Kumar, R., Neogi, A., Yeo, R. J., Zhang, M., Sankaranarayanan, S. K. R. S., Dhand, C., & Dwivedi, N. (2025). Extraordinary control of friction and wear enabled by ultrathin carbon and its atomic-scale interface and thickness manipulation. Carbon, 238, 120262. https://doi.org/10.1016/j.carbon.2025.120262
Abstract:
Overcoats are widely used to engineer the tribo-interface of moving mechanical systems for tailoring friction and wear. However, when tribological control is required with sub-3 nm thick overcoats, the structural and protective properties of overcoats degrade as the tribologically-inferior substrates dominate the tribo-interface, thus hindering their practical applications. Here, we demonstrate an extraordinary tribo-engineering approach using carbon-containing overcoats. By introducing a ∼1.7 nm-thick amorphous carbon (C) overcoat at the sliding Si–Al2O3 tribo-interface, a low and stable coefficient of friction (COF) of ∼0.23 and high wear-resistance was attained, as compared to an unmodified Si–Al2O3 tribo-interface (COF ∼0.45). Furthermore, by adding a nanometer-thick silicon nitride (SiNx) interlayer between the Si substrate and the carbon overcoat, the wear protection was further enhanced, although replacing the SiNx interlayer with NiFe failed to achieve the same result. Nonetheless, thermal annealing of the C/NiFe bilayer overcoat improved its tribological behavior. Slightly increasing the carbon layer thickness to 2.2 nm for both the C/SiNx and C/NiFe bilayer overcoats further boosted their friction and wear control, as evident from the drop in the average COF to ∼0.16–0.17. These results display a classic example of “materials engineering to achieve outstanding tribo-engineering” which is further supported by large-scale atomistic simulations.
License type:
Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Funding Info:
This research was supported by the Department of Science and Technology (DST), India through DST/TDT/AM/2022/253 project. R.K. acknowledges the Department of Science and Technology (DST), India for providing financial support through the DST INSPIRE Fellowship (IF200509).