The structural and electronic properties of pristine and H-passivated C-terminated beta-SiC(0 01)-c(2 x 2) surface are addressed by ab initio calculations. Here, we verify the formation of C chains composed by double-bonded dimers rows (C=C), separated by triple-bonded bridged dimers (C C). The surface states near the bandgap are confined along the C=C dimer rows, with no electronic contribution from the C C bridged dimers. After hydrogenation, the C-chains are strongly modified, forming subsurface voids or nanotunnel (NT) structures. By considering a plausible set of energy release steps for increasing hydrogenation, we obtain a C-rich NT ruled by the C=C dimer rows. Somewhat similar to that recently reported on the Si-rich termination, but 0.8 eV lower in energy. The electronic band structures of both Si-rich and C-rich NTs have been examined within the hybrid HSE06 functional, which are compared with those previously reported using a semilocal functional. (C) 2015 Elsevier B.V. All rights reserved.