Rapid annealing of strain-mediated elastic domains in MoS₂ revealed using coherent x-rays

MoS₂ is a 2D material with a wide variety of applications in electronics, optics, sensing, and more. It is one of several transition metal dichalcogenides (MoS₂, WS₂, MoSe₂, etc.).  These materials have versatile properties arising from their distinct van der Waals bonding, reminiscent of graphene. Many of the promising applications of these materials require angstrom thick films and flakes. These are often created using repeated mechanical exfoliation, reducing bulk crystals to the appropriate thickness. X-rays are uniquely suited to probing the residual strain created by this mechanically intensive synthesis method.

In this work, we use nanoscale x-ray diffraction to reveal a complex network of elastic domains created by a series of defects created by residual strain in the crystal. Upon gentle heating to 56 °C, we observe a dramatic change in the crystal diffraction pattern, far reported phase transformation in MoS₂. We show this transition is reversable, but results in a rapid annealing of the residual strain in the crystal. This work reveals more about the rich physics that underpins the unique properties of 2D materials such as graphene and transition metal dichalcogenides, and it paves the way for improved synthesis and novel devices from these materials.