Unveiling the oxidation stability of 2D gallium-intercalated monolayer epitaxial graphene through correlative microscopy

The oxidation- and air-stability of 2D gallium-intercalated monolayer epitaxial graphene was determined using correlative microscopy. Site-specific studies including AFM, scanning electron microscope, cross section STEM-HAADF, and EELS revealed that the oxygen signal detected by XPS and AES analyses originated from oxidized surface carbon contaminants without the presence of oxygen at the 2D gallium layers. In addition, the air-stability of the 2D gallium was correlated with the presence of intact epitaxial graphene. The absence of graphene leads to oxidation of the 2D gallium in air, consequently losing the crystallinity of the epitaxial gallium layer. This study invokes the importance of correlative microscopy to better understand defects in 2D metals that have been recently recognized through the confinement heteroepitaxy. In addition, this study highlights the advantage of using high spatial resolution STEM techniques in comparison with XPS that has relatively lower resolution.