Strain-controlled Quantum Dots in Atomically-Thin Semiconductors

The creation of laterally confined 0D structures in 2D van-der-Waals semiconductor layers opens many new possibilities for control of electronic properties and the localization of excitations. One approach to this challenge is to grow small islands of 2D materials. But this scheme is difficult to achieve site controllability and also creates edge states that must be passivated. Alternatively achieving lateral confinement, we present a novel method to produce a highly localized strain field in the layer, and describe the resulting change in the local optical band gap of the material: We first suspend a monolayer over a nanoscale cavity in the substrate, then deform the layer using high pressure gas. The strain profile is frozen in and maintained when the monolayer adheres to the surface of the cavity. Applying our method to a monolayer WSe2, we demonstrate controlled biaxial strain up to 2.8%, localized within a 250-nm width and produced at various defined positions on chip. The resulting reduction in the local bandgap is distributed symmetrically in space, yielding maximal red shifts in photoluminescence energy up to 200 meV, observable both under ambient conditions and at low temperature.