Nat. Commun. 10, 230 (2019)

Graphene quantum dots (GQDs), a relatively new addition to the nanocarbon materials family, have a number of advantageous tunable opto-electronic properties. However, the presence of localized edge states in GQDs, which inevitably occur during their formation, adversely affects the charge transport. Moreover, the fabrication of tunnelling contacts to GQDs with reproducible contact resistances has proved challenging. Now, G. Kim and colleagues have shown how to circumvent these issues by using a combination of in-plane and vertical heterostructures to build vertical single-electron tunnelling transistors.

The researchers synthesize the GQDs on top of an array of platinum nanoparticles embedded inside a hexagonal boron nitride (hBN) matrix through catalytic substitution of boron and nitrogen atoms by carbon. The GQD/hBN layer is sandwiched between two thin hBN layers to isolate the quantum dots from the contacts: this ensures a long lifetime of electrons and reduces the number of localized states. Next, multichannel single-electron tunnelling transistors are prepared by capping the GQD/hBN structure with graphene electrodes. Differential conductance measurements performed using tunnelling spectroscopy reveal the observation of multiple Coulomb diamonds originating from a Coulomb blockade regime in one particular GQD.