Structural and Electronic Properties of Mo _{1– x} Nb _x S ₂ Alloys: Insights from TERS and KPFM

The bandgap tunability of transition-metal dichalcogenide 2D materials is of interest in photonics and semiconductor applications for optimized control of photon emission and electron flow. The bandgap in MoS 2, direct or indirect, depends strongly on the number of layers of the flakes that can be exfoliated or grown by chemical vapor deposition (CVD). The bandgap can be further tuned via doping with other atoms within layered alloys. Here, we investigate the cosynthesis by salt-assisted CVD of Mo 1– x Nb x S 2 flakes. The role of the Nb dopant is examined using confocal and tip-enhanced Raman spectroscopy (TERS) in flakes grown with distinct contents of Nb. The Raman confocal and TERS spectra of the composite Mo 1– x Nb x S 2 show distinct behaviors depending on the Nb doping. Contact potential difference measurements further support a reduction of the work function of Mo 1– x Nb x S 2 as compared to pristine MoS 2 and NbS 2, highlighting a reduced contact resistance and thus facilitating charge carrier across the metal–semiconductor junction.