Formation of graphene nanoribbons on the macrofacets of vicinal 6H-SiC(0001) surfaces

Thermal decomposition of vicinal $6H$-SiC(0001) surfaces with miscut angles toward the $[1\overline{1}00]$ direction results in the appearance of pairs of (0001) macroterraces and $(1\overline{1}0n)$ macrofacets covered with graphene, as follows. A carpetlike carbon layer grows on the surface, covering both the macroterraces and macrofacets; it forms a $(6\sqrt{3}\ifmmode\times\else\texttimes\fi{}6\sqrt{3})$ buffer layer on the former ones, whereas its partial periodic bonding with the SiC steps on the latter ones generates a pseudographene nanoribbon (pseudo-GNR) array. The nanoribbons have a width of 1.7--1.8 nm and are aligned in the $[11\overline{2}0]$ direction with a spatial periodicity of 3.3 nm. Scanning tunneling spectroscopy at a nanoribbon indicated a 0.4--0.5 eV energy gap and the Raman spectroscopy analysis of the pseudo-GNR array showed the absence of the 2$D$ peak and the polarization dependence of the $G$ and $D$ peaks, which is typical of the armchair-edge nanoribbon.