Spontaneous Decoupling of Graphene from Sapphire

The synthesis of high-quality graphene on dielectric substrate is a topic with relevant technological implications. It has been shown that it is indeed possible to use α-Al₂O₃(0001) as a substrate for growing well aligned graphene of high crystalline quality. Nevertheless, due to the non-negligible interaction with the interface, transport figures are limited in comparison with the benchmark graphene, which is the one grown on copper foil and then transferred onto SiO₂/Si platforms. In this study, we first show how graphene can arrange on a commensurate structure over the Al-rich (√31×√31)R9 reconstruction of the α-Al₂O₃(0001) substrate. We then provide evidence of the fact that, oxygen-rich species spontaneously intercalate at room temperature at the heterointerface between graphene and the Al-rich reconstruction, strongly reducing the strain and doping level of the graphene and allowing it to reach considerable figures in transport. Raman spectroscopy as well as 4-point probe transport carried out on freshly made, as well as on aged samples vividly show the occurrence of this phenomenon. We will display a thorough characterization of the system, using a variety of complementary techniques, including X-ray photoelectron spectroscopy, scanning tunnelling microscopy and cross-sectional transmission electron microscopy, which allow us to convincingly describe the phenomenology of the decoupling between graphene and sapphire, highlighting a van der Waals gap between graphene and the substrate, as large as 3 nm. Our work proves to be instrumental for deeping the understanding of how graphene can be grown on sapphire, helping the community to reach the goal of wafer-scale single-crystal graphene synthesis. In addition, we also propose a possible method for speeding up and control the intercalation process in a way to make it compatible with industrial fabrication processes.

This work has received funding from “GRAPH-X” funded by the European Union through the HORIZON.2.4 – Digital, Industry and Space programme (GA 101070482).