Changing the Polymorphs of MoS₂ and MoSe₂with Ionic Liquid Field Effect Transistors.

Ionic liquids (IL), molten salts at room temperature with mobile cations and anions, have demonstrated the ability to electrostatically dope MoS₂ and MoSe₂ top gated field effect transistors to increase charge density, carrier mobility and induce superconductivity in MoS₂ and MoSe₂ [1]. When a gate voltage is applied to the ionic liquid, an electric double layer (EDL) is formed on the surface of the MoS₂/MoSe₂ sample as a layer of cations or anions accumulate at the sample/IL interface to create a high capacitance, highly doping the surface. Here, the ability to induce changes in the polymorphs of MoS₂ and MoSe₂ from the semiconducting 2H phase to the semi-metallic 1T’ and the metallic 1T phase through IL gating will be discussed. The fabrication and induction of phase-switching of MoS₂/MoSe₂ field effect transistors gated with the ionic liquid DEME-TFSI will be detailed. Finally, the use of in-situ Raman spectroscopy for simultaneous transport measurements and Raman spectroscopy throughout the phase switching process to understand the underlying mechanism will be discussed.

[1] Shi, W., Ye, J., Zhang, Y. et al. Superconductivity Series in Transition Metal Dichalcogenides by Ionic Gating. Sci Rep 5, 12534 (2015). https://doi.org/10.1038/srep12534