Properties of nanocrystalline Al–Cu–O films reactively sputtered by DC pulse dual magnetron

The article reports on the effect of the addition of copper in the Al2O3 film on its mechanical and optical properties. The Al–Cu–O films were reactively co-sputtered using DC pulse dual magnetron in a mixture of Ar + O2. One magnetron was equipped with a pure Al target and the second magnetron with a composed Al/Cu target. The amount of Al and Cu in the Al–Cu–O film was controlled by the length of pulse at the Al/Cu target. The Al–Cu–O films with ≤16 at.% Cu were investigated in detail. The addition of Cu in Al2O3 film strongly influences its structure and mechanical properties. It is shown that (1) the structure of Al–Cu–O film gradually varies with increasing Cu content from γ-Al2O3 at 0 at.% Cu through (Al8−2x,Cu3x)O12 nanocrystalline solid solution to CuAl2O4 spinel structure, (2) the Al–Cu–O films with ≥3 at.% Cu exhibit (i) relatively high hardness H increasing from ∼15 GPa to ∼20 GPa, (ii) enhanced elastic recovery We increasing from ∼67% to ∼76% with increasing Cu content from ∼5 to ∼16 at.% Cu and (iii) low values of Youngʹs modulus E* satisfying the ratio H/E* > 0.1 at ≥5 at.% Cu, and (3) highly elastic Al–Cu–O films with H/E* > 0.1 exhibit enhanced resistance to cracking during indentation under high load.