Biaxial Strain Engineering of MoSe2/WSe2 Heterostructures

Transition metal dichalcogenides (TMDs) have been studied intensely for their semiconducting properties that emerge at the atomically thin level. Van der Waals (vdW) heterostructure stacking of MoSe2 and WSe2 monolayers creates a type-II heterojunction which encourages the formation of strongly bound interlayer excitons due to the reduction in dielectric screening and increase in coulombic interaction strength [4, 5]. Interlayer excitons forming within the MoSe2/WSe2 heterobilayer have been shown to have increased lifetimes, large binding energies, and permanent dipole moments as opposed to “intralayer” excitons [5]. While TMD heterobilayers have undergone intense studies to better understand interlayer excitons, the effect of biaxial strain on these heterostructures are still unknown. Here we have designed and built a versatile biaxial straining platform for in situ Raman and Photoluminescence measurements of strained films. A thin polymer substrate (PET) is indented symmetrically by the platform to induce biaxial tensile strain via the change in the curvature of the substrate. The system is calibrated by mapping the location of features on the PET substrate as a function of indenter displacement. In this work, we will investigate strain induced PL and Raman peak shifting on biaxially strained MoSe2/WSe2 heterobilayers exfoliated from low point defect density bulk crystals which may correspond to excitonic emissions. From these observations, we may better understand the tunability of the interlayer exciton peak emission as a function of mechanical strain which may be useful for applications in enhancing properties like band gap and optical density in optoelectronic devices such as light emitters, photodetectors and photovoltaic cells.<br/><br/>References:<br/>[1] Carrascoso et al., Nano Mater. Sci., in press (2021).<br/>[2] Blundo et al., Appl. Phys. Rev. 8, 021318 (2021).<br/>[3] Peng et al. Light: Science & Applications 9:190 (2020).<br/>[4] Calman, NanoLett., 20, 1869−1875 (2020).<br/>[5] Zheng et al., arXiv: 1911.00087 (2019).