Pressure-Modulated Conductivity, Carrier Density, and Mobility of Multilayered Tungsten Disulfide.

Tungsten disulfide (WS2) is a layered transition metal dichalcogenide (TMD) that differs from other two-dimensional (2D) compounds such as graphene due to its unique semiconducting, tunable-band-gap nature. Multilayered WS2 exhibits an indirect band gap Eg of ∼1.3 eV, along with a higher load-bearing ability that is promising for strain-tuning device applications, but the electronic properties of multilayered WS2 at higher strain conditions (i.e., static strain >12%) remain an open question. Here we have studied the structural, electronic, electrical, and vibrational properties of multilayered WS2 at hydrostatic pressures up to ∼35 GPa experimentally in a diamond anvil cell and theoretically using first-principles ab initio calculations. Our results show that WS2 undergoes an isostructural semiconductor-to-metallic (S-M) transition at approximately 22 GPa at 280 K, which arises from the overlap of the highest valence and lowest conduction bands. The S-M transition is caused by increased sulfur-sulfur interactions as the interlayer spacing decreases with applied hydrostatic pressure. The metalization in WS2 can be alternatively interpreted as a 2D to 3D (three-dimensional) phase transition that is associated with a substantial modulation of the charge carrier characteristics including a 6-order decrease in resistivity, a 2-order decrease in mobility, and a 4-order increase in carrier concentration. These distinct pressure-tunable characteristics of the dimensionalized WS2 differentiate it from other TMD compounds such as MoS2 and promise future developments in strain-modulated advanced devices.