A new (2 × 1) reconstructed edge structure of zigzag Si nanoribbon: First principles study

Based upon the first principles calculations, a new (2 × 1) reconstructed edge structure (edge-4) with a triangle-pentagon pair topological defect at its edges is found for the zigzag Si nanoribbon, which is different from the previously found ones (edge-2 and edge-3) and more stable in energy than them. More interestingly, it is found that the edge-2 and edge-3 can transform into the new edge-4 under a little bit compression force along the ribbon edge, and the edge-4 could also be transformed into the edge-3 by a tensile strain larger than 9%. The calculated vibrational modes of the edge-4 show that two new characteristic vibrational edge defect modes appear at 434 cm^-1 and 515 cm^-1, which could be used in experiment to distinguish easily the new edge-4 from the edge-2 and edge-3. Finally, a sharp peak near the Fermi level is found to exist in the projected density of states from the edge's p_z orbital of edge-4, making its energy bands spin-split and the antiferromagnetic state to be its ground state.