Fig. 1. Schematic of the set-up of s-SNOM

Fig. 2. Near-filed signal of WTe₂ thin film of different sample thickness at different incident light frequency（a）70 nm，910cm^-1；（b）56 nm，1 550 cm^-1；（c）52 nm，910 cm^-1；（d）26 nm，1 550 cm^-1

Fig. 3. （a）-（d）correspond to the topography of WTe₂（black curve）and its O3A profile（red curve）along red dash line in figure 2，respectively

Fig. 4. The IR reflectance and optical conductance of WTe₂ fitting by Drude-Lorentz model（a）IR reflectance fitting of WTe₂ at 295 K，（b）IR conductance fitting of WTe₂ at same temperature

Fig. 5. The real and imaginary part of dielectric function fitting of WTe₂

Fig. 6. Illumination of tip-sample scattering in finite-dipole model

Fig. 7. The ratio of sample/substrate near field signal with different sample thickness at different incident frequency. Note：The hollow data point is the result of signal enhancement at the edge of the sample