Band-gap engineering with a twist: Formation of intercalant superlattices in twisted graphene bilayers

Abstract

Graphene-based materials have long been considered as promising building blocks for a new generation of high-frequency (terahertz) electronic devices, but their use is complicated by the lack of an intrinsic band gap in graphene itself. Here we exploit synthetically controllable incommensuration of twisted graphene bilayers as a scaffold for intercalation of alkali metal ions with the periodicity of the bilayer supercell. Systematic exploration of the energy profiles of the ions as a function of position suggests that the alkali metal ions aggregate commensurately with the symmetry of the twisted bilayer. The intercalated alkali metal ions act as a source of a periodic perturbation on the level of the bilayer supercell, which permits opening and engineering of a band gap between graphene's \ensuremath{\pi} bands. The twist angle between the graphene layers determines the structure and disorder of the intercalant sublattice and, consequently, the magnitude of the band gap. Appropriate choices of the intercalant and twist angle thus permit band-gap engineering in graphene. We offer arguments that the impact of intercalation on the all important charge mobility of graphene will be rather small.