Phase Transition-Induced Temperature-Dependent Phonon Shifts in Molybdenum Disulfide Monolayers Interfaced with a Vanadium Dioxide Film.

We report the optical phonon shifts induced by phase transition effects of vanadium dioxide (VO) in monolayer molybdenum disulfide (MoS) when interfacing with a VO film showing a metal-insulator transition coupled with structural phase transition (SPT). To this end, the monolayer MoS directly synthesized on a SiO/Si substrate by chemical vapor deposition was first transferred onto a VO/c-AlO substrate in which the VO film was prepared by a sputtering method. We compared the MoS interfaced with the VO film with the as-synthesized MoS by using Raman spectroscopy. The temperature-dependent Raman scattering characteristics exhibited the distinct phonon behaviors of the E and A modes in the monolayer MoS. Specifically, for the as-synthesized MoS, there were no Raman shifts for each mode, but the enhancement in the Raman intensities of E and A modes was clearly observed with increasing temperature, which could be interpreted by the significant contribution of the interface optical interference effect. In contrast, the red-shifts of both the E and A modes for the MoS transferred onto VO were clearly observed across the phase transition of VO, which could be explained in terms of the in-plane tensile strain effect induced by the SPT and the enhancement of electron-phonon interactions due to an increased electron density at the MoS/VO interface through the electronic phase transition. This study provides further insights into the influence of interfacial hybridization for the heterogeneous integration of 2D transition-metal dichalcogenides and strongly correlated materials.