Temporally and spatially resolved SPR imaging of electrical double layer dynamics in electrolyte-gated transistors with ionic liquid

Abstract

The use of ionic liquids to construct electrolyte-gated transistors (EGTs) has become a popular research topic because of their high carrier density, low driving voltage, and minimal power consumption. To address the technical challenges in comprehending the operational mechanism and optimising the performance of EGTs, we propose the use of a surface plasmon resonance microscope (SPRM) imaging detection method. This method enabled the real-time and in situ investigation of the channel/electrolyte interface in EGTs for the first time. An SPR microscope with a high spatial resolution was constructed, and an EGT-integrated SPR-sensing chip was fabricated and tested. Our study detected the hysteresis effect of ionic carriers at the channel/electrolyte interface, which was modulated by the gate voltage. The SPR signal, indicative of the dynamic behaviour of the ionic carriers, exhibited a strong correlation with the drain–source current (I_DS). During cyclic voltammetry and step-voltage modulation experiments, we observed irreversible mesoscopic changes at the channel/electrolyte interface. These irreversible changes were further confirmed by atomic force microscopy detection experiments. The temporally and spatially resolved imaging detection method provided a direct link between the mesoscopic phenomena and macroscopic operational state of EGTs, which could provide crucial insights into the mechanism of EGTs and promote the development of high-performance EGT chips.