Variation of the fundamental band gap nature in curved two-dimensional WS2

TL;DR

This study demonstrates how mechanical deformation via strain can induce a transition from direct to indirect band gap in WS2 monolayers, with implications for optoelectronic device engineering.

Contribution

It introduces a method to control the band gap nature in WS2 monolayers through strain induced by proton irradiation, expanding understanding of transition metal dichalcogenide electronic properties.

Findings

Strain causes direct-to-indirect band gap transition in WS2 MLs.

Curved WS2 MLs exhibit altered electronic properties under mechanical stress.

Similar phenomena observed in MoS2 and WSe2 monolayers.

Abstract

We report a strain-induced direct-to-indirect band gap transition in mechanically deformed WS2 monolayers (MLs). The necessary amount of strain is attained by proton irradiation of bulk WS2 and the ensuing formation of one-ML-thick, H2-filled domes. The electronic properties of the curved MLs are mapped by spatially- and time-resolved micro-photoluminescence revealing the mechanical stress conditions that trigger the variation of the band gap character. This general phenomenon, also observed in MoS2 and WSe2, further increases our understanding of the electronic structure of transition metal dichalcogenide MLs and holds a great relevance for their optoelectronic applications.