Relationship between mechanical properties and coefficient of friction of sputtered a-C/Cu composite thin films

The article reports on properties of a-C films containing different amount of Cu. Films were sputtered by unbalanced magnetron from a graphite target with Cu fixing ring in argon under different deposition conditions. Relationships between the structure, mechanical properties, macrostress σ and coefficient of friction (CoF) μ of a-C/Cu films sputtered on Si substrates were investigated in detail. Besides, a special attention was concentrated on investigation of the effect of a deposition rate a _D of the a-C/Cu film on its hardness H and macrostress σ. Four main issues were found: (1) the addition of Cu into a-C film strongly influences its structure and mechanical properties, i.e. the hardness H, effective Young's modulus E⁎ macrostress σ and CoF, and makes it possible to form electrically conductive films; here E⁎ = E / (1 - ν ²), E is the Young's modulus, and ν is the Poisson's ratio, (2) the hardness H and compressive macrostress σ of the a-C/Cu film decrease with increasing a _D due to decreasing of total energy E _T delivered to the film during its growth, (3) hard a-C/Cu films with low value of CoF (μ ≈ 0.1) can be sputtered at high deposition rates a _D ranging from ~ 10 to ~ 80 nm/min, and (4) CoF decreases with increasing (i) hardness H and (ii) resistance of film to plastic deformation characterized by the ratio H ³/ E⁎ ² but only in the case when compressive macrostress σ is low.