Erosion Mechanism of MoS₂-Based Films Exposed to Atomic Oxygen Environments

The erosion mechanism of magnetron sputtered MoS₂ films exposed to the atomic oxygen environment was studied and compared with the Ti-doped MoS₂ and MoS₂/Ti multilayer films. The compositional and structural changes were investigated as a function of incident fluence by Rutherford back scattering (RBS) and focused ion beam combining with scanning electron microscopy (FIB&SEM). The RBS results indicate that the sulfur atoms are eroded by the incident atomic oxygen atoms and the removed sulfur amount increases but the erosion rate decreases with increasing of incident fluence. For pure MoS₂ films the erosion process turns to saturate at the end of investigated fluence of 4.8 × 10²¹ O cm^-2, and for Ti-doped and MoS₂/Ti multilayer films the saturation of sulfur erosion is much earlier around incident fluence of 5.2 × 10¹⁹ and 2.6 × 10¹⁹ O cm^-2, respectively. FIB cross-section results reveal that pores structures present in the as-deposited MoS₂ films provide a reaction highway, which allows the incident atomic oxygen to be able to reach and react with the sulfur at bottom. Introducing titanium doping or MoS₂/Ti multilayer structures definitely reduce the density of pores and defects in the initial films, consequently, erosion process is suppressed or blocked, and the instinct lubricant properties of MoS₂ phases can be well-retained in vacuum sliding conditions.