A Method Toward Fabricating Semiconducting 3R-NbS2 Ultrathin Films

Ultrathin NbS2 films were synthesized from sputter-deposited ultrathin Nb films on SiO2/Si and quartz substrates at 850 degrees C under sulfur vapor pressure. The structure and surface composition of the synthesized films were characterized by grazing incidence X-ray diffraction and Xray photoelectron spectroscopy. The films have rhombohedral 3R-NbS2 structure and are nearly stoichiometric. The optical bandgaps of ultrathin NbS2 samples were determined from ultraviolet visible-near infrared spectrometry to be in the range of similar to 0.43 to similar to 0.90 eV and indirect. This implies that the ultrathin NbS2 film is semiconducting and differs from the metallic nature of bulk NbS2. The Raman shifts show distinct Raman active modes that depend on film thickness. The simple growth method developed can be applied to other TMDCs in which the metal has a high oxide heat of formation.