(615d) Bi- and Tri- Layer Graphene Solutions

Many applications of pristine, AB-stacked bilayer and trilayer graphene require synthesis methods to control the number of stacked layers. Solution dispersion is promising for printable electronics and nanocomposites. However, no method is currently available for the predetermined exfoliation of AB-stacked or large area flakes such that conventional photolithography is possible.  Here, we demonstrate that graphite intercalation with ionic, non-covalent intercalants to yield Stage-2 and Stage-3 compounds results in bilayer- and trilayer-enriched graphene dispersions, respectively. The intercalation and subsequent expansion of graphite allows mild sonication to yield stable dispersions, decreasing flake size reduction while maintaining AB stacking as confirmed by Raman spectroscopy.  An on-chip micro-hydrodynamic separation method localizes large area graphene flakes (up to 50 μm²). This constitutes the only viable route at this time for the mass-production of AB stacked bi- and tri- layer graphene. Unannealed bilayer flakes exhibit low resistivity (~1 kΩ) and mobilities which are higher (~400 cm²V^-1s^-1) than those attained utilizing other solution methods.