Solid-Phase Coalescence of Electrochemically Exfoliated Graphene Flakes into a Continuous Film on Copper

The ability to directly synthesize high-quality graphene patterns over large areas is important for many applications such as electronic and optoelectronic devices and circuits. Here, we report a facile and scalable approach to coalesce and recrystallize electrochemically exfoliated graphene flakes into a continuous film by thermal annealing on copper foils. The underlying growth mechanism involves defect-mediated decomposition of electrochemically exfoliated graphene flakes into active polycyclic carbon species, followed by coalescence of the active carbon species into a continuous, monolayer film of high material quality. First-principles calculations confirm that the enhanced affinity of the polycyclic carbon species with copper effectively prevents their surface desorption at elevated temperatures, which is distinct from graphene growth based on the decomposition of solid carbon sources into gaseous hydrocarbons. Significantly, the localized supply of active carbon species in our approach enables spatially confined growth of graphene. Combined with stencil printing of the exfoliated flakes, transparent and conductive graphene circuits have been directly synthesized over large areas.