Surface stability and electronic structure of hydrogen- and fluorine-terminated diamond surfaces: A first-principles investigation

Abstract

The effect of fluorine termination on the stability and bonding structure of diamond (111) surfaces were studied using first-principles calculations and compared with hydrogen termination by creating mixed F- and H-containing diamond surfaces. Surface F atoms, similar to H, formed sp3-type bonding with C atoms, which resulted in a more stable 1 × 1 configuration. The surface phase diagram built showed that the F-terminated surface was more stable in a larger-phase space than H termination, because of the formation of strong ionic C–F bonds and the development of attractive forces between F atoms, resulting in close packing of large F atoms. Hence, the F-terminated diamond surface was more chemically inert. A large repulsive force was required to bring two F-terminated surfaces together, because of the negative charge on F atoms, resulting in reduced adhesion tendency between two F-terminated diamond surfaces compared with H-terminated surfaces.

Recent advances in the mechanical and tribological properties of fluorine-containing DLC films

“…93 Though higher uorination DLC lms [F/(F + C) > 0.4] seem to be so and have no wear resistance, moderate uorinated DLC lms [F/(F + C) < 0.2] can have a similar friction level and a lower surface energy compared to conventional a-C:H lms. 93,96,97 Currently, it is widely believed that uorine, added into conventional DLC lms, plays two vital roles in the low friction behavior, which are passivation and repulsive forces. 95 It is still found that the repulsive force of F/F terminated surfaces is larger than that of H/H terminated surfaces under the same distance, whose repulsive force is greater than zero.…”

“…It has been reported that mutual action between two F-DLC surfaces have higher repulsive forces than that inicted by two H-DLC surfaces. 93,97,114 Alpas et al 114 calculated the change in total energy of the system interface energy (DE tot ) as a function of separation distance between Al and diamond:F surfaces. 8a illustrates the electrostatic effects, which exist in two F-DLC and two H-DLC counterfaces.…”

Tribology of fluorinated diamond‐like carbon coatings: first principles calculations and sliding experiments

“…Computations were performed using a projector augmented wave method and a generalised gradient approximation of exchange correlation energy, as implemented in the Vienna Ab Initio Simulation Package . The details of the computations can be found elsewhere …”

“…It was suggested that after some material transfer from DLC to counterface, frictional interactions occur between two H‐passivated surfaces, which according to the first principles calculations exerted repulsive forces to each other . First principles calculations also revealed that two F‐passivated diamond surfaces facing each other would exert higher repulsive forces than two H‐passivated surfaces and, thus, mutual interaction of two F‐DLC surfaces would result in a lower COF …”

Atomistic Frictional Properties of the C(100)2x1-H Surface

“…The mechanism for the marked decrease in interfacial friction on hydrogenated carbon surfaces has been further elucidated with surface spectroscopy and tightbinding quantum mechanical methods [15] showing that the bonded hydrogen atom passivates the carbon dangling bonds at the surface, thereby decreasing the adhesive interaction between surfaces [16]. Fluorination of these surfaces has also been explored in an effort to further reduce the coefficient of friction (COF); in particular it was noted that the significant accumulated negative charge on the surface fluorine atom and its tight surface structure, due to strong lateral interactions, lead to a strong repulsive force between interacting surfaces (larger than when hydrogen terminated) [17]. This decrease in friction between interacting surfaces can have far ranging industrial and environmental importance [5,18,19].…”