Achieving High Quality Factor Interband Nanoplasmonics in the Deep Ultraviolet Spectrum via Mode Hybridization

Interband plasmons (IBPs) enable plasmonic behavior in nonmetallic materials, such as semiconductors. Originating from interband electronic transitions, IBPs are characterized by negative real permittivity that can extend into deep ultraviolet (DUV) spectrum, as demonstrated using silicon. However, the practical applications of IBPs are limited by their inherently broad resonances. In this study, we address this limitation by hybridizing the localized plasmon resonance of silicon nanostructures with the Fabry-Pérot resonance of a SiO₂ dielectric layer atop a silicon substrate. This design achieves a simulated quality factor (<i>Q</i>-factor) of ∼43, with experimental measurements yielding a <i>Q</i>-factor of 37 at ∼4.6 eV within the DUV region. Furthermore, we demonstrate a 5.4-fold enhancement in DUV absorption for lignin-modified polyethylene glycol films when integrated with the hybridized DUV cavity, showcasing the potential for UV blocking applications. Our findings offer a versatile platform that can be adapted to other IBP systems and open new opportunities in UV-specific applications.