A novel approach to diamondlike carbon based mid-infrared attenuated total reflectance spectroelectrochemistry

Structural changes of an electroactive species during an electrochemical reaction cannot be determined from the electroanalytical technique alone. By incorporating spectroscopic techniques with electrochemistry, additional information about the analyte structure and composition of the double layer can be obtained during electrochemical processes. Several spectroscopic methodologies have been tailored for this purpose including electronic and vibrational spectroscopies. Mid-infrared attenuated total reflectance (mid-IR-ATR) spectroscopy is especially interesting as it provides in-situ information about adsorbates at the electrode surface. Mass transport limitations present in mid-IR external reflection and transmission spectroelectrochemistry are circumvented with ATR spectroelectrochemistry. However, limitations of appropriate electrode materials for the internal reflection configuration have hindered widespread adoption of the technique. The work described in this thesis focuses on the development and coupling of electrically conducting diamondlike carbon (DLC) films with mid-IR transparent multi-reflection waveguides for ATR spectroelectrochemistry.;DLC thin films were developed utilizing pulsed laser deposition systems in collaboration with Joanneum Research (Leoben, Austria) and at the University of North Carolina (Chapel Hill). Nitrogen doping and incorporation of noble and metal nanoclusters were investigated as approaches aimed at improving the electrical conductivity of DLC.;Detailed compositional studies of nitrogen-doped DLC layers showed that sp2-hybridized carbon is responsible for the observed electrochemical activity. Optical transparency of thin (∼40 nm) DLC layers in the mid-IR regime was confirmed by transmission-absorption measurements upon deposition on zinc selenide ATR waveguides. Additionally, the first spectroelectrochemical application of conducting DLC films was demonstrated via the electropolymerization of polyaniline onto coated ATR elements. Metal-DLC nanocomposite layers were investigated with various analytical techniques obtaining detailed compositional information. Improved electrochemical activity of metal-DLC demonstrated their suitability as electrode materials. Sufficient mid-IR transmissivity of metal-DLC coated germanium waveguides was displayed to enable spectroelectrochemical application.;Finally, electropolymerization of poly(4-vinylpyridine) in acetonitrile was pursued to produce highly cross-linked ion-exchange membranes for spectroelectrochemical sensing. The composition of the pre-polymerization mixture and deposition conditions were tailored to obtain uniform semipermeable membranes. Diffusion of cations to electrodes is restricted by performing the electropolymerization as established herein. By employing the described electropolymerization procedure at DLC-coated waveguides, spectroelectrochemical sensing strategies can now be extended into the mid-IR regime.