Nano-indentation Hardness of Compositionally Modulated Ti-TiN Multilayer Films

Ti-TiN multilayer films with thickness of 400 nm were deposited on TiO2-Ti underlayers on borosilicate glass substrate by changing N2 flow rate periodically in dc reactive magnetron sputtering. Composition of Ti-TiN multilayer films was measured by XPS. Hardness of Ti-TiN multilayer films was measured by a nano-indentation method. By XPS analysis, it was found that multilayer films consisted of repeated Ti0.7N0.3Ti0.55N0.45 layers and that the binding energy of Ti shifted toward high energy as nitrogen contents increased. Hardness was found to depend on the modulation period, yielding the maximum of 28.7 GPa at the modulation period of 20 nm. We concluded that the hardness enhancement obtained was caused by both changes in the number of interfaces penetrated during a nano-indentation and an interaction between the two layers with different mechanical properties.