Formation of oriented graphene nanoribbons over heteroepitaxial Cu surfaces by chemical vapor deposition

We demonstrate a new bottom-up approach to synthesize graphene nanoribbons (GNRs) on a Cu(100) film by chemical vapor deposition (CVD) without the use of any lithography and etching processes. Ambient pressure CVD with a low concentration CH₄ feedstock produced a number of GNRs with widths of 40-50 nm on a heteroepitaxial Cu(100)/ MgO(100) substrate. These nanoribbons are confined inside the nanoscale trenches formed on the Cu surface, and their orientations are highly controlled by the crystallographic orientation of the Cu(100) lattice. Raman spectra taken after the transfer indicated the growth of high-quality, single-layer GNRs. Moreover, low-energy electron microscopy revealed that all these aligned GNRs have the hexagonal orientations whose edges are terminated with zigzag edges. The GNR growth was not observed on Cu foil, and we discuss the growth mechanism of the oriented GNRs over epitaxial Cu(100) film. Our bottom-up approach offers a new method to grow single-layer GNRs which are oriented in a specific directions for future carbon-based nanoelectronics and spintronics applications.