Realizing Scalable Chemical Vapour Deposition of Graphene Films on Iron and Steels by In Situ Observations

Graphene has been suggested as an ultimately thin functional coating for metallurgical alloys such as steels. However, even on pure iron (Fe), the parent phase of steels, growth of high-quality graphene films remains largely elusive to date. We here report scalable chemical vapour deposition (CVD) of high-quality monolayer graphene films on pure Fe substrates and discuss the improvement of graphene growth conditions on steels. To achieve this, we elucidate the mechanisms of graphene growth on Fe substrates using complementary in situ X-ray diffractometry (XRD) and in situ near ambient pressure X-ray photoelectron spectroscopy (NAP XPS) during our scalable CVD conditions. We identify key factors that differentiate Fe from other common graphene CVD catalyst supports such as Ni or Cu. Firstly, that for Fe, carbothermal reduction of persistent Fe-oxides may take place during CVD and secondly, that the kinetic balancing of carbon uptake into the Fe during CVD near the Fe-C eutectoid is critical for monolayer graphene growth because of the complex multi-phased Fe-C phase diagram. Additionally, we establish that the carbon uptake into the Fe during graphene CVD is not only important in terms of growth mechanism but can also be advantageously utilized for concurrent surface hardening of the Fe during the graphene CVD process akin to carburization/case hardening. Our work thereby forms a framework for controlled and scalable high-quality monolayer graphene film CVD on Fe and more complex metallurgical substrates.