Biaxial Strain Engineering of Transition Metal Dichalcogenide Heterostructures

Van der Waals (vdW) heterostructure stacking of TMD monolayers with other TMD monolayers or organic molecules such as Tetracene have type-II band alignment which encourages the formation of strongly bound interlayer excitons due to the reduction in dielectric screening and increase in coulombic interaction strength. Interlayer excitons have been shown to have increased lifetimes, large binding energies, and permanent dipole moments as opposed to intralayer excitons. These heterostructures are atomically thin in nature which suggests they may be sensitive to mechanical strain which may alter material qualities such as bandgap. While such heterostructures have undergone intense studies to better understand interlayer excitons, the effects of biaxial strain on these interlayer excitons are still unknown. Heterostructures of organic and inorganic materials are particularly interesting because they open a new class of scalable heterostructures which also have interfacial tunability for device applications. 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 optoelectronic response through Raman and PL on biaxially strained organic-inorganic heterostructures made from CVD grown material and evaporated organic powders. From these observations, we may better understand the tunability of the interlayer exciton as a function of mechanical strain which may be useful for applications in enhancing properties like band gap and optical density in flexible optoelectronic devices such as light emitters, photodetectors and photovoltaic cells, enabling excitonic devices.