| Summary: | We studied the tribological properties of amorphous molybdenum sulfide (MoS<i><sub>x</sub></i>) thin-film coatings during sliding friction in an oxidizing environment at a low temperature (−100 °C). To obtain films with different sulfur contents (<i>x</i> ~ 2, 3, and 4), we used reactive pulsed laser deposition, where laser ablation of the Mo target was performed in H<sub>2</sub>S at various pressures. The lowest coefficient of friction (0.08) was observed during tribo-testing of the MoS<sub>3</sub> coating. This coating had good ductility and low wear; the wear of a steel counterbody was minimal. The MoS<sub>2</sub> coating had the best wear resistance, due to the tribo-film adhering well to the coating in the wear track. Tribo-modification of the MoS<sub>2</sub> coating, however, caused a higher coefficient of friction (0.16) and the most intensive wear of the counterbody. The MoS<sub>4</sub> coating had inferior tribological properties. This study explored the mechanisms of possible tribo-chemical changes and structural rearrangements in MoS<i><sub>x</sub></i> coatings upon contact with a counterbody when exposed to oxygen and water. The properties of the tribo-film and the efficiency of its transfer onto the coating and/or the counterbody largely depended on local atomic packing of the nanoclusters that formed the structure of the amorphous MoS<i><sub>x</sub></i> films.
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