Highly doped semiconductor plasmonic nanoantenna arrays for polarization selective broadband surface-enhanced infrared absorption spectroscopy of vanillin
Résumé
Tailored plasmonic nanoantennas are needed
for diverse applications, among those sensing. Surfaceenhanced
infrared absorption (SEIRA) spectroscopy using
adapted nanoantenna substrates is an efficient technique
for the selective detection of molecules by their vibrational
spectra, even in small quantity. Highly doped semiconductors
have been proposed as innovative materials for
plasmonics, especially for more flexibility concerning the
targeted spectral range. Here, we report on rectangularshaped,
highly Si-doped InAsSb nanoantennas sustaining
polarization switchable longitudinal and transverse
plasmonic resonances in the mid-infrared. For small array
periodicities, the highest reflectance intensity is obtained.
Large periodicities can be used to combine localized surface
plasmon resonances (SPR) with array resonances,
as shown in electromagnetic calculations. The nanoantenna
arrays can be efficiently used for broadband SEIRA
spectroscopy, exploiting the spectral overlap between the
large longitudinal or transverse plasmonic resonances
and narrow infrared active absorption features of an analyte
molecule. We demonstrate an increase of the vibrational
line intensity up to a factor of 5.7 of infrared-active
absorption features of vanillin in the fingerprint spectral
region, yielding enhancement factors of three to four
orders of magnitude. Moreover, an optimized readout for
SPR sensing is proposed based on slightly overlapping
longitudinal and transverse localized SPR.
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