Novel QCM humidity sensors using stacked black phosphorus nanosheets as sensing film

This work describes the fabrication of humidity sensors by depositing black phosphorous (BP) nanosheets (prepared by liquid exfoliation of bulk BP) onto a quartz crystal microbalance (QCM) in the form of a thin film. The surface morphology of the prepared BP nanosheets is characterized using a field-emission scanning electron microscope and transmission electron microscopy. The humidity sensing characteristics of the BP-based QCM sensors (such as frequency response, stability, humidity hysteresis, and repeatability) are investigated by using an oscillating circuit method. Experimental results indicate that the BP-based QCM sensors exhibit a well-defined logarithmic frequency response to humidity, and the sensitivity of the sensor is strongly related to the amount of BP nanosheets used in the deposition process. Additionally, the BP-based QCM sensors exhibit high stability over the wide relative humidity range of 11.3%–84.3% RH. The BP-based QCM sensors also exhibit little humidity hysteresis and fast dynamic response and recovery times. This work demonstrates that BP is a promising candidate material for humidity detection when combined with a QCM transducer.