A morphological, structural and electrochemical study of titanium nitride (TiNx) thin films, obtained by DC reactive sputtering on titanium substrates, was carried out for a wide range of compositions (0 < x < 1.34) aiming a selection of the best coatings for dry biomedical electrodes. The films displayed a columnar-type structure, with morphologies strongly dependent on the composition: a compact and smooth surface was found for the Ti-rich films, (x < 1), whereas the N-rich films, (x ≥ 1) displayed a rough and porous structure. The electrochemical study of the TiNx films was performed in synthetic sweat, aiming at simulating the contact with the skin. The voltammetric analysis showed anodic currents higher for TiNx films than for titanium for low and medium polarization potentials, whereas for potentials beyond 2 V the blocking behaviour of the TiNx films allowed them to display lower current values. The passive dissolution currents in the sub-μA/cm2 range and the charge transfer resistances of the order of
the MΩ proved the excellent stability of all films in sweat conditions. Finally, the electrochemical noise analysis showed that the near-stoichiometric and N-rich films display the lowest noise, being therefore the most suitable for electrode applications, where signals in the microvolt range, such as the electroencephalographic (EEG) signals, are to be monitored.
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