Strong substrate strain effects in multilayered WS2 revealed by high-pressure optical measurements

TL;DR

This study combines theoretical calculations and high-pressure optical measurements to investigate how substrate-induced strain affects the electronic and optical properties of multilayered WS2, revealing significant strain effects and potential for flexible applications.

Contribution

It provides a comprehensive analysis of strain effects on WS2's optical properties using combined experimental and theoretical approaches, highlighting large in-plane stress gauge factors.

Findings

WS2 remains adhered to substrates up to -0.6% compressive strain.

Large in-plane stress gauge factor of 24 meV/GPa for WS2 monolayers.

Pressure induces a direct-to-indirect bandgap transition in monolayer WS2.

Abstract

The optical properties of two-dimensional materials can be effectively tuned by strain induced from a deformable substrate. In the present work we combine first-principles calculations based on density functional theory and the effective Bethe-Salpeter equation with high-pressure optical measurements in order to thoroughly describe the effect of strain and dielectric environment onto the electronic band structure and optical properties of a few-layered transition metal dichalcogenide. Our results show that WS2 remains fully adhered to the substrate at least up to a -0.6% in-plane compressive strain for a wide range of substrate materials. We provide a useful model to describe effect of strain on the optical gap energy. The corresponding experimentally-determined out-of-plane and in-plane stress gauge factors for WS2 monolayers are -8 and 24 meV/GPa, respectively. The exceptionally large in-plane gauge factor confirm transition metal dichalcogenides as very promising candidates for flexible functionalities. Finally, we discuss the pressure evolution of an optical transition closely-lying to the A exciton for bulk WS2 as well as the direct-to-indirect transition of the monolayer upon compression.