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

Abstract

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(N-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 cm 2 areas, which can be used in real-world applications such as chemical and biological vibrational sensing, is now possible.

Versatile Direct Laser Writing Lithography Technique for Surface Enhanced Infrared Spectroscopy Sensors

“…The mm 2 arrays demonstrated uniform reflectivity over the whole area (inset of figure 10) with a writing time of 4min/mm 2 (for 2μm long Au antennas and Px=Py=4μm) -three times faster than the writing time of devices with similar array parameters written with single-beam research-level standard EBL system (eLINE, Raith, with 20μm aperture and 20kV beam). A ten-times increase in the throughput over such EBL systems may be achieved with better optimization of the writing parameters, as demonstrated in 16 .…”

“…Two notable examples for such detection methods are surface enhanced Raman scattering (SERS) 1-4 , and surface enhanced infrared absorption (SEIRA) [4][5][6][7][8][9][10][11][12][13][14][15][16] . In SEIRA spectroscopy, metallic and dielectric nanoantennas that exhibit plasmonic resonances in the Infra-Red (IR) regime are used to intensify the IR absorption signal of known vibrational modes of molecules, so that even small amount of analytes can be identified [4][5][6][7][8][9][10][11][12][13][14][15][16] . The improved detection originates from the excitation of localized surface plasmon resonances (LSPRs) -charge oscillations on the surface of the nano-structured surface -which give rise to a strong local electric field at the vicinity of the nanostructures and enhanced coupling between the textured surface and the vibrational modes of the adsorbed molecules.…”

“…A Two-Photon Polymerization (TPP) direct laser writing (DLW) technique 16,23,24 has been demonstrated recently as a fast route for fabricating multi-millimetres arrays of nano-antennas for sensing applications in the IR spectral region, with an ultimate flexibility in structures design and fast writing speed. For example, Bagheri et.…”

Surface-enhanced infrared absorption studies towards a new optical biosensor

“…But this is not the end of the story. The SEIRA effect can be enhanced by using specifically tailored nano-antennas, where enhancement factors up to 10,000 are reported [21]. Optimized nano-antennas with an optimized SEIRA effect, bio-functionalization of these antennas to avoid unspecific binding, and monitoring of film thickness growth by RIfS interference can be combined as a potential means to identify and quantify large molecules or even bacteria in an aqueous system.…”

Periodic array-based substrates for surface-enhanced infrared spectroscopy

“…Another approach for the fast fabrication of arrays of linear nanoantennas is femtosecond direct laser writing lithography [81]. The authors were able to produce highquality large-area substrates with this method.…”