Using first-principles calculations, we investigate the electronic and optical properties of zigzag silicene nanoribbons substituted with double carbon chains. The results show that the chains are pulled nearly straight and produce a rather obvious transverse contraction in the width direction of the ribbon. The double carbon chains introduce defect states that appear as two degenerate bands across the Fermi level. These nanoribbons are always metallic regardless of the position of the carbon chains or the ribbon width. Under the same bandwidth, the imaginary parts of the dielectric functions in the Ex and Ey directions reveal red- and blue-shifts, respectively, with increasing distance between the two C chains. The imaginary parts of the dielectric functions in the Ex and Ey directions reveal blue- and redshifts, respectively, with increasing ribbon width. Three major peaks in the imaginary part of the dielectric function correspond to the intrinsic plasma frequencies originating from electron transitions of silicon and carbon. Such excellent electronic and optical properties may lead to some important applications of the nanoribbons in short-wavelength optoelectronic devices.
