Scaling graphene down to nanoribbons is the most promising route for the implementation of this material into devices. In this context, bilayer thick graphene nanoribbons (GNRs) are of special interest, as they are expected to combine the structurally and dimensionally dependent electronic properties of a GNR (ex.: quantum confinement of charge carriers), with the unusual features of bilayer graphene, such as its electric ﬁeld tunable band gap. Hence, achieving the direct synthesis of bilayer GNRs on an insulating template, by employing a method that allows exerting control over dimensions and edge structures, would be extremely advantageous for fundamental investigations of the pristine properties of these nanostructures, as well as for applications.
Figure 1. Atomic force microscopy phase contrast image taken from a sample containing 320 nm wide bilayer GNRs.
Figure 2. Raman mapping (8x13 μm2) for the intensity of the graphene-related G peak taken from a bilayer GNR. These results illustrate the isolated and continuous nature of the GNRs. Note that for the Raman result, the width of the GNR displayed in the mapping does not correspond to its real dimension, as the spatial resolution of the Raman set-up is about 1 μm. The real width is, in this case, about 200 nm.
In this work, we demonstrate a novel approach for the fabrication of isolated bilayer GNRs on SiC(0001) surfaces. It is based on the precise control of the layer-by-layer growth of graphene (via Si surface sublimation) and a simple annealing step in air. With this method, we are able to prepare μm-long bilayer GNRs exclusively over step edge regions of a SiC surface. The lateral width of the nanoribbons can be varied by changing either the temperature or time during growth. The present results open a new perspective on the tailored fabrication of bilayer graphene nanostructures for different applications in nanoelectronics.