Structure and Tribological Properties of MoS₂/DLC Multilayer Films with Different Modulation Periods

A series of MoS₂/diamond-like carbon (DLC) multilayer films with three different modulation periods (i.e. Λ of 54 nm, 30 nm and 18 nm) were deposited on silicon wafers (100) using a multi-target radio frequency magnetron sputtering system. The influence of modulation periods on the morphology, microstructure and mechanical properties of multilayer films were investigated with scanning electron microscope, Raman spectrometer, X-ray diffractometer, transmission electron microscope and nanoindentation. The lubricating properties of the films were investigated by the ball-on-disk friction tester in ambient atmosphere. Results show that the alternative deposition MoS₂/DLC multilayer films effectively suppressed the growth of columnar structure in sputtered MoS₂ and thus the produced films had compact structure. The hardness of multilayer films increased as the modulation period increased. Transmission analysis of cross-sectioned multilayer films revealed that the interface between layer was not smooth whereas the periodic structure was dense and well-defined. In addition, the thickness of modulation period was basically consistent with the initial set value. Compared with pure MoS₂ film, the multilayer film with modulation period of 54 nm had better load-bearing capacity and elastic recovery capacity, and the corresponding hardness reached the highest value (7.15 GPa). Furthermore, the film exhibited the lowest friction coefficient (0.09) and wear rate of 1.34×10^–7 mm³/(N·m) under a normal load of 5 N in ambient atmosphere (with relative humidity of about 30%).