Study of the Deposition of Mixed Cerium oxide Thin Films by Reactive Magnetron Sputtering for the Development of Corrosion Protective Coatings

摘要

CeO_x thin films (100 nm) were synthesized by direct current (DC) reactive magnetron sputtering (MS) on Al substrates. Depositions were performed at 5 mTorr with varying O_2 content in order to affect plasma chemistry and properties of the films. X-ray photoelectron spectroscopy (XPS) data revealed that, whatever the deposition conditions, the top surface is strongly oxidized. By depth profiling it appears that the chemical profile is composed (from film-surface to films-substrate interface) of three regions: the Ce~(4+) top surface, a Ce~(4+)/Ce~(3+) oxides mixture and finally a Ce~(3+) oxide region. Oxidation state gradient suggests a post-deposition oxidation of the surface of the coatings, propagating at a different rate depending on the microstructure of the films. Cross-sectional investigations by field emission gun scanning electron microscope (FEG-SEM) allowed identifying and visualizing microstructural differences. Results of corrosion tests (polarization curves, electrochemical impedance spectroscopy) support spectroscopic and microstructural findings.