(invited) Metal-Catalyzed Etching of Graphene Layers

Abstract

We present a comparative investigation on the etching of graphene layers catalyzed by Fe and Cu and demonstrate that their strikingly different etching behaviors are governed by their distinct interactions with carbon. Metal thin films are deposited by sputtering onto mechanically exfoliated graphene, few-layer graphene (FLG), and graphite flakes on a Si/SiO2 substrate. When the sample is rapidly annealed in forming gas or nitrogen, particles are produced due to the dewetting of the metal thin film. The evidence from the low-voltage scanning electron microscopy and Raman spectroscopy reveals that, at 950 oC in forming gas, the particles catalytically etch channels in graphite. No etching is observed on graphite for the Fe thin film annealed in nitrogen, indicating that this graphite etching process is catalyzed by Fe particles through the carbon hydrogenation reaction. Due to the strong Fe-C interactions, graphene and FLG are severely damaged through not only catalytic carbon hydrogenation but also carbon dissolution into Fe alone. By comparing with the etched monolayer and FLG in nitrogen, we identify that, in forming gas, the catalytic etching of monolayer and FLG is through carbon hydrogenation. During carbon hydrogenation, Fe particles are catalytically active in the dissociation of hydrogen into hydrogen atoms and in the production of hydrogenated amorphous carbon through hydrogen spillover. For the Cu case, while no etching takes place for Cu particles on graphite in either gas environment at 1050 oC, Cu particles catalyze the carbon hydrogenation reaction on graphene and FLG. The weak interaction between Cu and graphene, along with the low solubility of carbon in Cu, makes the Cu particles ideal for tracking their etching paths on graphene layers. Further temperature-dependent study shows that no catalytic etching occurs at 850 oC. Both etching from the graphene step edge and on the graphene basal plane are observed for Cu particles at 950 oC and vertical etching takes place in graphite at 1150 oC, resulting in the formation of hexagon pits with all zigzag edges.