Surface-Sensitive Raman Response of Metal-Supported Monolayer MoS2

The Raman spectrum of monolayer (ML) MoS2 is remarkably affected by the interaction with metals. In this work, we studied ML-MoS2 supported by the Ag(111) and Ag(110) surfaces by using a combined experimental and theoretical approach. The MoS2 layer was directly grown on atomically clean Ag(111) and Ag(110) surfaces by pulsed laser deposition, followed by in situ thermal annealing under ultrahigh vacuum conditions. The morphology and structure of the two systems were characterized in situ by scanning tunneling microscopy, providing atomic-scale information on the relation between the MoS2 lattice and the underlying surface. Raman spectroscopy revealed differences between the two MoS2-metal interfaces, especially concerning the behavior of the out-of-plane (Formula Presented) vibrational mode, which splits into two contributions on Ag(110). The metal-induced effects on MoS2 vibrational modes are further evidenced by transferring MoS2 onto a more inert substrate (SiO2/Si), where the MoS2 Raman response displays a more “freestanding-like” behavior. The experimental data were interpreted with the support of ab initio calculations of the vibrational modes, which provided insight into the effect of interface properties, such as strain and out-of-plane distortion. Our results highlight the influence of the interaction with metals on MoS2 vibrational properties and show the high sensitivity of MoS2 Raman modes to the surface structure of the supporting metal.