Improving Graphene Conductivity through Selective Atomic Layer Deposition

One of the most promising approaches for massive production of transparent conducting electrodes (TCE) is roll-to-roll printing of graphene flakes solution. However, graphene flakes inevitably contain structural defects like grain boundaries and dislocations, together with macroscopic defects such as wrinkles and cracks during transfer. In addition, the printed flakes can’t align with each other perfectly. All these defects and the gaps between detached flakes hinder electrical transport and limit the mechanical strength and reliability of the graphene. 

Here we report a technique to electrically heal and connect graphene flakes via selective atomic layer deposition (ALD) of conductive materials. We have demonstrated selective growth of ALD aluminum-doped zinc oxide, ruthenium and platinum on pristine graphene surface prepared from exfoliated highly ordered pyrolytic graphite (HOPG). ALD materials nucleate on graphene cracks and edges but exhibit a significant nucleation barrier on intact basal planes due to the chemical inertness from delocalized π-orbitals. We also present a high-throughput fabrication method to create graphene patterns via metal shadow mask and O₂ plasma. This model system of patterned CVD graphene islands demonstrates electrical connection of separated graphnene flakes by selective ALD processes. In addition, shadow-mask-patterned CVD graphene field effect transistors (FETs) are used to monitor graphene carrier density and mobility variation after ALD growth. We found considerable carrier density and conductivity increase of a single graphene flake after V₂O₅ ALD, which can be explained by p-doping of graphene due to the high work function V₂O₅.