Solid–liquid contacts MoS _₂ transistors with <i>in-situ</i> ionic-potential probing

Solid-liquid gating is a promising route to probe the electrostatics of two-dimensional semiconductors, yet its mechanisms are easily obscured by interface defects and discharge paths introduced by ionic double layers in conventional measurement circuits. We address these issues with two advances: (i) a damage-free all-solid-liquid contact that suppresses interface degradation and trapping, and (ii) a measurement architecture that isolates the ionic-liquid (IL) double layer from circuit discharge, employing an ultrahigh-input-impedance follower to read the gate potential in operando. These measures deliver accurate and highly reproducible gate potentials. With this direct potential metrology, we measured the IL potential at the mid-channel, providing a more direct basis for explaining the apparent long-channel pinch-off effect. Crucially, we find that threshold voltage shifts correlate with the gate metals' intrinsic open-circuit potentials, not their work-function differences, overturning a common assumption. Together, these results clarify the mechanism of solid-liquid gating and establish a reliable foundation for designing low-power, solution-gated nanoelectronics.