonic nanocavity, with numerous reports been already reported resulting in superior localized surface plasmon resonance (LSPR) and enhancement properties. The conventional spherical NP on a metallic mirror (NPOM) nanostructure’s plasmonic characteristics deteriorates with minor changes in dielectric layer thickness (t ≤ 6 nm). Alternatives like nanocube on mirror (NCOM), nanodisk on mirror (NDOM), provided better options towards LSPR tuning and near field enhancement. In recent times there are few reports based on faceted spherical NPOM design emerged. But however, the so far reported FNPOM nanostructures lacked the following: “facet width control, a clear SEM/TEM image of full geometry, and larger “t” with superior plasmonic characteristics”. In this work, for the first time, we report a clear FNPOM nanostructure with better control in facet fabrication using reactive thermal annealing (RTA) method. We used Ag NP on an Au mirror with SiO2 as a dielectric layer with different NP diameters of 50 nm, 70 nm and 100 nm with a precise facet width control (from 90% sphere to hemisphere). We employed a larger “t” ranging between 10 nm – 40 nm to display superior properties. From our dark field and LSPR mapping measurements, 70% of the sample are showed similar plasmonic characteristics from a 1 cm x 1 cm substrate. Our experiment results showed that it is possible to tune the LSPR resonance wavelength till 40 nm dielectric thickness reflecting it as a superior plasmonic nanocavity device. The reason behind this enhanced plasmonic characteristics is due to the introduction of facet in NPs and our three-dimensional finite difference time domain (3D FDTD) simulations results agreed well with experiment. For a final comparison, we checked our hemispherical shaped FNPOM versus NCOM design for NPs with diameter of 100 nm, where we find our FNPOM nanostructures showcased superior plasmonic properties.
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