A comparative AFM study of carbon alloyed Mo–Se–C and W–S–C films for tribological applications

Transition metal dichalcogenides have a layered structure and are therefore promising self-lubricating films. They can be considered as potential substitutes for carbon based films in various environmental conditions. In this work, a comparative atomic force microscopy study of co-sputtered Mo–Se–C and W–S–C films is performed to evaluate their nanotribological performances. Both films are alloyed with carbon. The microstructural features of these films are characterised using scanning electron microscopy and X-ray diffraction. The hardness and elastic modulus of these films are measured employing nanoindentation. The topography, friction forces and pull off forces of the films are evaluated by means of atomic force microscopy and force spectroscopy. The results show that the roughness parameters of Mo–Se–C films are lower than that of W–S–C films at high carbon content whereas the reverse is true at low carbon content. Adhesion forces of these films based on pull-off force measurements show that Mo–Se–C films have higher pull off forces than W–S–C films. An atomic force microscopy technique is developed to estimate microscopic values of friction coefficients and to characterise the nature of surface changes due to nanotribological experiments. The friction coefficient of Mo–Se–C films is higher than that of W–S–C films at low carbon content and these friction coefficients are comparable at high carbon content.