Fig. 6: The mechanical properties of MoN–TaN superlattice thin films.

The hardness as a function of the bilayer period is shown in (a). The vertical dashed line indicates the bilayer period where we assume the formation of a second phase in the TaN layer. Young’s modulus over Λ is shown in (b). Here, besides the computational Young’s modulus (Grimsditch and Nizzoli) including a second phase in TaN, we also plotted the one without it. The sketch in (c) shows the proposed coating architecture. The SEM micrograph (d) shows a cantilever before micromechanical testing in a 10° inclined view including the dimensions of the lever arm l, cantilever width b, cantilever height w, the initial notch, and the point of application of force. The fracture cross sections in (e) (1.5 nm) and (f) (8.3 nm) show the depth of the initial notch a; exemplary marked are the thin bridges necessary for our micromechanical tests. The plots (g) and (h) show the derived fracture toughness K_IC and the empirical H/E toughness criteria, respectively. All mechanical properties were determined on sample deposited on Si (100), additionally, Young’s modulus was cross-checked by performing nanoindentation experiments also on MgO (100), sapphire, and austenitic steel. All error bars represent standard deviation. The scale bar in (d) is 5 µm long, in (e), and (f) the scale bar is 1 µm long.