Speaker
Description
Molybdenum disulfide (MoS₂) is a layered material from the transition metal dichalcogenide (TMD) family, widely applied in areas ranging from tribological coatings to electronics, optics, and catalysis. However, pure TMD coatings face limitations in tribological applications due to their low hardness and poor oxidation resistance. To address these issues, combining TMDs with carbon has emerged as a promising strategy. Carbon contributes to increased hardness, while the TMD forms tribolayers during use, reducing friction.
The structure and evolution of TMD-C coatings during tribological processes are subjects of great interest, requiring both experimental and computational approaches. These coatings exhibit complex structural and bonding environments that are challenging to capture experimentally, particularly under tribological conditions. Simulations offer the ability to model these interactions in a controlled virtual environment, providing a dynamic view of how the structure evolves over time or in response to external factors.
Using our developed ReaxFF parameter set, we investigated the structure and properties of TMD-C films. First, we studied the bonding in amorphous Mo-S-C and observed a strong tendency for phase separation into MoS₂ and C phases. Our results on the kinetics of this phase separation suggest that it likely occurs during the deposition of Mo-S-C films, which aligns with experimental observations: Mo-S and C-C bonds dominate, with Mo-C bonds forming only when the S-to-Mo ratio significantly deviates from 2:1.
Further structural exploration of Mo-S-C revealed notable variations in the carbon phase's morphology depending on carbon content. Models with 25 atom-% carbon displayed a one-dimensional carbon phase in the form of a tube within the MoS₂ matrix. At 50 atom-% carbon, two-dimensional carbon sheets emerged, while models with 75 atom-% carbon formed a three-dimensional carbon phase with embedded MoS₂.
We also examined sliding behavior and its relationship to structural changes in these models. Friction coefficients were notably low, below 0.02 for "carbon in MoS₂" configurations, and below 0.2 for "MoS₂ in carbon" configurations. The crystallization of MoS₂ plays a significant role in reducing friction.
