Sorption/desorption hysteresis of thin-film humidity sensors based on graphene oxide and its derivative

We study the sorption/desorption hysteresis of thin-film humidity sensors using graphene oxide (GO) and amine-modified GO (GO-NH2) as sensing materials for relative humidity (%RH in unit) based on capacitance and conductance measurements. GO sensors present a lower level of hysteresis-induced errors in both capacitance (3.1±0.5%RH) and conductance (2.2±0.2%RH) measurements in the humidity range from 5%RH to 95%RH at 25°C, whereas GO-NH2 sensors show a higher degree of hysteresis, resulting in errors of 5.9±1.0%RH and 7.9±0.4%RH by capacitance and conductance measurements, respectively. We discuss a possible mechanism behind the hysteretic behavior of these sensors based on molecular compositions and their interactions with water molecules by using Fourier transform infrared (FT-IR) spectroscopy and by elevating the experimental temperature, respectively. We find the hysteresis-induced errors present a trade-off relationship with the sensitivity between these sensors, emphasizing the importance of studying the sorption/desorption hysteresis as an essential factor in the development of humidity sensors.