In-operando photoemission spectroscopy reveals gate-modulated amplification of ammonia sensitivity in flexible carbon nanotube based thin-film transistor

We report an in-operando X-ray photoelectron spectroscopy (XPS) study revealing gate-induced amplification of ammonia sensitivity in flexible carbon nanotube (CNT) thin-film transistors (TFTs). Using scanning photoemission microscopy (SPEM) under operating conditions, we directly probe surface charge-transfer processes at the CNT surface during NH3 exposure while electrostatically modulating the carrier density in the transistor channel. Flexible CNT-TFTs fabricated on polyimide substrates operate at low voltages (± 5 V) and exhibit typical p-type behavior. Upon exposure to NH3 at a nominal concentration of ∼8 ppm, the C 1s core level shifts by ∼0.5 eV toward higher binding energy in the unbiased state, consistent with electron donation from NH3 to the CNT network. Strikingly, applying a −5 V gate bias approximately doubles the magnitude of this shift to ∼1.0 eV, providing direct spectroscopic evidence that electrostatic gating enhances gas-induced charge transfer at the CNT surface. These findings reveal how transistor gating can modulate gas–surface interactions at the electronic level and demonstrate the capability of in-operando photoemission spectroscopy to uncover sensing mechanisms beyond conventional electrical measurements. The approach provides a pathway toward the rational design of flexible, low-power chemical sensors with tunable sensitivity.