Layer-dependent anisotropic structural evolution in 1T′-ReSe2: Pressure-induced phonon dynamics

Rhenium diselenide (ReSe2) presents pronounced lattice anisotropy and relatively weak interlayer interactions, which can result in its superior compressibility under pressure, as compared to other two-dimensional (2D) transition metal dichalcogenides (TMDs). Here, we employed diamond anvil cells (DAC) to apply stress fields up to 15.90 GPa, unveiling the intricate relationships among layer numbers, anisotropic properties, and specific structural variations in ReSe2. A rapid decrease in the anisotropic parameter σ from the Eg-like modes can be observed at 6-8 GPa. It was found that the layers (3, 10, and 17 L) could be correlated with the ratio of the ab-plane to c-axis components (Iab/Ic), ultimately identifying the anisotropic structural deformation as either hydrostatic strain or uniaxial strain. Moreover, the pressure-dependent band gap analysis elucidated the interlayer interactions along the c axis. The present findings deepen understanding of ReSe2's structural response to stress field and facilitating advancements in strain-based device applications.