Nanoscale Wear of Carbon Overcoat Subjected to Laser Heating in an Inert Gas Environment

摘要

Because the diamond-like carbon (DLC) thin film overcoat on either a hard disk surface or an air bearing surface plays an important role in maintaining the reliability and durability of the head-disk interface, nanoscale DLC wear and degradation is a critical issue in heat-assisted magnetic recording (HAMR). The use of helium in hard disk drives (HDDs) has been developed and put into practical use to decrease air-induced structural vibrations, and temperature rise. In this study, fundamental experiments were conducted to understand the wear and related degradation characteristics of an ultra-thin DLC overcoat subjected to laser heating in both air and inert gas environments, using a pin-on-disk tester. An inert gas environment was simulated using helium gas. The experiments were conducted using DLC-coated glass pins and actual magnetic disks without a lubricant film. The differences in the wear and degradation characteristics of a DLC overcoat on the pin and disk surfaces between inert gas and air environments were investigated after wear tests were performed, primarily through Raman spectroscopy. We found that wear and graphitization of DLC films became greater with laser heating, while the friction coefficients between the pin and magnetic disk became markedly smaller. However, our tests also revealed that wear and graphitization of the DLC film were significantly less in an inert gas environment than in an air environment. This is because the wear observed in this experiment was predominantly due to a wear mechanism that is based on tribo-chemical oxidation.