Structural and tribological characterization of protective amorphous diamond-like carbon and amorphous $CNx$ overcoats for next generation hard disks Available to Purchase

Further insight into processing-structure-property relationships have been carried out for existing and candidate carbon-based protective overcoats used in the magnetic recording industry. Specifically, 5 nm thick amorphous diamond-like carbon $(a:C)$ and nitrogenated diamond-like carbon $(a:CNx)$ overcoats were deposited by low deposition rate sputtering onto a thin film disk consisting of either CoCrPt/CrV/NiP/AlMg or CoCrPt/CrV/glass. The wear durability and frictional behavior of these hard disks were ascertained using a recently developed depth sensing reciprocating nanoscratch test. It was determined that the $CN0.14/CoCrPt/CrV/glass$ disk exhibited the most wear resistance, least amount of plastic deformation, and lowest kinetic friction coefficient after the last wear event. Core level x-ray photoelectron spectroscopy (XPS) results of sputter cleaned overcoats indicated that nitrogen up to 14 at. % incorporated into the amorphous network resulted in these improvements near the overcoat/magnetic layer interface, since there was an increase in the number of $N-sp3$ C bonded sites in a predominantly $N-sp2$ C bonded matrix. However, nonsputter cleaned overcoats exhibited a more graphitic pyridine-like (nondoping configuration) structure near the surface as evidenced by the increase in $C=N$ versus C–N bonds and the valence band XPS determined appearance of the $2p-π$ band near the Fermi level $(EF).$ Therefore, XPS sputter cleaning revealed a gradient in the chemical nature of the overcoats through the thickness. In addition, micro-Raman spectroscopy established that a further increase of nitrogen (⩾18 at. %) weakened the overcoat structure due to the formation of terminated sites in the amorphous carbon network, since nitrogen failed to connect the $sp2$ domains within the network. This, in conjunction with an increase in the intensity of the $2p-π$ band from the valence band XPS spectra and the increase in the G-band position and $ID/IG$ ratio from the Raman spectra, confirmed the increase in the size and number of $sp2$ bonds in the $CN0.18$ overcoat.