Width-dependent band gap of arm-chair graphene nanoribbons formed on vicinal SiC substrates by MBE

Formation and electronic states of graphene nanoribbons with arm-chair edges (AGNR) are studied on the SiC(0001) vicinal surfaces toward the [ 1 1 ˉ 00 ] direction. The surface step and terrace structures of both 4H and 6H-SiC substrates are used as the growth templates of one-dimensional arrays of AGNRs, which are prepared using the carbon molecular beam epitaxy followed by hydrogen intercalation. A band gap is observed above the π-band maximum by angle-resolved photoelectron spectroscopy (ARPES) for the both samples. The average widths of the AGNRs are 6 and 10 nm, and the estimated average band gaps are 0.40 and 0.28 eV for the 4H- and 6H- substrates, respectively. A simple and phenomenological inverse relation between the energy gap and AGNR width works in the analyses of the ARPES data.