Graphene Imaging Using Scanning Electron Microscopy: Mechanism of Secondary Electron Contrast Formation

For growth control of graphene, observation techniques, particularly those allowing in situ imaging during synthesis, are essential. Scanning electron microscopy (SEM) is a conventional surface observation method capable of in situ imaging of graphene segregation or growth in chemical vapor deposition, as well as ex situ imaging of synthesized materials. However, secondary electron (SE) emission from graphene is not fully understood, and the contrast formation mechanism of the monolayer material remains unclear. This review summarizes the SEM imaging of graphene, with a focus on SE contrast mechanisms under different conditions. The monolayer graphene layer does not greatly affect SE emission. Its SE contrast is brought from the charging effect, oxidation effect, or attenuation effect of backscattered electron (BSE) from the substrate. Characteristics of SE detectors, such as energy window, acceptance angle, and detected SE/BSE ratio, also contribute to the graphene contrast formation.