Fabrication of Square-Centimeter Plasmonic Nanoantenna Arrays by Femtosecond Direct Laser Writing Lithography: Effects of Collective Excitations on SEIRA Enhancement

We demonstrate the use of femtosecond direct laser writing lithography for a fast and homogeneous large-area fabrication of plasmonic nanoantennas on a substrate by creating a patterned polymer as an etch mask on a metal layer. Subsequent argon ion beam etching provides plasmonic nanoantennas with feature sizes below the diffraction limit of the laser light. They exhibit tunable high-quality plasmon resonances in the mid-infrared spectral range, which are ideally suited for surface-enhanced infrared absorption (SEIRA). In the present work, we demonstrate reliable, fast, and low-cost fabrication of a wide variety of antenna arrays and examine particularly the influence of plasmonic coupling between neighboring antennas on the SEIRA enhancement effect. Specifically, we measure the enhanced infrared vibrational bands of a 5 nm thick 4,4′-bis­(<i>N</i>-carbazolyl)-1,1′-biphenyl layer evaporated on arrays with different longitudinal and transversal spacings between antennas. An optimum SEIRA enhancement per antenna of 4 orders of magnitude is found close to the collective plasmon excitation in the nanoantenna array, rather than at the highest antenna density. Our method establishes a low-cost replacement technique for electron beam lithography. Simple, fast, and straightforward fabrication of optimized SEIRA antenna arrays with cm² areas, which can be used in real-world applications such as chemical and biological vibrational sensing, is now possible