Atomic-scale solid-gas interface (SGI) dynamics remain elusive due to transient intermediates, complex interfacial environments, and challenges of real-time characterization. Using an environmental transmission electron microscopy cell as a microreaction chamber combined with atomic-resolution in-situ imaging, here we directly visualize SGI reactions at the interface of transition metal oxidate WO2.72 nanowire under reactive gas environments. We reveal that initial SGI interactions trigger surface restructuring into a dual-layer configuration, consisting of an uppermost amorphous layer and an underlying lattice-distorted condensed region. The amorphous surface layer acts as a quasi-liquid precursor reservoir that promotes reversible crystalline-amorphous transformations and short-range ordering for critical nucleus formation, while the roughened, defect-rich subsurface interface provides energetically favorable sites for WS2 nucleation and vertical growth. Furthermore, in-situ atomic-scale observations of MoS2 nucleation and growth via SGI reactions demonstrate the generality of this mechanism. The atomistic processes governing interfacial reconstruction and nucleation are further corroborated by theoretical calculations. Our results establish a dual-layer-mediated reconstruction pathway during SGI reactions, overturning the conventional view of atomically sharp and static reaction fronts. Moreover, these findings provide insights into multistep phase-transition-governed WS2 nucleation and growth, enabling controlled synthesis of 2D WS2 and MoS2 toward atomic-scale manufacturing.
© 2026. The Author(s).