Characterization of aluminium surface treatments with electrochemical impedance spectroscopy and spectroscopic ellipsometry

The characterization of barrier and porous anodic oxide films on aluminium by means of Electrochemical Impedance Spectroscopy (EIS) and Spectroscopic Ellipsometry (SE) is reported. Both techniques are used to investigate the sealing of the porous film. To determine the accuracy of quantitative characterizations of the anodic films, the EIS and SE data are correlated to TEM results. It is concluded that ellipsometry yields accurate values for the thickness, the growth rate and the interface properties of the barrier film and the porous film. The characterization of the porosity of the porous film is also in good agreement with the results obtained by TEM. It is shown that ellipsometry gives more information than EIS, where information about the pore structure of porous oxide films can not be achieved from measurements in aqueous solutions. For the investigation of the sealing of the porous film, SE is more sensitive, but less quantitative than EIS, even though the potential for quantitative characterization is present.