Extended Data Fig. 1: XRD patterns, Raman spectra, fluorescence spectra, and EELS in the low-loss region of the recovered samples.

a, XRD patterns of samples synthesized from different precursors: C₆₀ (top), type-1 glassy carbon (middle), and carbon onion (bottom) at 30 GPa and 1400-1800 K, respectively. At 1800 K, the appearance of weak Bragg diffraction peaks indicates nano-crystallization in the non-crystalline diamond formed from C₆₀. At 1600 K, fully sp³-bonded p-D was identified. By contrast, in cases of using type-1 glassy carbon and carbon onion as the starting material, crystallization precedes the complete conversion of sp² to sp³ carbon at 30 GPa and 1400-1600 K, preempting the formation of fully sp³-bonded paracrystalline diamond. The experiments demonstrate the importance of the structure of the starting material in the formation pathway of p-D. b, Visible Raman (532 nm) spectrum of the sample recovered at 30 GPa and 1400 K, with background removed. The broadened Raman peak can be fit with a D peak at 1378 cm⁻¹ and a G peak at 1556 cm⁻¹. The peak intensity ratio of I_D/I_G is 0.66 and the full width at half maximum (FWHM) of the G peak is 175 cm⁻¹. Similar to our work, the presence of sp² bonds results in a wide Raman peak between 1400 cm⁻¹ and 1700 cm⁻¹ in the visible Raman spectra of diamond-like carbon (DLC) films²⁷. c, Ultraviolet (UV) Raman spectra of the samples recovered from 1400 and 1500 K, respectively. The strong peak at 1110 cm⁻¹ in the UV Raman spectrum of the sample recovered at 30 GPa and 1400 K is attributed to the T peak caused by sp³ bonds²⁷. Fitting the Raman profile yields a peak intensity ratio of I_T/I_G 0.91, which is higher than that of DLC films with 88% sp³ bonds, indicating a higher concentration of sp³ bonds in the sample²⁷. On the other hand, for the sample recovered from 1500 K, no obvious peaks are discernible in the UV Raman spectrum, indicating the absence of sp² bonds in the as-synthesized disordered carbon⁸. d, Fluorescence spectra (excitation wavelength of 532 nm) of the sample from 1600 K and type Ia diamond. A main fluorescence peak centered around 702 nm suggests the high background in the Raman spectra is due to a fluorescence effect. e, EELS in the low-loss region of diamond crystal, single-crystal graphite, and samples synthesized from C₆₀ under 30 GPa and 1400-1500 K. Based on plasmon peak energy derived from low-loss EELS²⁸, the densities of the recovered samples at 1400-1600 K were calculated to be 3.11, 3.20, and 3.25 g/cm³, respectively. Due to the presence of ~5.2% sp² carbon, the sample recovered from 1400 K has a lower density of 3.11 g/cm³.