Synthesis of metallic mixed 3R and 2H NbS nanoflakes by chemical vapor deposition.

In this work, we report the synthesis and characterization of mixed phase NbS nanoflakes prepared by chemical vapor deposition. The as-grown samples show a high density of flakes (thickness ∼50 nm) that form a continuous film. Raman and X-ray diffraction data show that the samples consist of both 2H and 3R phases, with the 2H phase containing a high concentration of Nb interstitials. These Nb interstitials sit in between the NbS layers to form NbS. Cross-sectional Energy Dispersive Spectroscopy analysis with transmission electron microscopy suggests that the 2H NbS region is found in thinner flakes, while 3R NbS is observed in thicker regions of the films. The evolution of the phase from 2H NbS to 3R NbS may be attributed to the change of the growth environment from Nb-rich at the start of the growth to sulfur-rich at the latter stage. It was also found that the incorporation of Nb interstitials is highly dependent on the temperature of the NbCl precursor and the position of the substrate in the furnace. Samples grown at high NbCl temperature and with substrate located closer to the NbCl source show higher incorporation of Nb interstitials. Electrical measurements show linear I-V characteristics, indicating the metallic nature of the NbS film with relatively low resistivity of 4.1 × 10Ω cm.