Voltage-Dependent Structural Dynamics measured with 2D IR spectroscopy

Strong electric fields exist between the electric double layer and charged surfaces. These fields impact molecular structures and chemistry at interfaces. We have developed a transparent electrode with infrared plasmonic enhancement sufficient to measure FTIR and two-dimensional infrared spectra at submonolayer coverages on the surface to which a voltage can be applied. Our device consists of an infrared transparent substrate, a 10–20 nm layer of conductive indium tin oxide (ITO), an electrically resistive layer of 3–5 nm Al₂O₃, and a 3 nm layer of nonconductive plasmonic gold. The materials and thicknesses are set to maximize the surface number density of the monolayer molecules, electrical conductivity, and plasmonic enhancement while minimizing background signals and avoiding Fano line shape distortions. Data will be presented on a monolayer of 4-mercaptobenzonitrile and 4-mercaptobenzoic acid methyl ester. We have observed that the timescale for hydrogen bonding to the nitrile of 4-mercaptobenzonitrile depends on the applied voltage, which has important implications for chemistry at electrode surfaces.