Highly reliable and selective ethanol sensor based on α-Fe₂O₃ nanorhombs working in realistic environments

A highly reliable and selective ethanol gas sensor working in realistic environments based on alpha-Fe₂O₃ (α-Fe₂O₃) nanorhombs is developed. The sensor is fabricated by integrating α-Fe₂O₃ nanorhombs onto a low power microheater based on micro-electro-mechanical systems (MEMS) technology. The α-Fe₂O₃ nanorhombs, prepared via a solvothermal method, is characterized by transmission electron microscopy (TEM), Raman spectroscopy, x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The sensing performances of the α-Fe₂O₃ sensor to various toxic gases are investigated. The optimum sensing temperature is found to be about 280 ℃. The sensor shows excellent selectivity to ethanol. For various ethanol concentrations (1 ppm-20 ppm), the response and recovery times are around 3 s and 15 s at the working temperature of 280 ℃, respectively. Specifically, the α-Fe₂O₃ sensor exhibits a response shift less than 6% to ethanol at 280 ℃ when the relative humidity (RH) increases from 30% to 70%. The good tolerance to humidity variation makes the sensor suitable for reliable applications in Internet of Things (IoT) in realistic environments. In addition, the sensor shows great long-term repeatability and stability towards ethanol. A possible gas sensing mechanism is proposed.