Self-assembled Triangular Graphene Nanostructures

Quantum dots in graphene systems are currently of interest due their electronic and optical properties and possible use in innovative device applications. Researchers from CFM and DIPC have studied the growth of triangular nanostructures patterned on bilayer graphene films on SiC(0001) surface using hydrogen intercalation.

Bilayer graphene with triangular nanostructures scanned by the STM tip. Schematic view and simulation of the STM measurement on the triangular nanostructure.

We report on triangular nanostructures using scanning tunneling microscopy and spectroscopy in collaboration with international, experimental partners. The triangular islands arise from extended stacking faults in the SiC substrate and the effects can be seen on graphene layers that are formed on top of them. Depending on the local hydrogen intercalation the spectroscopic measurements reveal distinct electronic responses that range from single- to double-layer graphene. Intermediate states were also found as a consequence of the partial hydrogen intercalation process. High resolution topographic scanning tunneling microscopy images at resonant bias voltages inside triangular nanostructures show that the bottom layer of the bilayer graphene film is still bonded to the substrate. Therefore, within the triangular nanostructures there is a coexistence of carbon atoms bounded and unbounded to the substrate. For a better understanding of the phenomena we have advanced a theoretical model using atomistic calculations. The local density of states for free standing bilayer graphene is modified locally, within the triangular, nanometer-size structures, showing confinement effects because of the strong interaction with the substrate depending on incomplete hydrogen intercalation.

These findings on triangular graphene nanostructures could be promising from the point of view of applications, as arrays with distinct electronic response are potentially interesting for high-density data storage with hidden bit capabilities.