Materialistic difference in macroscopic friction coefficients of sputtered metal oxide thin films deposited on glass

The origin of the difference in macroscopic friction coefficients of various metal oxide thin films sputtered on glass substrates was investigated from viewpoints of surface roughness and adhesion. Surface roughness and adhesive force were evaluated by atomic force microscopy (AFM). Thin films of the ZrO2-SiO2 system showed a minimum friction coefficient at 50 mol% SiO2-ZrO2. This could be explained by an increase in the number of smooth areas on the film surface. ZnO, Al2O3, SnO2, TiO2 and Ta2O5 thin films showed friction coefficients which varied from material to material. Oxide films with weaker metal-oxygen (M-O) bond were found to become highly frictive. This could be understood by the difference in the number of bonds formed between the film surface and the opponent material.