Atomic resolution detection of gallium-filled 2D silicon vacancies at the epitaxial graphene/SiC interface

In this study, the generation of Si vacancies during epitaxial graphene (EG) formation and the mechanism of Ga filling the Si vacancies during Ga intercalation are determined. The formation of EG and the subsequent generation of Si vacancies were investigated. Prior to Ga intercalation during the EG formation process, Si vacancies form in the topmost layer of the SiC substrate. Furthermore, these vacancies change the stacking sequence of SiC from its original 6H configuration to a 3C structure. After metal intercalation, the topmost SiC layer showed increased high-angle annular dark-field (HAADF) intensity relative to the bulk, suggesting the incorporation of heavier metals into this layer. This top SiC layer showed a sensitivity to e-beam damage, similar to the metallic bonding observed in two-dimensional (2D) metals. Finally, EELS analysis confirmed the presence of a 2D metal layer at the topmost SiC layer, supporting the conclusion that Ga atoms occupy the Si vacancies formed during Si sublimation.