The use of impedance spectroscopy and optical reflection spectroscopy to study modified aluminium surfaces

Porous-type anodic oxide Al films were investigated by means of two non-destructive, in situ applicable analysis techniques, electrochemical impedance spectroscopy (EIS) and spectroscopic ellipsometry (SE). The porous part of the porous film cannot be characterized with EIS measurements in aqueous solutions due to short-circuiting of the porous oxide by the electrolyte in the pores. By introducing an optical model which matches previous TEM investigations it is shown that SE characterizes the porous film morphology, including the porous part and the barrier part thicknesses, porosity and film-substrate interface roughness throughout the entire growth process. SE also allows us to determine the change in growth rate for films formed at increasing current density.