Figure 5.

(a) Raman spectra with different WS₂ thicknesses; (b) frequency change of A_1g and ${\mathrm{E}}_{2\mathrm{g}}^1$ with different thicknesses; (c) $I_{{\mathrm{E}}_{2\mathrm{g}}^1}/I_{{\mathrm{A}}_{1\mathrm{g}}}$ ratio with different layers.