Noncatalytic Synthesis of High‐Density and Small‐Diameter WS 2 Nanotubes

A substrate‐engineered, noncatalytic strategy is developed for the controlled synthesis of high‐density WS 2 nanotubes by decoupling nanowire precursor growth from vapor‐phase sulfuration. The process enables precise structural control and yields dense nanotube networks with high crystallinity. Systematic investigations across planar and fibrous substrates reveal that nucleation is governed by surface‐energy variations, allowing uniform growth on both flat and curved architectures without the need for metal catalysts. The transformation from solid nanowires to hollow nanotubes is directly visualized along individual structures, providing insight into the structural evolution during sulfuration. The approach is further extended to high‐surface‐area fiber substrates, demonstrating its scalability. As a proof of concept, a two‐terminal device based on individual WS 2 nanotubes exhibits clear photoresponse with a responsivity of 0.36 A/W, an external quantum efficiency of 83.6%, and a specific detectivity of 1.16 × 10 10 Jones, confirming the optoelectronic functionality of the catalyst‐free material. These results establish a scalable route for high‐quality WS 2 nanotubes and highlight their potential for integrated optoelectronic applications.