Wear of ultrathin carbon overcoat characterized by microwear scan and Auger electron spectroscopy

Abstract

A new methodology was developed to characterize the tribological performance of ultrathin carbon coatings by the microwear scan and Auger electron spectroscopy. With the magnetic recording application in mind, two 5-nm-thick carbon coatings were deposited on magnetic disks for the study. In a microwear scan process, there were two competing mechanisms that lead to the carbon coating failure—the coating wearoff and the coating structural damage mechanisms. The coating wearoff was a continuous process and always active, whereas the coating structural damage appeared more in a disruptive manner as the applied normal load approached a critical level. The term coating wear rate, defined as the coating thickness reduction per unit applied normal load, was adopted in this microwear scan test. Two simulation models based on carbon (272 eV) and cobalt (775 eV) Auger electron signals, respectively, were developed to calculate the carbon residual thickness inside the wear track. Because of the difference in signal intensities, the coating residual thickness acquired from the carbon Auger electron signal turned out to be much more robust and reproducible than the cobalt signal. Based on these results, a tribological characteristic chart, which contained both the coating wear rate and critical load parameters, is proposed to offer a better understanding and ranking capability towards the tribological performance of ultrathin coating systems.