Progressive Micromodulation of Interlayer Coupling in Stacked WS/WSe Heterobilayers Tailored by a Focused Laser Beam.

When a vertically stacked heterobilayer comprising of a WSe monolayer on a WS monolayer is first fabricated, the heterobilayer behaves like two independent monolayers because of the presence of a large interlayer separation. However, after the stacked heterobilayer is subjected to a focused laser treatment, the interlayer separation between the two monolayers becomes progressively reduced which transforms the WS/WSe heterostructure from the noncoupling to the strongly coupling regime. This strong coupling induces the charge transfer between two layers and thus lowers the exciton recombination rate in the individual layer. This changes the optical properties of the heterobilayer from a fluorescence-active species into one where the fluorescence is quenched. The focused laser beam scanning method is therefore able to serve as a localized annealing tool to progressively modulate the interlayer separation and enable the micropatterning of the heterobilayer to achieve distinct regions with different degrees of fluorescence quenching. Systematic studies are carried out to gain an insight into the mechanism involved in the onset of the interlayer coupling in the material. Our method is also successfully extended to a WS/WS homobilayer structure.