  Tuning the electronic properties of a material by subjecting it to strain
constitutes an important strategy to enhance the performance of semiconducting
electronic devices. Using local strain, confinement potentials for excitons can
be engineered, with exciting possibilities for trapping excitons for quantum
optics and for efficient collection of solar energy. Two-dimensional materials
are able to withstand large strains before rupture, offering a unique
opportunity to introduce large local strains. Here, we study atomically thin
MoS2 layers with large local strains of up to 2.5% induced by controlled
delamination from a substrate. Using simultaneous scanning Raman and
photoluminescence imaging, we spatially resolve a direct bandgap reduction of
up to 90 meV induced by local strain. We observe a funnel effect in which
excitons drift hundreds of nanometers to lower bandgap regions before
recombining, demonstrating exciton confinement by local strain. The
observations are supported by an atomistic tight-binding model developed to
predict the effect of inhomogeneous strain on the local electronic states in
MoS2. The possibility of generating large strain-induced variations in exciton
trapping potentials opens the door for a variety of applications in atomically
thin materials including photovoltaics, quantum optics and two-dimensional
optoelectronic devices.
