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

Abstract

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.

A review on mechanics and mechanical properties of 2D materials—Graphene and beyond

“…In disordered 2D systems, such as Mo1-xWxS2 alloy with randomly dispersed Mo and W at the metal atom cites of TMDs, disorder-activated Raman modes were observed in addition to the modes of pure end members [247,248]. More interestingly, some additional disorder-activated Raman modes denoted A * and A † were observed only under high pressure, ~8 GPa and ~30 GPa, respectively.…”

2D MoSe2 Structures Prepared by Atomic Layer Deposition

“…In contrast to graphene, monolayers of 2D TMDC possess a direct band gap that is crucial for optoelectronic applications . Additionally, the direct band gap can be easily tuned by either chemical composition or external stimuli, such as external fields or external pressure . Next to the optoelectronic applications, where a monolayer planar structure is necessary to employ, a layer of standing flakes, which possesses a large surface area, can be used in fields of a hydrogen evolution, a photodegradation of organic dyes or as electrodes in Li ion batteries …”

“…[3] Additionally, the direct band gap can be easily tuned by either chemical composition [6,7] or external stimuli, such as external fields [1] or external pressure. [8,9] Next to the optoelectronic applications, where a monolayer planar structure is necessary to employ, a layer of standing flakes, which possesses a large surface area, can be used in fields of a hydrogen evolution, [10,11] a photodegradation of organic dyes [12] or as electrodes in Li ion batteries. [13,14] In principle, TMDCs can be prepared in two ways, i.e., top-down and bottom-up techniques.…”

Origin of superconductivity in the Weyl semimetal WTe2 under pressure

“…This can be further justified by comparing with WS 2 , which has stable 2H phase in ambient condition. WS 2 does not undergo any structural phase transition up to 60 GPa [25] nor abrupt metallization.…”