A dual infrared frequency comb spectrometer with heterodyne detection has been used to perform time-resolved electrochemical attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). The measurement of the potential dependent desorption of a monolayer of a pyridine derivative (4-dimethylaminopyridine, DMAP) with time resolution as high as 4 μs was achieved without the use of step-scan interferometry. An analysis of the detection limit of the method as a function of both time resolution and measurement coadditions is provided and compared to step-scan experiments of an equivalent system. Dual frequency comb spectroscopy is shown to be highly amenable to time-resolved ATR-SEIRAS. Microsecond resolved spectra can be obtained with high spectral resolution and fractional monolayer detection limits in a total experimental duration that is 2 orders of magnitude less than the equivalent step-scan experiment.

The influence of a thin film of a supporting layer of conductive metal oxide (CMO) on the surface-enhanced infrared spectra generated from metal island layers is studied using an effective medium (EM) approximation and compared to experimental results. Gold island films electrodeposited on indium tin oxide (ITO) coated on an internal reflection element (IRE) give rise to asymmetric (bimodal or derivative-looking) line shapes and have strong surface-enhanced infrared absorption spectroscopy (SEIRAS) intensities for adsorbed cyanate using both p- (transverse magnetic) and s- (transverse electric) plane-polarized light. The dependence of the SEIRAS intensity on the angle of incidence is very different compared to metal films directly deposited on the surface of the IRE, as larger magnitude SEIRAS intensities are observed at angles close to the critical angle. The role of additional enhancement effects from possible plasmonic phenomena arising in the ITO layer is shown not to contribute to the ATR-SEIRAS mechanism. The observed spectra are modeled using an EM treatment of the gold island film, and a good qualitative and semiquantitative agreement is found between the calculated and experimental results. Using the Fresnel equations and EM-determined optical constants, the reflectivity of the interface is shown to be highly dependent on the volume fraction of gold in the enhancing layer, and asymmetric and even inverted bands arise near the metal percolation threshold. Electric field analysis shows that the low free charge carrier density (relative to metals) of ITO gives rise to field distributions similar to those of an absorbing dielectric layer on the surface of an IRE.

An evaluation of several experimental aspects that can optimize electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) performance using a commercially available, specular reflection accessory is provided. A comparison of different silicon single-bounce internal reflection elements (IREs) is made with emphasis on different face-angled crystal (FAC) options. Selection of optimal angle of incidence for maximizing signal and minimizing noise is shown to require consideration of the optical throughput of the accessory, reflection losses at the crystal surfaces, and polarization effects. The benefits of wire-grid polarizers and antireflective (AR) coatings on the IREs is discussed. High signal-to-noise ratios can be achieved by omitting polarizers, using an AR-coated FAC with a larger face angle, and working at angles of incidence close to the maximum throughput angle of the accessory.

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