Electronic and magnetic properties of perfect, vacancy-doped, and nonmetal adsorbed MoSe2, MoTe2 and WS2 monolayers

Abstract

Very recently, two-dimensional nanosheets of MoSe(2), MoTe(2) and WS(2) were successfully synthesized experimentally [Science, 2011, 331, 568]. In the present work, the electronic and magnetic properties of perfect, vacancy-doped, and nonmetal element (H, B, C, N, O, and F) adsorbed MoSe(2), MoTe(2) and WS(2) monolayers are systematically investigated by means of first-principles calculations to give a detailed understanding of these materials. It is found that: (1) MoSe(2), MoTe(2) and WS(2) exhibit surprising confinement-induced indirect-direct-gap crossover; (2) among all the neutral native vacancies of MoSe(2), MoTe(2) and WS(2) monolayers, only the Mo vacancy in MoSe(2) can induce spin-polarization and long-range antiferromagnetic coupling; (3) adsorption of nonmetal elements on the surface of MoSe(2), MoTe(2) and WS(2) nanosheets can induce a local magnetic moment; H-absorbed WS(2), MoSe(2), and MoTe(2) monolayers and F-adsorbed WS(2) and MoSe(2) monolayers show long-range antiferromagnetic coupling between local moments even when their distance is as long as ∼12 Å. These findings are a useful addition to the experimental studies of these new synthesized two-dimensional nanosheets, and suggest a new route to facilitate the design of spintronic devices for complementing graphene. Further experimental studies are expected to confirm the attractive predictions.

Valley Hall effect in disordered monolayerMoS2from first principles

“…It is well established that sulfur vacancies constitute the main source of disorder in MoS 2 [13][14][15][16][17][18]. The formation energies and thermodynamics of these defects have been thoroughly studied [19], but their influence on transport and optical properties remains largely unexplored.…”

“…Recent experimental as well as theoretical studies have demonstrated that sulfur vacancies are the dominant source of disorder in MoS 2 [13][14][15][16][17][18]. In the following we will therefore focus exclusively on sulfur vacancies, and calculate their effect on the VHC.…”

Atomic defect states in monolayers of MoS2 and WS2

“…Nevertheless, the sulphur vacancy is the predominant point defect compared to Mo vacancy, regardless of the type of preparation method. 18 The effects of point defects on the electronic structure of LTMDs have also been theoretically studied by several groups using first principles calculations 16,17,[19][20][21][22][23][24][25] and 6-band tight-binding (TB) model 26 . Although, ab initio methods based on density functional theory (DFT) can achieve a good degree of accuracy to describe the electronic structure of pristine LTMD materials, they are limited in their application by the presence of defects in the samples.…”

Quantum spin Hall effect and topological phase transition in two-dimensional square transition-metal dichalcogenides

“…Unlike semimetallic graphene, pristine monolayers of MX 2 are direct band gap semiconductors with band gap values ranging from 1.1 to 1.9 eV. [5][6][7][8][9] With relative fabrication easiness, chemical stability, relatively high mobility, and strong spin-orbit coupling (SOC), these materials are expected to have a significant impact on next-generation ultrathin electronic, optoelectronic, and valleytronic devices. 10-13 3 Following the known theoretical verification of quantum spin Hall (QSH) effect in 2D topological insulators (TIs) graphene, 14 extensive effect has been devoted to the search for new 2D materials or new schemes to obtain 2D TIs with large band gaps.…”