Surface potentials of few-layer graphene films in high vacuum and ambient conditions

The surface potentials of few-layer graphene (FLG) films in high vacuum and ambient conditions have been investigated by employing electrostatic force microscopy. It is found that the surface potential of FLG films in ambient air has a constant large depression compared to that measured in a high vacuum. Our experimental results indicate that the shift is most likely caused by the presence of ambient adsorbates on the outmost graphene surfaces. The surface potentials increase with the number of graphene layers and approach the bulk value for five or more graphene layers in high vacuum as well as in ambient air. Since the contribution of the surface adsorbates is a constant value, we further show that the thickness dependence of the surface potential can be sufficiently explained by the nonlinear Thomas–Fermi Theory in both conditions.

► The surface potentials of few-layer graphene films have been investigated via employing the electrostatic force microscopy technique. ► The surface potential in ambient air has a depression compared to that in high vacuum. ► The shift is most likely caused by the ambient adsorbates on the graphene surfaces. ► Surface potentials of graphene flakes increase with the number of graphene layers, and approach the bulk value under high vacuum and in ambient environment.