First-principles Calculations Reveal Frictional Advantage for C₂ N/C₆ N₆ van der Waals Heterostructures

Friction at the atomic scale is determined for three different carbon nitride structures namely C₂ N/C₂ N, C₆ N₆ /C₆ N₆ and C₆ N₆ /C₂ N employing ab-initio density functional theory (DFT). The sliding path along the lowest energy corrugations determines the static frictional forces. Both the homo-layer structures (C₂ N/C₂ N and C₆ N₆ /C₆ N₆ ) have higher corrugation energy and correspondingly higher static lateral forces with respect to the hetero-layer structure (C₂ N/C₆ N₆ ). The corrugation energy for the C₂ N/C₆ N₆ heterostructure ( $$ =0.29 meV/atom) is one-order lower than C₂ N/C₂ N ( $$ =2.08 meV/atom) and C₆ N₆ /C₆ N₆ ( $$ =4.37 meV/atom). Such a significantly lower corrugation energy for the heterostructure arises due to the reduced fluctuation in the interfacial charge density along the sliding pathway. Moreover, the change in the interlayer distance along the sliding pathway is only 0.2 Å for the heterostructure while its 0.3 Å and 0.4 Å for C₂ N and C₆ N₆ homo-layers respectively. The friction coefficients (F_L /F_N , F_L =static lateral force; F_N =normal force) decrease with increasing load for all the systems with the lowest value (0.04) for C₂ N/C₆ N₆ at 2 GPa. The van der Waals heterostructures are, therefore, predicted to be highly efficient lubricant materials for reducing friction at the atomic scale.