Thickness Dependence of Superconductivity in Ultrathin NbS2

We report a systematic study of thickness-dependent superconductivity and carrier transport properties in exfoliated layered 2H-NbS2. Hall-effect measurements reveal 2H-NbS2 is a p-type metal with hole mobility of 1–3 cm2 V−1 s−1. The superconducting transition temperature is found to decrease with thickness. However, we find that superconductivity is suppressed due to disorder resulting from the incorporation of atmospheric oxygen. Cross-section transmission electron microscope imaging reveals a chemical change of NbS2 in the ambient, resulting in the formation of amorphous oxide layers sandwiching crystalline layered NbS2. Though few-nm-thick 2H-NbS2 completely converts to amorphous oxide in the ambient, PMMA encapsulation prevents further chemical change and preserves superconductivity in thicker samples.