Nanoindentation of chromium zigzag thin films sputter deposited

Chromium thin films exhibiting a columnar microstructure were prepared by dc magnetron sputtering. The glancing angle deposition technique (GLAD) combined with the periodical changing of the incidence flux angle from α to −α was used to sculpt chromium thin films following a zigzag microstructure. The zigzag microstructure was systematically modified varying the flux angle α from 0 to 50° and the half-period thickness λ from 50 to 1000 nm. The changes in the microstructure were correlated with the evolution of the film's hardness and reduced Young's modulus obtained by nanoindentation. The drop of the film's hardness from H = 10 to 1.4 GPa and the reduced Young's modulus from Er = 245 to 91 GPa was noted with increasing flux angle α and half-period thickness λ. In agreement with the Hall-Petch effect, the diminution of the half-period thickness of chromium zigzag thin films led to an improvement of the nanohardness of chromium thin films deposited at the normal incidence up to 160%. The surface roughness and film's porosity depend strongly on the microstructure of the zigzag thin films. The influence of these parameters on the indentation of the zigzag thin films was also discussed. It was shown, that the Young's modulus depends on the films porosity. Correcting the films porosity using the mixing rule, the contribution of the flux angle and the number of layers could be easily demonstrated. For the small half-period thicknesses, values of Young's modulus of the coatings tend to be that of the bulk chromium.