A SIMPLE ELECTROCHEMICAL STRATEGY FOR THE CHARACTERIZATION OF DEFECTS IN ALUMINA-COATED SUBSTRATES

A simple electrochemical procedure is proposed for the evaluation of average size and visualisation of defects in alumina films coated platinum substrates, prepared by r.f. magnetron sputtering. The method makes use of cyclic voltammetry, chronoamperometry and scanning electrochemical microscopy (SECM), the alumina-coated samples (Pt/Al2O3) being the working electrodes. Cyclic voltammograms, performed in solutions containing Ru(NH3)63+ and Cu2+ ions, indicated that the systems investigated, due to the presence of defects on alumina layers, behaved as arrays of recessed microelectrodes with no overlap of individual diffusion layers. These features, along with data obtained from steady-state voltammetry, nucleation of metallic copper in defect sites and SECM images of copper-decorated defects, provided information on defect density and their spatial distribution, as well as on average defect sizes.