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.This research is partially sponsored by FEDER funds through the programme COMPETE - Programa Operacional Factores de Competitividade, by national funds through FCT – Fundação para a Ciência e a Tecnologia, under the projects PEst-C/EME/UI0285/2011, PTDC/SAU-ENB/116850/2010, PTDC/CTM-NAN/112574/2009 and Programa Pessoa 2012/2013 Cooperação Portugal/França, Project no. 27306UA Porous architectures in GRAded CERamic thin films for biosensors — GRACER. The authors would also like to acknowledge to the European Union (FP7-PEOPLE Marie Curie IAPP, project 610950), to CEMUP for SEM analysis and Yantai Wanhua Polyurethanes Co., Ltd. for providing the thermoplastic polyurethane pellets. P. Pedrosa acknowledges FCT for the Ph.D. grant SFRH/BD/70035/2010