Mechanical and thermal properties of h-MX₂ (M = Cr, Mo, W; X = O, S, Se, Te) monolayers: A comparative study

Using density functional theory, we obtain the mechanical and thermal properties of MX2 monolayers (where M = Cr, Mo, W and X = O, S, Se, Te). The Γ-centered phonon frequencies (i.e., A1, A2″, E′, and E″), relative frequency values of A1, and E′ modes, and mechanical properties (i.e., elastic constants, Young modulus, and Poisson's ratio) display a strong dependence on the type of metal and chalcogenide atoms. In each chalcogenide (metal) group, transition-metal dichalcogenides (TMDCs) with W (O) atom are found to be much stiffer. Consistent with their stability, the thermal expansion of lattice constants for TMDCs with O (Te) is much slower (faster). Furthermore, in a heterostructure of these materials, the difference of the thermal expansion of lattice constants between the individual components becomes quite tiny over the whole temperature range. The calculated mechanical and thermal properties show that TMDCs are promising materials for heterostructures.