Subsurface cleavage of diamond after high-speed three-dimensional dynamic friction polishing

To unfold the promise of diamond as an advanced technical material, single-crystal diamonds (SCDs) and polycrystalline diamonds (PCDs) were smoothed by high-precision three-dimensional movement dynamic friction polishing (3DM-DFP) to achieve the ultra-smooth surface with roughness <5 nm (even 1 nm) more effectively. However, this inevitably leads to subsurface damage growth, i.e., subsurface defects evolved from nearly damage free to partial defects, and to cleavage faults beneath the SCD surface, resulting from mechanical fatigue and/or the rate of energy input by increasing the linear polishing velocity (from 12 m s−1 to 60 m s−1). In this study it was elucidated, for the first time, the subsurface uniform tile-roof-like cleavage faults and its formation mechanism of diamond after 3DM-DFP at the superhigh speed of linear sliding velocity of 60 m s−1. And the generated subsurface damage would be extended to about 10 μm in depth of the (100) SCD and manifested as micro-cleavage fault region, transition area and compressive zone. Meanwhile, two Raman peaks of 1425 cm−1 (first-order) and 2200 cm−1 (second-order) are assigned to the subsurface damage, which is the amorphous carbon (quasi sp3 + sp2) resulting from the cleavage along (111) crystal planes, based on the fine analysis of Raman spectroscopy and the study of subsurface defect evolution in different types of diamonds. Moreover, the assignment of concomitant peaks of 1750 cm−1 (localized defects) and 2100 cm−1 (sp1 chains) were revealed.