Microstructure and electrochemical characterization of Ti-Al-C-N coatings as biological dry electrodes

Ti-Al-C-N coatings were deposited on 316L and Si (100) substrates by adjusting the Al target power using unbalanced magnetron sputtering. Their microstructure was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The result indicated that Ti-Al-C-N coatings consists of single and poly crystalline grains of AlN and TiAlN, as well as amorphous carbon (a-C) and amorphous carbon nitride (a-CN). The electrochemical noise (EN), contact impedance of electrode/skin were measured using an electrochemical workstation. The lower potential drift amplitude and current shift amplitude of TiAlCN coatings mainly concentrated in the range of 0.15-0.35 mV and 0.1-0.25 nA respectively. Moreover, their noise impedance also increased to a certain extent (1.60-2.09 x 106 Omega) than TiCN coating (1.30 x 106 Omega). However, incorporation of Al atoms in TiCN coating led to an increased corrosion current density (icorr), along with a reduction in polarization impedance in electrochemical polarization testing, which might be due to the dissolution of the passivation film caused by the applied current. The open circuit voltage (OCP) and contact impedance of electrode/skin after Al atoms doping in TiCN coating, which was attributed to their smoother surface and thereby facilitating the formation of conductive regions characterized by an enhanced ion concentration within the limited sweat electrolyte.