Interlayer reconstruction phase transition in van der Waals materials.

Van der Waals materials display rich structural polymorphs with distinct physical properties. An atomistic understanding of the phase-transition dynamics, propagation pathway and associated evolution of physical properties is essential for capturing their potential in practical technologies. However, direct visualization of the rapid phase-transition process is fundamentally challenging due to the inherent trade-offs among atomic resolution, field of view and imaging frame rate. Here we exploit a controllable current-driven phase transition and utilize in situ scanning transmission electron microscopy to visualize dynamic atomic rearrangements during the 2H-α to 2H-β transition in layered InSe. We identify a unique intralayer-splitting (unzipping) and interlayer-reconstruction (zipping) pathway, driven by an energy-cascading mechanism through which bond formation across the van der Waals gap facilitates bond cleavage in the covalent layers. We also observe current-direction-dependent asymmetric phase-transition propagation and attribute it to a temperature profile induced by the Peltier effect at the heterophase interface. These findings provide insights that are essential for designing tailored structural phase transitions in advanced technologies.