Unexpected Rapid Strain Relaxation in Exfoliated MoS₂ near 56 °C Revealed by Nanoscale Coherent X-ray Diffraction

Transition metal dichalcogenides such as MoS₂ exhibit rich electronic and mechanical behavior governed by van der Waals bonding. In order to create the thin films needed for these applications, it is common to use mechanical exfoliation methods to thin the material to angstrom scale thicknesses. However, exfoliation-induced strain and its thermal relaxation remain poorly understood, despite their strong influence on device stability and performance [1].

X-rays are uniquely suited to probing strain in materials due to their high sensitivity to atomic periodicity. Using nanoscale X-ray diffraction, we tracked the local lattice strain in exfoliated MoS₂ during controlled heating. We observed a previously unreported structural relaxation near 56 °C, well below any known phase transition [2], marking a sharp reconfiguration of the strain landscape. The transition is reversible and occurs without chemical change, suggesting a thermally activated strain-relief mechanism driven by the unique van der Waals bonding and emergent twin defects. This finding offers new routes for low-temperature strain and defect engineering in one of the most studied materials of recent years.

 

[1] K. Yang et al., Advanced Science, p. e06488, Aug. 2025, doi: 10.1002/advs.202506488

[2] N. Bandaru et al., J. Phys. Chem. C, vol. 118, no. 6, pp. 3230–3235, Feb. 2014, doi: 10.1021/jp410167k