Plasmonic bar-coupled dots-on-pillar cavity antenna with dual resonances for infrared absorption and sensing: performance and nanoimprint fabrication.

We report the structure, performance and large-area fabrication of a thin plasmonic infrared absorber, termed "bar-shaped disk-coupled dots-on-pillar antenna-array" (bar-D2PA). The bar-D2PAs, which are simple to fabricate, demonstrate the following, experimentally: (i) a different light-absorption resonance for each polarization with the resonance peak tunable by the bar-to-backplane gap and the bar size; (ii) for the geometry tested, the reflection is nearly constant at ∼10%, but the transmission and absorption highly depend upon the bar size and the gap between the bar and the backplane (e.g., the absorption of 77% (30%), the transmission of 9% (62%), and the resonance peak at 3.12 μm (3.04 μm) for the polarization along 700 nm long (185 nm short) axis and a 20 nm gap); (iii) a smaller gap significantly enhances the normalized extraordinary transmission, and (iv) the extraordinary transmissions become larger as the polarized bar side is in deeper subwavelength. The bar-D2PAs were fabricated in large area using nanoimprint lithography, etching plus one metal deposition that forms all metal structures in one step with excellent self-alignment and self-assembly. The design and fabrication can be extended to broad plasmonic applications.