EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The lack of a CMOS-compatible transfer process restricts the realization of large-scale-high-quality monolayer graphene (MLG) applications. Although wafer-scale single-crystal MLG films can be synthesized on epitaxially deposited single-crystal Cu(111) on c-plane sapphire (Al$_2$O$_3$) templates, the non-straightforward intercalation base transfer process becomes a bottleneck. Hence, an interfacial release layer between Cu and sapphire could provide an alternative route for the graphene transfer process.
In this study, we report on the synthesis of large-area multilayer graphene at the interface of epitaxial Cu(Ni)(111)/ Al$_2$O$_3$(0001) using atmospheric pressure chemical vapor deposition (CVD). The interfacial carbon layer (ICL) was synthesized by introducing CH$_4$ and H$_2$ gases into a cold-wall CVD system, and characterized by micro-Raman spectroscopy, XRD, and AFM. Layered carbon with thickness up to 80nm was observed at the interface between 500nm thick Cu and Al$_2$O$_3$.
The effects of the partial pressure of the gases and the template substrate on the growth dynamics were investigated systematically. The growth rate and coverage of ICL increase with $P_{CH_4}$. With the Cu$_{85}$Ni$_{15}$(111) template, the significantly lower ICL coverage indicates the access of carbon to the interface of Cu(Ni)/Al$_2$O$_3$ was blocked by the fast-growing top surface MLG. A higher $P_{H_2}$ slows down the MLG growth, leading to a denser ICL deposition. These findings suggest the growth of ICL to be the result of the competition between diffusion of carbon species in copper and blockage of the species by top surface MLG formation.
After process optimization, the ICL could be synthesized simultaneously with top layer high-quality CVD MLG. In the future, this process could provide opportunities to enable CMOS-compatible large-scale-high-quality MLG transfer.