▎ 摘　　要

Understanding the transition from sp(2) to sp(3) bonding between graphene layers remains a challenge for the development of thin diamond films. Herein, in situ Raman spectroscopy is used to trace the structural evolution of bilayer graphene (BLG) films under high pressures applied by a diamond anvil cell. When water is used as the pressure transmission medium (PTM), the G peak of BLG disappears at similar to 37GPa, accompanied by vanishing of the 2D peak after pressure release, together considered as evidence of sp(2)-sp(3) transition in BLG under high pressures. In contrast, BLG in silicone oil PTM or single layer graphene in water PTM does not experience such changes in Raman spectra with pressure, suggesting that water is critical for the formation of sp(3) bonding under high pressures, e.g., by providing functional groups on the surface of BLG. Published under license by AIP Publishing.