Local work function and STM tip-induced distortion of graphene on Ir(111)

Abstract

The contact conductance and the apparent barrier height ϕ of graphene on Ir(111) are measured with a cryogenic scanning tunneling microscope. A strong dependence of ϕ on the tip–sample distance is found and explained by a local lifting of the graphene film by van-der-Waals forces. Variations of ϕ observed within the moiré unit cell of the graphene layer are interpreted in terms of differences in the local work function and the buckling of the graphene film. Comparison to results based on density functional theory indicates that a modulation of the charge transfer between graphene and Ir(111) is the origin of the work function variations.