Bulk and Few-Layer 2D, p-MnPS3 for Sensitive and Selective Moisture Sensing

In this study, the humidity sensing properties of two dimensional (2D), few-layer p-MnPS3 is explored. Few-layer of p-MnPS3 is obtained by exfoliating highly oriented bulk crystals and assembled as thin films on various substrates. The performance of p-MnPS3 thin film sandwiched between two similar metal electrodes (Ag or Au) toward various levels of moisture under ambient conditions is investigated. The results depict that p-MnPS3 nanosheets based humidity sensors are highly sensitive and show fast response and recovery times with good repeatability. It is observed that the resistance of the films decreases five to six orders of magnitude with a change in relative humidity (RH) from 0% to 98%. A fast response time of approximate to 1-2 s and recovery time of approximate to 4 s are observed. The mechanism of sensing is understood based on AC impedance spectroscopy. Extrinsic mechanism such as filamentary conduction is ruled out based on the data obtained using devices with different channel lengths. Ionic conduction within the channel is mainly responsible for the observed increase in conductivity in presence of moisture. The humidity sensors are shown to be effective in monitoring human respiration as well as water evaporation on skin without physical contact.