Large trion binding energy in monolayer WS2 via strain-enhanced electron–phonon coupling

Abstract Transition metal dichalcogenides and related layered materials in their monolayer and a few layers thicknesses regime provide a promising optoelectronic platform for exploring the excitonic- and many-body physics. Here, we have investigated the effects of nanoparticle-induced local strain on the optical properties of exciton, X 0 , and trion, X − , in monolayer WS 2 . Biaxial tensile strain up to 2.0% was quantified and verified by monitoring the changes in three prominent Raman modes of WS 2 : $${{{{\rm{E}}}}}_{2g}^{1}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>g</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> (Γ), A 1 g , and 2LA(M). We obtained an increase of 34 meV in X − binding energy with an average tuning rate of 17.5 ± 2.5 meV/% strain across all the samples irrespective of the surrounding dielectric environment of monolayer WS 2 and the sample preparation conditions. Strain-induced linewidth broadening and deformation potentials of both X 0 and X − emission elucidate that X − binding energy increases due to strain-enhanced electron–phonon coupling. This work holds relevance for future X − -based nano-opto-electro-mechanical systems and devices.