Ab initio studies on the atomic-scale origin of friction between diamond (111) surfaces

Ab initio Hartree-Fock method was used to examine the atomic-scale friction that occurs when two diamond (111) hydrogen-terminated surfaces are placed in sliding contact. The orientations of the hydrogen atoms at the surfaces and the formation of wear particles were investigated by geometry optimiza tion, but the main interest was in the interaction energies, friction force , and the coefficient of friction. Optimized structures of the diamond surf aces showed that no wear occurred at the applied pressures when the two sur faces were placed in sliding contact. The vibrational motions of the hydrog en atoms accommodated the stress due to the pressure of the surfaces. The f riction force was found to increase linearly with the normal load, indicati ng that Amontons' law also holds true in the microscale world. The calculat ed coefficient of friction was mu approximate to 0.22, which is in agreemen t with the results of molecular dynamic and experimental studies.