Using In Situ Raman Spectroscopy to Probe Structural Dynamics

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A research team from Qingdao University investigated metal oxide semiconductor (MOS) gas sensing. This study, which was led by researchers Xianghong Liu and Jun Zhang of Qingdao University and published in the journal Angewandte Chemie, explored how structural phase changes inside sensing materials dynamically influence performance during gas exposure (1). The results present evidence that MOS materials undergo reversible phase transitions that directly dictate sensing behavior (1). This conclusion is important because it can potentially accelerate the development of highly sensitive, low-energy gas sensors for environmental monitoring, industrial safety, and wearable electronics.

MOS gas sensors are used in a variety of application areas. Some of the most common usages of MOS gas sensors include smoke detectors, medical diagnostics, environmental monitoring, and other domestic appliances (2). These sensors generally have required high operating temperatures to function properly, and this has limited their efficiency, stability, and portability (1,2).

Although recent material engineering approaches have enabled room-temperature sensing, the underlying mechanisms remained unclear because standard characterization tools could not monitor structural shifts as sensing occurred (1).

In their study, the researchers designed phase-engineered In₂O₃ homojunctions (cubic/rhombohedral) using a graphene-assisted hydrothermal synthesis strategy. The structure was then incorporated into an In₂O₃/graphene (In₂O₃/G) hybrid to investigate how the material evolves during interaction with nitrogen dioxide (NO₂) (1).

The research team noted that the In₂O₃/G hybrid displayed a 20-fold improvement in sensing response at 5 ppm (1). The key to this leap in performance emerged from in situ Raman spectroscopy, which allowed the scientists to observe atomic-level changes during gas exposure. The team found that the material flips between cubic and rhombohedral phases, and that the rhombohedral phase is the active center for NO₂ adsorption and desorption (1). This reversible switching provides a direct structural explanation for the amplification of the sensor’s response.

As a result, this study unveils new information about MOS sensing mechanisms. The findings establish a methodological blueprint for connecting nanoscale material behavior with device-scale functionality (1). More importantly, the approach could be widely applied to design the next generation of room-temperature, ultra-sensitive gas sensors, reducing energy consumption without compromising performance.

References

1. Zhao, N.; Chang, X.; Liu, X.; et al. Probing the Structural Dynamics of In₂O₃ Using in Situ Raman Spectroscopy: Bridging Material Dynamics and Sensor Functionality. Angewandte Chem. 2025, 64 (45), e202512808. DOI: 10.1002/anie.202512808
2. Chen, Y.; Li, M.; Yan, W.; et al. Sensitive and Low-Power Metal Oxide Gas Sensors with a Low-Cost Microelectromechanical Heater. ACS Omega 2021, 6 (2), 1216–1222. DOI: 10.1021/acsomega.0c04340