Two-dimensional diamond-diamane from graphene precursor with tilt grain boundaries: Thermodynamics and kinetics

We delve into the kinetics of intricate phase transformation of graphene to atomically thin diamond, i.e., diamane, to uncover the role of grain boundary (GB) type and configuration in precursor graphene structures in determining the uniformity and transformation conditions. The occurrence of a phase transition of this nature is fundamentally associated with nanoscale dimensions, wherein the structure of graphene directly influences the thermodynamic properties. We revealed that the transformation stress, sigma t, exhibits significant dependence on both the thickness of the precursor graphene layer and the temperature. In contrast, the transformation strain, epsilon t, is independent of the number of layers and type of GBs. The heterogeneous nucleation of the diamond phase within the GBs is also discovered, which differs from the interlayered nucleation and layer-by-layer transformation of diamond phases in pristine graphene.