Synthesis of high-density arrays of graphene nanoribbons by anisotropic metal-assisted etching

We demonstrate the synthesis of highly aligned dense arrays of graphene nanoribbons (GNRs) based on metal-assisted etching of chemical vapor deposition-grown single-layer graphene. In order to obtain GNR arrays, controlling the direction of the etching becomes an important task. Crystalline surfaces of r- and a-planes of sapphire (α-Al₂O₃) were found to induce anisotropic etching of the graphene along their specific crystallographic directions. In contrast, anisotropic surface of ST-cut quartz induced few etching lines. We found that the graphene etching is strongly dependent on the metal species; the order of the catalytic activity of metal nanoparticles is Ni > Fe > > Cu. Etching temperature and H₂ concentration also strongly influenced the density and quality of the etching lines. Our anisotropic graphene etching is expected to offer a new route toward the synthesis of high density GNR array in large area without relying on any lithographic techniques for future electronic devices.