Liquid metal intercalation of epitaxial graphene: Large-area gallenene layer fabrication through gallium self-propagation at ambient conditions

We demonstrate the fabrication of an ultrathin gallium film, also known as gallenene, beneath epitaxial graphene on 6H-SiC under ambient conditions triggered by liquid gallium intercalation. Gallenene has been fabricated using liquid metal intercalation, achieving lateral intercalation and diffusion of Ga atoms at room temperature on square centimeter areas limited only by the graphene samples' size. The stepwise self-propagation of the gallenene film below the epitaxial graphene surface on the macroscopic scale was observed by optical microscopy shortly after the initial processing without further physical or chemical treatment. Directional Ga diffusion of gallenene occurs on SiC terraces since the terrace steps form an energetic barrier (Ehrlich-Schwoebel barrier), retarding the gallenene propagation. The subsequent conversion of the epitaxial graphene into quasi-free-standing bilayer graphene and the graphene-gallenene heterostack interactions have been analyzed by x-ray photoelectron spectroscopy and Raman measurements. The results reveal an alternative approach for the controlled fabrication of wafer-scale gallenene as well as for two-dimensional heterostructures and stacks based on the interaction between liquid metal and epitaxial graphene.