Adhesion, friction and tribochemical reactions at the diamond–silica interface

Nanotribological Properties of Oxidized Diamond/Silica Interfaces: Insights into the Atomistic Mechanisms of Wear and Friction by Ab Initio Molecular Dynamics Simulations

“…AIMD simulations were performed using a modified version of the Quantum Espresso package, which allows simulating the tribological conditions. The code has been successfully used for studying the tribochemistry of different systems, including diamond–silica interfaces. , The generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE) method was used as the exchange–correlation functional. The plane-wave basis set was used to expand the electronic wave function, and the core electrons were represented by ultrasoft pseudopotentials with the cutoff energies of 30 Ry for the wave function and 240 Ry for the charge density, respectively.…”

“…The amorphous silica was built as technically described in our previous work . The surface termination contains sixloxane (Si–O–Si) and silanol (Si–OH) groups as a result of silicon oxide in contact with the environment.…”

“…The interfacial distance was calculated by the subtraction of the average z coordinates of Si and C atoms at the interfacial layers. The resistive forces are the sum of the x component of Si atoms to which the external forces and velocity constraints were applied. , The average values and errors of the interfacial distance and forces were estimated by using the block average procedure as reported by Templeton et al The movies of the AIMD simulations of silica sliding against oxidized diamond surfaces are provided as a part of the Supporting Information.…”

“…Various mechanisms have been reported to explain the ultralow friction and wear at diamond–diamond interfaces. ,, One key mechanism is the passivation of reactive dangling bonds, which effectively reduces adhesive friction at diamond sliding contacts. ,,, So far, hydrogen and oxygen have been recognized as effective passivating species for friction reduction at diamond–diamond contacts . Apart from surface adsorbed species, the concentration of passivating agents and the nature of counter surfaces , can profoundly influence the friction and wear performance of diamond. Wang et al have proposed that oxygen coverage greater than 0.5 is necessary to effectively prevent chemical bonding at diamond–diamond interfaces .…”

“…Wang et al have proposed that oxygen coverage greater than 0.5 is necessary to effectively prevent chemical bonding at diamond–diamond interfaces . When it comes to silica–diamond contacts, O-terminated diamond surfaces exhibit lower adhesion and larger separation compared to H-passivated surfaces, mainly due to the large atomic size of oxygen, which induces higher steric hindrance compared to hydrogen . The presence of C–O and CO functional groups can alter the diamond surface chemistry and its reactivity. , As oxygen is dissociated on diamond at a lower energy barrier than those of H 2 and H 2 O, the oxygenation of diamond surfaces tends to be more prevalent than hydrogenation and hydroxylation.…”