The effect of the metal-MoS2 interaction is evident in the measured Raman spectra of MoS2/Au and MoS2/Ag, which were recorded by a confocal Raman microscope under ambient conditions. The Raman modes of the MoS2/Au, MoS2/Ag, and SiO2/Si substrates are shown in Figure . It should be noted that bulk MoS2 belongs to the D6h symmetry group and freestanding or monolayer MoS2 on dielectric substrates belongs to the D3h symmetry group, which is further reduced to C3v on metal substrates due to the lack of inversion symmetry. Thus, we used the notation corresponding to the C3v group for the MoS2 monolayer on metals, represented in Figure . In general, the E mode is sensitive to strain and the A1 is sensitive to both the electrostatic interactions and strain, which are induced by the interaction between the metal and MoS2. The electrostatic interaction between the metal and MoS2 caused the layer to be strongly bound to the metal surface, where the lattice mismatch induces the strain and electronic transfer causes doping. Hence, the observed splitting and dramatic phonon softening can be attributed to the high magnitude of the interaction potential. The appearance of the geometrically forbidden E mode around 280 cm -1 and symmetry-forbidden infrared mode A1 around 450 cm - 1 originates from monolayer MoS2 on both Au and Ag substrates. The high intensity of these modes and their uniform variation over the layers (Supplementary Figure ) suggests a much stronger interaction between MoS2 and the metal layers compared to previous reports .