Atomic insights into the graphitization behavior of (001)-diamond with Ni catalysis

Understanding the graphitization behavior of diamond is crucial for improving its conductivity and advancing all‑carbon diamond-based electronic devices. Using nickel (Ni) as catalyst combining with annealing treatment provides a simple method to achieve the graphitization of diamond. However, investigations of the Ni-catalyzed diamond-to-graphite transformation at the atomic level are limited and its underlying mechanisms remain unclear. In this study, atomic insights into the graphitization transformation behavior of Ni-catalyzed diamond were investigated in detail through rapid annealing at different temperatures and in situ heating observations using the transmission electron microscope. The results revealed that Ni recrystallized first as the temperature increased. Then, C atoms in the diamond gradually diffused and migrated into the Ni layer, leading to the formation of a metastable CNi compound. As the temperature-induced migration of C atoms continued, the C concentration in the CNi compound became supersaturated, resulting in ordered precipitation and forming the graphite layer on the diamond surface. In addition, graphite layers with excellent conductivity and controllable thickness were also achieved at elevating temperatures, demonstrating its potential advantageous of diamond graphitization by Ni catalysis. The results of this work support the development of diamond-based all‑carbon devices incorporating high-quality graphite or graphene.