Abstract
Tailored plasmonic nanoantennas are neededfor diverse applications, among those sensing. Surfaceenhancedinfrared absorption (SEIRA) spectroscopy usingadapted nanoantenna substrates is an efficient techniquefor the selective detection of molecules by their vibrationalspectra, even in small quantity. Highly doped semiconductorshave been proposed as innovative materials forplasmonics, especially for more flexibility concerning thetargeted spectral range. Here, we report on rectangularshaped,highly Si-doped InAsSb nanoantennas sustainingpolarization switchable longitudinal and transverseplasmonic resonances in the mid-infrared. For small arrayperiodicities, the highest reflectance intensity is obtained.Large periodicities can be used to combine localized surfaceplasmon resonances (SPR) with array resonances,as shown in electromagnetic calculations. The nanoantennaarrays can be efficiently used for broadband SEIRAspectroscopy, exploiting the spectral overlap between thelarge longitudinal or transverse plasmonic resonancesand narrow infrared active absorption features of an analytemolecule. We demonstrate an increase of the vibrationalline intensity up to a factor of 5.7 of infrared-activeabsorption features of vanillin in the fingerprint spectralregion, yielding enhancement factors of three to fourorders of magnitude. Moreover, an optimized readout forSPR sensing is proposed based on slightly overlappinglongitudinal and transverse localized SPR.