Odd-even effect and bandgap modulation by C-H doping in armchair nanoribbons of monolayer WS₂

Breaking the symmetry in out-of-plane direction in monolayer structures to trigger peculiar electronic features has long been predicted. Inspired by the recent experimental progress on the doping of carbon-based units in monolayer transition-metal dichalcogenide (TMD), we investigate the electronic structure and transport of armchair WS2 nanoribbons doping with C-H units in one face, using first-principle calculations. An odd-even effect is found, where the ribbons doped with even number of C-H units exhibit semiconducting behavior, and that with even number are metallic. With the increase of ribbon width, the band gap is found to decrease smoothly and finally trigger a semiconducting-metallic transition. Moreover, a periodically oscillatory variation of band gap is observed. Analysis shows it is resulted by the asymmetric edge effect induced by Janus-face doping. Our findings provide another way to modulate the electronic structure of TMDs, and can be extended to other TMD structures.