Mechanical damage-free surface planarization of single-crystal diamond based on carbon solid solution into nickel

Abstract Polishing diamond is the key process for diamond semiconductor research as well as gemology field. In this study, we proposed a novel method based on carbon solid solution into nickel (Ni) via high-temperature annealing, without mechanical damage formation. Single-crystal (100) diamond substrates were surface-planarized by putting them in contact with flat and mirror-surface Ni substrates via thermal annealing; the sample prepared through two annealing steps, at 1150 °C for 4 h and then at 900 °C for 4 h, exhibited the best surface morphology compared with the unannealed and one-step annealed (at either temperature) ones. For the diamond substrate with two-step annealing process, the surface roughness, measured in terms of root mean square roughness (Sq) via laser microscopy (LM) analysis over a scanning area of 129 × 130 μm2, was reduced by almost one order of magnitude compared to the unannealed sample (i.e., from ~0.67 to 0.07 μm). Moreover, atomic force microscopy (AFM) over a scanning area of 300 × 300 nm2 revealed a local reduction of Sq down to 0.62 nm. Then, diamond surfaces prepared via the proposed method and mechanical polishing were irradiated with hydrogen plasma to examine and compare their surface damages. The mechanical-polished sample showed characteristic linear and deep pits that, in contrast, were not observed on the two-step annealed sample, which, in comparison, also exhibited a density of shallow V-shaped pits of typical ~104–105 cm−2 which is about two orders of magnitude lower.