Pressure and Nitrogen Induced Phase Transition in Bilayer CVD Graphene

Abstract Pressure‐activated phase‐transitions in 2D materials like graphene open new possibilities for developing materials with exceptional mechanical properties. Previous studies show that pressure‐induced sp 2 ‐to‐ sp 3 phase‐transitions occur only in epitaxial graphene on SiC. Unfortunately, this system has limitations for industrial applications. On the other hand, graphene synthesized by chemical vapor deposition (CVD) is cost‐effective, scalable, and transferable on different substrates. However, pressure‐activated sp 2 ‐to‐ sp 3 phase‐transitions are absent in exfoliated graphene. Here, this work demonstrates that nitrogen‐doping can enable pressure‐induced graphene‐to‐diamond phase transitions in bilayer CVD graphene films on SiO 2 at room temperature. The sp 2 ‐to‐ sp 3 phase transition is verified by measuring with modulated nanoindentation (MoNI) the stiffness of the films as a function of the number of layers. Specifically, the indentation stiffness of a SiO 2 substrate covered with a nitrogen‐doped bilayer CVD graphene film almost doubles compared to bare SiO 2 ; in contrast, nitrogen‐doped single and multi‐layer graphene films do not improve the stiffness of a SiO 2 substrate. Molecular dynamics simulations confirm that nitrogen favors the formation of sp 3 ‐coordinated carbon atoms and covalent bonding between two graphene layers when the films are under compression. Nitrogen‐doping emerges as an effective way to obtain exceptional lightweight protective coatings utilizing scalable large‐size CVD bilayer graphene films.