How does intercalation affect the structure and dynamics of bilayer graphene?

The intercalation of graphene on silicon carbide (SiC) does not only offer the possibility to study unique two-dimensional polar metals such as Ga, it also provides a route to tune the properties of graphene-based systems and develop novel materials with tailored functionalities. Herein, we present a study of how the intercalation affects the surface structure and dynamics of bilayer graphene (BLG) on SiC, by comparing epitaxial BLG grown from a silicon carbide substrate, with a 2D gallium intercalated sample, and a hydrogen intercalated sample. Using Helium Atom Scattering (HAS), we probe surface characteristics such as the in-plane thermal expansion, the surface electronic corrugation, and the atom-surface interaction potential. Moreover, the electron–phonon (e-ph) coupling strength is determined from the thermal attenuation of specular helium scattering. Due to HAS probing exclusively the top-most graphene layer, we establish an unusually large negative thermal expansion, while the e-ph coupling is slightly larger than the values found for metal-supported single layer graphene. Despite the surface sensitivity of HAS we are also able to detect subtle differences likely to be related to the varying characteristics of the intercalated materials beneath.