Mid-Infrared Plasmonic excitation in Indium Tin Oxide micro-hole arrays

Transparent Conducting Oxides (TCOs) are emerging as possible alternative constituent materials to replace noble metals such as silver and gold for low-loss plasmonic applications in the Near-Infrared (NIR) and Mid-Infrared (MIR) regimes. In particular, TCO-based nanostructures are extensively investigated for biospectroscopy exploiting their surface enhanced infrared absorption (SEIRA). The latter enhances the absorption from vibrational and rotational modes of nearby bio-molecules making TCO nanostructures, a promising candidate for IR sensing applications. Nevertheless, in order to produce inexpensive devices for lab-on-chip diagnostics, it would be auspicable to achieve surface enhanced infrared absorption with very simple microstructures not requiring nano-size control. In this work, we attempt to demonstrate SEIRA effect with the least challenging fabrication, μm-scale instead of nm-scale, by tailoring both device design and charge density of ITO film. We show that micro-periodic hole arrays in a ITO film are able to produce SEIRA via grating coupling. Such a study opens the way for innovative and disrupting biosensing devices.