CO2-assisted nucleation of twisted graphene on graphene/SiC templates

Abstract

In this study, we demonstrated controlled nucleation and growth of monolayer graphene on the terraces of a clean graphene/SiC (SiC-G) template using a chemical vapor deposition (CVD)-based method incorporating CO₂-assisted etching. To this end, a sequential thermal process that integrates SiC-G growth, CO₂ etching, and CVD graphene (CVD-G) growth was employed, all performed without air exposure. Raman spectroscopy, atomic force microscopy, and scanning electron microscopy confirmed that temperature-controlled CO₂ etching had a direct influence on the nucleation behavior of CVD-G. To elucidate the link between etching and nucleation, detailed examinations of the surface structure were conducted on pristine, CO₂-treated, and CVD-performed SiC-G templates. The results indicated an unexpected restoration of the etched SiC-G surface during CVD-G growth. This restoration led to the formation of active sites, namely structural defects that serve as essential nucleation centers for CVD-G. When properly controlled, the restoration yielded isolated active sites that promoted single-site nucleation and monolayer growth, a key prerequisite for high-quality graphene synthesis. By contrast, insufficient restoration resulted in multiple active sites, thereby leading to undesirable multiple nucleation. These findings highlight the critical balance between etching-induced activation and surface restoration in achieving controlled nucleation of graphene. This work offers a pathway to synthesizing twisted graphene structures with controlled nucleation sites.