Electrochemical characterization of nanostructured Ag:TiN thin films produced by glancing angle deposition on polyurethane substrates for bio-electrode applications

Abstract

Flexible polyurethane substrates were coated with Ag:TiN thin films (N/Ti atomic ratio = 0.7; 10 at.% Ag), with different column inclinations (α = 0°, 40° and 80°) and architectures (columnar, zigzag with 2 and 4 periods), using the Glancing Angle Deposition (GLAD) technique. The coatings were characterized in order to assess the best thin film architecture to suit the bio-potential electrode applications. An abrupt increase of porosity of the samples was perceivable with increasing α angles (particularly from 40° to 80°). Hence, the sputtered films could be divided into dense (Ag:TiN 0° and Ag:TiN 40°) and porous (Ag:TiN 80°, Ag:TiN 80° 2Z and Ag:TiN 80° 4Z) samples. The electrochemical behaviour of the sampleswas consistently linked to the porosity differences,which was accompanied by an increase of the surface Ag content. Furthermore, the porous samples exhibited lower impedances (~104 Ωcm2 at 2 MHz), as well as electrochemical noise and drift rate values similar to those of the commercial Ag/AgCl electrodes. Hence, the porous Ag:TiN 80°, Ag:TiN 80° 2Z and Ag:TiN 80° 4Z porous Ag:TiN GLAD coatings seem to be the most promising architectures for the envisaged bio-potential electrode applications.