Experimental demonstration and transformation mechanism of quenchable two-dimensional diamond

Two-dimensional (2D) diamond has aroused remarkable interest in nanoelectronics and optoelectronics, owing to its superior properties and flexible characteristics compared to bulk diamond. Despite significant efforts, great challenges lie in the experimental synthesis and transformation conditions of 2D diamond. Herein, we have demonstrated the experimental preparation of high quality 2D diamond with controlled thickness and distinguished properties, realized by laser-heating few-layer graphene in a diamond anvil cell. The quenched 2D diamond exhibited a narrow T_2g Raman peak (linewidth ~3.6 cm^-1) and intense photoluminescence of SiV^- (linewidth ~6.1 nm) and NV⁰ centers. In terms of transformation mechanism, atomic structures of hybrid phase interfaces suggested that the intermediate rhombohedral phase subtly mediate hexagonal graphite to cubic diamond transition. Furthermore, the tunable optical bandgap and thermal stability of 2D diamond sensitively depend on its sp³ concentration. We believe our results can shed light on the structural design and preparation of many carbon allotropes and further uncover the underlying transition mechanism.