Strain in Epitaxial Graphene Visualized by Intercalation

Intercalation of Eu under graphene on Ir(111) results in patterns oriented along the graphene moire and quantized in size by its unit mesh. The patterns are formed by stripes, compact islands, and channels. Over a wide range of intercalated amounts the step concentration of the pattern has a rather constant saturation value. These findings are explained by the chemically modulated binding of graphene to the substrate and the preexisting strain in graphene due to its cooldown from the growth temperature. Local variations in the intercalation step density appear to reflect local variations in the preexisting strain. DOI: 10.1103/PhysRevLett.110.086111