Abstract
Flexible carbonnanotube(CNT) chemoresistors offer a scalable, low cost platform for wearable gas detection. However,a clear understanding of their sensing mechanism remains essential to optimize sensitivity, selectivity, and overall reliability. In this work, we complement electrical response measurements in both dry air and ultra-highvacuum(UHV) with synchrotron-basedinsitu X-ray photoelectron spectroscopy(XPS) to directly probe ammonia(NH3)–CNT interactions. In both environments, the response can be described by Langmuir-type adsorption–desorption kinetics. Indryair(3–50ppm), the devices exhibit a reproducible increase inresistance with a sensitivity of ∼0.4% ppm −1. Under UHV, anominal NH3 concentration of ∼8 ppm produces a small errelative response of ∼0.5%, comparable to that obtained at 3 ppm in dry air. In situ micro-focused XPS reveals reversible (≈1eV) shifts in the C1 score-level bind in genergy duringNH3exposure,confirming that NH3 acts as an electrondonor.This spectroscopic evidence correlates quantitatively with the chemoresistive response, establishing intra-CNT charge transfer as the dominant transduction mechanism.These findings underscore the effectiveness of coupling XPS with electrical analysis to unravel gas sensor transduction in nanomaterials and pavetheway for the rational design of high-performance CNT-basedsensors.