One-step fabrication of β-Ga2O3-amorphous-SnO2 core-shell microribbons and their thermally switchable humidity sensing properties

We reported the fabrication of a highly sensitive, fast, and thermally switchable humidity sensor based on a beta-Ga2O3-amorphous-SnO2 core-shell microribbon, which was synthesized via a simple one-step chemical vapour deposition. The as-grown microribbons were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) and the results indicated that the microribbon has a well-defined core-shell structure with beta-Ga2O3 in the core and amorphous SnO2 in the shell. At 25 degrees C, the conductivity of the humidity sensor at 75% relative humidity (RH) was three orders of magnitude larger than that in dry air (5% RH). The response time and recovery time were similar to 28 and similar to 7 s, respectively, when RH was switched between 5 and 75%. Interestingly, by changing the temperature between 12 and 40 degrees C at 75% RH, the sensitivity can be tuned between similar to 10(5) (12 degrees C) and similar to 10(2) (40 degrees C). Typical thermally switchable properties of beta-Ga2O3-amorphous-SnO2 core-shell microribbons at 75% RH were demonstrated using a heating-cooling cycle between 20 and 30 degrees C. The possible mechanisms have been proposed based on the novel core-shell structures and water adsorption-desorption processes. Our findings pave the way for new types of humidity sensors and thermal switches.