Raman spectroscopic determination of the bandgap for layered (Mo, W)-(S2, Se2)

Abstract

Based on the bond order-length-strength mechanism and the layer number-dependent Raman shifts, the functional relation of the bandgap to the layer number was established. The equivalent coordination number, bond energy, and bandgap at the different layer numbers for transition metal dichalcogenides were quantitatively obtained. It is found that (ⅰ) with the gradual decrease in layer number, the equivalent coordination number lowers, the bond energy heightens, and the band gap increases; and (ⅱ) the differences in bond energy and ionization potential between the monolayer and bulk for TMDs dictate the strength of the layer number-dependent bandgap. The current method not only displays a new penetration into the layer number effect of bandgap, but also extends the applications of Raman shift.