Modulation Of Electronic Structure Of MoS₂ Nanoribbon And Phoshorene Nanoribbon

Recent years, Mo S2 and phosphorene are increasingly found in nanoelectronic and new photonic devices due to their remarkable electronic properties. More recently, their one-dimensional(1D) nanostructures, such as nanoribbons, nanotubes, wires, and rods, have drawn considerable attentions to study their intrinsic properties. From a nanostructure perspective, 1D structures show a range of potential applications which are quite different from those presented by their 2D and 3D counterparts.This thesis has investigated the electronic structures of Mo S2 and phosporene nanoribbons by performing first-principles calculations. On one hand, compared to bare edge armchair Mo S2 nanoribbons(AMo S2NRs) or purely hydrogen(H) edge-terminated AMo S2NR(AMo S2NR-H), it is found that hydrogen and oxygen(O) hybrid edge-terminated AMo S2NR(AMo S2NR-H-O) is more stable. AMo S2NR-H-O exhibits a direct band gap of about 1.43 e V, which is larger than those of pristine AMo S2NR(about 0.61 e V) and AMo S2NR-H(about 0.60 e V), even exceeds the band gap of bulk Mo S2(about 0.86 e V),and is close to that of monolayer Mo S2(about 1.67 e V). The remarkable band gap of AMo S2NR-H-O is attributed to the charge redistribution on the edge atoms of the Mo S2 nanoribbon, especially the charges on the edge Mo atoms. Detailed calculations of AMo S2NR-H-O reveal that over 70% of the total density of states(DOS) of the conduction band minimum and the valence band maximum are contributed by the Mo atoms. In particular, edge Mo atoms play a crucial role in modulating the electronic structure. In addition, a series of functionalized AMo S2NR-H-X with X = S, F, C, N, and P are studied, respectively. It is found that AMo S2NR-H-X with X = S, 2F, C possess remarkable electronic band gaps, whereas AMo S2NR-H-X with X = F, N, P are metallic. The result suggests that non-metal atom hybrid passivation can efficiently tune the electronic band gap of Mo S2 nanoribbon and open a new route to obtain a Mo S2-based practical nanoelectronic device and a photovoltaic device.On the other hand, the calculations show that edge hydrogenation or fluorination can efficiently tune the electronic band structure of phosphorene nanoribbon(PNR). Besides, the band gap of PNR with hydrogenation or fluorination can be significantly reduced and even closed by transverse electric field, which gives rise to the change of PNR from semiconductor to metal. In consideration of the special electronic properties and high stabilities of the PNRs, the conclusion is that PNR with edge fluorination would be the most promising candidate among those PNRs for the application in novel functional nanoelectronic devices.