Infrared study of the pressure-induced isostructural metallic transition in Mo$_{0:5}$W$_{0:5}$S$_{2}$

TL;DR

This study investigates how applying high pressure affects the lattice vibrations and electronic properties of Mo0.5W0.5S2, revealing a transition from semiconductor to metal at 18 GPa through infrared spectroscopy.

Contribution

First infrared transmission measurements on Mo0.5W0.5S2 under high pressure, identifying phonon behavior and the pressure-induced isostructural semiconductor-to-metal transition.

Findings

Infrared-active phonons classified at ambient conditions.

Lattice dynamics and free carrier density evolve with pressure.

Semiconductor-to-metal transition occurs above 18 GPa.

Abstract

Ternary compounds of Transition Metal Dichalcogenides are emerging as an interesting class of crystals with tunable electronic properties, which make them attractive for nano-electronic and optoelectronic applications. Among them, Mo$_x$W$_{1-x}$S$_2$ is one of the most studied alloys, due to the well-known, remarkable features of its binary constituents, MoS$_2$ and WS$_2$. The band-gap of this compound can be modelled varying Mo and W percentages in the sample, and its vibrational modes result from a combination of MoS$_2$ and WS$_2$ phonons. In this work, we report transmission measurements on a Mo$_{0:5}$W$_{0:5}$S$_2$ single crystal in the far-infrared range. Absorbance spectra collected at ambient conditions enabled, for the first time, a classification of the infrared-active phonons, complementary to Raman studies. High-pressure measurements allowed to study the evolution of both the lattice dynamics and the free carrier density up to 31 GPa, indicating the occurrence of an isostructural semiconductor-to-metal transition above 18 GPa.