The interplay of charge-density wave (CDW) and superconductivity is a key issue in low-dimensional materials, whereas it has yet to be clarified even in simple two-dimensional materials such as monolayer transition-metal dichalcogenide. We fabricated a monolayer 1H-${\mathrm{NbS}}_2$ film on bilayer graphene/SiC(0001) by combining the molecular-beam epitaxy and topotactic chemical reaction, and investigated the electronic structure by angle-resolved photoemission spectroscopy in collaboration with first-principles calculation. We found that although the Fermi surface of monolayer 1H-${\mathrm{NbS}}_2$ consists of large hole pockets centered at the $\mathrm{\Gamma }$ and K points similarly to isostructural monolayer 1H-${\mathrm{NbSe}}_2$, the shape of the pocket at the K point is more triangular shaped in ${\mathrm{NbS}}_2$. Scanning tunneling microscopy and transport measurements at low temperature show no evidence for CDW or superconductivity in ${\mathrm{NbS}}_2$ in stark contrast to ${\mathrm{NbSe}}_2$. The degradation of CDW in ${\mathrm{NbS}}_2$ is likely caused by the suppression of quasiparticle scattering between the hot spots connected by the $2/3\mathrm{\Gamma }\mathrm{M}$ nesting vector associated with the change in the shape of the K-centered pocket. The present results suggest the highly susceptible nature of CDW and superconductivity to the subtle change of the fermiology in Nb dichalcogenides.

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• Electronic structure
• First-principles calculations
• Transition metal dichalcogenides
• Angle-resolved photoemission spectroscopy
• Molecular beam epitaxy
• Scanning tunneling microscopy