Emergent high conductivity in size-selected graphene networks

Nanomaterial networks are attractive for a diverse range of printed device applications including electronics, sensing, energy capture and storage. At present, the influence of morphology on the network properties, such as electrical transport, is poorly understood. Here, we develop an understanding of structure-property relationships in these systems by performing size selection from bulk to few-layer graphene. We observe size-dependent electrical conductivity spontaneously during film formation, with the smallest nanosheets realizing electrical conductivity exceeding 105 S/m, a record value for liquid-exfoliated graphene and competitive with electrochemically-exfoliated graphene. Given the high electrical conductivity exhibited by these networks, and the applicability of graphene as a model layered nanosheet system, we explore the use of this size-selected graphene for thermoelectric applications. We interpret our understanding of the high conductivities obtained in terms of nanosheet packing and its influence on the number density and nature of inter-sheet junctions. This work represents an approach to overcome junction-limited electronic transport and enable nanoparticulate networks for printed device applications.