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.
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ABSTRACT: The isolation of few-layered transition metal dichalcogenides has mainly been performed by mechanical and chemical exfoliation with very low yields. In this account, a controlled thermal reduction-sulfurization method is used to synthesize large area (~1cm2) WS2 sheets with thicknesses ranging from monolayers to a few layers. During synthesis, WOx thin films are first deposited on Si/SiO2 substrates, which are then sulfurized (under vacuum) at high temperatures (750-950°C). An efficient route to transfer the synthesized WS2 films onto different substrates such as quartz and transmission electron microscopy (TEM) grids has been satisfactorily developed using concentrated HF. Samples with different thicknesses have been analyzed by Raman spectroscopy, TEM, atomic force microscopy (AFM), and their photoluminescence properties have been evaluated. We demonstrated the presence of single-, bi- and few-layered WS2 on as-grown samples. It is well known that the electronic structure of these materials is very sensitive to the number of layers, ranging from indirect band-gap semiconductor in bulk phase to direct band-gap semiconductor in monolayers. This method has also proved successful in the synthesis of heterogeneous systems of MoS2 and WS2 layers, thus shedding light on the controlled production of hetero-layered devices out of transition metal chalcogenides.ACS Nano 05/2013; · 12.06 Impact Factor