A simple electrochemical strategy for the characterisation of defects in alumina-coated metal substrates

A simple electrochemical procedure is proposed to obtain defect information in alumina-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 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 in 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 the defect sites and SECM images of copper-decorated defects, provided information on defect density and spatial distribution, as well as on average defect sizes.