In Situ Single‐Atom Decoration of Transition Metal Dichalcogenides by Millisecond Flash Thermal Synthesis Toward High Performance Room Temperature Chemiresistors

ABSTRACT Transition metal dichalcogenides (TMD) are attractive for adsorption‐driven reactions, yet their activity is strongly site‐dependent. Activity is concentrated at edge motifs, whereas most exposed area resides on inert basal planes. Dual‐site designs that enrich edges while activating basal planes with catalysts remain challenging to realize without coarsening and metal aggregation during thermal processing. Here, an intense pulsed light‐driven flash thermal synthesis route is demonstrated that directly converts ammonium tetrathiomolybdate ((NH 4 ) 2 MoS 4 ) into few‐layer, edge‐rich MoS 2 nanoflakes (FTS‐MoS 2 ) within 10 ms pulse in ambient‐air. Ultrafast photothermal shock (1192–1811°C; ∼10 5 /10 4 °C s − 1 heating/cooling rates) suppresses in‐plane coarsening and out‐of‐plane stacking, while Pt, Ir, or Au single atoms are uniformly anchored on MoS 2 via rapid metal‐sulfur coordination without aggregation. As a proof‐of‐concept, FTS‐MoS 2 exhibits a 23.6‐fold higher NO 2 response at 5 ppm than solvothermally synthesized MoS 2 . Pt single atom functionalization (FTS‐Pt SA ‐MoS 2 , 1.2 wt%) further boosts the response by 22.8‐fold versus pristine FTS‐MoS 2 and achieves 100.8% response toward 400 ppb NO 2 at room temperature. Density functional theory supports enhanced NO 2 adsorption and charge transfer on FTS‐Pt SA ‐MoS 2 . With a low electrical energy input (8.6 kJ g −1 ) and scalable irradiation, ultrafast FTS enables industrially relevant active‐site and single‐atom engineering in TMDs for high‐performance gas sensors.