Mechanism for etching of exfoliated graphene on substrates by low-energy electron irradiation from helium plasma electron sources

The authors investigate the mechanism for etching of exfoliated graphene multilayers on SiO ₂ by low-energy (50 eV) electron irradiation using He plasma systems for electron sources. A mechanism for this etching has been previously proposed in which the incident electrons traverse the graphene and dissociate oxygen from the SiO ₂ substrate at the graphene/SiO ₂ interface. The dissociated oxygen reacts with carbon defects formed by the electron irradiation and thereby etches the graphene from below. They study etching using graphene flakes of various thicknesses on SiO ₂ , low and higher resistivity Si, indium tin oxide (ITO), and silicon carbide (SiC). They find that thicker layer graphene on SiO ₂ does not etch less than thinner layers, contrary to the previously proposed model. They find that etching does not occur on low-resistivity Si and ITO. Etching occurs on higher resistivity Si and SiC, although much less than on SiO ₂ . This is attributed to He ion sputtering and vacancy formation. From these observations, they propose that oxygen etches graphene from above rather than below. In addition, they propose He ions instead of incident electrons cause the defects that oxygen reacts with and etches.