Microsphere Probe-Assisted Trapping and Enhancement of Interlayer Excitons in WSe2/MoSe2 Heterostructures under Ultralow Pressure

Interlayer excitons, bound states of electrons and holes residing in opposite layers of a heterostructure, are vital for the optical properties of van der Waals semiconducting heterostructures. Effective mechanical control of interlayer excitons in van der Waals heterostructures is crucial for fundamental research and optoelectronic applications. However, existing techniques face challenges in simultaneously achieving high-precision mechanical loading on microscale heterostructure samples and detecting enhanced excitonic response therein. In this work, we demonstrate a dynamic control of intralayer and interlayer excitons in MoSe2/WSe2 heterostructures by employing a mechanical-optical synchronous characterization technique with a designed "microsphere probe". By combining microsphere-induced pressure with substrate engineering, we demonstrate precise (resolution: 0.1 μm displacement, 3 μN force control) and localized (∼1 μm2) stress control in MoSe2/WSe2 heterostructures, enabling effective manipulation of intralayer excitons. Highly controlled localized compressive (or tensile) stress is achieved on rigid Si/SiO2 (or flexible polyethylene terephthalate) substrates, as confirmed by the blue shift (or red shift) of the exciton emission in in situ photoluminescence spectroscopy. Remarkably, synergistic out-of-plane compression and in-plane tension induced by the microsphere-probe on flexible PET substrates enhance interlayer coupling of the MoSe2/WSe2 heterostructure, facilitating unambiguous observation of interlayer excitons at ultralow compressive stresses (∼0.1 GPa) at room temperature. These findings contribute to a better understanding of how mechanical modulation finely affects exciton formation and dynamic behavior, providing important guidance for developing advanced low-dimensional optoelectronic devices.