Oxidative pit formation in pristine, hydrogenated and dehydrogenated graphene

We study oxidative pit formation in pristine, hydrogenated, and dehydrogenated monolayer graphene (MLG), bilayer graphene (BLG) and trilayer graphene (TLG). Graphene samples are produced by mechanical exfoliation of highly oriented pyrolytic graphite (HOPG) onto SiO ₂ substrates. Etching is carried out by exposing samples to O ₂ gas at 450-700 °C. Using atomic force microscopy, we observe that pre-heating pristine MLG in vacuum at 590 °C increases the onset temperature for pit formation to values comparable to those in HOPG. We attribute this decrease in reactivity to an increase in adhesion between the MLG and substrate. In hydrogenated MLG and BLG, we observe a significant decrease in the onset temperature for pit formation. Dehydrogenation of these materials results in a decrease in the density of pits. We attribute the decrease in onset temperature to H-related defects in their sp ³ -bonded structure. In contrast, hydrogenated TLG and thicker-layer samples show no significant change in pit formation. We propose that this is because they are not transformed into an sp ³ -bonded structure by hydrogenation.