Probing the Structural Dynamics of In₂O₃ Using in Situ Raman Spectroscopy: Bridging Material Dynamics and Sensor...

Metal oxide semiconductor (MOS) gas sensors still face the critical challenge of high operating temperatures. While material engineering strategies have enabled room-temperature operation, the dynamic evolution of active phases during sensing-a key factor governing structure-activity relationships-remains poorly understood due to the lack of real-time characterization techniques. Here, we design phase-engineered In₂O₃ homojunctions (cubic/rhombohedral) via graphene-assisted hydrothermal synthesis and demonstrate their exceptional NO₂ sensing performance at room temperature. The optimized In₂O₃/graphene (In₂O₃/G) hybrid exhibits a 20-fold enhancement in response (1208 versus 58 for pure In₂O₃ at 5 ppm NO₂), achieving ultrahigh sensitivity with minimal power consumption. By employing in situ Raman spectroscopy to probe structural dynamics during gas exposure, we identify a reversible phase transition between cubic and rhombohedral In₂O₃, with the rhombohedral phase acting as the dominant active site for NO₂ adsorption/desorption. This real-time observation of phase-dependent reactivity establishes a direct correlation between transient structural changes and sensor response, resolving a long-standing ambiguity in MOS-based sensing mechanisms. Our findings not only pinpoint the active phase but also provide a generalizable methodology to bridge nanoscale material dynamics with macroscopic device functionality, paving the way for rational design of high-performance sensors.