Synthesis of two-dimensional diamond by phase transition from graphene at atmospheric pressure

It is a key challenge to prepare two-dimensional diamond (2D-diamond). Herein, we develop a method for synthesizing 2D-diamond by depositing monodisperse tantalum (Ta) atoms onto graphene substrates using a hot-filament chemical vapor deposition setup, followed by annealing treatment under different temperatures at ambient pressure. The results indicate that when the annealing temperature increases from 700 °C to 1000 °C, the size of the 2D-diamond found in the samples gradually increases from close to 20 nm to around 30 nm. Meanwhile, the size and number of amorphous carbon spheres and Ta-containing compounds between the graphene layers gradually increase. As the annealing temperature continues to rise to 1100 °C, a significant aggregation of Ta-containing compounds is observed in the samples, with no diamond structure detected. This further confirms that monodisperse Ta atoms play a key role in graphene phase transition into 2D-diamond. This study provides a novel method for the ambient-pressure phase transition of graphene into 2D-diamond.