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In order to characterize the adhesive properties and failure mechanisms of diamond-like carbon (DLC) films of two different thicknesses (130 nm and 1.2 μm), deposited by plasma-enhanced chemical vapor deposition on a Si substrate, scratch testing with a micro-indenter (12.5 μm tip radius) was performed under a linearly increasing load. These scratch tests were conducted under the same test conditions for both films. The critical load of each film was estimated from the scratch test results, based on a sharp increase in the coefficient of friction and a clear distinction of failure modes. The critical load was the basis for evaluating the adhesion strength of the films, and the 1.2 μm-thick DLC film had superior adhesion strength. For better understanding of the failure modes, the following analyses were conducted: friction behavior and scratch tracks analysis using scanning electron microscopy, energy-dispersive spectroscopy, and 3-D profilometry. The scratch test results showed that failure modes were related to the thickness of the films. The 130 nm-thick DLC film underwent cohesive failure modes (cracks and chipping) before reaching to a gross failure stage. On the other hand, the thicker DLC film (1.2 μm-thick) did not exhibit micro cracks before a sudden gross failure of the film together with the evidence of cracking and chipping of the Si substrate.
