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      Structural phase transitions in two-dimensional Mo- and W-dichalcogenide monolayers.

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          Abstract

          Mo- and W-dichalcogenide compounds have a two-dimensional monolayer form that differs from graphene in an important respect: it can potentially have more than one crystal structure. Some of these monolayers exhibit tantalizing hints of a poorly understood structural metal-to-insulator transition with the possibility of long metastable lifetimes. If controllable, such a transition could bring an exciting new application space to monolayer materials beyond graphene. Here we discover that mechanical deformations provide a route to switching thermodynamic stability between a semiconducting and a metallic crystal structure in these monolayer materials. Based on state-of-the-art density functional and hybrid Hartree-Fock/density functional calculations including vibrational energy corrections, we discover that MoTe2 is an excellent candidate phase change material. We identify a range from 0.3 to 3% for the tensile strains required to transform MoTe2 under uniaxial conditions at room temperature. The potential for mechanical phase transitions is predicted for all six studied compounds.

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          Most cited references 37

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              Is Open Access

              Atomically thin MoS2: A new direct-gap semiconductor

              The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N = 1, 2, ... 6 S-Mo-S monolayers have been investigated by optical spectroscopy. Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure. With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 0.6 eV. This leads to a crossover to a direct-gap material in the limit of the single monolayer. Unlike the bulk material, the MoS2 monolayer emits light strongly. The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 1000 compared with the bulk material.
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                Author and article information

                Journal
                Nat Commun
                Nature communications
                2041-1723
                2041-1723
                2014
                : 5
                Affiliations
                [1 ] Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA.
                [2 ] 1] Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA [2] Department of Applied Physics, Stanford University, Stanford, California 94305, USA.
                Article
                ncomms5214
                10.1038/ncomms5214
                24981779

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