Hybrid Structures and Strain-Tunable Electronic Properties of Carbon Nanothreads

The newly synthesized ultrathin carbon nanothreads have drawn great attention from the carbon community. Here, based on first-principles calculations, we investigate the electronic properties of carbon nanothreads under the influence of two important factors: the Stone Wales (SW) type defect and the lattice strain. The SW defect is intrinsic to the polymer-I structure of the nanothreads and is a building block for the general hybrid structures. We find that the bandgap of the nanothreads can be tuned by the concentration of SW defects in a wide range of 3.92-4.82 eV, interpolating between the bandgaps of sp(3)-(3,0) structure and the polymer-I structure. Under strain, the bandgaps of all the structures, including the hybrid ones, show a nonmonotonic variation: the bandgap first increases with strain, then drops at large strain above 10%. The gap size can be effectively tuned by strain in a wide range (>0.5 eV). Interestingly, for sp(3)-(3,0) structure, a switch of band ordering occurs under strain at the valence band maximum, and for the polymer-I structure, an indirect-to-direct-bandgap transition occurs at about 8% strain. The result also indicates that the presence of SW defects tends to stabilize the bandgap size against strain. Our findings suggest the great potential of structure- and strain-engineered carbon nanothreads in optoelectronic and photoelectrochemical applications as well as stress sensors.