Correlation between sp3‑to-sp2 Ratio and Surface Oxygen Functionalities in Tetrahedral Amorphous Carbon (ta-C) Thin Film Electrodes and Implications of Their Electrochemical Properties

Detailed information about the physicochemical properties of a given surface is important in order to understand and predict the performance of materials in electrochemical applications. Here we present a detailed X-ray absorption spectroscopy study of two different tetrahedral amorphous-carbon (ta-C) thin films and their subsequent electrochemical characterization. The results show marked differences in ta-C surface and bulk properties, namely differences in the amount of surface functional groups and their sp3/sp2 ratios, respectively. In particular, the variation in the oxygen content of the surface leads to significantly different behavior in electrochemical measurements, such as a 10-fold increase in sensitivity for dopamine and stronger response to ascorbic acid. Results of the surface properties were further analyzed by simulations carried out within the framework of density functional theory (DFT) as well as by utilizing Raman spectroscopy.