Use of in-situ spectroscopic ellipsometry to study aluminium/oxide surface modifications in chloride and sulfuric solutions

In-situ visible spectroscopic ellipsometry (VISSE) is used to study the influence of 0.1 M HCl, pH 1.2 and H2SO4 with equal pH on electropolished Al with and without thicker barrier oxide film. A clear connection between VISSE results and open circuit potential (OCP) is shown: both techniques confirm the process of dissolution and regrowth of a new layer in-situ. For immersion of electropolished Al in both solutions, dissolution of the film corresponds to a decrease in OCP followed by an increase in thickness and OCP to reach a constant potential. For the electropolished Al film immersed in HCl also surface roughening occurs induced by the attack of Cl− ions. For immersion in H2SO4, the sample is less roughened as compared to immersion in HCl. In the case of a barrier oxide film on Al, only dissolution of the film is noted for both solutions.