Characterization of metal-supported Al 2O 3 thin films by scanning electrochemical microscopy

Abstract

In this paper, physiochemical properties of amorphous alumina thin films, grown by the metal organic chemical vapour deposition process on the surface of platinum (Pt/Al 2O 3) and stainless steel (SS/Al 2O 3), were investigated in aqueous media. The study was performed by the use of scanning electrochemical microscopy (SECM), which allowed obtaining information on uniformity, topography and chemical stability/reactivity of the alumina coatings with high spatial resolution. In particular, the effects due to local acid, base and fluoride ions attack on alumina layers of thickness of about 250 nm (in the Pt/Al 2O 3 sample) and 1000 nm (in the SS/Al 2O 3 sample) were investigated. In the acid and base attack, high concentrations of H 2SO 4 and KOH were electrogenerated locally by the use of a 25 μm diameter platinum microelectrode. The latter was also used as SECM tip to monitor the chemical effect on the alumina layers. It was found that, regardless of the thickness of the film, alumina provided good resistance against local attack of concentrated H 2SO 4; instead, the film dissolved when subjected to KOH attack. The dissolution rate depended on several experimental parameters, such as SECM-tip to substrate distance, electrolysis time and alumina film thickness. The alumina layer proved also relatively poor resistance to etching in 0.1 M NaF solutions.