Self-Organized Graphene Nanoribbons on SiC(0001) Studied with Scanning Tunneling Microscopy

Graphene nanoribbons grown directly on nanofacets of SiC$(0001)$ offer an attractive union of top-down and bottom-up fabrication techniques. Nanoribbons have been shown to form on the $<1\bar{1}0n>$ facets of templated silicon carbide substrates,\footnote{Sprinkle et al., \emph{Nat. Nanotech.} \textbf{5}, 727 (2010).} but also appear spontaneously along step-bunches on vicinal SiC(0001) miscut slightly towards $<1\bar{1}00>$. These self-organized graphene nanoribbons were characterized with low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES) in ultra-high vacuum. Our measurements indicate that the graphene forms a continuous ``buffer layer'' across the SiC(0001) terraces during nanoribbon formation, with the zigzag edge of the buffer layer aligned parallel to the step-bunched nanofacets. Scanning tunneling microscopy/spectroscopy (STM/STS) was used to characterize the topography and electrical characteristics of the graphene nanoribbons. These measurements indicate that the graphene nanoribbons are highly-crystalline with predominantly zigzag edges.