Lithographically-defined strain control in atomically-thin semiconductors

Frontier quantum science calls for a large-scale deployment of solid-state artificial atoms, or quantum dots (QDs). But the progress has been limited due to the lack of simultaneous control of a material’s bandgap spatially and in energy. Here, we present a new approach based on lithographically-defined strain to achieve control of both the spatial position and bandgap energy in atomically-thin semiconductors. In our method, we first suspend a monolayer over a nanoscale cavity in the substrate; we then deform the layer using high-pressure gas, atomic force microscopy or thermal molding. With an optimized new process, we have produced localized biaxial strain down to 40-nm widths at defined positions in a WSe2 monolayer and in other atomically-thin semiconductors. Tensile strains up to 3.5% have been achieved by appropriate design of the cavity depth and can be maintained without any external pressure or voltage. Because of the strain-induced reduction in the bandgap, these QDs exhibit emission peaks spectrally separated from the intrinsic peaks by more than 100 meV. We discuss potential applications of such localized QD structures in 2D semiconductors.