A variable-speed drag test for characterizing wear of ultra-thin carbon films

A drag test with a speed alternating between two levels was developed to create wear tracks on disk surfaces. This approach reduces the uncertainty involved in the contact start/stop (CSS) test of thin carbon overcoats. The wear tracks were identified with an optical surface analyzer as regions with higher values of the absorption ratio calculated from reflectivity data of both P- and S-polarized lights. Calibrated with scanning micro-ellipsometry, the absorption ratio was converted to a wear depth. The amount of wear in a drag test increased with time, and a low-flying head resulted in more wear than a high-flying head. The 45-angstrom nitrogenated carbon film sputtered at a lower temperature exhibited a smaller wear depth. The higher wear resistance of the low-temperature sputtered film is supported by less wear in a nanowear test, a lower Raman G-peak position, and less frequent crashes in CSS tests