Corrosion resistance of nitrogenated amorphous carbon films prepared by facing target sputtering

Nitrogenated amorphous carbon (a-CNx) films were prepared by facing target sputtering (FTS) technique. The nitrogen content in deposited films determined by X-ray photoelectron spectroscopy (XPS) measurement increases from 0 to 19.6 at.% as N2/Ar ratio varies from 0 to 0.4. Several sets of disks with a layer structure of AlMg substrate/CoCrPtB (30 nm)/a-CNx (2 nm) were prepared for accelerated environmental corrosion test. The corrosion spots on the disks are mainly located in the fourth quadrant in the Pq-Sq 2D histogram. Both the corrosion areas in the third and fourth quadrants have a similar trend, increasing with N content in the overcoats. Other techniques, such as Raman spectroscopy and ellipsometric spectroscopy, were used to characterize the a-CNx films deposited on silicon substrates. As N content increases, the G peak width decreases from 187 to 182 cm−1, the ID/IG intensity ratio increases from 1.75 to 1.99, and the Tauc optical band gap decreases from 2.1 to 1.4 eV. Both Raman and ellipsometric results indicate that the sp3 fraction of carbon atoms decreases with N content. This fact can result in a loose carbon network, which interprets the increase of corrosion spots on the surface of a-CNx films.