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Aluminum Bowties for Plasmonic‐Enhanced Infrared Sensing

Plasmonic nanoantennas have earned outstanding credits for their powerful ability to couple light from free‐space into sub‐wavelength‐sized structures and to enhance the electric field confinement. One of the most appealing plasmonic applications is biosensing: to detect and identify many bio‐information of a molecule in a single test. Consequently, surface enhanced spectroscopy in a broad infrared (IR) range is required. In this article, a barcode‐like nanostructured surface of a metal‐insulator‐metal (MIM) platform serves as optical transducer with tunable localized surface resonances (LSPR). The conception, fabrication, and optical characterization of periodic arrays of aluminum bowties (Al‐BT) within a MIM structure compatible with Si‐technology are reported. LSPR positions are extended by controlling the side length of the tip‐to‐tip facing triangles. The reflectance measurements correlate extremely well to numerical simulations. The simulated electrical field confinement provides up to 103 of intensity relying on the tip‐to‐tip nanogap value. Surface‐enhanced infrared absorption (SEIRA) gives simultaneously spectral information on both far‐field behavior and near‐field enhancement of several vibrational lines of our trial molecule (vanillin) achieved with the barcode‐like Al‐BT. The analysis of Fano‐like profiles is concluded with SEIRA enhancement factors higher than 107 for frequency tuning ratios below 1 between the far‐field plasmonic resonances and the selected vanillin IR absorption lines.