Inducing Phase Transitions in MoS2 by Ionic Liquid Gating

A spectrum of material phases can be accessed by tuning the density of carriers and their interaction. Using ionic-liquid gating technique, extremely high electric fields, ~ 10 MV/cm, can be induced in the channel/electrolyte interface and in turn, carrier concentrations in the 1014–1015/cm2 regime can be can accessed. Exotic phenomena such as quantum phase transitions and two-dimensional (2D) superconductivity have been observed by exploiting this technique. Ionic liquids have a low vapour pressure and a high molecular weight so that they are stable at ultra-high vacuum and remain liquid at room temperature. Here we use this technique to induce phase transitions on a few-layered MoS2, a promising 2D semiconducting material for device applications. MoS2 flakes are micromechanically exfoliated and devices are fabricated by photo lithography and Cr/Au metallization. Low-noise transport measurements are performed in the temperature range of 4–300 K. We report a transition from the semiconducting to the metallic state on MoS2 with Field Effect (FET) geometry as a function of the liquid gate voltage (VIL). Our transport studies show signatures of the metallic phase and also exhibit a re-entrant insulating phase in MoS2 at a higher carrier concentration regime.