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

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 MoTe 2 is an excellent candidate phase change material. We identify a range from 0.3 to 3% for the tensile strains required to transform MoTe 2 under uniaxial conditions at room temperature. The potential for mechanical phase transitions is predicted for all six studied compounds.

Electronic and Optoelectronic Applications Based on 2D Novel Anisotropic Transition Metal Dichalcogenides

“…Researches based on Raman spectroscopy, polarization‐resolved reflectance spectroscopy, and photoluminescence spectroscopy have demonstrated the strong anisotropic characteristics of these materials 31, 32, 33. In addition to their anisotropic properties, these materials have many other fascinating properties.…”

Quantum Effects and Phase Tuning in Epitaxial Hexagonal and Monoclinic MoTe2 Monolayers

“…[22] The large difference in electrical properties between 2H and 1T' (Td) phases of MX 2 further makes them promising for phase-change electronics. [23,24] Therefore, tuning and stabilizing the different phases of MX 2 can be of great scientific and application relevance.Among the various TMDs, MoTe 2 takes a special place as there is a small energy difference between its 2H and 1T' phases (~ 43meV per formula unit [5] ). The hexagonal phase of MoTe 2 is slightly more stable than 1T' MoTe 2 under ambient conditions, while the latter becomes more favorable at high temperature and/or under 3 tensile strain.…”

“…The hexagonal phase of MoTe 2 is slightly more stable than 1T' MoTe 2 under ambient conditions, while the latter becomes more favorable at high temperature and/or under 3 tensile strain. [5,24] In any case, due to the small energy difference between the two structures, there is a high chance for one to obtain samples containing coexisting phases or to purposely tune the structure of MoTe 2 crystal by applying external constraints. This would lead to many new applications of the TMD thin films.…”

“…[1,2,[3][4][5][6][7] The 2H phase is most common including, for example, metal disulfides (MS 2 ) and diselenides (MSe 2 ), which are direct gap semiconductors for monolayer (ML) thin films. [1,8] They have attracted extensive research attention in recent years due to their appeals in microelectronic, optoelectronic, spin and valley electronic applications.…”

“…Among the various TMDs, MoTe 2 takes a special place as there is a small energy difference between its 2H and 1T' phases (~ 43meV per formula unit [5] ). The hexagonal phase of MoTe 2 is slightly more stable than 1T' MoTe 2 under ambient conditions, while the latter becomes more favorable at high temperature and/or under 3 tensile strain.…”