Fig. 1: Experimental synthesis of 2D diamond under high pressure and high temperature (HPHT).

a Schematic strategy to prepare 2D diamond from graphene in laser-heated diamond anvil cell (DAC). Re foil (light blue), polished down to ~10 μm with surface roughness around 3.9 nm, was used as graphene (pink) substrate and thermal absorber for near-infrared (NIR) laser heating. b Illustration of phase transformation from bilayer graphene/graphite to hexagonal diamond (HD) and cubic diamond (CD) under HPHT. The dashed arrows denote the energy profile of phase transition, with CD having lower free energy. The transition pressure and temperature gradually decrease with increasing graphene thickness, as illustrated by the red-to-blue gradient arrow. c–f Optical evolution of few-layer graphene (FLG) on Re substrate under HPHT. The 3L graphene (inset, optical image before transfer) was transferred onto Re surface and then compressed to 0.5 GPa at 300 K (c); Graphene/Re compressed to 32.0 GPa at 300 K (d); Graphene/Re heated to ~2924 K under 32.3 GPa (e); The sample quenched to ambient condition finally (f). Scale bars in (c–f) are 30 μm. The yellow dashed line highlights the morphology of graphene before laser heating. g Raman spectra showing the phase evolution from the initial 3 L graphene (exfoliated and after being transferred) to the quenched 2D diamond synthesized after HPHT, identified by the characteristic T_2g band. The spectra of quenched 2D diamond correspond to the positions marked as pink and violet in (f). Arb. u. means arbitrary unit. h Cross-sectional high-resolution transmission electron microscopy (HRTEM) characterization of 2D diamond. Low-magnification TEM image reveals the uniform morphology (top). HRTEM image shows the 2D diamond extent highlighted by green dashed lines, indicating a thickness of ~1.0 nm (bottom). i Energy-dispersive X-ray spectroscopy (EDS) elemental mapping images of the 2D diamond cross-section for Au (top), C (middle) and Re (bottom) elements.