Smoothing of single crystal diamond by high-speed three-dimensional dynamic friction polishing: Optimization and surface bonds evolution mechanism

The high-speed three-dimensional movement dynamic friction polishing (3DM-DFP) has been recognized as an efficient approach for ultra-smoothing single crystal diamond (SCD) surface. Continuing from the previous works focusing on the subsurface cleavage of diamond after 3DM-DFP, process optimization and surface reaction evolution mechanism as a fundamental building block is investigated, for the first time, for comprehensively understanding this fast-smoothing manner. By systematically adjusting the controlling factor, stronger load (0.3 MPa) and appropriate duration (0.5 h) as well as moderate sliding speed (in the range of 30 to 45 m s−1) is found to be able to obtain the smooth surface of SCD without uncontacted traces or break-surface cleavage. Subtle residual clues on SCD surface as a function of progressive DFP procedure indicate that Fe catalytic oxidation mainly produce Fe2O3 and partial intermediate oxides Fe1-yO. Meanwhile, the activated oxygen inserts sp3 CC bonds could form CO or CO and C-O-V (vacancy) at existing reactive surface sites. The (100) favorable CO bonds can be rebuilt if (100) surface is reformed, although the CO bonds associated with non-(100) rough surface would replace them during DFP procedure. The formed COC and concomitant C-O-V as well as the oxidized graphite give rise to the increase of CO proportion, and finally the covered defective graphitic phase has an approximate CO/CO ratio of 1.25. All these are endowed potential value for future upgrading of DFP technique for diamond surface smoothing.