Atomic dynamics of solid-gas interfaces unveil dual-layer formation and WS₂ nucleation driven by multistep phase-transition.

Abstract

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 WO_2.72 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.