Visualization of graphene grain boundaries through oxygen intercalation

Efficient control over the grain boundaries (GBs) is a vital aspect in optimizing the graphene growth conditions. A number of methods for visualization of GBs were developed for graphene grown on weakly interacting surfaces. Here, we utilize oxygen intercalation to reveal GBs and study their morphology for graphene strongly bound to the cobalt surface. We demonstrate that upon the intercalation of oxygen, GBs in polycrystalline graphene become easily detectable due to graphene cracking and selective oxidation of the substrate, thus giving a direct insight into the graphene micro- and nanostructure by means of different electron microscopy methods, including scanning electron microscopy, photoemission microscopy and low-energy electron microscopy. • Grain boundaries of graphene strongly bound to the Co(0001) surface are visualized. • Patterned distribution of domains is revealed in polycrystalline graphene/Co. • Graphene coverage prevents the Co(0001) surface from oxidation at low exposures. • Lateral growth of cobalt oxide areas is observed under polycrystalline graphene. • After deintercalation of oxygen a part of graphene remains quasi-freestanding.