Surface analysis of Cu coated with ALD Al2O3 and its corrosion protection enhancement in NaCl solution: EIS and polarization

Abstract

Al2O3 was coated on copper substrates with a thickness of 62 nm at 473 K temperature using atomic layer deposition method. The morphology of the produced samples was obtained by scanning electron microscope and atomic force microscope while the latter instrument also provided information on the surface roughness and grain sizes formed on the surface of the samples. Energy dispersive spectroscopy was employed for obtaining abundances of different elements in the samples before and after corrosion tests. Corrosion behavior of Cu and Al2O3/Cu was investigated by means of electrochemical polarization and electrochemical impedance spectroscopy analyses in 3.5% (0.6 M) NaCl solution. The validity of the data obtained from the latter method is investigated by Kramers-Kronig transformations. Also simulation of this data by equivalent electrical circuits resulted in a corrosion inhibition enhancement factor of η = 97.48% which indicates high improvement in corrosion resistance of Cu by Al2O3 coating. Corrosion parameters were also obtained from the polarization curves by fitting the experimental results with Stern-Geary relation near the open circuit potential. Negative shift of corrosion potential for the Al2O3 coated Cu relative to uncoated Cu indicates that Al2O3 coating is blocking the cathodic reaction. Corrosion inhibition efficiency/yield (PE%) obtained from anodic and cathodic branches of polarization curves showed high enhancement with values of 69% and 93%, respectively while the latter is consistent with the corrosion inhibition enhancement factor of η = 97.48% mentioned above. Results are compared with the published data and good agreements are obtained, deviation of those results from the rest is discussed considering all parameters involved in the ALD deposition.