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Despite the advanced stage of diamond thin-film technology, with applications ranging from superconductivity to biosensing, the realization of a stable and atomically thick two-dimensional diamond material, named here as diamondene, is still forthcoming. Adding to the outstanding properties of its bulk and thin-film counterparts, diamondene is predicted to be a ferromagnetic semiconductor with spin polarized bands. Here, we provide spectroscopic evidence for the formation of diamondene by performing Raman spectroscopy of double-layer graphene under high pressure. The results are explained in terms of a breakdown in the Kohn anomaly associated with the finite size of the remaining graphene sites surrounded by the diamondene matrix. Ab initio calculations and molecular dynamics simulations are employed to clarify the mechanism of diamondene formation, which requires two or more layers of graphene subjected to high pressures in the presence of specific chemical groups such as hydroxyl groups or hydrogens.

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A high-pressure resonance Raman spectroscopy study of linear carbon chains encapsulated inside multiwalled carbon nanotubes (MWCNTs) is reported. While the frequencies of the tangential modes of carbon nanotubes (G band) harden as the pressure increases, the vibrational frequencies of the chain modes (around 1850 cm −1 ) decrease, thus indicating a softening of the carbon−carbon bonds in this 1D solid. Pressure-induced irreversible structural changes in the linear carbon chains are unveiled by the red shift in the vibrational modes when pressure is released. These results have been interpreted as being due to a coalescence of carbon chains, and this hypothesis is supported by state-of-the-art atomistic reactive molecular dynamics simulations.