Strain-modulated half-metallic properties of carbon-doped silicon nanowires with single surface dangling bonds

The electronic and magnetic properties of hydrogen-passivated silicon nanowires (SiNWs) doped with an interstitial carbon atom are investigated by spin polarized first-principles calculations. It is found that the doped nanowire can have a novel ferromagnetic ground state when a surface dangling bond is created by removing a terminated H atom. In particular, when interstitial carbon is inserted at the core hollow sites, the nanowires with a dangling bond can become half-metallic with 100% spin polarization, independent of wire size and the doped concentration of C atoms. It is interesting that the half-metallicity and ferromagnetic states can be enhanced when the nanowires are axially tensioned but can be quenched when compressed. This magnetic modulation is derived from the interplay between the localization of the defect states and pairwise π-π interaction among the unsaturated surface Si dangling bond states, carbon atom, and its neighboring Si atoms. Our results highlight a new physical coupling between the doped states and surface dangling bonds in silicon nanowires and open a new opportunity for the development of nanoscale spintronics.