Fig. 1. (a) The schematic diagrams of atomic arrangement of 2H_c- and 2H_a-MoS₂ structures, where the Mo and S atoms are represented by blue and yellow balls, respectively. (b) Pressure-dependent variations of lattice parameter a, intralayer S–S distance c, and Mo–S bond length d. (c) Bond angles θ and ψ as a function of pressure. (d) Interlayer distance t as a function of pressure.

Fig. 2. (a) Pressure-dependent unit volume of MoS₂ in both 2H_c and 2H_a phases. (b) Pressure-dependent relative Gibbs free energy of 2H_a- and 2H_c-MoS₂ phases. (c) Phase diagram of MoS₂ from 2H_c-to-2H_a as a function of thickness. The solid line is the dividing line.

Fig. 3. (a) The pressure-dependent energy gain of single Mo–S bond including bond stretching, bond angle distortion, and electrostatic interaction energies. (b) The pressure-dependent interlayer interaction energy of an S atom in 2H_c and 2H_a phases. (c) The metallization transition of MoS₂ as a function of layer number. The solid line is the dividing line. The inset is the pressure-dependent bandgaps for monolayer, bilayer, bulk 2H_c- and 2H_a-MoS₂.

Fig. 4. Phase diagram of MoS₂ under the condition of hydrostatic pressure. The blue line represents the boundary between 2H_c and 2H_a phases. There is no interlayer interaction in monolayer represented by 2H phase. The semiconductor to metal transition is separated by the red line, while the pale green region denotes semiconducting.

Table 1. Calculated transition pressure (in GPa) of two types of phase transitions of MoS₂ for different cases.