Using Ions to Control Transport in Two-Dimensional Materials for Ion-Controlled Electronics

Summary form only given, as follows. Electric double layer (EDL) gating is a powerful tool for exploring transport in two-dimensional (2D) materials. Mobile ions in an electrolyte are drifted by field-effect to the surface of a semiconducting channel and image charges are induced. The resulting sheet carrier densities are large (~1013-1014 cm-2), and if this amount of reconfigurable doping could be achieved over fast (ps - ms) timescales at the device level, then novel device functionalities could be enabled for iontronic devices (i.e. electronic properties/functions are controlled by ionic motion and arrangement) in applications such as memory, security and computing. To understand the fundamental limits to EDL formation, we measure the EDL dynamics of polyethylene oxide (PEO):CsClO4 on graphene FETs in response to voltage pulsed over μs – ms, and model the system using molecular dynamics (MD) simulation over ps – ns. EDL formation occurs on the timescale of ns when the field strength is ~ 100 mV/nm, which is suitable for high performance ion-controlled electronics. Not only can ions be used to modulate channel conductance at high speed, they could also be used to induce additional phenomena in 2D crystals – such as the strain-induced semiconductor-to-metal phase transition. Single-ion conductors (i.e., ionomers) can induce strain resulting from an electrostatic imbalance, which has been previously demonstrated in ionic polymer metal composites (IPMCs) for applications in biomimetic actuators and artificial muscle, but has not yet been applied to 2D electronics. If this strain can be transferred to a 2D crystal channel, a gate-tunable semiconductor-to-metal transition could be induced, providing an abrupt switch. I will introduce this new approach to access the strain-induced phase transition in MoTe2 FETs, using a custom synthesized, single-ion conductor as the ion gate.