Ultrahigh mechanical robustness of vertical graphene sheets covalently bonded to diamond

Vertical graphene sheets (VGs), covalently bonded to diamond substrate, can exhibit ultra-high mechanical robustness against scratching, friction, and compression. In this study, AFM tests with a diamond probe were preformed to investigate the interfacial mechanical properties of VGs film fabricated on diamond substrate. The unique bonding structure between VGs and diamond, featured with an ultra-strong C–C covalent bonds, effectively inhibited VGs being uprooted from diamond substrate even under a contact pressure as high as 53.7 GPa. Despite the inevitable breakage of graphene sheets under a contact pressure exceeds 25 GPa, the fractured graphene sheets residuals, which retain their covalent bonds to diamond substrate, could still act as a mechanically robust VGs film. Furthermore, in a long-duration AFM friction test, the VGs exhibited a highly stabilized coefficient of friction around 0.03 and a nearly ignorable specific wear rate as low as 2.0 × 10−4 mm3/Nm. Due to the relative slipping between adjacent graphene sheets was inhibited by the interfacial covalent C–C bonds between VGs and diamond substrate, the compressed VGs film transformed into a scale-like structure that consist of compactly stacked graphene sheets with a certain concentration of sp3 bonds (up to 8%) forming inside. This structure, characterized with extremely high elastic modulus and compressive strength, substantially attributed to the ultrahigh stability and sustainability exhibited by VGs upon friction and compression. The findings presented here is expected to boost utilizations of VGs and diamond combined in electronics, optical, mechanical, and tribological fields.