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Low-cost infrared resonant structures for surface-enhanced infrared absorption spectroscopy in the fingerprint region from 3 to 13 µm

: Hoffmann, J.M.; Yin, X.; Richter, J.; Hartung, A.; Maß, T.W.W.; Taubner, T.


Journal of physical chemistry. C, Nanomaterials and interfaces 117 (2013), No.21, pp.11311-11316
ISSN: 1932-7447
ISSN: 1932-7455
Journal Article
Fraunhofer ILT ()

We use low-cost colloidal lithography with micrometer-sized polystyrene spheres to fabricate arrays of triangular gold microstructures on different infrared-transparent substrates while varying the structures' lateral size. The refractive index n of the substrate in the infrared spectral range can be varied strongly, e.g., from n = 1.4 (calcium fluoride) to n = 4.0 (germanium) for the used materials. Variation of antenna size and substrate material allows us to tune the spectral resonance position of the fabricated antennas from 3 to 13 µm and therefore to cover the absorption bands of the infrared fingerprint region and functional groups. The easy handling and good tunability is demonstrated with surface enhanced infrared absorption (SEIRA) spectroscopy measurements on poly(methyl methacrylate) (PMMA) covered antennas on two different substrate materials (calcium fluoride and silicon) but equal spectral resonance positions of the antennas to ensure the comparability. Ad ditional near-field measurements show that large antennas on a low-index substrate yield stronger local field enhancement compared to smaller antennas on a higher-index substrate, despite the same far-field response.