Antibacterial Cr-Cu-O films prepared by reactive magnetron sputtering

The paper reports on the effect of Cu content in the Cr-Cu-O film and its structure on its antibacterial activity and mechanical properties. The Cr-Cu-O films were prepared by reactive magnetron sputtering from composed Cr/Cu targets using a dual magnetron. The antibacterial activity of Cr-Cu-O films was tested on the killing of Escheria coli bacteria. Correlations between the structure of the Cr-Cu-O film, the content of Cu in the film and its (i) antibacterial efficiency and (ii) mechanical properties were investigated in detail. It was found that the 100% efficiency of the killing of E. coli bacteria on the surface of the Cr-Cu-O film is achieved if (1) the Cu content in the film is ≥15 at.% and (2) the film is either X-ray amorphous or crystalline with the CuCrO2 delafossite structure. These Cr-Cu-O films need no excitation and very effectively kill E. coli bacteria in the daylight as well as in the dark. The X-ray amorphous Cr-Cu-O films with ~20 at.% Cu exhibit a higher (i) hardness H ≈ 4 GPa, (ii) effective Young's modulus E* ≈ 72 GPa and (iii) elastic recovery We ≈ 37% compared with the crystalline Cr-Cu-O film with the CuCrO2 delafossite structure exhibiting H ≈ 1.2 GPa, E* ≈ 21 GPa and We ≈ 21%. Both films very effectively kill the E. coli bacteria, however, exhibit a low ratio H/E* < 0.1.