Dynamics and temperature dependence of etching processes of porous and barrier aluminum oxide layers

• Published in: Electrochimica acta Vol. 49; no. 15; pp. 2487 - 2494
• Main Authors: Brevnov, Dmitri A., Rama Rao, G.V., López, Gabriel P., Atanassov, Plamen B.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 30.06.2004; Elsevier
• Subjects: Anodic aluminum oxide; Barrier oxide layer; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Impedance spectroscopy; Materials science; Physics; Spectroscopic ellipsometry; Surface treatments; Barrier oxide layer; Anodic aluminum oxide; Impedance spectroscopy; Spectroscopic ellipsometry; Temperature dependence; Scanning electron microscopy; Metallic thin films; Aluminium base alloys; Surface treatments; Electrodissolution; Electrochemical etching
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2004.02.003

Electrochemical impedance spectroscopy (EIS) and ex situ spectroscopic ellipsometry (SE) are applied to study the growth and etching of porous and barrier oxide layers formed during anodization of 99.5% aluminum and 0.5% copper films. The equivalent circuit, which includes two parallel combinations each containing a constant phase element (CPE) and a resistor (R) connected in series with the cell uncompensated resistance, is suggested for description of the electrolyte/alumina/aluminum interface. While EIS is sensitive only to barrier oxide layer properties (the dielectric constant and thickness), SE provides information about both the porous and barrier oxide layers. SE is used to determine a thickness of the barrier oxide layer formed after 1-min anodization at a corresponding dc voltage. The EIS data combined with the ellipsometrically determined thickness of the barrier oxide layer allow for calculation of the dielectric constant of aluminum copper oxide. A previously established two-step anodization procedure is applied to grow ordered anodic aluminum oxide (AAO) arrays. EIS is shown to provide an accurate approach to monitor etching of the barrier oxide layer in a mixture of chromic and phosphoric acids. At a constant temperature, the thickness of the barrier oxide layer decreases almost linearly with time. The temperature dependence of the barrier oxide layer etching is studied for the first time and the activation energy of this process is found to be 42kJ/mol. EIS is suggested to be a convenient method to determine the necessary duration of the etching process during application of the two-step anodization procedure. Non-destructive monitoring of growth and dissolution of alumina layers by means of EIS and SE is important to optimize conditions necessary for growth of ordered AAO arrays from aluminum films on solid supports.