Lithographic bandgap engineering of graphene on the 10 nm scale: the role of edges*

In the light of graphene’s rich electronic properties and potentially high performance in applications, one of the most obnoxious roadblocks have been to pattern graphene on a small scale. Early theoretical work predicted that the bandstructure of graphene could be engineered by nanopatterning, such as nanoribbons and antidot lattices. Unfortunately, edge disorder and contamination associated with typical lithographic processes have strong detrimental effects on the transport properties. This has held back efforts to utilize quantum confinement in practical graphene devices as well as downscaling graphene components to a scale comparable to mainstream silicon electronics. The key is to control the chemistry and roughness of the edges, which has a striking impact on charge distribution and scattering in graphene, as illustrated by breakdown of the Quantum Hall Effect and ferroelectric behavior in graphene devices. By careful patterning through the hexagonal boron nitride encapsulation layer, we fabricated graphene devices with 35 nm pitch hole arrays and nm-scale edge roughness, yet exceptionally high carrier mobility. The distinct magnetotransport features are in quantitative agreement with zero-parameter tight-binding calculations and analytical models, including a ca. 150 meV bandgap. In addition we find that the subtle moiré-superlattice signatures associated with a small finite twist angle between the graphene and hexagonal boron nitride survives the aggressive lithographic patterning, suggesting that nanoscale circuits and components that exploit the novel properties of twisted 2D layers are feasible.