Ballistic transport in natural and lithographically patterned epigraphene sidewall ribbons*

One-dimensional single-channel, ballistic transport observed in epitaxial graphene nanoribbons is currently not understood, not even in principle. Epitaxial graphene nanoribbons can be produced (by thermal decomposition) on the sidewalls of ≈20 nm deep trenches etched in the silicon terminated face of SiC. For these sidewall nanoribbons, sidearms form at the edges of the naturally occurring SiC terraces that intercept the trench (due to the unavoidable slight miscut of the crystal). Alternatively, sidearm-free nanoribbons can be produced by properly annealing SiC whereby step bunching produces large (≈20 nm high) substrate steps on which graphene subsequently grows. Conductive probe potentiometry was performed on both types of sidewall nanoribbons, providing transport characteristics as a function of length. As might be expected, the sidearms are found to significantly reduce the mean free paths (≈1µm) compared with the sidearm free ribbons (>10µm). In contrast, mean free paths of about 20nm are found for lithographically produced epigraphene nanoribbons and about <50 nm for graphene on the Si face of SiC. Surprisingly, the sidearms do not simply serve as localized scattering centers but their effect appears to be delocalized.