Revealing the Polaron State at the MoS 2 /TiO 2 Interface.

Interfacial polarons determine the distribution of free charges at the interface and thus play important roles in manipulating the physicochemical properties of hybridized polaronic materials. In this work, we investigated the electronic structures at the atomically flat interface of the single-layer MoS 2 (SL-MoS 2 ) on the rutile TiO 2 surface using high-resolution angle-resolved photoemission spectroscopy. Our experiments directly visualized both the valence band maximum and the conduction band minimum (CBM) of SL-MoS 2 at the K point, which clearly defines a direct bandgap of ∼2.0 eV. Detailed analyses corroborated by density functional theory calculations demonstrated that the CBM of MoS 2 is formed by the trapped electrons at the MoS 2 /TiO 2 interface that couple with the longitudinal optical phonons in the TiO 2 substrate through an interfacial Fröhlich polaron state. Such an interfacial coupling effect may register a new route for tuning the free charges in the hybridized systems of two-dimensional materials and functional metal oxides.