RESUMEN
Nonlinear optical responses in second harmonic generation (SHG) of van der Waals heterobilayers, Janus MoSSe/MoS2, are theoretically optimized as a function of strain and stacking order by adopting an exchange-correlation hybrid functional and a real-time approach in first-principles calculation. We find that the calculated nonlinear susceptibility, χ(2), in AA stacking (550 pm/V) becomes three times as large as AB stacking (170 pm/V) due to the broken inversion symmetry in the AA stacking. The present theoretical prediction is compared with the observed SHG spectra of Janus MoSSe/MoS2 heterobilayers, in which the peak SHG intensity of AA stacking becomes four times as large as AB stacking. Furthermore, a relatively large, two-dimensional strain (4%) that breaks the C3v point group symmetry of the MoSSe/MoS2, enhances calculated χ(2) values for both AA (900 pm/V) and AB (300 pm/V) stackings 1.6 times as large as that without strain.
RESUMEN
Using first-principle density functional calculations, we investigate electromechanical properties of two-dimensional MX2 (M = Mo, W; X = S, Se, Te) monolayers with the 1H and 1T structures as a function of charge doping for both electron and hole doping. We find that by increasing the atomic number, Z X, of X atoms (Z S < Z Se < Z Te), the work density per cycle of the MX2 monolayers are increased and decreased for the 1H and 1T structures, respectively. On the other hand, the work density per cycle of the WX2 monolayers are higher than that of the MoX2 monolayers for both the 1H and 1T structures. Therefore, WTe2 and WS2 monolayers for the 1H and 1T structures, respectively, have the best electromechanical performances in the MX2 compounds. In addition, the MX2 monolayers show a reversible strain up to 3%, which is higher than that of graphene (â¼1%). Our results provide an important insight into the electromechanical properties of the MX2 monolayers, which are useful for artificial muscles applications.
