Orientation\nSensitive SEIRA Sensors Based on Single-Walled\nCarbon Nanotube Near Fields

Molecular vibrations that bear information about intrinsic\nproperties\nof chemical compounds are challenging to detect at submonolayer densities.\nSurface-enhanced infrared absorption (SEIRA) spectroscopy has been\nproven to be a viable approach to enhance and detect weak vibration\nsignals. Here, we report a SEIRA sensor based on mid-infrared surface\nplasmon resonances supported by single-walled carbon nanotubes (SWCNTs).\nDue to the 1D nature of SWCNTs, their plasmon modes are highly polarized\nwith the electromagnetic fields spatially confined to nanometer scales.\nLeveraging these characteristics of SWCNTs, we observe a polarization\nselective coupling between their surface plasmons and vibrational\nmodes of chemical bonds introduced onto their surfaces. A maximum\nmodulation of ∼15% to the plasmon resonance peak is obtained\nfor a submonolayer chemical group coverage. These findings suggest\nthat SWCNTs may potentially serve as a highly sensitive SEIRA platform\nfor revealing intricate information about molecular compositions and\nbond orientations.