Symmetry-broken MoS₂ nanotubes through sequential sulfurization of MoO₂ nanowires

Transition metal dichalcogenide (TMD) nanotubes are emerging quantum materials with distinctive symmetry-breaking properties, offering significant potential for energy conversion technologies. However, the direct synthesis of crystalline MoS₂ nanotubes remains challenging due to limited understanding of their high-temperature growth mechanisms. Here, we present a robust and controllable strategy for the direct growth of crystalline MoS₂ nanotubes with well-defined tubular morphology and high structural uniformity. This approach features two key innovations: first, the controlled introduction of hydrogen reduces MoO₃ into one-dimensional (1D) tetragonal MoO₂ (space group I4/m) chains via a vapor-liquid-solid (VLS) mechanism; second, precise temperature zoning ensures timely sulfur vapor infusion for complete sulfurization. The intermediate MoO₂ phase, with its singular crystallographic orientation, acts as an ideal template for nanotube formation. Tellurium (Te) serves as a fluxing mediator to promote the formation of uniform MoO₂ nanowires, which are subsequently converted into MoS₂ nanotubes. By systematically tuning the hydrogen concentration, we reveal its critical role in directing product morphology. The resulting MoS₂ nanotubes exhibit pronounced symmetry breaking and significant bulk photovoltaic performance, achieving a photoresponsivity of 510 A cm^-2 under 1.88 × 10⁴ W cm^-2 illumination. This work advances both the fundamental understanding of nanotube growth and the development of symmetry-engineered optoelectronic materials.