Superlubricity of Molybdenum Disulfide

This chapter investigates the chemical composition of molybdenum disulfide (MoS2) coatings. High resolution TEM (HR-TEM) and extended X-ray absorption fine structure (EXAFS) are used to investigate the short-range order in the MoS2 crystallites of the coating. HR-TEM studies show that most of MoS2 crystallites exhibit many imperfections including faults, kinks, and curvature. Most of the vacuum-deposited MoS2 coatings contain significant amounts of oxygen in their structure, mainly because small amounts of water are present during the sputtering process. The oxygen incorporation affects the crystalline structure, the orientation, and the film morphology. A typical shift of the (100) peak is observed in X-ray diffraction and is strongly correlated with the oxygen content in the film. This shift has been attributed to the (100) lattice contraction. It is also correlated with a lattice expansion of the (002) basal planes in the c direction. For higher values of the oxygen content, molybdenum oxides (MoOy) are formed.