Study on incompatible mechanism in chemical mechanical polishing of the novel graphite/diamond composite

The novel graphite/diamond composite (Gradia) possesses semiconducting instinct characteristics with controllable resistivity. Surface finishing plays a crucial role in using Gradia. However, controlled removal of the Gradia surface is challenging because physical and chemical properties differ between the graphite and diamond components. The impact of incompatibility on the material removal of Gradia is unclear. This study employed chemical mechanical polishing (CMP) to finish the Gradia surface with K2FeO4 oxidant. First, the sub-nano-scale roughness of the Gradia surface was attained by applying optimized polishing parameters. Then, the polished subsurface was examined. The incompatible graphite and diamond lattice distortion was the primary damaged mechanism rather than amorphization. The chemical reaction in CMP was analyzed with X-ray photoelectron spectroscopy and reactive molecular dynamics simulation. The carbon atoms formed a variety of chemical groups with the oxidizing of hydroxyl. The chemical activity of the graphite phase was superior to the diamond phase, leading to more types of reaction and a higher percentage of products. In the material removal stage, experimental observations and simulation analyses revealed that the diamond of sp3-carbon transformed to sp2carbon, softened, and subsequently removed together with the graphite by abrasive scratching.