Host: The Japan Society of Vacuum and Surface Science
Name : Annual Meeting of the Japan Society of Vacuum and Surface Science 2023
Location : [in Japanese]
Date : October 31, 2023 - November 02, 2023
In the field of nanotribology, anisotropy of friction [1-3] has been understood by the incommensurability of the crystal lattice at the interface [4,5]. Incommensurability is a physical origin of superlubricity, ultralow friction state, which is key to the energy-saving problem. On the other hand, in the field of materials science, it has been recently clarified that the incommensurability of layered materials has played important roles in electronics, magnetics, optics, and spintronics and it has been discussed by the science of Moiré pattern. Therefore, in this work, the mechanism of superlubricity of the twisted graphene interface, the monolayer graphene sheet absorbed onto the graphite substrate surface, was studied based on Moiré science.
First, the two-dimensional map of superpositions of graphene lattices, interaction energy, and force map were calculated as a function of the twisted angle and sliding distance, which showed the long-range periodic Moiré pattern. As illustrated in Figure 1, the pseudo-AB and AA stacking regions formed honeycomb and triangular lattices, respectively. The unit-cell size of the Moiré pattern rapidly became smaller as the twisted angle increased, which could explain the anisotropic behavior of the maximum lateral force plotted as a function of the twisted angle.
Next, the anisotropy spectra of the loading and lateral forces showed a strong sheet size dependence. The larger the sheet became, the sharper the anisotropy peak became, which resulted in a wider superlubric region.
Furthermore, if the loading and lateral forces and the misfit angle were normalized, the universal scaling law of the anisotropy spectrum independent of the sheet size was obtained. Thus, it is clarified that the correlation between the true contact area (Moiré pattern) and the vertical and lateral forces is independent of the sheet size, suggesting the possibility of controlling adhesion and superlubricity based on universal scaling laws.
References
[1] M. Dienwiebel et al., Phys. Rev. Lett. 92, 126101 (2004).
[2] N. Sasaki et al., Tribol. Online 7, 96 (2012).
[3] N. Sasaki et al., e-J. Surf. Sci. Nanotech. 14, 204 (2016).
[4] M. Hirano and K. Shinjo, Phys. Rev. B41, 11837 (1990).
[5] K. Shinjo and M. Hirano, Surf. Sci. 283, 473 (1993).
