Phase and Defect Engineering of Transition Metal Dichalcogenides Via Carbon-Nanotube-Induced Photothermal Effect

Molybdenum disulfide (MoS₂), a representative transition metal dichalcogenide (TMD), exists in semiconducting 2H and metallic 1T phases; however, the chemically inert basal plane and intrinsically low conductivity of the stable 2H phase limit its sensing performance. To overcome these limitations, 1T-rich MoS₂-decorated single-walled carbon nanotube heterostructures, i.e., SWCNT@1T-rich MoS₂, were synthesized via flash-thermal shock (FTS), using SWCNTs as both conductive and photothermal supports. The intense pulsed light-driven FTS process enables ultrafast annealing, reaching temperatures up to 3047 K within 20 ms, which facilitates the direct growth of phase-tailored MoS₂ from ammonium tetrathiomolybdate ((NH₄)₂MoS₄) precursors on the SWCNT framework. By controlling the FTS temperature, systematic phase modulation of MoS₂ is achieved, spanning the 2H phase, mixed 1T-2H phases, and 1T-rich phases. Notably, at an extreme FTS temperature of 3047 K, a defect-rich and metastable SWCNT@1T-rich MoS₂ heterostructure is formed. Active charge transfer from the defect-rich MoS₂ to the SWCNTs network induces n-type doping, enhancing charge transport and consequently delivering excellent sensing performance toward NO₂ gas even at sub-ppm concentrations. Overall, these results demonstrate that FTS provides a scalable, ambient-condition platform for non-equilibrium phase and defect engineering of TMD hybrids, enabling ultrafast access to defect-rich metastable architectures and tunable interfacial electronic structures.