Strain Engineering of Transition Metal Dichalcogenides: A Combined First-Principles and Experimental Study

Abstract

Strain engineering is a powerful tool for tuning the electronic and optical properties of two-dimensional transition metal dichalcogenides (TMDs). This work presents a combined computational and experimental investigation of strain-induced band structure modulation in monolayer group-VI TMDs. First-principles density functional theory (DFT) calculations are performed for MoS2, MoSe2, MoTe2, WS2, and WSe2 under biaxial strains from -10% to +10%, revealing systematic trends in bandgap evolution according to transition metal and chalcogen elements, as well as strain classification (compressive or tensile). Among these materials, WS2 exhibits the strongest bandgap tunability, while sulfide-based TMDs demonstrate consistently strain tunability factors compared to their selenide and telluride counterparts. Across materials, the strain-induced bandgap tunability is dominated by conduction-band modulation, with significantly weaker valence-band strain tunability. Complementary uniaxial tensile strain experiments are conducted for WS2 using both elongation and bending techniques, probing optical bandgaps through photoluminescence (PL) spectroscopy. Using the bending method, a maximum A-exciton energy shift of -48.3meV is achieved; another bending experiment yields a maximal gauge factor of -19.62meV/%. These results clearly establish the viability of strain-induced band structure modulation of monolayer WS2, validating trends predicted by first-principles calculations. Finally, guided by the computational and experimental findings, a WS2/MoSe2 heterostructure is proposed as a promising platform for strain-tunable optoelectronic devices, leveraging the favorable band alignment and large tunability difference between materials. This structure exhibits promising strain tunability under both compressive and tensile strains, for both electron and hole carriers. Overall, this work provides a thorough fundamental overview of strain engineering in TMD monolayers, with direct implications for the design of flexible and tunable nanoscale devices.