Corrosion behavior of magnetron sputtered tantalum coating

In this study, tantalum (Ta) thin film was deposited on Si(100) and 316L stainless steel (SS) substrates by DC magnetron sputtering. The structural properties of Ta film were investigated by X-ray diffraction analysis. In addition, the scanning and transmission electron microscopies as well as atomic force microscopy were used to study the cross-section and the morphology of the coating. The corrosion behavior of the bare and Ta-coated 316L SS was evaluated by potentiodynamic polarization test. The electrochemical impedance spectroscopy was employed to study the corrosion mechanisms. The results revealed that the structure of Ta coating on either Si and SS substrates is a mixture of αβ phases, while pre-deposition of a thin tantalum nitride seed layer causes to the deposition of pure α-Ta and decrease the sheet resistance from 90 µΩ.cm to 15 µΩ.cm. Microscopic evaluations shows that the Ta coating is compact, homogeneous and defect-free, exhibiting a columnar structure with a surface roughness of less than 6 nm. Furthermore, the corrosion studies show that the Ta coating perform as a physical barrier between corrosive electrolyte and substrate and, in this way, provide a protective efficiency of more than 70%. In this regard, the diffusion of corrosive electrolyte toward the substrates through open porosities was found to be the corrosion mechanism of the Ta coating and the porosity index of the coating was calculated to be about 6%.