Hydrogen-plasma patterning of multilayer graphene: Mechanisms and modeling

We study the atomic-scale etching mechanisms of multilayer graphene, and the subsequent formation of nanopores, when exposed to downstream hydrogen plasma. Our molecular dynamics simulations based on reactive force-field potential reveal precise energy regimes for the transport of ions through, and selective etching of, individual graphene layers within the multilayer structure. Etching initiates with hydrogenation of the graphene basal plane, followed by localized C[sbnd]C bond breaking which leads to the formation of CH₂, and subsequently, unstable CH₃ bond configurations. We establish the basal plane and edge etching rates of the individual graphene layers as a function of ion energy, and introduce a micromechanics model to predict the 3D-patterned pore structure at experimental length- and time-scales. Our results demonstrate the development of columnar holes in multilayered graphene, which transition to stepped-edge holes at higher fluence due to cumulative effects of basal-plane etching. The contributions of thermal radicals and dehydrogenation effects on the hole growth process are discussed.