Operando XPS monitoring of MoS₂ nanoflake nucleation on carbon nanotubes via integrated CVD-MBE

Abstract

Hybrid nanostructured materials have attracted significant attention due to their robust multifunctional properties. Among them, 2D@1D nanostructures are particularly promising. The rational design of such heterostructures requires synthesis routes that combine interfacial cleanliness, structural control, and real-time mechanistic insight. In this study, we report a solvent-free strategy for growing high-crystalline MoS₂ nanoflakes on single-walled carbon nanotubes (SWCNTs) using an integrated chemical vapor deposition/molecular beam epitaxy (CVD/MBE) platform coupled with operando X-ray photoelectron spectroscopy. This setup enables continuous monitoring of nucleation and growth under ultra-high vacuum, and allows atomically sharp interfaces. We achieved uniform coverage of SWCNT sidewalls with MoS₂ nanoflakes about 4-5 layers thick (~4 nm) and spanning areas exceeding 100 nm². Operando XPS uncovers a stepwise growth pathway from sulfur adsorption on CNTs to Mo–S₃ cluster formation, and the subsequent transformation into crystalline 2H-MoS₂ domains. Complementary in-situ XPS validation confirms the high crystallinity, stoichiometry, and van der Waals interfacial coupling of the final heterostructure. The resulting heterostructures exhibit abundant exposed edge sites, strong interfacial coupling, and p-doping of SWCNTs without covalent disruption. This work establishes a versatile route for precision engineering of hybrid nanostructures while providing insights into their atomistic growth mechanisms.