Mechanical and tribological properties of Sn-Cu-O films prepared by reactive magnetron sputtering

Tin-copper-oxide (Sn-Cu-O) thin films were deposited by reactive magnetron sputtering in an argon-oxygen atmosphere. The effect of the substrate temperature Ts and the amount of Cu in the Sn-Cu-O film on its mechanical and tribological properties was investigated in detail. It was found out that (i) the Sn-Cu-O films prepared at Ts = 500 °C are more crystalline and exhibit a higher hardness H (up to 19.5 GPa) compared with the Sn-Cu-O films sputtered on unheated substrates at room temperature (H ≈ 11 GPa), (ii) the coefficient of friction μ of the Sn-Cu-O film is relatively high and decreases from ∼0.9 to ∼0.5 with a decreasing ratio H/E* of the hardness H and the effective Young's modulus E*; here E* = E/(1 − ν2), E is the Young's modulus and ν is the Poisson's ratio, (iii) the coefficient of friction μ strongly depends on the relative humidity RH and decreases with an increasing RH of air used in the tribological test, and (iv) the sputtered Sn-Cu-O films exhibit a very low wear rate k, less than ∼2 × 1...