Atomistic-scale simulation of the thinning process of multilayer graphene with low-energy helium plasma

The graphene thinning by low-energy helium plasma etching offers a nonrandom method with precise control over the number of layers. This study uses molecular dynamics simulations to investigate the etching process of multilayer graphene (MLG) under low-energy (≤1 keV) He+ irradiation. It is shown that low-energy He+ ions induce layer-by-layer thinning without creating deep pits or reducing the lateral dimensions of graphene. It is observed that increasing the energy of the He+ ion enhances the etching rate. The thinning process from 4L to 3L-graphene has an etching rate comparable to 4L to 1L-graphene, indicating consistency regardless of the thickness of MLG. During the thinning process before the complete removal of one layer, interlayer distance expands, and the interlayer expansion increases with He+ ion density until it reaches saturation. The saturation value of interlayer expansion decreases with higher ion energy, occurring at a lower He+ ion density.