Ionic Liquids at the Interface With the Transition Metal Dichalcogenide MoS₂: Effect of the Chemical Structure on...

Transition metal dichalcogenides (TMDs) are emerging layered materials suited for applications in electronics, optoelectronics, and sensing thanks to their semiconductor nature. More recently, electric-field tuning of surface carrier density through carrier accumulation or depletion in TMDs-based field-effect-transistor devices has been attracting a great deal of interest as a new method to control superconductivity in this class of materials. Such results were achieved by means of ionic liquids (ILs) acting as a gating medium for MoS₂ crystals. Despite the intensive use of ILs for gating TMDs-based transistors, the impact of the chemical structure of the ions on the induced charge density, a key parameter for controlling the critical temperature (T_c) in superconducting MoS₂ crystals, is still lacking. Here we demonstrate that ionic liquid gating of MoS₂ channels using [EMIM][TFSI] or [EMIM][BF₄] can lead to different carrier densities. [TFSI]-based systems exhibit steeper voltage decay (compared to [BF₄]-based systems) meaning the potential drops more rapidly across the electric double layer, indicating stronger local electric fields and more efficient charge accumulation in the MoS₂ channel. Our findings represent the first, yet important, step that paves the way towards controlling charge carrier densities on demand in TMDs by chemical design of the anion and cation pair.