Atomic-scale probing of defect-assisted Ga intercalation through graphene using ReaxFF molecular dynamics simulations

We report a joint theory and experimental investigation on the defect-mediated surface interactions of gallium (Ga) metals and trimethyl-gallium (TMGa) molecules with graphene. A combination of Raman spectra, X-ray photoelectron spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS) reveal defects in graphene, which can act as pathways for Ga intercalation. These experimental results are connected to ReaxFF simulations, which further confirm that the Ga and TMGa adsorption on graphene is strongly impacted by the presence and size of defects. These defects catalyze the surface reactions by lowering the temperature for Ga-deposition on the surface. Moreover, multivacancy defects promote Ga intercalation through graphene by reducing the kinetic barrier while the migration through single vacancy or 5-8-5 defect is kinetically hindered. The ReaxFF results indicate that TMGa exposure leads to defect healing by the passivation of carbon-dangling bonds by hydrocarbon and organometallic adducts, which is supported by the decreased Raman D:G ratio in Ga-intercalated graphene and by STM images. Since probing and controlling graphene defects constitutes a key step in the intercalation mechanism, this work provides an in-depth atomic scale understanding into the complex interplay between defects and precursors, thus providing an effective way to design defects for 2D metal fabrication.