Browsing by Author "Pablo, Ricardo"

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    Hard, transparent, sp3 -containing 2D phase formed from few-layer graphene under compression.
    (2021) Martins, Luiz Gustavo Pimenta; Silva, Diego L.; Smith, Jesse S.; Lu, Ang-Yu; Su, Cong; Hempel, Marek; Occhialini, Connor; Ji, Xiang; Pablo, Ricardo; Alencar, Rafael Silva; Souza, Alan Custodio dos Reis; Pinto, Alysson Alves; Oliveira, Alan Barros de; Batista, Ronaldo Junio Campos; Palacios, Tomas; Mazzoni, Mário Sérgio de Carvalho; Matos, Matheus Josué de Souza; Comin, Riccardo; Kong, Jing; Cançado, Luiz Gustavo de Oliveira Lopes
    Despite several theoretically proposed two-dimensional (2D) diamond structures, experimental efforts to obtain such structures are in initial stage. Recent high-pressure experiments provided significant advancements in the field, however, expected properties of a 2D-like diamond such as sp3 content, transparency and hardness, have not been observed together in a compressed graphene system. Here, we compress few-layer graphene samples on SiO2/Si substrate in water and provide experimental evidence for the formation of a quenchable hard, transparent, sp3 -containing 2D phase. Our Raman spectroscopy data indicates phase transition and a surprisingly similar critical pressure for two-, five-layer graphene and graphite in the 4e6 GPa range, as evidenced by changes in several Raman features, combined with a lack of evidence of significant pressure gradients or local non-hydrostatic stress components of the pressure medium up to z 8 GPa. The new phase is transparent and hard, as evidenced from indentation marks on the SiO2 substrate, a material considerably harder than graphene systems. Furthermore, we report the lowest critical pressure (z 4 GPa) in graphite, which we attribute to the role of water in facilitating the phase transition. Theoretical calculations and experimental data indicate a novel, surfaceto-bulk phase transition mechanism that gives hint of diamondene formation.