Fig. 3
From: Wear-resistant surface coloring by ultrathin optical coatings
Scratch tests of a TiAlN(30nm)-TiN(50nm) coating on a sapphire substrate, and b Si(50nm)-Cu(50nm) coating on a sapphire substrate. F: load in the form of mechanical force on the coating; AE: acoustic emission; Rd: residual depth of the sample after the scratch tests. The black arrows indicate the optical microscopy observation of the starting point of damage (critical loads) on the coatings, which is confirmed by the simultaneous measurement of Rd (blue arrows). The Rd rapidly decreases after the critical loads is reached. The red arrows mark the critical loads for the dramatic increase of AE