The Role of Defects and Mechanical Deformations in Transition Metal dichalcogenides

In recent years, Van der Waals (2D) materials, have attracted increasing attention due to their distinctive physical properties. 2D materials, specifically the class of transition metal dichalcogenides (TMDC) possess a large density of defects that can govern many of their physical properties. In addition, as layered materials, they have been considered for flexible electronics as they can sustain strain higher than 10% without breaking down, although they are only 1-3 atom thick. In this talk I will present 2 different experimental observations where defects play a major role in the physical processes, with or without mechanical strain.

In the first experiment, we show the nature of gas sensing at low temperatures (<240K). We reveal the pure intrinsic behavior of the defects in MoS₂ (the Sulfur vacancies) and the influence of extrinsic O₂ molecules on the photoluminescence spectrum ^[1].

In the second experiment, I will show how we can apply non-uniform strain to a suspended WS₂ monolayer and alter the dynamics of excitons and trions. Surprisingly, we find that as we increase the non-uniformity of the strain, we are able to convert the excitons into trions with almost 100% efficiency without any electrostatic gating, due to the presence of defects in TMDC ^[2].

[1] Greben K, Arora S, Harats MG et al., Nano Letters, 20, 4, 2544-2550, 2020

[2] Harats MG et al., Nature Photonics, 14, 5, 324-329, 2020