Strain Control of Exciton–Phonon Coupling in Atomically Thin Semiconductors

Abstract

Semiconducting transition metal dichalcogenide (TMDC) monolayers have exceptional physical properties. They show bright photoluminescence due to their unique band structure and absorb more than 10% of the light at their excitonic resonances despite their atomic thickness. At room temperature, the width of the exciton transitions is governed by the exciton-phonon interaction leading to strongly asymmetric line shapes. TMDC monolayers are also extremely flexible, sustaining mechanical strain of about 10% without breaking. The excitonic properties strongly depend on strain. For example, exciton energies of TMDC monolayers significantly redshift under uniaxial tensile strain. Here, we demonstrate that the width and the asymmetric line shape of excitonic resonances in TMDC monolayers can be controlled with applied strain. We measure photoluminescence and absorption spectra of the A exciton in monolayer MoSe, WSe, WS, and MoS under uniaxial tensile strain. We find that the A exciton substantially narrows and becomes more symmetric for the selenium-based monolayer materials, while no change is observed for atomically thin WS. For MoS monolayers, the line width increases. These effects are due to a modified exciton-phonon coupling at increasing strain levels because of changes in the electronic band structure of the respective monolayer materials. This interpretation based on steady-state experiments is corroborated by time-resolved photoluminescence measurements. Our results demonstrate that moderate strain values on the order of only 1% are already sufficient to globally tune the exciton-phonon interaction in TMDC monolayers and hold the promise for controlling the coupling on the nanoscale.

Strain-tunable orbital, spin-orbit, and optical properties of monolayer transition-metal dichalcogenides

“…For the other TMDCs, the situation is similar, but for different strain amplitudes. Tuning the gap with uniaxial or biaxial strain consequently modifies the optical properties, such as the photolominescence spectrum, exciton-phonon coupling and circular dichroism [46,[82][83][84]. It has also been shown that strain applied to MoS 2based photodetectors can control the response time of the devices [49].…”

Dynamics and efficient conversion of excitons to trions in non-uniformly strained monolayer WS2

“…Physical properties of TMDCs change under mechanical strain 18 . In the simple case of constant uniaxial strain, the band-gap energy is reduced by 50 meV /% 19,20 and the phonon-assisted coupling is altered 20,21 . The band-gap reduction is twice higher, 100 meV /%, for uniform biaxial strain 22 .…”

Unveiling the Interfacial Effects for Enhanced Hydrogen Evolution Reaction on MoS2/WTe2 Hybrid Structures

“…Our results suggest that using low‐Schottky barrier contacts or 2D support materials whose Fermi level is closely aligned with 2D semiconducting catalysts are promising strategies for reducing E B . Recent advances in strain engineering of 2D TMDs have shown that their electronic band structure is sensitive to strain, and could be used to tune the contact resistance at semiconductor–metal interfaces. Some work has demonstrated that strain engineering can also be used to improve the HER activity of TMDs by modifying Δ G H .…”