However, the contact between the bulk crystal and the substrate is also an important factor that limits layer homogeneity and exfoliated flake size. Even though we flattened the bulk crystals before mounting, there was still a heterogeneous distribution of layer height, which, on a rigid substrate, hindered the complete contact between the bulk crystal and the substrate used for exfoliation. To address this issue, we mounted the crystals on a UHV-compatible elastic spacer between the crystal and the metal sample holder plate. Moreover, the soft spacer also induced a gentler contact and retraction of the bulk crystals, preventing the tearing of the exfoliated monolayers. Note that the Raman spectra of the layers produced without the elastic spacer did not show any substantial difference with respect to the spectra presented in Figure . Thus, we conclude that the pristine nature of the as-prepared metals under UHV conditions is the key factor that determines the exfoliation yield, where the soft spacer plays a key role in ensuring full contact between the substrate and the parent crystal. The changes in the phonon modes observed for the monolayer MoS2 on metal, are attenuated in the bilayer/multilayer MoS2 (Figure ). The observed broadening of the E mode in the bilayer can be interpreted as the combined emissions from the altered phonons in the strained layer attached to the metal and the natural phonons in the second layer. Similarly, the modified A1 phonons are only visible as a shoulder peak in the bilayer, suggesting a nearly complete restoration of the phonon mode frequencies in the second layer. The modifications of the Raman peaks can be barely traced in the case of tri-layer samples.