Effect of nitrogen concentration on the electrochemical behavior of amorphous hydrogenated carbon a-C:H:N films.

Nitrogen-incorporated hydrogenated amorphous carbon a-C:H:N thin films have been grown by using an Integrated Distributed Electron Cyclotron Resonance Microwave assisted plasma reactor. The electrochemical behavior of such films deposited on Si and Ti substrates has been studied by voltammetry and impedance spectroscopy, as a function of the nitrogen content (0.05<N/(N+C+H) <0.24). In this range, the lower are the N content and the film conductivity, the faster is the electron transfer rate for the Fe(II/III) redox reaction. The impedance response is interpreted as the series combination of the respective contributions of the n-Si/ a-C:H:N (absent for Ti substrates) and the a-C:H:N/solution interfaces without considering any frequency dispersive elements, except a diffusion impedance. It is concluded that a-C:H:N thin film electrodes can constitute promising substitutes for diamond materials in view of sensor or environmental applications.