Probing Material and Geometry Dependent Plasmonic Performance of Nanoantennae via STEM-EELS

Plasmonic nanoantennae provide exceptional light confinement and field enhancement, making them promising platforms for label-free biosensing and bio-optoelectronic applications. However, the relationship between material composition, geometry, and plasmonic response at the nanometer scale remains unclear. Here, we systematically investigate nanoantennae made from Au, Al, NbN, and Cu using monochromated low-loss STEM-EELS. Arrays with controlled variations in length, width, and inter-antenna gap were fabricated via e-beam lithography. EELS mapping reveals strong correlations between geometry, localized surface plasmon resonance energies, and mode distributions. Au exhibits sharp resonances with strong field localization, Al supports UV-range plasmons for integrated photonics, and NbN offers improved stability and CMOS compatibility. Embedding these antennae in nanofluidic channels enables direct correlation between spectral shifts and refractive-index changes during analyte flow. Linking EELS-mapped modes with simulations establishes design principles for optimizing resonance tunability and field enhancement. This approach informs the development of durable, high-sensitivity plasmonic biosensors and metasurfaces for next-generation diagnostic technologies