High pressure Raman study of layered Mo _0.5 W _0.5 S ₂ ternary compound

Abstract

Ternary two-dimensional (2D) transition metal dichalcogenide compounds exhibit a tunable electronic structure allowing for control of the interlayer and the intralayer atomic displacement to efficiently tune their physical and electronic properties. Using a diamond anvil cell, hydrostatic pressure was applied to Mo 0.5 W 0.5 S 2 up to 40 GPa in order to study the optical phonon vibrational modes. Analysis of the high-pressure Raman spectra shows that the two in-plane E 2g modes resembling that of pristine MoS 2 and WS 2 , as well as disorder-activated longitudinal acoustic phonon mode, are hardened and suppressed as pressure increases. The two A 1g modes of the ternary compound that resemble the A 1g modes of pristine MoS 2 and WS 2 , displayed similar Raman shifts to the pristine compounds as pressure increases. A Raman peak at 470 cm −1 that is close to A 1g peaks emerges at ∼8 GPa, which represents a disorder-activated pressure-induced out-of-plane Raman mode observed only in the ternary compound under high pressure. At pressures above ∼30 GPa, a Raman peak at approximately 340 cm −1 is observed, signifying additional disorder-activated vibration mode. Our results reveal the enhanced interactions in the structural and vibrational behavior of the MoS 2 and WS 2 domains in the Mo 0.5 W 0.5 S 2 compound under hydrostatic pressure. These results could have implications in understanding the electronic, optical, and structural properties of the new 2D ternary compound materials under extreme mechanical conditions.

Determining alloy composition in MoxW(1 − x)S2 from low wavenumber Raman spectroscopy

“…Two‐dimensional (2D) materials are considered to have a remarkable potential for applications in future electrical and optoelectronic devices. Of these materials, the semiconducting transition metal dichalcogenides (TMDs) are of particular interest for their tunable mechanical and electronic properties …”

“…These ternary 2D compounds exhibit different electronic properties depending on their compositions . Within the bulk 2D alloy family, the most explored one is Mo x W (1 − x ) S 2 , for which the Raman scattering, piezoreflectence, reflectance, and scanning transmission electron microscopy have been investigated.…”

Pressure‐Induced Photoluminescence Adjustment and Lattice Disorder in Monolayer WSe2

“…The A 1 ′ mode originates from transverse vibration of Se−Se atoms and the E′ mode originates from longitudinal vibration of W−Se atoms in opposite directions; they correspond to the A 1g and E 1 2g modes in bulk WSe 2 , respectively . The LA(M) mode is the longitudinal acoustic phonon at the M symmetry point in the Brillouin zone, it is usually activated by lattice structural disorder …”

“…[22] The LA(M) mode is the longitudinal acousticp honon at the Ms ymmetry point in the Brillouin zone, [39,[42][43][44] it is usuallya ctivated by lattice structural disorder. [42][43][44][45][46][47][48][49] From the Raman spectra at 0t o3 1.37 GPa, shown in Figure 4, we can see the LA(M) ando ther second order vibrations give ar elatively weak intensity initially,b ut that as the pressure increases the intensity of the LA(M) mode clearly grows.A ll other main Raman peaks give ab roader width at high pressures;t hey are extracted by Lorentz profile function fittings and the pressure evolution of peak positions are summarized. We noticed that the E' vibration abates after the sample was sealed in DAC with pressure applied, and becomes broader after around1 0GPa.…”

Synthesis and applications of multinary layered metal chalcogenide nanomaterials

“…nanosheet was performed by Akinwande and coworkers. [89] It was concluded that there are some new appearing peaks with the increasing of pressure to a certain GPa. For instance, a new peak at 470 cm -1 was only observed in the alloyed Mo0.5W0.5S2 nanosheet but not in the pristine MoS2 and WS2 nanosheet, which can be assigned to the disorder-activated outof-plane Raman mode resulted from the pressure.…”