Hyperthermal Atomic Oxygen Interaction with MoS2 Lubricants Relevance to Space Environmental Effects in Low Earth Orbit?Atomic Oxygen-Induced Oxidation

Abstract

Effect of 5 eV atomic oxygen beam exposure on the surface properties of sputter-deposited and single-crystal molybdenum disulfide (MoS2) were evaluated in the light of space environmental effects in low earth orbit. X-ray photoelectron spectra indicated that the loss of sulfur from the atomic oxygen exposed MoS2 surface was significant, especially for the sputter-deposited samples. This is due to the formation and gasification of the volatile product, SO. It was also identified that Mo atoms at the surface were oxidized to form MoO3. The amount of oxygen increased within a depth of 22 nm from the surface, whereas loss of sulfur was only observed within 3 nm. It was thus concluded that the chemical change of MoS2 due to atomic oxygen attack is limited to the surface layer of the MoS2-sputtered lubricant.